Displays

The Upper Ocean Process Group of the Woods Hole Oceanographic Institution deploys moorings with surface buoys instrumented with incoming shortwave and longwave radiometers at locations around the world.  The procedures used to calibrate the radiometers in the laboratory and to assess their performance at sea are discussed.  Some mooring deployments are done during collaborative field experiments and are months to a year in length.  Three other sites are being maintained as long-term Ocean Reference Stations (ORS), with sequential one-year deployments being used to collect ongoing time series.  The Stratus ORS, located under the marine stratus clouds off northern Chile, has been collecting surface radiation observations since 2000.  The NTAS ORS in the western tropical Atlantic has collected surface radiation data since 2001; and the WHOTS ORS north of island of Oahu, Hawaii has collected surface radiation data since 2004.  Challenges encountered in making the surface radiation observations are discussed, and the best estimates of observational uncertainties are presented.  With this understanding of the accuracies of the observations, comparisons between the buoy observations and surface radiation values from models and reanalyses are shown.  Work underway on further improvements to the approaches taken to make surface radiation observations from moored buoy are discussed, and a suggestion for field intercomparisons with other oceanic and land-based surface radiation observing platforms is put forward.

How to cite: Weller, R., Farrar, J. T., Bigorre, S., Smith, J., Potemra, J., and Santiago-Mandujano, F.: Best practices for surface radiation observations from long-term moored buoys, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2025, https://doi.org/10.5194/egusphere-egu2020-2025, 2020.

Brightening and dimming of solar irradiance at Earth’s surface is a multidecadal phenomenon that occurs globally. Generally, over the past century, there have been two brightening periods (1920s to 1950s, 1980s to the early 2000s) and one dimming period (1950s to mid-1980s). Exceptions are the evolving industrial regions of India and parts of China that have only experienced dimming owing to aerosol effects. The two most recent dimming and brightening periods in Europe were attributed to both aerosol and cloud variability. In the U.S., especially since the 1990s, the systematic variation of cloud cover has been the dominant influence on brightening and dimming.

From 1996 through 2011 downwelling surface solar irradiance over the U.S. increased by +6.6 Wm^-2/decade in an environment of decreasing cloud cover and decreasing aerosol optical depth (AOD) [Augustine and Dutton 2013]. Results presented here extend the brightening/dimming trend for the U.S. through 2018 and show that brightening continued for only one more year after 2011. Following 2012, solar irradiance at the surface abruptly retreated to the long-term mean (±1 Wm^-2) and stabilized at that level through 2017. In 2018 there was a slight decrease of solar irradiance at the surface resulting in a slight dimming trend of -1.7 Wm^-2/decade from 2013 through 2018. During that period AOD continued to decrease but mean cloud cover increased by about 1%, thus cloud variability continued to be the dominant influence on brightening/dimming in the U.S.

It has been shown that the direct effect of aerosols cannot account for the magnitudes of observed trends of surface solar irradiance over the U.S. [Augustine and Dutton 2013]. Here, we show that the second indirect effect of aerosols is consistent with the magnitudes of cloud and AOD reduction from 1996 through 2011. However, over the latest 6-year period analyzed, trends in cloud cover and AOD are not consistent with the stabilization (or small reduction) of solar irradiance at the surface with respect to both the direct and second indirect effect of aerosols. Therefore, systematic changes in circulation and weather must be considered to explain the observed variability, especially with regard to clouds. In this presentation we present evidence for a mechanism that could possibly have been a major contributor to brightening and dimming in the U.S. and western Europe over the past century.

Augustine, J. A., and E. G. Dutton (2013), Variability of the surface radiation budget over the United States from 1996 through 2011 from high-quality measurements, J. Geophys. Res.,118, doi:10.1029/2012JD018551.

How to cite: Augustine, J.: An update on brightening and dimming in the United States, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2453, https://doi.org/10.5194/egusphere-egu2020-2453, 2020.

The Early Twentieth Century Warming (ETCW) period includes a time when a clear increase in actinometric observations was noted in the Arctic, which is defined for the purpose of the present paper after Atlas Arktiki (Treshnikov ed., 1985). Nevertheless, available information about energy balance, and its components, for the Arctic for the study period is still very limited, and therefore solar forcing cannot be reliably determined. As a result, the literature contains large discrepancies between estimates of solar forcing. For example, reconstructions of the increase of terrestrial solar irradiance (TSI) during the ETCW period range from 0.6 Wm^-2 (CMIP5, Wang et al., 2005), through 1.8 Wm^-2 (Crowley et al., 2003), to 3.6 Wm^-2 (Shapiro et al., 2011). Suo et al. (2013) concluded that the collection and processing of solar data is of paramount and central importance to the ability to take solar forcing into account, especially in modelling work.

            Having in mind the weaknesses of our knowledge described above, we decided to present in the paper a summary of our research concerning the availability of solar data in the Arctic (including measurements taken during land and marine expeditions). A detailed inventory of data series for the ETCW period (1921–50) also containing all available metadata will be an important part of this work. Based on the gathered data, a preliminary analysis will be presented of the general solar conditions in the Arctic in this time in terms of global, diffuse and direct solar radiation, and their changes from the ETCW period to present times (mainly 1981–2010).

            The research work in this paper was supported by a grant entitled “Causes of the Early 20th Century Arctic Warming”, funded by the National Science Centre, Poland (grant no. 2015/19/B/ST10/02933).

References:

Crowley T.J., Baum S.K., Kim K., Hegerl G.C. and Hyde W.T., 2003. Modeling ocean heat content changes during the last millennium. Geophys. Res. Lett. 30, 1932

Shapiro A.I., Schmutz W., Rozanov E., Schoell M., Haberreiter M. and co-authors, 2011. A new approach to the long-term reconstruction of the solar irradiance leads to large historical solar forcing. Astron. Astrophys. 529, A67.

Suo L., Ottera O.H., Bentsen M., Gao Y. and Johannessen O.M., 2013. External forcing of the early 20th century Arctic warming, Tellus A 2013, 65, 20578, http://dx.doi.org/10.3402/tellusa.v65i0.20578

Treshnikov A.F. (ed.), 1985. Atlas Arktiki. Glavnoye Upravlenye Geodeziy i Kartografiy: Moscow.

Wang Y.M., Lean J.L. and Sheeley Jr. N.R., 2005. Modeling the sun’s magnetic field and irradiance since 1713. Astroph. J. 625, 522.

How to cite: Przybylak, R., Sviashchennikov, P., Uscka-Kowalkowska, J., and Wyszyński, P.: Solar radiation in the Arctic during the Early Twentieth Century Warming period (1921–50), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6930, https://doi.org/10.5194/egusphere-egu2020-6930, 2020.

We use the new Copernicus ERA5 reanalysis dataset to evaluate the global atmospheric energy budget using a consistent diagnostic framework and  improved numerical methods. A main outcome of this work are mass consistent divergences of moist static plus kinetic energy fluxes. These divergences are combined with top-of-the-atmosphere fluxes based on satellite observations and reconstructions back to 1985 to obtain net surface energy fluxes (F_S) with unprecedented accuracy. The global mean of these F_S fields is unbiased by construction. Hence, this product is well-suited for climate studies and model evaluations.  Here, the temporal variability and stability of inferred F_S, the land-ocean energy transport and the corresponding water cycle are presented and compared with previous evaluations, which used ERA-Interim. 

The inferred F_S fields exhibit a much smaller noise level, and sampling errors are drastically reduced due to the high temporal resolution (hourly) of the ERA5 dataset. Energy budget residuals over land are on the order of 17.0 Wm^-2, which represents a 63 % reduction compared to ERA-Interim. We also present time series of F_S averaged over the global ocean. Its global mean is 2.0 Wm^-2, which is in much better agreement with ocean heat uptake than widely used satellite-derived surface flux products. Moreover, it exhibits reasonable temporal stability at least from 2000 onwards. We compare the annual cycles of F_S over the ocean and ocean heat content variations derived from ocean reanalysis products and find good agreement. Overall, our results demonstrate clear improvements over earlier evaluations, but more work is needed to optimally use the available data and further reduce uncertainties.

How to cite: Mayer, J., Mayer, M., and Haimberger, L.: Temporal variability of inferred surface energy fluxes derived from the ERA5 energy budget , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7499, https://doi.org/10.5194/egusphere-egu2020-7499, 2020.

A better knowledge of the present–day aerosol forcing requires an accurate estimation of the historical evolution of aerosol optical depth (AOD), which is also crucial to better understand the role played by atmospheric aerosols in the dimming/brightening phenomena that have occurred since the mid-20^th century. A physically-based approach using daily sunshine duration and cloud cover measurements is applied over Europe for retrieving AOD (Wandji Nyamsi et al., 2019). Both European Climate Assessment & Dataset (ECA&D) and national meteorological offices/institutes provide suitable measurements, from ~ 1000 ground-based stations, to carry out our study.

