Multidecadal dimming and brightening of solar radiation at Earth’s surface has been shown to occur over all continents. Trends have been especially well documented over the Northern Hemisphere (NH) with dimming from the 1950s through the middle 1980s followed by brightening through the first decade of the 2000s in the United States, Europe, and parts of Asia. Trends in Europe and China have been attributed to both aerosols and clouds, but in the U.S. cloud variability has been dominant. A recent analysis shows that U.S. brightening of 7.4 Wm^-2/decade peaked in 2012 and then dramatically dropped to near normal values in 2013. Since then, surface solar radiation in the U.S. has remained within 1 Wm^-2 of the long-term average. However, in Europe surface solar radiation has remained high, at least through 2017.

It has been shown that the direct effect of aerosols cannot account for the magnitude of the latest brightening in the U.S. It has also been shown that the second indirect effect of aerosols may explain brightening into the first decade of the 2000s, but is in opposition to the observed dimming after 2012. High aerosol content does explain perpetual dimming in India and industrial parts of China, but, given that the magnitude and period of dimming and brightening trends from the 1950s through the first decade of the 2000s are similar over North America, Europe, and parts of Asia, I speculate the primary cause is meteorological. A recent study documents a strong association between multidecadal surface solar radiation trends over NH continents and long-term North Pacific and North Atlantic sea surface temperature (SST) patterns. For example, the reversal of the Pacific Decadal Oscillation (PDO) index in the mid-1980s is nearly simultaneous with the change from dimming to brightening over NH continents. A similar association is shown between Atlantic SST patterns and continental surface solar radiation trends but with a decade lag. Using reanalysis and observed SST patterns it is demonstrated that persistent warm SST anomalies support overlying semipermanent geopotential height ridges at tropospheric mid-levels that dynamically induce persistent troughs downstream over adjacent continents, if positioning is favorable. Semipermanent troughs over the continents cause greater than average cloud cover and dimming. Conversely, long-term cool SSTs produce the opposite scenario and yield less clouds and brightening downstream over the continents. Further, marine heat waves on either side of North America are shown to be associated with the recent dimming in the midcontinent from 2013 to the present, and warm SSTs in the Mediterranean and North Seas in the last decade are likely responsible for a persistent midlevel geopotential ridge pattern and continued high surface solar radiation there. Recent studies present evidence that the observed increase in frequency and variability of marine heat waves in the past few decades may be associated with global warming, possibly linking warming to trends in surface solar radiation.

How to cite: Augustine, J.: Contributors to multidecadal dimming and brightening of surface solar radiation over Northern Hemisphere continents, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8365, https://doi.org/10.5194/egusphere-egu23-8365, 2023.

Sea Surface Temperature (SST) plays a major role in the unforced variability of the climate system on decadal scales via the interplay between ocean and atmosphere, and associated changes in cloud cover and water vapor. The ocean modes, such as El Nino Southern Oscillation (ENSO) and Interdecadal Pacific Oscillation (IPO), are major coherent manifestations of SST variability. This means that the impacts of the ocean modes might be reflected in several components of the climate system, such as the energy budget. At the surface, this can be observed in the decadal trends in surface solar radiation (SSR). In this study we investigated the impacts of IPO and ENSO and associated cloud cover and water vapor variability on the decadal trends in SSR at 6 island stations scattered in the western Pacific (two stations in Fiji, one in New Caledonia, Nauru, Papua New Guinea and Marshall Islands). We combined between 15 and 40 years of daily SSR observations (depending on the station) with cloud cover from ERA5 reanalysis, aerosol optical depth (AOD) from CAMS reanalysis, and time series of IPO and ENSO. The comparison between clear-sky and all-sky SSR trends show that the all-sky trends strongly dominate in 5 out of the 6 stations. The exception is New Caledonia, where the clear-sky seems to also play an important role in the overall trend. This is the least cloudy station, and also the closest station to eastern Australia, an important source of aerosols in the region. Maps of cloud cover trends show two distinct regions which can be approximately separated by the average climatological position of the South Pacific Convergence Zone (SPCZ): one where cloud cover trends follow the phase of the IPO (positive IPO phase = positive cloud cover trend; N-NE of the SPCZ) and one where the opposite happens (positive IPO phase = negative cloud cover trend; S-SW of the SPCZ). The direct comparison between annual time series of all-sky SSR and IPO shows correlations stronger than 0.5 at two stations in Fiji and the one in New Caledonia (SW of the SPCZ). At the station in Nauru (North of the SPCZ) there is a negative correlation stronger than -0.5. When comparing annual all-sky SSR to the ENSO index, significant negative correlations are found at Momote-Papua New Guinea (-0.41) and at Nauru (-0.96), both located in the Western Pacific Warm Pool, near the Equator. In all cases strong negative correlations (<-0.7) between SSR and cloud cover using both annual and 11-year moving means time series support the hypothesis of strong cloud control over SSR interannual and decadal variability. The results indicate that IPO and ENSO play a major role in the SSR variability over the Western Pacific by controlling different cloud cover regimes in the region. This reveals a real world case of the importance of unforced internal variability to the SSR decadal and sub decadal changes.