The retrieved long-term AOD shows reasonable seasonal and annual variabilities including signals induced by major volcanic eruptions. The trends of atmospheric aerosols and associated increase and decrease of AOD over the periods 1960–1984 and 1985–2010, respectively, are in good agreement with the dimming/brightening periods reported before. In addition, a more dominant decrease in AOD including high variability from the early-1900s to the 1950s is observed, which agrees with some earlier studies reporting “early brightening” for this period. The high inter-annual AOD variability during that period may be partly due to the transition from coal to gas in some European countries and also due to the possible influence of the Word Wars I & II.

References

Wandji Nyamsi, W.; Lipponen, A.; Sanchez–Lorenzo, A.; Wild, M. and Arola, A. (2019), A hybrid method for reconstructing the historical evolution of aerosol optical depth from sunshine duration measurements, submitted.

How to cite: Wandji, W., Lipponen, A., van den Besselaar, E., Sanchez–Lorenzo, A., Wild, M., and Arola, A.: Decadal variations in retrieved aerosol optical depth from sunshine duration measurements over Europe since the late 19th century, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1351, https://doi.org/10.5194/egusphere-egu2020-1351, 2020.

How to cite: Elsey, J., Coleman, M., Gardiner, T., Menang, K., and Shine, K.: Atmospheric observations of the water vapour continuum in the near-infrared windows, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17654, https://doi.org/10.5194/egusphere-egu2020-17654, 2020.

The uninterrupted, 41-year-long, spaceborne total solar irradiance (TSI) record has recently undergone several changes in the instruments contributing to these measurements of the net incoming radiant energy providing nearly all the power driving the Earth’s climate system. Two long-term instruments, NASA’s SORCE/TIM and TCTE/TIM, have recently been powered off. This ends the 17-year record from the SORCE/TIM, which established the currently-accepted TSI value of 1361 W m^‑2 after its launch in 2003. ESA’s SoHO/VIRGO continues to acquire measurements that extend its 24-year record, but data availability has been on hold as a new processing methodology is implemented. NASA’s recently-launched TSIS‑1/TIM is presently continuing the measurements of these stalwart legacy instruments. This new TSI instrument is demonstrating higher on-orbit accuracy than any prior such instrument has achieved, with daily measurement updates that are available to the community for climate- and solar-research purposes. I will discuss the many recent changes to the spaceborne TSI measurement record, the current measurement-accuracy improvements and stabilities achieved and their implications for Earth energy-balance studies, and the future plans to maintain measurement continuity.

How to cite: Kopp, G., Harber, D., Heuerman, K., and Stone, B.: Changing of the Guard for the Total Solar Irradiance Record, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11489, https://doi.org/10.5194/egusphere-egu2020-11489, 2020.

The effective radiative forcing, which includes the instantaneous forcing plus adjustments from the atmsophere and surface, as emerged as the key metric of evaluating human and natural influence on the climate. We evaluate effective radiative forcing and atmospheric adjustments in 13 contemporary climate models that are participating in CMIP6 and have contributed to the Radiative Forcing Model Intercomparison Project (RFMIP). Present-day (2014) global mean anthropogenic forcing relative to pre-industrial (1850) from climate models stands at 1.97 (± 0.26) W m^-2, comprised of 1.80 (± 0.11) W m^-2 from CO₂, 1.07 (± 0.21) W m^-2 from other well-mixed greenhouse gases, -1.04 (± 0.23) W m^-2 from aerosols and -0.08 (± 0.14) W m^-2 from land use change. Quoted ranges are one standard deviation across model best estimates, and 90% confidence in the reported forcings, due to internal variability, is typically within 0.1 W m^-2. The majority of the remaining 0.17 W m^-2 is likely to be from ozone. As determined in previous studies, cancellation of tropospheric and surface adjustments means that the "traditional" stratospherically adjusted radiative forcing is approximately equal to ERF for greenhouse gas forcing, but not for aerosols, and consequentially, not for the anthropogenic total forcing. The spread of present-day aerosol forcing has narrowed compared to CMIP5 models to the range of -0.63 to -1.37 W m^-2, with a less negative mean. The spread in CO₂ forcing has also narrowed in CMIP6 compared to CMIP5, which may be a consequence of improving radiative transfer parameterisations. We also find that present-day aerosol forcing is uncorrelated with equilibrium climate sensitivity. Therefore, there is no evidence to suggest that the higher climate sensitivity in many CMIP6 models is a consequence of stronger negative present-day aerosol forcing.

How to cite: Smith, C., Kramer, R., Myhre, G., Alterskjær, K., Collins, B., Pincus, R., and Forster, P. and the RFMIP modelling groups: Effective Radiative Forcing and Adjustments in CMIP6, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10294, https://doi.org/10.5194/egusphere-egu2020-10294, 2020.

The Earth’s climate is rapidly changing. Over the past century, aerosols, via their ability to absorb or scatter solar radiation and alter clouds, played an important role in counterbalancing some of the greenhouse gas (GHG) caused global warming. This, over a century-long anthropogenic aerosol cooling effect, prevented present day climate to have yet reached even higher surface air temperatures and subsequent more dramatic climate change impacts. Trends in aerosol concentrations and optical depth show that in many formerly highly polluted regions such as Europe and the United States of America aerosol precursor emissions have already decreased back to pollution levels of the 1950s. More recent polluting countries such as China may have reached a turning point in recent years as well, while India keeps still following an upward trend. Here we study aerosol trends in the CMIP6 simulations of the GISS ModelE climate model using a fully coupled atmosphere composition configuration, including interactive gas phase chemistry, and either an aerosol microphysical (MATRIX) or a mass based (OMA) aerosol module. Results show that the question if we are already at a period where aerosol radiative forcing continuously declines globally depends on the aerosol scheme used. Using the aerosol microphysical scheme, where the aerosol system reacts stronger to the trend in sulfur dioxide (SO₂) emissions, global peak direct aerosol forcing was reached in the 1980’s, whereas the mass-based scheme simulates peak direct aerosol forcing around 2010. The models are tested again ice core records, satellite and surface network datasets. An evaluation with satellite data between 2001 and 2014 demonstrates that the model that better reproduces the satellite retrieved trends has reached maximal aerosol direct forcing in the 1980s, and is since on a decreasing global forcing trajectory. As a consequence, we expect that the recently observed global warming which is primarily driven by greenhouse gases has been augmented by the effect of a decreasing aerosol cooling effect on the global scale.

How to cite: Bauer, S. E. and Tsigaridis, K.: The end of the anthropogenic aerosol era?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1780, https://doi.org/10.5194/egusphere-egu2020-1780, 2020.

The albedo of trees is lower than the one of crops and grasses, especially in the presence of snow. It is therefore understood that the replacement of forests by croplands and grasslands used for agricultural purposes that has occurred since pre-industrial times led to large-scale albedo increases. This is reflected by the estimate of the Radiative Forcing (RF) from historical Land-Cover Changes (LCC) of the Fifth Assessment Report (AR5) of the IPCC, which amounts to -0.15 +/- 0.10 W/m². However, this expert judgment was intended to both account for a few studies using single climate models which put forward values close to 0.2W/m², and the finding that climate models usually overestimate the albedo difference between natural vegetation and croplands in comparison to satellite-derived observational evidence. Further uncertainties around this number have also been suggested by studies revealing a substantial model spread in the albedo response to historical LCC. This points at the need to revisit the IPCC AR5 conclusions in light of recent model intercomparison efforts and observational data.

In this study, we reconstructed the local albedo changes induced by conversions between trees and crops/grasses since 1860 for 15 CMIP5 models. We evaluated the employed methodology using factorial experiments isolating the historical LCC forcing in four models for which the required simulations are available, and obtained very similar results. Using an empirical parameterisation of the radiative kernel, we then derived estimates of the associated RF ranging between 0 and -0.22 W/m², with a multi-model mean value of -0.07 W/m².

Furthermore, we constrained the RF estimates with observations by replacing the albedo response to the transition between trees and crops/grasses from the models by that provided by satellite-derived data. This led to an unexpected increase in the range between the models, due to two models having unrealistic conversion rates from trees to crops/grasses. Excluding these two models, we obtain a revised multi-model mean estimate of -0.11 W/m² (with individual model results between -0.04 and -0.16 W/m²). We were also able to link the differences between the unconstrained and constrained RF estimates to some of the model biases in the albedo sensitivity to deforestation.

Since the conversions between trees and crops/grasses are responsible for almost the totality of historical albedo changes in CMIP5 models, our findings are comparable to previous estimates of the RF from all LCC. They point at values that are at the lower end of the range provided by the IPCC AR5. The approach described in this study can be applied on other model simulations, such as those from CMIP6.

How to cite: Lejeune, Q., Davin, E., Duveiller, G., Crezee, B., Meier, R., Cescatti, A., and Seneviratne, S.: Observation-constrained Radiative Forcing from historical land-cover changes in CMIP5 models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19472, https://doi.org/10.5194/egusphere-egu2020-19472, 2020.

It is crucial to reduce uncertainties in our understanding of the climate impacts of short‐lived climate forcers, in the context that their emissions/concentrations are anticipated to decrease significantly in the coming decades worldwide. Using the Community Earth System Model (CESM1), we performed time‐slice experiments to investigate the effective radiative forcing (ERF) and climate respons to 1970–2010 changes in well‐mixed greenhouse gases (GHGs), anthropogenic aerosols, and tropospheric and stratospheric ozone. Once the present‐day climate has fully responded to 1970–2010 changes in all forcings, both the global mean temperature and precipitation responses are twice as large as the transient ones, with wet regions getting wetter and dry regions drier. The temperature response per unit ERF for short‐lived species varies considerably across many factors including forcing agents and the magnitudes and locations of emission changes. This suggests that the ERF should be used carefully to interpret the climate impacts of short‐lived climate forcers. Changes in both the mean and the probability distribution of global mean daily precipitation are driven mainly by GHG increases. However, changes in the frequency distributions of regional mean daily precipitation are more strongly influenced by changes in aerosols, rather than GHGs. This is particularly true over Asia and Europe where aerosol changes have significant impacts on the frequency of heavy‐to‐extreme precipitation. Our results may help guide more reliable near‐future climate projections and allow us to manage climate risks more effectively.

How to cite: Zhao, A., Stevenson, D., and Bollasina, M.: Climate forcing and committed global warming: GHGs, aerosols and ozone 1970-2010, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19702, https://doi.org/10.5194/egusphere-egu2020-19702, 2020.

Equilibrium climate sensitivity (ECS), the change in surface temperature in response to a doubling of atmospheric CO2, is arguably one of the most important quantities when discussing climate change. Despite major improvements in climate modelling over the last decades, ECS estimates lie within a rather constant range between 1.5-4 K. The cause of this spread is not obvious as the comparison of comprehensive climate models is difficult due to the complexity of their formulations.

We are revisiting one of the simplest climate models, one-dimensional radiative-convective equilibrium (RCE). Despite their simple and concise model formulation, RCE models include the most dominant clear-sky radiative feedbacks. In our study, we quantify the strength of the Planck, water-vapor, and lapse-rate feedback by turning them on or off using different model configurations. This method allows us to compare the effect of different model assumptions, e.g. the vertical distribution of water vapor, on the decomposed radiative feedbacks. We find that the interplay of the water-vapor and the lapse-rate feedback is especially affected by the relative humidity in the upper troposphere.

The RCE model is run with a state-of-the-art radiation scheme, that is also used in comprehensive  Earth system models. A line-by-line radiative transfer model is used to both verify the performance of the fast radiation scheme, and to attribute changes in the radiative feedbacks to specific regions in the electromagnetic spectrum.

In a further step, conceptual rectangular clouds are added to investigate possible cloud masking effects on both the radiative forcing and feedback. A large Monte Carlo ensemble is used to tune the cloud optical parameters in a way that the resulting cloud radiative effect matches satellite observations. Preliminary results suggest a near zero long-wave feedback, in contrast to previous studies.

How to cite: Kluft, L., Dacie, S., Buehler, S. A., Schmidt, H., and Stevens, B.: Radiative feedbacks in a 1D radiative-convective equilibrium model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15422, https://doi.org/10.5194/egusphere-egu2020-15422, 2020.

Solar Radiation Management (SRM) and Carbon Dioxide Removal (CDR) have been proposed to mitigate global warming in the event of insufficient greenhouse gas emission reductions. We have studied temperature and precipitation responses to CDR and SRM with the RCP4.5 scenario using the MPI-ESM and CESM Earth System Models (ESMs). The two SRM scenarios were designed to meet different climate targets to keep either global mean 1) surface temperature or 2) precipitation at the 2010-2020 level via stratospheric sulfur injections. This was done in two-fold method, where global aerosol fields were first simulated with aerosol-climate model ECHAM-HAMMOZ, which were then used as prescribed fields in ESM simulations. In the CDR scenario the annual CO₂ increase based on RCP4.5 was counteracted by a 1% annual removal of the atmospheric CO₂ concentration which decreased the global mean temperature back to the 2010-2020 level at the end of this century. 

Results showed that applying SRM to offset 21st century climate warming in the RCP4.5 scenario led to a 1.42%  (MPI-ESM) or 0.73% (CESM) reduction in global mean precipitation, whereas CDR increased global precipitation by 0.5% in both ESMs for 2080-2100 relative to 2010-2020. To study this further we separated global precipitation responses to a temperature-dependent and a fast temperature-independent components. These were quantified by a regression method. In this method the climate variable (e.g. precipitation) is regressed against the temperature change due to the instantaneous forcing. Temperature-dependent slow response and temperature independent fast response are given by the fitted regression line. We showed that in all simulated geoengineering scenarios, the simulated global mean precipitation change can be represented as the sum of these response components. This component analysis shows that the fast temperature-independent component of atmospheric CO₂ concentration explains the global mean precipitation change in both SRM and CDR scenarios. Results showed relatively large differences in the individual precipitation components between two ESMs. This component analysis method can be generalized to evaluate and analyze precipitation, or other climate responses, basically in any emission scenario and in any ESM in a conceptually easy way. 

Based on the SRM simulations, a total of or 292-318 Tg(S) (MPI-ESM) or 163-199 Tg(S) (CESM) of injected sulfur from 2020 to 2100 was required to offset global mean warming based on the RCP4.5 scenario. The distinct effects of SRM in the two ESM simulations mainly reflected differing shortwave absorption responses to water vapor. To prevent a global mean precipitation increase, only 95-114 Tg(S) was needed. Simultaneously this prevent the global mean climate warming from exceeding 2 degrees above preindustrial temperatures in both models. 

How to cite: Laakso, A., Snyder, P., Liess, S., Partanen, A.-I., and Millet, D.: Representing transient precipitation change of Solar Radiation Management and Carbon Dioxide Removal with fast and slow precipitation components, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8050, https://doi.org/10.5194/egusphere-egu2020-8050, 2020.

How to cite: Vanderkelen, I., van Lipzig, N. P. M., Lawrence, D., Droppers, B., Golub, M., Gosling, S. N., Janssen, A. B. G., Marcé, R., Müller Schmied, H., Perroud, M., Pierson, D., Pokhrel, Y., Satoh, Y., Schewe, J., Seneviratne, S. I., Stepanenko, V. M., Woolway, R. I., and Thiery, W.: Global heat uptake by inland waters, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18875, https://doi.org/10.5194/egusphere-egu2020-18875, 2020.

In-situ shortwave or solar radiation and longwave or thermal radiation are observed at the earth’s surface on both the land and the ocean.  In addition, satellites are used to develop fields of surface radiation balance.  Planning for the Global Ocean Observing System (GOOS) and the Global Climate Observing System (GCOS) has identified surface heat flux, including the radiative fluxes, as an Essential Ocean Variable (EOV) and Essential Climate Variable (ECV), respectively.  The GOOS and GCOS requirements for surface radiative fluxes (spatial and temporal sampling, accuracies) are summarized here.  Surface radiation sites will continue to be sparse in the future, especially in the ocean; and satellite-derived products developed in concert with in-situ observing system will be important.  To make better progress towards meeting those requirements, we propose the goal of establishing dialog across the different methods of in-situ observing surface radiation and with the remote sensing community.  Objectives of the effort would include sharing knowledge and experience of how to make the observations, documentation of calibration methods, and assessment of the uncertainties to be associated with the different observing methods.  The resulting metadata and quantitative understanding of the different approaches would support improved combination of surface radiation observations across land and sea into homogeneous products at global scale.  At the same time, improved in-situ sampling would help assess and validate climate models and contribute to our understanding of the earth’s energy balance.  We review here the different observing methods now in use on land and at sea and discuss the challenges faced in making the observations.  We also propose future field inter-comparison and standardization of calibration methods to better establish the accuracy and comparability of surface radiation observations on land and at sea.

How to cite: Weller, R., Lanconelli, C., Wild, M., and Trenmann, J.: Developing Best Practices for Observing Global Surface Shortwave and Longwave Radiation across the Land and Ocean, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6018, https://doi.org/10.5194/egusphere-egu2020-6018, 2020.