How to cite: Ferreira Correa, L., Folini, D., Chtirkova, B., and Wild, M.: Impacts of the Ocean Modes on the Surface Solar Radiation decadal variability over the western Pacific, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4469, https://doi.org/10.5194/egusphere-egu23-4469, 2023.

Unmasking the Effects of Aerosols on Greenhouse Warming Over Europe

P. Glantz¹, O. G. Fawole², J. Ström¹, M. Wild³ and K. J. Noone¹

¹Department of Environmental Science, Stockholm University, Stockholm, Sweden

²Dept. of Physics and Engineering Physics, Obafemi Awolowo University, Ile-Ife, Nigeria

³Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland

This work with corresponding publication in Journal of Geophysical Research: Atmospheres, 127, e2021JD035889. https://doi.org/10.1029/2021JD035889 is supported by FORMAS, grant 2018-01291.

Aerosol optical thickness (AOT) has decreased substantially in Europe in the summer half year (April–September) since 1980, with almost a 50% reduction in Central and Eastern Europe, according to Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) reanalysis. At the same time, strong positive trends in ERA5 reanalysis surface solar radiation downward for all-sky and clear-sky conditions (SSRD and SSRDc, respectively) and temperature at 2 m are found for Europe in summer during the period 1979–2020. The Global Energy Balance Archive (GEBA) observations show as well strong increases in SSRD during the latest four decades. Estimations of changes in SSRDc, using the Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART) model, show similarly strong increases when fed by MERRA-2 AOT. The estimates of warming in this study, caused by increases in SSRD and SSRDc, are based on energy budget approximations and the Stefan Boltzmann law. The increases in near surface temperature, estimated both for clear-sky and all-sky conditions, are up to about 1°C for Central and Eastern Europe. The total warming over large parts of this region for clear-sky conditions is however nearly double the global mean temperature increase of 1.1°C, while somewhat less for all-sky conditions. Although the largest effects from aerosols on the radiation balance occurred in the 1980s and 1990s, the total warming has continued to increase more or less at the same rates during the latest four decades over large parts of Europe, considering both all-sky and clear-sky situations. Thus, decline in aerosols can certainly not explain all warming observed and particularly not considering the southern Iberian Peninsula where the aerosol effects on warming are weaker compared to countries further north. The largest increases in sensible heat flux at the expense of latent heat flux have occurred in Iberian Peninsula, which is probably a result of drier surface conditions. This means a positive feedback associated with reduced evaporate cooling and warming of the lowest air layers. Decline in water vapor in combination with the warming may have contributed to decreased cloud cover, which is found for large parts of Europe in the summer half year during the latest four decades. Anthropogenic aerosols over large parts of Europe have thus temporarily masked, until around 1980, parts of rapid warming from increases in greenhouse gases. CO₂ from fossil fuels is of particularly serious concern, since it can continue to affect climate for thousand years.

How to cite: Glantz, P.: Unmasking the Effects of Aerosols on Greenhouse Warming Over Europe, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15351, https://doi.org/10.5194/egusphere-egu23-15351, 2023.

The absorption and scattering by aerosols and clouds greatly affect surface solar irradiance and the Earth's energy budget. Large uncertainties still remain on the current estimates of these radiative effects because of an incomplete knowledge of their spatial and temporal variabilities.

We analyze coincident daytime ground-based measurements of aerosol optical properties from AERONET photometer and of direct and diffuse horizontal surface irradiances from a set of pyrheliometer and pyranometer routinely performed at the ATOLL (Atmospheric Observations in LiLle) platform in north of France over the period 2010-2020. The site is located in a highly populated area greatly influenced by clouds and aerosol pollution. In order to isolate the radiative effect of aerosols from that of cloud occurences, a separation between cloudy-sun, clear-sun with surrounding clouds and clear-sky moments is performed using two cloud detection algorithms at 1-min resolution. The measurements are further analyzed using a radiative transfer code to simulate the spectrally integrated solar global horizontal irradiance and its components in clear-sky conditions with and without aerosols (pristine like conditions).

Our analysis shows that on average in ATOLL over the period 2010-2020, the sky is cloudy 89% of the time with around 67% of cloudy-sun situations and 22% of clear-sun with clouds moments. The proportion of clear-sky conditions is relatively low (11%) with a minimum in winter (6%) and a maximum in spring (15%).

In summer, we observe over the period a robust increasing trend in measured total irradiances in all-sky conditions of +5.2 ± 1.8 W/m²/year. This evolution is mainly explained by a positive trend in the occurrence of clear-sky situations (+0.7 ± 0.3% per year) to the detriment of cloudy-sun moments.