In this study, ship based observations obtained from Indian Meteorological Department (IMD) and Naval Operations Data Processing and Analysis Centre (NODPAC) observed across Tropical Indian ocean (TIO) are combined with International Comprehensive Ocean-Atmosphere Dataset (ICOADS R3.0) and several climatology are generated for TIO. The ship observations from the Voluntary Observing Ships (VOS) have been found to contain both random and systematic errors. An attempt is made to apply a systematic correction upon wind speed (WS) and random error correction upon sea level pressure (SLP), dry bulb temperature (DBT), sea surface temperature (SST), dew point temperature (DPT). The systematic error correction upon WS is actually a correction applied to the old World Meteorological Organization (WMO) 1100 scale, i.e. the Beaufort estimated wind speeds are corrected as the old WMO 1100 scale was found to have errors. The new July scale derived exclusively for TIO rightly reduces the over estimation of high WS and increases the under estimation of lower WS as given by the old WMO 1100 scale. The systematic bias between anemometer measured wind speeds and Beaufort estimated wind speeds reduced from 0.52 m/s (obtained after the correction done by previous scale) to 0.08 m/s with the new scale. The random errors are calculated based on a technique called semi-variogram analysis technique. The fluxes derived from the observation error corrected variables are analyzed and the net heat flux across TIO was observed to reduce by 14 W/m².

How to cite: Nunna, K., Tata Venkata Sai, U. B., Eluri, P. R. R., and Jampana, V.: Systematic and Random error correction of ship based marine meteorological parameters observed across Tropical Indian ocean, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-933, https://doi.org/10.5194/egusphere-egu2020-933, 2020.

The global-mean surface air temperature change due to a doubled carbon dioxide concentration in the atmosphere (equilibrium climate sensitivity, ECS) is an important measure to quantify the impact of predicted anthropogenic climate change. The latest climate modeling intercomparison project (CMIP6) exhibits a higher ECS compared to the previous climate model generation (1.8 to 5.6 K for CMIP6 versus 1.5 to 4.5 K for CMIP5). The increase in ECS is likely due to decreases in extratropical low cloud coverage and albedo, caused by improvements in the numerical aerosol schemes. Our state-of-the-art Earth system model AWI-ESM, developed at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, yields an ECS of 3.59-3.62 K, which is close to the CMIP5 mean. Using a set of varying model configurations, we identify dynamic vegetation and model resolution as the primary driving factors which influence the modeled global response to an increased greenhouse gas forcing.

How to cite: Danek, C., Gierz, P., Stepanek, C., and Lohmann, G.: Equilibrium Climate Sensitivity in AWI-ESM: Mechanisms and Effects, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17981, https://doi.org/10.5194/egusphere-egu2020-17981, 2020.

Natural and anthropogenic aerosol particles are major drivers of the Earth’s radiation budget, which they affect directly (through scattering and absorption) and indirectly (through modification of cloud scattering and precipitation properties), while they semi-directly influence atmospheric stability and convection, mainly through modification of solar radiation absorption by the atmosphere. Despite the important climatic role of aerosols, large uncertainties in their radiative effects remain due to limited knowledge of the aerosol spatio-temporal distribution and physico-chemical properties. The interaction of aerosols with radiation is strongly dependent on their optical properties, which in turn are controlled by the particles’ size distribution, shape, chemical composition and mixing state. In order to accurately estimate the magnitude of the aerosol direct radiative effect (DRE), detailed knowledge of their optical properties with high spatial and temporal resolution is required.

The European continent is a region of particular interest for studying atmospheric aerosol effects, because of the presence of  numerous and varying sources of particles and their precursors, such as industries, large urban centers and biomass burning, especially when combined with high levels of solar insolation during summer. In this study, the aerosol DRE over Europe is examined using the FORTH deterministic spectral radiative transfer model (RTM) and aerosol data from the chemical transport model PMCAMx. Chemically and size resolved aerosol concentrations predicted by PMCAMx are combined with a Mie model to calculate key aerosol optical properties (i.e. vertically resolved aerosol optical depth, single scattering albedo and asymmetry parameter) that are necessary to compute aerosol DRE using the RTM. The Mie model takes into account concentrations of organics, black carbon, sulfate, nitrate, ammonium, chlorine, sodium, water, and crustal material, and calculates aerosol optical properties assuming that the aerosol particles of the same size are internally mixed. The DRE is estimated at the Earth’s surface, within the atmospheric column and at the top of the atmosphere (TOA), at high spatial and temporal resolution (36 × 36 km grids, 27 vertical layers, hourly), during June and July 2012.

Initial modelling results reveal that DREs exhibit significant spatio-temporal variability, due to the heterogeneity of source emissions rates, mostly with regard to wildfires, and the varying synoptic conditions. Emphasis is thus given to biomass burning aerosols, which are among the most significant radiative forcing agents in Europe during summer. Their relative forcing is computed by performing model computations with and without biomass burning emissions.

How to cite: Korras Carraca, M. B., Manetas, D., Patoulias, D., Pandis, S., Hatzianastassiou, N., Vardavas, I., and Matsoukas, C.: High resolution Aerosol Radiative Effects over Europe using detailed optical properties from the Chemical Transport Model PMCAMx, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-884, https://doi.org/10.5194/egusphere-egu2020-884, 2020.

In this research project we studied the climatic effects of anthropogenic aerosol emissions originating from Chile and Mexico. In particular, we studied black carbon (BC), organic carbon (OC) and sulfur dioxide (SO₂).

By using aerosol-climate model ECHAM6.3.0-HAM2.3-MOZ1.0, we analyzed how each aerosol species affects the local cloud properties and radiative balance in the atmosphere. As we here are interested in the maximum impact, we simulated each aerosol species with separate model runs. The reference scenario (BASE) was simulated with the full representation of anthropogenic aerosol emissions from the ECLIPSEV6a emission inventory for the year 2015.Then, we constructed otherwise identical scenarios but the anthropogenic aerosol emissions from Chile and Mexico for each aerosol type were removed (NO_BC, NO_OC and NO_SO2). 

The results indicate that for Chile the sulfur emissions seem to have the greatest impact on both cloud condensation nuclei (CCN) and cloud droplet number concentration. This result is plausible since there the SO₂ emissions are much higher than BC and OC emissions. For Mexico, the OC emissions had the most notable effect on CCN, but the cloud droplets are more affected by the SO₂ emissions. When looking at the radiative properties, we found out that the direct effects were rather minor compared to semi-direct and indirect effects. This indicates that aerosol-cloud interactions have much larger regional effect on radiation than the aerosol direct effect.

How to cite: Miinalainen, T., Kokkola, H., Lehtinen, K. E. J., and Kühn, T.: The Effects of Anthropogenic Aerosol Emissions from Chile and Mexico in ECHAM-HAMMOZ, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9976, https://doi.org/10.5194/egusphere-egu2020-9976, 2020.

Anthropogenic aerosol emissions over the industrial period have caused a negative but highly uncertain radiative forcing. This negative radiative forcing has had a cooling effect mainly over the northern hemisphere, affecting the atmospheric interhemispheric energy balance. Consequently aerosols have been linked to observed dynamical responses over the industrial period that depend on the atmospheric interhemispheric energy balance, such as changes in the position of the Intertropical Convergence Zone (ITCZ) and resultant tropical precipitation shifts. However, over the course of the 21^st century anthropogenic aerosol emissions are predicted to decline. The reduction in anthropogenic aerosol emissions will cause a positive radiative forcing relative to present day, creating a warming effect in the northern hemisphere. Hence, if the strength of aerosol radiative forcing modulates the magnitude of shifts in the ITCZ, then the large uncertainty in aerosol radiative forcing will limit our understanding of how tropical precipitation will shift in the near-term future.

We use a perturbed parameter ensemble (PPE) of a global coupled climate model to investigate the link between aerosol radiative forcing and ITCZ and tropical rainfall shifts in the near-term future. The PPE consists of 20 simulations of the UK Met Office’s GC3.05 model with parameters perturbed from a range of model schemes. The ensemble was designed to sample uncertainties in future changes, and as a result spans a range of aerosol radiative forcings.

The PPE reveals both northward and southwards shifts in the ITCZ position across the ensemble in the latter half of the 20^th century and first half of the 21^st century, as well as changes in width and intensity of the ITCZ. We find a correlation between the shift in the ITCZ position and the magnitude of aerosol radiative forcing and AOD trends. However, the correlations in our ensemble are not as strong as those cited in previous studies that use multi-model ensembles. The potential causes of this difference are investigated. We also compare our model output to aerosol, cloud and radiation observations in attempt to identify the most plausible future aerosol-driven climate responses.

How to cite: Peace, A., Booth, B., Carslaw, K., Regayre, L., Lee, L., Sexton, D., and Rostron, J.: Exploring the impact of aerosol radiative forcing uncertainty on shifts in ITCZ position and tropical rainfall in the near-term future , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10202, https://doi.org/10.5194/egusphere-egu2020-10202, 2020.

Aerosols offset poorly quantified fraction of anthropogenic greenhouse gas warming, whereas the aerosol impact on clouds is the most uncertain mechanism of anthropogenic climate forcing. In this research, we extend satellite observations of polluted cloud tracks from Toll et al. (2019, Nature, https://doi.org/10.1038/s41586-019-1423-9) with analysis of larger scale polluted cloud areas detected in MODerate-resolution Imaging Spectroradiometer satellite images. We demonstrate that large-scale anthropogenic aerosol-induced cloud perturbations exist at various major industrial aerosol source regions. The areal extent of the polluted cloud areas detected in MODIS satellite images extended to hundreds by hundreds of kilometres. Polluted clouds detected in satellite images in the global anthropogenic air pollution hot spot of Norilsk, Russia, and in other regions show close compensation between aerosol-induced cloud water increases and decreases. On average, there is relatively weak decrease in cloud water in the large areas with strong decreases in cloud droplet radii. This is in very good agreement with previous results based on small-scale polluted cloud tracks (Toll et al., 2019) and strongly disagrees with unidirectionally increased liquid water path in global climate models.

How to cite: Trofimov, H. and Toll, V.: Large-scale industrial cloud perturbations confirm bidirectional cloud water responses to anthropogenic aerosols, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8909, https://doi.org/10.5194/egusphere-egu2020-8909, 2020.

Land cover conversion affects climate by imposing perturbations in the surface properties and greenhouse gas fluxes. Forest management systems often disregard that modification in surface albedo influences the exchange of energy and greenhouse gases. In this study, we examine the net climatic effect of clear-cutting in high-latitude regions by comparing the importance of biogeophysical (albedo) and biogeochemical (carbon dioxide release) changes in Sweden. The hypothesis is that the albedo effect of high-latitude clear-cutting can reduce climate warming.

Data on incoming and reflected shortwave radiation was obtained from four-component net radiometers installed in the forest and neighbouring clear-cut sites, in southern (56°N), central (60°N) and northern (64°N) Sweden. The study site pairs along a latitudinal gradient were chosen to account for different climatic conditions. Data at these station pairs covered a continuous period of three (2016-2018), five (2014-2018) and one year (2014), respectively. Due to lack of clear-cut measurement stations in close vicinity to the northernmost forest site, the shortwave radiation data was retrieved from an open mire, where albedo and its temporal dynamics are similar to a clear-cut. All the forest stations and the mire station are part of ICOS Sweden network. Data on carbon dioxide release from clear-cutting was estimated as a difference in the aboveground carbon stock of the standing biomass between forest and clear-cut sites. The estimated carbon dioxide release was translated into an equivalent change in absorbed shortwave radiation and compared to the radiative forcing by albedo difference between forest and clear-cut sites.

Our results underline results from previous studies showing that the magnitude of the net radiative forcing by clear-cutting varies considerably depending on the latitudinal position of the examined sites. Based on available data, clear-cutting in southern and central Sweden had a warming effect on the climate while in northern Sweden clear-cutting had a net cooling effect. However, large inter-annual variability (central Sweden) and lack of available continuous data (northern Sweden) resulted in high uncertainty of the climatic effects of changes in net radiative forcing due to clear-cutting. Our study indicates that the albedo effect has an essential role in the estimation of the climatic effect of clear-cutting and should thus be incorporated in future forest management strategies.

How to cite: Mužić, I., Vestin, P., Lindroth, A., Mölder, M., Biermann, T., Heliasz, M., and Rinne, J.: Changes in radiative forcing due to clear-cutting in Sweden, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-885, https://doi.org/10.5194/egusphere-egu2020-885, 2020.

The WCRP Coupled Model Intercomparison Project (CMIP) simulations expect increasing downward longwave radiation (DLR, surface LW down) from a human-enhanced greenhouse effect during the 21^st century in the range of 10 – 40 Wm^-2. We announce a public challenge to these predictions based on a long known but rarely referred theoretical constraint. Following the logic of original radiative transfer equations of Schwarzschild (1906, Eq. 11), a relationship connects surface net radiation to the effective emission, independent of the optical depth. This relationship is reproduced by several textbooks on atmospheric radiation like Goody (1964, Eq. 2.115), Goody and Yung (1989, Eq. 2.146), Houghton (2002, Eq. 2.13), Pierrehumbert (2010, Eq. 4.44-4.45). In CERES notation: Surface [shortwave (SW) + longwave (LW)] net = OLR/2. A specific “gross” version is: Surface (SW net + LW down) = 2OLR. These are for the cloudless case. Their all-sky form includes longwave cloud radiative effect (LWCRE): Surface SW+LW net = (OLR – LWCRE)/2 and Surface (SW net + LW down) = 2OLR + LWCRE. Controlling these four equations on CERES EBAF Edition 4.1, 18 years of data, and on EBAF Ed4.1 Data Quality Summary Table 2-1 and Table 4-1, each of them is valid within 3 Wm^-2. The all-sky versions are satisfied by the IPCC-AR5 (2013) global energy budget (Fig. 2.11) and a water cycle assessment (Stephens and L'Ecuyer 2015) within 2 Wm^-2. We couldn't find any reference to these equalities in the literature on general circulation models or climate sensitivity. Applying known definitions, the equations can be solved for LWCRE, resulting in a set of small integers (Zagoni, EGU2019). All-sky fluxes: Surface SW net = 6; Surface LW net = –2; DLR = 13; OLR = 9. Clear-sky fluxes: Surface SW net = 8; Surface LW net = –3; DLR = 12; OLR = 10; Surface LW up (ULW) = 15 (both for all-sky and clear-sky); LWCRE (surface and TOA) = 1. From this solution it comes for all-sky: DLR = (13/9)OLR, ULW = (15/9)OLR, and for clear-sky ULW = (15/10)OLR. Since the physical principles and conditions behind these equations are solid and justified by observations, we expect them to remain valid in the forthcoming decades as well. CMIP6 models might represent regional distribution changes and cloud feedbacks correctly, in lack of global constraints they may lead to profoundly different outcomes in the long run. This is a testable difference. To check the robustness and stationarity of our equations, we challenge published CMIP5 predictions. We predict for the 21^st century: all-sky DLR = (13/9)OLR ± 3.0 Wm^-2; ULW = (15/9)OLR ± 3.0 Wm^-2 and clear-sky ULW = (15/10)OLR ± 3.0 Wm^-2. Initial status (CERES EBAF Edition 4.1 annual global means for 2018): all-sky OLR = 240.14, DLR = 344.82, ULW = 399.37, hence all-sky DLR = (13/9)OLR – 2.05 and ULW = (15/9)OLR – 0.86 (Wm^-2); clear-sky ULW = 399.05, OLR = 265.80, hence ULW = (15/10)OLR + 0.35 Wm^-2. Greenhouse effect: g(theory) = G/ULW = (ULW–OLR)/ULW = (15 – 9)/15 = 0.4, g(observed) = 0.399.

How to cite: Zagoni, M.: Challenging CMIP6 model predictions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1, https://doi.org/10.5194/egusphere-egu2020-1, 2020.

Solar Radiation Management (SRM) is regarded as a tool which could potentially mitigate or completely offset global warming by increasing planetary albedo. However, this approach could potentially reduce precipitation as well, as shown in the latest Intergovernmental Panel on Climate Change (ICPP) 5^th report. Thus, although SRM might weaken global climate risks, it may enhance those in some regions. Here, using the Globally Resolved Energy Balance (GREB) model, we present experiments designed to completely offset the temperature and precipitation response due to a CO₂-doubling experiment (abrupt2×CO2). The main idea around which our study is built upon is to employ a localized and seasonally varying SRM, as opposed to the most recent Geo-Engineering experiments which just apply a global and homogeneous one. In order to achieve such condition, we carry out the computation by using an “artificial cloud cover”. The usage of this localized approach allows us to globally cut down temperature warming in the abrupt2×CO2 scenario by 99.8% (which corresponds to an increase of 0.07 °C on a global average basis), while at the same time only having minor changes in precipitation (0.003 mm/day on a global average basis). To achieve this the cloud cover is increased by about 8% on a global average. Moreover, neither temperature nor precipitation response are exacerbated when averaged over any IPCC Special Report on Extremes (SREX) region. Indeed, for temperatures, 90% of SREX regions averages fall within 0.3 °C change, with all regional mean anomalies being under 0.38 °C. Whereas, as far as precipitation is concerned, changes go up to 0.01 mm/day for 90% of SREX regions, with all of them changing by less than 0.02 mm/day. Similar results are achieved for seasonal variations, with Seasonal Cycle (DJF-JJA) having no major changes in both surface temperature and precipitation.

How to cite: Marchegiani, D. and Dommenget, D.: Counteracting global warming by using a locally variable Solar Radiation Management, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12307, https://doi.org/10.5194/egusphere-egu2020-12307, 2020.