In spring, we highlight a high variability of cloud occurences and mean solar irradiances. Indeed, the mean proportion of clear-sky moments varies more than fourfold between 2013 (8%) and 2020 (35%), leading to corresponding all-sky irradiance extrema of 285 and 389 W/m² respectively. Moreover, in clear-sky conditions, an important variability is observed between the maximum of seasonal global irradiance of spring 2018 (522 W/m²) and the minimum of spring 2014 (435 W/m²). The latter variability is emphasised by a significative positive trend in direct irradiances observed for springtime clear-sky conditions of +5.3 ± 2.3 W/m²/year. A sensitivity analysis based on our radiative simulations shows that it is partly explained by a significant decrease in measured AOD_{440 nm} (-0.006 ± 0.002 per year) and a change in the proportion of high aerosol loads over 2010-2020. This is also consistent with a negative trend of the diffuse component (-1.2 ± 0.4 W/m²/year) observed for clear-sky conditions in spring.

Finally, besides showing the highest proportion of clear-sky moments, spring is also the most polluted season in aerosol, with more than 80% of AOD_{440 nm} higher than 0.1. This translates to an average seasonal maximum of aerosol direct radiative effect in spring of -22.6 W/m² (-6.1%), with a loss of -69.3 W/m² (-19.2%) of direct irradiance partially compensated by an increase of the diffuse radiation of +46.6 W/m² (101.0%).

How to cite: Chesnoiu, G., Ferlay, N., Auriol, F., Catalfamo, M., Jankowiak, I., and Chiapello, I.: Contribution of cloudy/clear-sky partitions and aerosol variability to the solar irradiance measured over 2010-2020 in Northern France, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11280, https://doi.org/10.5194/egusphere-egu23-11280, 2023.

Ground heat flux constitutes the conductive component of the surface energy budget. Quantifying this energy component is important to close the surface energy balance and to understand the energy exchanges between the lower atmosphere and the shallow subsurface. Furthermore, ground heat storage accounts for approximately 90 % of the continental heat storage, and 4-5 % of the total Earth heat storage. Therefore, monitoring changes in ground heat flux at global scale is of critical importance to quantify and understand the evolution of the Earth heat inventory, and thus climate change. However, the main sources of information about past and present ground heat flux are measurements of subsurface temperature profiles and micrometeorological observations, which are incomplete records biased towards northern extratropical latitudes.

Here, we present preliminary estimates of global ground heat flux derived from remote sensing products from the European Space Agency (ESA) Climate Change Initiative (CCI). Estimates from four land surface temperature (LST) products (MODIS-Terra, MODIS-Aqua, ENVISAT-AATSR, and SSMI-SSMIS) are evaluated against FLUXNET observations, obtaining a range of root mean squared errors from 3.8 to 5.2 W m^-2 at monthly resolution. Nevertheless, there are some spatial inconsistencies among estimates from different LST products, as well as in long-term trends during the period 2003-2013. Several factors affecting the estimated ground heat flux are analyzed, with soil water and land cover having the largest effect on the retrieved values. These results suggest that land surface temperature from satellite observations may be able to provide global long-term ground heat flux estimates, although some issues still need to be solved.

How to cite: Cuesta-Valero, F. J. and Peng, J.: Global ground heat flux from remote sensing data: preliminary results and evaluation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2608, https://doi.org/10.5194/egusphere-egu23-2608, 2023.

Under current climate-change conditions, the energy imbalance at the top of the atmosphere results in an uptake of energy by the Earth system. Previous efforts have identified the magnitude and proportions of this energy excess and how it is distributed among the different components of the climate system. However, the bulk of the Earth System Models (ESMs) participating in CMIP5/6 deliver Earth energy inventory estimates that differ substantially from recent observations. Particularly for the land component, there is a significant underestimation of simulated continental energy uptake, which was hypothesized to be caused by too shallow land surface model components in current-generation ESMs. Support for the latter was given by previous modeling estimates based on analytical heat conduction models and standalone land surface model simulations. Here we use a suite of current-generation fully-coupled CMIP6 ESMs and a version of the MPI-ESM that includes a deep land model component, accommodating the required space for increased terrestrial energy storage. The simulations show that a sufficiently deep land model leads to more realistic subsurface energy storage - correlating with model depth rather than climate sensitivity, and an adjusted estimate of energy uptake ratios among the Earth system components compared to observational estimates. However, the impact of changes in the land energy budget from the perspective of the entire Earth system appears to have only a marginal influence due to its relatively small fraction of the Earth energy inventory.

How to cite: Steinert, N. J., González-Rouco, J. F., de Vrese, P., Cuesta-Valero, F. J., García Pereira, F., and Melo Aguilar, C. A.: Global energy budget changes from underestimated land heat uptake in CMIP6 models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8463, https://doi.org/10.5194/egusphere-egu23-8463, 2023.