Deliberate climate intervention by injection of sulfate aerosols in the stratosphere is a method proposed to counter anthropogenic climate warming. In such an injection scenario, an improved understanding of the microphysical and optical properties of the injected aerosols is important as these properties alter the radiative forcing and resulting climate. Here we analyze the effect of a specific microphysical property of sulfate aerosols in the stratosphere: hygroscopic growth – the tendency of aerosol particles to grow by accumulating water. In the NCAR CESM model, using idealized climate simulations, we find that, for a given mass, stratospheric sulfate aerosols cause more cooling when prescribed at the lower levels of the stratosphere because of increased hygroscopic growth of the aerosols due to larger relative humidity. The relative humidity in the stratosphere typically decreases rapidly with the increasing altitude. The larger relative humidity in the lower stratosphere causes an increase in the aerosol size through hygroscopic growth, which leads to a larger scattering efficiency. The increase in shortwave back-scattering due to the size change is found to be the primary factor contributing to the additional surface cooling as the aerosols are prescribed in the lower levels of the stratosphere. In our simulations, hygroscopic growth provides an additional cooling of 23% (0.7 K) when 20 Mt-SO4 of sulfate aerosols are prescribed at 100 hPa, relative to a non-hygroscopic simulation where hygroscopic growth is not allowed in the stratosphere. This additional cooling due to hygroscopic effect becomes weaker higher in the stratosphere where relative humidity is lower. Hygroscopic growth also leads to additional warming in the layers where the aerosols are prescribed due to an increase in near-IR shortwave absorption. This warming causes secondary effects such as a decrease in high clouds and an increase in stratospheric water vapor, which affects the effective radiative forcing. This altitude dependence of the cooling effects of hygroscopic growth is opposite to the altitude dependence of sedimentation effects;  while the hygroscopic effect produces larger cooling when aerosols reside in the lower stratosphere, the sedimentation effect produces less cooling when aerosols are injected into the lower stratosphere as the residence time becomes shorter.

How to cite: Krishnamohan, K.-P. S.-P., Bala, G., Cao, L., Duan, L., and Caldeira, K.: Climatic Effects of Hygroscopic Growth of Sulfate Aerosols in the Stratosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3241, https://doi.org/10.5194/egusphere-egu2020-3241, 2020.

Under present day conditions the observations approximately show a hemispheric symmetry of the top of atmosphere (TOA)  short wave (SW) reflection despite the asymmetry of surface SW reflection. This has been confirmed by climate models. With models in an aqua planet setup, Voigt et al. (2014) found that tropical clouds largely compensate surface SW hemispheric asymmetries, however to a different degree in dependence on the convection scheme.

In this study, we question, whether there is also a hemispheric symmetry of TOA SW radiation under changed atmospheric radiation conditions. For that reason, we analyze experiments performed with a set of fully coupled general circulation models. The experiments were performed with either a) hemispheric asymmetric incoming radiation, b) increased atmospheric CO2 concentrations, c) increased atmospheric CO2 concentrations combined with increased stratospheric aerosol burden, or d) increased atmospheric CO2 concentration in conjunction with increased ocean albedo.

We show that generally, a hemispheric symmetry of TOA SW radiation does not occur. Overall, among the group of models, the hemispheric TOA SW radiation budgets are roughly similar for the distinct experiments, although the models utilyze different convection schemes.  We discuss the role of surface and atmospheric feedbacks in the different experiments, especially of tropical and extratropical clouds.

Reference:
Voigt, A., B. Stevens, J. Bader, and T. Mauritsen, 2014: Compensation of Hemispheric Albedo Asymmetries by Shifts of the ITCZ and Tropical Clouds. J. Climate, 27, 1029–1045, https://doi.org/10.1175/JCLI-D-13-00205.1.

How to cite: Crueger, T., Schmidt, H., and Stevens, B.: Hemispheric TOA SW radiation budgets under changed atmospheric radiation conditions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7017, https://doi.org/10.5194/egusphere-egu2020-7017, 2020.

In recent decades climate variability and change have caused impacts on natural and human systems on all continents. Observations are needed to understand and document these interactions. These observations are increasingly based on remote sensing from satellites which offer global scale and continuous coverage. Only long-term and consistent observations of the Earth system allow us to quantify impacts of climate variability and change on the natural and human dimension. From this understanding one can estimate and eventually predict future states of the Earth system and quantify its vulnerability and resilience to continuing anthropogenic forcing.

Since nearly 20 years, the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) Satellite Application Facility on Climate Monitoring (CM SAF, www.cmsaf.eu) develops capabilities for a sustained generation and provision of Climate Data Records (CDRs) derived from operational meteorological satellites. The ultimate aim is to make the resulting data records suitable for the analysis of climate variability and the detection of climate trends. The product portfolio of the CM SAF comprises long time series of Essential Climate Variables (ECVs) related to the energy and water cycle as defined by the Global Climate Observing System (GCOS). Several data records have been released to the public by CM SAF and new editions of CDRs will be published in the coming years which will extend the time-range and the portfolio. In particular, existing products include, among others, surface and top of the atmosphere radiative fluxes, surface albedo, cloud products, as well as latent heat flux and freshwater flux over the global ice-free oceans. New products related to the following topics are currently developed and provided in near future: global precipitation (ocean and land) and global high clouds. All products are well-documented, carefully validated and were externally reviewed prior to product release.

This presentation will highlight results from the currently available CDRs from CM SAF. A focus will be on uncertainty characterisation and results from validation as well as exemplary applications. Finally, the presentation will present an overview of the upcoming new editions of CDRs.

How to cite: Schröder, M., Hollmann, R., and Trentmann, J.: Climate Monitoring SAF: Sustained Generation of Satellite based climate data records, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13239, https://doi.org/10.5194/egusphere-egu2020-13239, 2020.

The surface radiation budget is defined by the difference between the downward and upward components of shortwave and thermal infrared longwave radiation at the surface. The instability of the surface radiation budget plays a significant role in climate change and variability through the modulation of temperature, precipitation, atmospheric circulation, etc. Clouds are believed to be a key factor to regulate such energy imbalance at the surface, as they generally reflect shortwave radiation from the sun and emit infrared radiation. Specifically, we are going to focus on the continental United States and answer the following questions: How is the surface radiation budget varied with time and space in the observations? How do clouds impact variations of surface radiation budget? How do state-of-the-art global climate models capture these observed features? What can they tell us about future changes in the surface radiation budget?

To investigate these questions, the NASA Clouds and the Earth's Radiant Energy System (CERES) observations will be used, along with model simulations from Phase 6 of the Coupled Model Intercomparison Project (CMIP6). We will first focus on the surface radiation budget from CERES observations in the 21st century, and examine their seasonal cycles, spatial patterns, long-term trends, and interannual variations over the continental United States. More importantly, we are going to investigate how cloud variability, including cloud types, cloud amount and cloud water content, influences the surface radiation budget. Then the CMIP6 historical simulations will be compared with CERES observations over the same time period. In addition, the CMIP6 future scenario simulations will be used to investigate how the surface radiation budget changes from the middle and late 21st century to the early 21st century. Overall, this study will help us to better understand the cloud and radiation variations in the past, as well as build credibility in the hindcast and future projections of surface energy budget over the continental United States.

How to cite: Fu, D.: Linking Cloud Variability with Surface Radiation Budget over the Continental United States Using NASA CERES Satellite Observations and CMIP6 Model Simulations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6165, https://doi.org/10.5194/egusphere-egu2020-6165, 2020.

The NASA/GEWEX Surface Radiation Budget (SRB) project is finalizing a 3-hourly shortwave and longwave surface and top-of-atmosphere radiative fluxes for a 34-year period from July 1983 through June 2017. The new Release 4 Integrated Product (IP) uses the newly recalibrated and processed ISCCP HXS product as its primary input for cloud and radiance data, replacing ISCCP DX with a ninefold increase in pixel count (10 km instead of 30 km).  This first version retains a 1°x1° resolution for intercomparison against previous versions and other data sets such as CERES. ISCCP also provides an atmospheric temperature and moisture dataset known as nnHIRS which we use and discuss radiative flux sensitivities to in this presentation.  In addition to the input data improvements, several important algorithm improvements have been made since Release 3. These include recalculated SW atmospheric transmissivities and reflectivities yielding a somewhat less transmissive atmosphere. Ocean albedo and snow/ice albedo are also improved from Release 3. Total solar irradiance is now variable consistent with SORCE measurements. The LW code has been updated to improve the optical property treatment for clouds, particularly ice clouds, and aerosols are included in this version.  The variable aerosol composition are specified using a detailed aerosol history from the Max Planck Institute Aerosol Climatology (MAC).  Seasonally dependent spectral surface emissivity maps are now also included.  In this presentation, we analyze the new SW and LW SRB datasets, comparing them to the previous Release 3, BSRN, GEBA and PMEL surface measurements, and ERBE and CERES satellite datasets.  For surface flux validation besides ensemble comparisons, we show the variability of SRB vs surface measurements from BSRN beginning in 1992 and GEBA from 1983.  For the early period, comparison of top-of-atmosphere flux variability is made to latest version of ERBE fluxes.  For the latter period, we provide comparisons to CERES SYN1Deg and EBAF datasets for a benchmark.  Long-term changes in the surface radiation budget components and cloud radiative effects are shown and discussed relative to CERES and surface measurements.   An assessment of long-term changes are made including an assessment of uncertainties due to satellite artifacts.