In this study, we examine whether the interhemispheric symmetry observed
in broadband shortwave albedos also applies to the
hemispheric-mean visible and near-infrared albedos.  While
several recent exploratory studies have examined this question
using climate models, we explore this
question using direct observations of the visible and
near-infrared albedos collected by the Nimbus-7 satellite. This
study builds upon earlier intercomparisons of cloud spectral
albedos from Nimbus-7 and from climate models using the same
combinations of Nimbus-7 measurements used here (Collins, 1998).

We find that the hemispheric-mean spectral partitioning of albedo is
consistently and statistically significantly different between the two
hemispheres.  Consistent with prior studies, the origin of these
differences is due to interhemispheric differences in cloud cover.
Over oceans, the regional daily-mean differences between visible and
near-IR albedos are closely correlated with cloud amount.  The
relative differences are maximized for clear-sky conditions and
minimized for overcast conditions.

Background: The shortwave broadband albedo is a weighted sum of the albedos
in the visible and near-infrared bands.  Under condensate-free
conditions, the interactions of solar insolation in these bands
with the atmosphere and surface are quite different.  To an
excellent approximation, the condensate-free atmosphere is a
conservative Rayleigh-scattering medium in the visible.  Solar
radiation that is not reflected back to space is, to leading
order, transmitted to the surface.  In the near-infrared, the
interactions of sunlight with the atmosphere are dominated by
absorption, primarily with water vapor.  Additional absorption is
contributed by well-mixed greenhouse gases, oxygen, and other
gaseous constituents. The solar radiation
reaching the surface has therefore been reduced both by
reflection to space (from atmospheric condensates and the surface
albedo) and by absorption in the atmosphere. Hence, the relative
partitioning of net TOA insolation between the visible and
near-infrared bands will affect the relative partitioning between
atmospheric absorption and transmission to the surface.

How to cite: Collins, W. and Feldman, D.: Evidence for Hemispheric Spectral Albedo Inequality, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12, https://doi.org/10.5194/egusphere-egu23-12, 2023.

We use 19 years of continuous near-global land and ocean direct AIRS satellite measurements combined with detailed atmospheric radiative transfer modelling to demonstrate strong strengthening in the greenhouse effect caused by CO₂ and detectable, but comparatively smaller strengthening, by CH₄ and N₂O. An increase in the outgoing longwave radiation is found in the 800-1000 cm⁻¹ atmospheric window resulting from the Planck response to surface heating. The combined use of satellite measurements and the radiative transfer model also demonstrate that reductions in concentrations of prohibited ozone depleting substances have weakened the greenhouse effect in the spectral region where these gases absorb thermal infrared radiation. The strong greenhouse effect strengthening signal in the satellite data in the spectral region 710-720 cm⁻¹ is a fingerprint of CO₂ increase since we demonstrate that other factors could not cause such a robust spectral feature. We show how the spectral clear sky instantaneous change in TOA flux relates to the greenhouse gas radiative forcing over the 19-year period.

How to cite: Rentsch, C. and Myhre, G.: Fingerprint of CO2 and other gases on the greenhouse effect from direct satellite observation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11930, https://doi.org/10.5194/egusphere-egu23-11930, 2023.

Instantaneous radiative forcing (IRF) is a fundamental metric for measuring the extent to which anthropogenic activities and natural events perturb the Earth's energy balance. This perturbation initiates all other forced climate responses. Among all the anthropogenic forcing agents, CO₂ is the dominant driver of warming over the past century and the defining forcing variable for quantifying climate sensitivity. When evaluating the effect of CO₂ changes on the earth’s climate, it is universally assumed that the IRF from a doubling of a given CO₂ concentration (IRF_2×CO2) is constant and that variances in climate sensitivity arise from differences in radiative feedbacks, or a dependence of these feedbacks on the climatological base-state. In this paper, we show that the IRF_2×CO2 is not constant, but also depends on the climatological base-state, increasing by ~25% for every doubling of CO₂, and has increased by ~10% since the pre-industrial era, implying a proportionate increase in climate sensitivity. This base-state dependence also explains about half of the intermodel spread in IRF_2×CO2, a problem that has persisted among climate models for nearly three decades. It may also have important implications for elucidating the causes and consequences of deep-time paleoclimates, where changes in the climatological base-state can strongly modulate the magnitude of the CO₂ IRF.

How to cite: Soden, B., He, H., Kramer, R., and Jeevanjee, N.: State Dependence of CO2 Forcing and Its Implications for Climate Sensitivity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1015, https://doi.org/10.5194/egusphere-egu23-1015, 2023.

Aerosols directly affect Earth’s radiation budget by scattering and absorbing incoming solar radiation and outgoing terrestrial radiation. While the uncertainty in aerosol radiative forcing (ARF) has decreased over the years, it is still higher than that of greenhouse gas forcing, particularly in the South Asian region, due to high heterogeneity in aerosols’ chemical properties. India has been identified as an aerosol hotspot. Understanding the Spatiotemporal heterogeneity of aerosol composition is critical in improving ARF estimation.                            

In this study, we have taken aerosol data from Multi-angle Imaging Spectro-Radiometer (MISR) level-2 version 23 aerosol products retrieved at 4.4 km and radiation data from Clouds and the Earth’s Radiant Energy System (CERES, spatial resolution=1^ox1^o), for 21 years (2000-2021) over the Indian subcontinent. MISR aerosol product includes size and shapes segregated aerosol optical depth (AOD), Angstrom exponent (AE), and single scattering albedo (SSA). Additionally, 74 aerosol mixtures included in version 23 data are used for aerosol speciation. In addition, we have used CERES radiation data in four different atmospheric conditions: all-sky (AS), clear-sky (CS), pristine (PR) and no aerosol (NAER), for estimating aerosol radiative forcing in different aerosol-cloud conditions.

We have seasonally mapped aerosol optical and microphysical properties from MISR for India at quarter degrees resolution. Results show strong Spatio-temporal variability, with a constant higher value of AOD for the Indo-Gangetic Plain (IGP). The fractional contribution of small-size particles to AOD is higher (>0.4) throughout the year, spatially during post-monsoon and winter seasons (October to February). SSA is found to be overestimated by MISR, where absorbing particles are present. The climatological map of short wave (SW) ARF at the top of the atmosphere (TOA) shows a strong cooling except in only a few places (values ranging from +2.5W/m² to -22.5 W/m²). Cooling due to aerosols is higher in the absence of clouds. Higher aerosol cooling is found over the IGP region, given the high aerosol concentration over the region. Aerosols are causing a surface cooling effect over our study domain, which is higher in clear conditions. The results strongly correlate with AOD from MISR and ARF from CERES. 

How to cite: Srivastava, S., Ghosh, S., and Dey, S.: Aerosol Radiative Forcing Over Indian Subcontinent for 2000-2021 using satellite observations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5727, https://doi.org/10.5194/egusphere-egu23-5727, 2023.

Anthropogenic aerosol particles affect clouds by serving as cloud condensation nuclei, thus significantly influencing Earth’s energy balance. The magnitude of aerosol-induced changes in cloud properties is still uncertain. This is primarily due to the meteorological covariability between aerosols and clouds, which hinders inferring causal relationships. Industrial air pollution sources serve as natural experiments to study strong anthropogenic cloud perturbations (Toll et al. 2019 Nature https://doi.org/10.1038/s41586-019-1423-9) and allow us to infer causal relationships between aerosols and clouds.

We use geostationary satellite observations to study the temporal evolution of polluted clouds. Polluted clouds are usually thinner than nearby unpolluted clouds. But in some cases, the polluted clouds grow much thicker in the afternoon than the nearby unpolluted clouds. We find that continental polluted cloud tracks are relatively long-lived, with a median lifetime of 18 hours. Moreover, there are many cases where polluted cloud tracks are visible for multiple consecutive days. This means polluted cloud tracks live long enough for clouds to fully adjust to aerosol-increased cloud droplet numbers. Future work is needed to combine geostationary and polar orbiting satellite observations of polluted cloud tracks to develop stronger observational constraints for aerosol-cloud interactions.

How to cite: Rahu, J. and Toll, V.: Novel insights into aerosol-cloud interactions enabled by analysing the temporal evolution of strong anthropogenic cloud perturbations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7090, https://doi.org/10.5194/egusphere-egu23-7090, 2023.

How to cite: Lac, J., Chepfer, H., Gallagher, M. R., and Arouf, A.: Low opaque clouds formed over Baffin Sea enhances Greenland's west coast surface cloud warming, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14718, https://doi.org/10.5194/egusphere-egu23-14718, 2023.

Climate models often ignore cloud scattering and surface emissivity in the longwave (LW) for computational efficiency. Such approximations can cause biases in radiative fluxes and affect simulated climate, especially in the Arctic because of its large sensitivity to perturbations. We implemented treatments to both physics into the Energy Exascale Earth System Model (E3SM) version 2 by DoE and assessed their impacts on the simulated mean-state global climate as well as climate feedback and sensitivity.

By turning on and off the switches in the modified E3SMv2 model, we studied the changes in mean-state climate due to cloud LW scattering and surface emissivity effects by comparing four 35-year fully-coupled simulations. Cloud LW scattering warms the entire global troposphere by ~0.4 K on average; the warming is stronger in the Arctic (~0.8 K) than in the tropics, which is a manifestation of the polar amplification phenomenon. When realistic emissivity is incorporated into the model, the surface skin temperature increases by 0.36 K instantaneously on a global average, especially in the Sahara Desert (~0.7 K) where the surface emissivity is low. Surface skin temperature, as well as surface air temperature and tropospheric temperature, further increases by 0.19 K due to the inclusion of surface spectral emissivity. The mean-state climate changes due to both effects are linearly additive. The latitudinal and seasonal pattern of surface air temperature warming resulting from both effects is very similar to the response due to CO₂ increase in the standard E3SMv2 model.