How to cite: Stackhouse, P., Cox, S., Mikovitz, J. C., and Zhang, T.: A 34 Year Assessment of Surface and Top-of-Atmosphere Radiative Fluxes from the NASA’s GEWEX Surface Radiation Budget Release 4 Integrated Product, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10403, https://doi.org/10.5194/egusphere-egu2020-10403, 2020.

The solar radiation reaching the Earth’s surface determines our climate and is therefore important to be monitored as consistent and complete as possible. Even though surface reference measurements of surface solar radiation are available (e.g. from the Baseline Surface Radiation Network (BSRN)), their density remains low and large areas, like the oceans, remain poorly covered. To fill the gaps in space and time, satellite-based data records (like CLARA-A2 and SARAH-2.1 from the EUMETSAT Satellite Application Facility on Climate Monitoring (CM SAF)) or model-based reanalysis data records (like ERA-5) are used. They provide surface solar radiation data with regional and global coverage, which are needed to understand its distribution and variability from the regional to the global scale.

Here we present a validation and analysis of monthly mean surface solar irradiance from multiple satellite-based and reanalysis data sets on the regional and global scale with reference to a data base of hundreds of surface measurements over land and ocean, collected from different sources (incl. BSRN, GEBA, WRDC, and buoy networks). This study provides new insights about the quality and uncertainty of available state-of-the-art satellite-based and reanalysis data records for climate studies. Regions of agreement as well as areas where the gridded data records exhibit larger differences are identified, providing important information on our current knowledge of the surface solar radiation climatology and possible improvements for future developments.

How to cite: Trentmann, J., Pfeifroth, U., Cremer, R., and Stengel, M.: Global validation of satellite-based and reanalysis surface solar radiation data sets, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1303, https://doi.org/10.5194/egusphere-egu2020-1303, 2020.

The EUMETSAT Satellite Application Facility on Climate Monitoring (CM SAF) generates satellite-based  high-quality climate data records, with a focus on the global energy and water cycle. The new concept of Interim Climate Data Records (ICDRs) that extent the fixed-length Climate Data Records (CDRs) into 'near-realtime' in a consistent way, enables climate monitoring at a higher level of accuracy.

It has been found in recent studies based on surface and satellite data that on average SSR has been increasing in the last 3 decades in Europe (e.g. Sanchez-Lorenzo et al. 2017, Pfeifroth et al. 2018) - especially in spring and summer. Here we use the latest SARAH-2.1 TCDR (1983-2017), potentially together with its corresponding ICDR (2018 onwards), to analyze if the found positve trends in SSR are about to continue. In this respect, the satellite-based data record will be compared and validated with surface measurements given by the Baseline Surface Radiation Network (BSRN), the  World Radiation Data Center (WRDC) and the Global Energy Balance Archive (GEBA). A reasonable line of potential reasons for the found spring and summertime brightening in Europe is discussed.

How to cite: Pfeifroth, U. and Trentmann, J.: Variability and Trends of Surface Solar Radiation in Europe based on satellite- and surface-based data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-241, https://doi.org/10.5194/egusphere-egu2020-241, 2020.

The main advantage of remote sensing products is that they are reasonably good in terms of temporal and special coverage, and they are available in a near real time. Therefore, an understanding of the strengths and weaknesses of satellite data is useful to choose it as an alternative source of information with acceptable accuracy.  On the first hand, this study assesses an Inter-comparison between CMSAF Sunshine Duration (SD) data records and ground observations of 30 data sets from 1983 to 2015. the correlation is very significant and the satellite data fits very closely to in situ observations. On the other hand, trend analysis is applied to SD and Solar Incoming Direct radiation (SID) data, a number of stations show a statistically significant decreasing trend in SD and also SID shows a decreasing trend over Morocco in most of regions especially in summer. The results indicate a general tendency of decrease in incoming solar radiation mostly during summer which could be of some concern for solar energy.

How to cite: Moutia, S.: Spatial variation and temporal trends of solar radiation over Morocco based on ground observations and CMSAF data records., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20470, https://doi.org/10.5194/egusphere-egu2020-20470, 2020.

Surface longwave (LW) radiation plays an important rolein global climatic change, which is consist of surface longwave upward radiation (LWUP), surface longwave downward radiation (LWDN) and surface longwave net radiation (LWNR). Numerous studies have been carried out to estimate LWUP or LWDN from remote sensing data, and several satellite LW radiation products have been released, such as the International Satellite Cloud Climatology Project‐Flux Data (ISCCP‐FD), the Global Energy and Water cycle Experiment‐Surface Radiation Budget (GEWEX‐SRB) and the Clouds and the Earth’s Radiant Energy System‐Gridded Radiative Fluxes and Clouds (CERES‐FSW). But these products share the common features of coarse spatial resolutions (100-280 km) and lower validation accuracy.

Under such circumstance, we developed the methods of estimating long-term high spatial resolution all sky  instantaneous LW radiation, and produced the corresponding products from MODIS data from 2000 through 2018 (Terra and Aqua), named as Global LAnd Surface Satellite (GLASS) Longwave Radiation product, which can be free freely downloaded from the website (http://glass.umd.edu/Download.html).

In this article, ground measurements collected from 141 sites in six independent networks (AmerciFlux, AsiaFlux, BSRN, CEOP, HiWATER-MUSOEXE and TIPEX-III) are used to evaluate the clear-sky GLASS LW radiation products at global scale. The bias and RMSE is -4.33 W/m² and 18.15 W/m² for LWUP, -3.77 W/m² and 26.94 W/m² for LWDN, and 0.70 W/m² and 26.70 W/m² for LWNR, respectively. Compared with validation results of the above mentioned three LW radiation products, the overall accuracy of GLASS LW radiation product is much better. We will continue to improve the retrieval algorithms and update the products accordingly.

How to cite: Zeng, Q., Cheng, J., and Yang, F.: Validation of Clear-Sky Global LAnd Surface Satellite (GLASS) Longwave Radiation Product, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2036, https://doi.org/10.5194/egusphere-egu2020-2036, 2020.

Downwelling surface solar irradiance (DSSI) is one of the Essential Climate Variables defined by the Global Climate Observing System. The knowledge of its space and time variabilities is of primary importance for different applications, including Earth sciences, agriculture and renewable solar energies. To characterize such variabilities, the retrieval of long time series and of a dense kilometric global spatial coverage is required. The Heliosat methods are developed by Mines ParisTech since the mid-1980’s to estimate DSSI from the imagery produced by geostationary meteorological satellites. A challenge today is to use imagery from different satellites, including non-geostationary. This raises a number of issues, related among others to the different viewing geometries and spectral sensitivities of the sensors. These issues motivate the evolution of the Heliosat methods toward a more flexible version: the versatile Heliosat-V method. Other difficulties, mainly of operational types, such as massive data retrieval/processing, geometric correction, radiometric cross-calibration, missing data, seamless mosaicking, etc. are out of the scope of this communication.

Heliosat-V is designed to produce estimates of DSSI that can cover a wide variety of satellite optical sensors that have at least one radiometric channel with sensitivity in the 400-1000-nm part of the electromagnetic spectrum. The method is capable of using calibrated imagery from geostationary and also non-geostationary satellites. External remote-sensed data of surface reflectance anisotropy (Ross-Li model parameters derived from the imagery of the Moderate-Resolution Imaging Spectroradiometer (MODIS)) and atmospheric composition (ozone, water vapour and aerosol types and optical depths) from coupled meteorological and chemical transport models (Copernicus Atmospheric Monitoring Services) are used to produce fast radiative transfer simulations. Typical reflectances of cloudy scenes at the top of the atmosphere are produced via look-up tables derived from a radiative transfer model (libRadtran). They can adapt to the spectral sensitivity of the satellite channel, and to the solar and viewing geometries. This algorithm setup allows its use without past data, which were necessary for previous Heliosat methods. This is a real asset for its implementation to non-geostationary satellites.

We test the validity of the method, by comparing DSSI estimates derived from one year of Meteosat Second Generation 0° imagery, with ground-based pyranometer measurements from 10 stations of the Baseline Surface Radiation Network, on different continents and environments. Our results show root-mean square errors of 15-min averaged DSSI between 12% and 35% (71 and 133 W m^-2 in absolute value), similarly to existing surface irradiance products based on Heliosat-2 or Heliosat-4.

How to cite: Tournadre, B., Gschwind, B., Saint-Drenan, Y.-M., and Blanc, P.: The versatile Heliosat-V method for estimating downwelling surface solar irradiance from satellite imagery, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1630, https://doi.org/10.5194/egusphere-egu2020-1630, 2020.