We also carried out four 35-year simulations under the abrupt 4xCO₂ scenario, with cloud LW scattering and/or surface emissivity effects on and off. Based on standard radiative kernel analysis, we found that total global-mean climate feedback does not change significantly after including either or both physics. Nevertheless, lapse rate feedback, water vapor feedback, and cloud feedbacks in the tropics have changes by up to 10%. They are primarily associated with high cloud fraction response in the upper troposphere. Our study suggests that both the cloud LW scattering effect and the surface spectral emissivity effect should be included in climate models for a faithful representation of the radiative process in the atmosphere, especially at regional scales.

How to cite: Fan, C., Chen, Y.-H., Chen, X., Lin, W., Huang, X., and Yang, P.: Including Ice-Cloud Longwave Scattering and Surface Spectral Emissivities in Climate Models Leads to More Impacts on Mean-State Climate than Climate Feedbacks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2448, https://doi.org/10.5194/egusphere-egu23-2448, 2023.

The spectral longwave feedback parameter λ_ν represents how Earth’s outgoing longwave radiation adjusts to temperature changes and is thus the detailed fingerprint of all longwave feedbacks, directly impacting Earth’s climate sensitivity. Most research so far has focused on the spectral integral of λ_ν. Spectrally resolving λ_ν permits inferring information about the vertical distribution of longwave feedbacks, thus gaining a better understanding of the underlying processes. However, investigations of λ_ν have so far been largely limited to model studies, and no observational study we are aware of has inferred the global all-sky λ_ν.

Here we show that it is possible to directly observe the global all-sky λ_ν using satellite observations of seasonal and interannual variability taken by the Infrared Atmospheric Sounding Interferometer (IASI). We find that spectral bands subject to strong water vapour absorption exhibit a substantial stabilising net feedback. We demonstrate that this stabilising feedback is partly caused by changes in relative humidity with warming, the radiative fingerprints of which can be directly observed. Therefore, our findings emphasise the importance of better understanding processes affecting future trends in relative humidity. This first observational constraint on the global all-sky λ_ν can be used as a powerful tool to evaluate the representation of longwave feedbacks in global climate models and to better constrain Earth’s climate sensitivity.

How to cite: Roemer, F. E., Buehler, S. A., Brath, M., Kluft, L., and John, V. O.: Direct observation of Earth’s spectral longwave feedback parameter, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5372, https://doi.org/10.5194/egusphere-egu23-5372, 2023.

An outstanding question in climate science is how much the change in tropical anvil cloud clover with warming influences Earth's climate sensitivity. Here, we construct a simple model of cloud radiative effects to obtain an analytical equation for the tropical anvil area “iris” feedback. Our equation shows how the feedback is constrained by the fractional change in anvil cloud area, the anvil cloud radiative effect, and the radiative masking of low clouds that live beneath anvils.  We then look at satellite observations to diagnose these quantities. We find that the inferred values of anvil cloud radiative effect and low cloud masking effects sum to 1 Wm^-2. Owing to this small radiative effect, the observed changes in anvil cloud cover in interannual variability implies an iris feedback that is wholly insufficient to strongly influence climate sensitivity. We then extend our equation to address whether anvil clouds might affect climate sensitivity through their masking of other forcings  or feedbacks.

How to cite: McKim, B., Bony, S., Saint-Lu, M., and Dufresne, J.-L.: Constraining the tropical anvil cloud "iris" feedback, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3896, https://doi.org/10.5194/egusphere-egu23-3896, 2023.

Observations from the Clouds and the Earth’s Radiant Energy System (CERES) show a marked increase in Earth’s energy imbalance (EEI) since 2000. At the same time, we’ve seen marked changes in numerous geophysical variables that influence EEI. While observations alone cannot quantify the anthropogenic and natural contributions to changes in these quantities, they can provide insight into how changes in different components of the climate system have led to the observed EEI trend. Using additional data from MODIS, CALIPSO, Cloudsat, and reanalysis, we find the increase in EEI to be due to decreased reflection by clouds and sea-ice, which cause a pronounced increase absorbed solar radiation (ASR), and a decrease in outgoing longwave radiation (OLR) due to increases in trace gases and water vapor. The ASR increases are largest over the subtropics and mid-latitudes in regions with decreases in low and middle cloud fraction, which likely occur in response to observed increases in sea-surface temperature (SST) in those locations. We diagnose the SST changes by performing an ocean mixed layer energy budget analysis at regional, hemispheric, and global scales using TOA and surface radiation observations from CERES, SST and temperature/humidity fields from ERA-5, and ocean mixed layer depth from ocean reanalysis. This analysis suggests that heating of the mixed layer and the subsequent increase in SST stems from ocean mixing/advection rather than from surface forcing. 

How to cite: Loeb, N., Thorsen, T., Ham, S.-H., Rose, F., and Kato, S.: Observational Assessment of Changes in Earth’s Energy Imbalance Since 2000, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2962, https://doi.org/10.5194/egusphere-egu23-2962, 2023.

Earth Energy Imbalance (EEI) results from a net positive radiative flux at the top of atmosphere. Over 90% of this excess energy is stored as heat in the ocean causing present day ocean heat content (OHC) change. This in turn leads to volumetric or steric expansion of the water column and sea level rise. Utilizing observed bias-corrected short- and long-wave energy fluxes from the CERES project, it is possible to estimate EEI at the top of atmosphere. However, bias corrections rely on reanalysis OHC, potentially resulting in overestimation of ocean heat uptake (OHU).

Combining GRACE(-FO) and altimetry observations and constructing global sea level budgets allows to derive (thermo-)steric sea level change and convert this to OHU; the latter is generally achieved considering a literatute-based ocean-mean expansion efficiency of 0.52 [W/m^2 / mm/yr]. Nonetheless, this approach is valid for global mean steric sea level change only and it is unclear to what extent one can use it for investigating regional OHU.

Here, we develop a novel approach for deriving global and regional observation based OHC and OHU, which consists of three steps. (1) Fitting mass and steric spatial patterns, so called fingerprints, to GRACE(-FO) and altimetry data in a joint least-squares inversion. (2) Projecting reanalysis OHC onto the same spatial patterns that we use to explain steric variability. (3) Rescaling reanalysis OHC based on the observed steric sea level changes and reconstruction of spatial maps of OHC. These can then be further analyzed in order to derive global and regional OHU.

Based on preliminary results for years 2005-01 till 2015-12, we find ~1.2 mm/yr (thermo-)steric sea level change. Global-mean OHU of 0.62 [W/m^2] can be derived from the literature expansion efficiency above, while we find 0.63 [W/m^2] from the novel rescaling approach and 0.87 [W/m^2] based on ORAS5 ocean model data only. Regionally analyzing these results regarding individual ocean contributions reveals that the ocean model seems to significantly overestimate the uptake of the Atlantic and Pacific oceans, while slightly underestimating the Indian ocean contribution.

How to cite: Uebbing, B., Vielberg, K., Aschenneller, B., Rietbroek, R., Köhl, A., and Kusche, J.: A novel approach for assessing regionally differentiated ocean contributions to Earth Energy Imbalance from GRACE(-FO) and multi-mission altimetry, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2796, https://doi.org/10.5194/egusphere-egu23-2796, 2023.

The Earth’s energy imbalance (EEI) is the difference in the net solar radiative flux and outgoing longwave radiative flux at the top-of-atmosphere. It has been shown that the positive EEI trend in the previous two decades is unexplained by internal variability and caused by anthropogenic forcing and response, such as that resulting from anthropogenic CO₂ emissions. In this work we apply two state-of-the-art global climate models, the CESM2 and ICON-HAM, forced with observed (evolving) sea-surface temperature fields for the period 2000-2019 and with multiple ensemble members, to explore causes for the positive trend in EEI. Both models are able to reproduce the observed EEI trend from the CERES satellite product relatively well. Sensitivity simulations with aerosol emissions kept constant at year 2000 values indicate a relatively strong influence of recent aerosol emission reductions on the EEI trend. Preliminary results further indicate a considerable effect of using the latest CEDS emission version, as opposed to the CMIP6 CEDS version, on the EEI trend.

How to cite: Hodnebrog, Ø., Myhre, G., Jia, H., Quaas, J., Jouan, C., and Forster, P. M.: Earth’s energy imbalance trend strengthened by recent aerosol emission reductions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14330, https://doi.org/10.5194/egusphere-egu23-14330, 2023.

The long term global temperature rise caused by increased greenhouse gas radiative forcing is partially masked by temporary aerosol radiative cooling, which remains poorly known.

I present a new purely observation based estimate of Aerosol Radiative Forcing (ARF) due solely to the direct radiative effect of aerosols over clear sky ocean, and its time variation over the period 2003-20204 from combined MODIS and CERES aerosol, cloud, and radiation measurements. The resulting mean 2003-2020 ARF is -1.16 +/- 0.39 W/m2 , with no significant trend within an uncertainty of +/- 0.025 W/m2dec.

Combining this ARF with the best estimate of the greenhouse gas and solar radiative forcing, and the most likely value of the Equilibrium Climate Sensitivity, produces a plausible Earth Energy Imbalance as a residual of the energy balance equation at the top of the atmosphere.

How to cite: Dewitte, S.: Aerosol Radiative Forcing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3268, https://doi.org/10.5194/egusphere-egu23-3268, 2023.