The Earth’s Outgoing Longwave Radiation (OLR) is a key component in the study of climate feedbacks and processes. As part of the Earth’s radiation budget, it reflects how the Earth-atmosphere system compensates the incoming solar radiation at the top of the atmosphere. It can be retrieved from the radiance intensities measured by satellite sounders and integrated over all the zenith angles of observation. Since satellite instruments generally acquire the radiance at a limited number of viewing angle directions and because the radiance field is not isotropic, the conversion is however not straightforward. This problem is usually overcome by the use of empirical angular distribution models (ADMs) developed for different scene types that directly link the directional radiance measurement to the corresponding OLR.

OLR estimates from dedicated broadband instruments are available since the mid-1970s; however, such instruments only provide an integrated OLR estimate over a broad spectral range. They are therefore not well suited for tracking separately the impact of the different parameters affecting the OLR (including greenhouse gases), making it difficult to track down deficiencies in climate models. Currently, several hyperspectral instruments in space acquire radiances in the thermal infrared spectral range, and in principle, these should allow to better constrain the OLR. However, as these instruments were not specifically designed to measure the OLR, there are several challenges to overcome. Here we propose a new retrieval algorithm for the estimation of the spectrally resolved OLR from measurements made by the IASI sounder on board the Metop satellites. It is based on a set of spectrally resolved ADMs developed from synthetic spectra for a large selection of scene types associated with different states of the atmosphere and the surface. Atmospheric and surface parameters are derived from the Copernicus Atmosphere Monitoring Service (CAMS) reanalysis dataset and selected using a dissimilarity-based subset selection algorithm. These spectral ADMs are then used to convert the measured IASI radiances into spectral OLR.

We then evaluate how the IASI OLR compare with the CERES and the AIRS integrated and spectral OLR. We analyze the interannual variations in OLR over 10 years of IASI measurements for selected spectral channels using EOF analysis and we connect them with well-known climate phenomena such as El Niño-Southern Oscillation (ENSO), the Pacific Decadal Oscillation (PDO), the Atlantic Multidecadal Oscillation (AMO).

How to cite: Whitburn, S., Clarisse, L., Bauduin, S., Dewitte, S., George, M., Safieddine, S., Hurtmans, D., Coheur, P.-F., and Clerbaux, C.: Spectrally resolved OLR from IASI measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14878, https://doi.org/10.5194/egusphere-egu2020-14878, 2020.

The change of its annual cycle is extremely important due to global warming. A widely used method to analyze the changes of temperature annual cycle is based on the decomposition to phase, amplitude and baseline terms. Solar radiation as the leading energy source of temperature changes can directly influence temperature annual cycle. In this study, we investigate the phase, amplitude and baseline of temperature and solar radiation annual cycle after Fourier transform during 1960-2016 in China. The results show that annual cycle of maximum, minimum and mean surface air temperature are advancing in time (-0.08, -0.27 and -0.33 days per ten years), decreasing in range (-0.07, -0.25 and -0.18 degrees per ten years) and rising in baseline (0.20, 0.34 and 0.25 degrees per ten years). To further quantify the effect of surface solar radiation to temperature, we remove the effect from its original time series of maximum and mean temperature, based on a linear regression. The compare of raw and adjusted temperature shows that surface solar radiation advancing the time by 0.19 and 0.19 days per ten years, reduces the range by 0.14 and 0.13 degrees per ten years, and reduces the baseline by 0.08 and 0.04 degrees per ten years, for surface maximum and mean daily air temperature. The result can explain parts of seasonal temperature variation. Effect of surface solar radiation is most obvious Yunnan-Guizhou Plateau for maximum phase. The low phase value in this area is corrected and well-match with other same latitude area after adjusted.

How to cite: Zhao, R., Wang, K., Wu, G., and Zhou, C.: Temperature Annual Cycle Variation and Response to Solar Radiation during 1960 to 2016 in China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3777, https://doi.org/10.5194/egusphere-egu2020-3777, 2020.

Previous studies have documented that the surface solar radiation (SSR) over most regions of China has shifted from the ‘global dimming’ since the 1950s to the ‘global brightening’ after 2005. In this paper, the potential factors that affect the annual trends of SSR over East China from 2005 to 2018 based on different satellite-derived products are analyzed. Then, due to the lack of long-term various aerosol species from observation data, the focus of this study is to calculate the contributions from direct effects of different types of cloud fraction on SSR relative to the effects of total cloud fraction over East China during the same period using a BCC_RAD radiative transfer model. The results show that clouds and aerosols are the primary factors that affect the SSR over East China from 2005 to 2018, followed by water vapor and ozone.

The annual mean all-sky SSR from 2005 to 2018 is significantly increased over the North China Plain, Northeast China, Yunnan, and Eastern Sichuan provinces, with the increases up to 0.6 W m^-2 yr^-1. This is probably due to the combined reductions of aerosols and clouds during this period, but clouds even play a more important role over Shanxi and northern Shaanxi. Changes in aerosols dominate the increase of SSR over Hunan, Jiangxi, and Fujian provinces, whereas clouds contribute more to the decreases of SSR over Guangdong, Guangxi, Guizhou, and Zhejiang provinces. Meanwhile, the simulations indicate that the marked annual mean decreases in high cloud fraction, especially for low cloud fraction, are the main causes of simulated increases in SSR due to total cloud fraction over most regions of East China, while the increases in high, medium-high, especially for medium-low cloud fraction, play more important roles in reductions of SSR over southern China. Moreover, the direct effects of various types of cloud fraction on changes in SSR for each season are also examined. It seems that the direct effects of low cloud fraction on SSR are likely the strongest among all kinds of clouds. Take southern China as an example, the direct effects of medium-low and low cloud fraction are stronger for spring and autumn, while contributions from low cloud fraction are largest in winter. However, the combined increases in high, medium-high, medium-low cloud fraction exceed decreases in low cloud fraction, thus causing the reduction in SSR in summer. This study highlights that different types of clouds may have different impacts on SSR not only on the annual mean scale but also on seasonal scales.

Keywords: surface solar radiation, aerosols, different types of cloud fraction

How to cite: Wang, Q., Zhang, H., and Wild, M.: Effects of potential factors on changes in surface solar radiation in East China over recent decade, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5699, https://doi.org/10.5194/egusphere-egu2020-5699, 2020.

The local contribution of clouds to the surface energy balance and temperature variability is an important topic in order to apprehend how this intake affects local climate variability and extreme events, how this contribution varies from one place to another, and how it evolves in a warming climate. The scope of this study is to understand how clouds impact temperature variability, to quantify their contribution, and to compare their effects to other surface processes. To do so, we develop a method to estimate the different terms that control temperature variability at the surface (∂T_2m /∂t) by using this equation: ∂T_2m /∂t=R+HA+HG+Adv where R is the radiation that is separated into the cloud term (R_cloud) and the clear sky one (R_CS), HA the atmospheric heat exchange, HG the ground heat exchange, and Adv the advection. These terms are estimated hourly, almost only using direct measurements from SIRTA-ReOBS dataset (an hourly long-term multi-variables dataset retrieved from SIRTA, an observatory located in a semi-urban area 20-km South-West of Paris; Chiriaco et al., 2019) for a five-years period. The method gives good results for the hourly temperature variability, with a 0.8 correlation coefficient and a weak residual term between left part (directly measured) and right part of the equation.

A bagged decision trees analysis of this equation shows that R_CS dominates temperature variability during daytime and is mainly modulated by cloud radiative effect (R_cloud). During nighttime, the bagged decision trees analysis determines that R_cloud is the term controlling temperature changes. When a diurnal cycle analysis (split into seasons) is performed for each term, HA becomes an important negative modulator in the late afternoon, chiefly in spring and summer, when evaporation and thermal conduction are increased. In contrast, HG and Adv terms do not play an essential role on temperature variability at this temporal scale and their contribution is barely considerable in the one-hour variability, but still they remain necessary in order to obtain the best coefficient estimator between the directly measured observations and the method estimated. All terms except advection have a marked monthly-hourly cycle.

Next steps consist in characterize the types of clouds and study their physical properties corresponding to the cases where R_cloud is significant, using the Lidar profiles also available in the SIRTA-ReOBS dataset.

How to cite: Rojas, O., Chiriaco, M., Bastin, S., and Ringard, J.: Contribution of clouds radiative forcing to the local surface temperature variability, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14932, https://doi.org/10.5194/egusphere-egu2020-14932, 2020.

How to cite: Lee, B. J. and Lee, J. I.: A study on the determination method of Global Warming Potential (GWP) by measuring the experiment-based infrared absorption spectra and the reactivity of the hydroxyl radical, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2310, https://doi.org/10.5194/egusphere-egu2020-2310, 2020.