The Earth’s energy balance and radiation budget, which play a key role in the Earth’s climate system, are driven by the incident solar radiation at surface (surface solar radiation, SSR). Over the past few decades, changes in the SSR (ΔSSR) have been observed that are dependent on the transparency of the terrestrial atmosphere. This phenomenon, called global dimming and brightening (GDB), is a significant factor in climate change and modulates global warming. This study examines the interdecadal variability of SSR based on computations of the FORTH radiative transfer model, using as input data cloud optical properties taken from the International Satellite Cloud Climatology Project H Series (ISCCP-H) and aerosol optical properties and meteorological data taken from the Modern-Era Retrospective analysis for Research and Applications, version 2 (MERRA-2) Reanalysis. Ground-based measurements of SSR from the Global Energy Balance Archive (GEBA) and Baseline Surface Radiation Network (BSRN) networks are utilized to evaluate the FORTH’S SSR fluxes and GDB. The FORTH RTM computations are made on a monthly basis from 01/1984 - 12/2018 at 51 atmospheric levels and a spatial horizontal resolution of 0.5°×0.625° (with a conversion of the original input data to the same spatio-temporal resolution). Firstly, the FORTH SSR fluxes are evaluated against ground measurements from GEBA and BSRN. This comparison reveals a general underestimation of the FORTH SSR fluxes, with a satisfactory evaluation metrics, such as the relative bias, which is equal to –2.9% and –7.7% against GEBA and BSRN, respectively or the correlation coefficient values, computed using deseasonalized SSR anomalies, being equal to 0.72 and 0.8 against GEBA and BSRN, respectively. Then, the SSR changes (or GDB) for each pixel, also calculated using deseasonalized SSR anomalies, were compared with the GDB from the corresponding GEBA/BSRN station, lying in that pixel, for their common time period. This comparison reveals an agreement between the sign of the FORTH’s pixels and the corresponding stations’ GDB equal to 63.5% for the GEBA and 54.5% for the BSRN sites. Finally, the GDB was also calculated on global (land & ocean), hemispherical and regional scales, either for the entire period and for sub-periods too. The computed GDB for the period 01/1984-12/2018 is equal to –2.22 ± 0.38 W/m² for the Globe, -0.48 ± 0.39 W/m² for the Northern Hemisphere and -2.73 ± 0.54 W/m² for the Southern Hemisphere. Larger GDB values are estimated over oceans than land (-2.56 ± 0.44 versus -1.04 ± 0.47 W/m², respectively), suggesting that the atmosphere over oceans got less transparent than over continents during the 35-year study period. During this period, a brightening has taken place over Europe, Middle East, Mexico against a dimming over India, Maritime Continent, Australia and Southern Ocean.

How to cite: Stamatis, M., Hatzianastassiou, N., Korras Carraca, M. B., Matsoukas, C., Wild, M., and Vardavas, I.: The Global Dimming & Brightening based on FORTH radiative transfer model during 1984-2018 and its evaluation against GEBA & BSRN ground-based networks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13064, https://doi.org/10.5194/egusphere-egu23-13064, 2023.

The outgoing longwave radiation (OLR) at the top of the atmosphere is a critical component of the Earth's radiation energy budget. A substantial portion of the OLR energy lies in the far-infrared (FIR) spectrum, which has not been directly measured for understanding weather and climate variations. Several satellite projects under development, including the Thin Ice Cloud in Far Infrared Experiment (TICFIRE, Blanchet et al. 2011) funded by the Canadian Space Agency, the Polar Radiant Energy in the Far Infrared Experiment (PREFIRE, L’Ecuyer et al., 2021) of U.S. NASA, and the Far-Infrared Outgoing Radiation Understanding and Monitoring (FORUM, Palchetti et al., 2020) of the European Space Agency, are being developed to fill this observation gap. Given that the FIR observation data is not available yet, we use simulations to acquire prior knowledge of the climatological mean distribution of the OLR in FIR, by using a rapid radiative transfer model, RRTMG, to simulate spectrally decomposed OLR in different spectral bands from global instantaneous atmospheric profiles of the fifth generation European Centre for Medium-Range Weather Forecasts atmospheric reanalysis (ERA5). Based on the radiative transfer equation, we dissect the OLR by attributing its distribution and variation to spectrally and vertically decomposed contributions of the atmosphere and Earth surface. Our results disclose that the relatively higher far-infrared fraction of the OLR in polar region is due to stronger surface contribution and identify a minimum atmospheric contribution layer around the tropopause. On the other hand, the variability of the spectrally decomposed OLR field is dissected with the aid of a new set of radiative sensitivity kernels. This analysis discovers that the non-cloud longwave climate feedback, as well as its inter-climate model discrepancy, mainly results from the upper tropospheric thermodynamic fields (temperature and water vapor) and their effects on the FIR radiation.

How to cite: Huang, H. and Huang, Y.: The spectrally and vertically decomposed outgoing longwave radiation and its climate trends in the far-infrared, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10455, https://doi.org/10.5194/egusphere-egu23-10455, 2023.

The slope of the quasi-linear relation between planetary outgoing longwave radiation (OLR) and surface temperature (T_S) is an important parameter measuring the sensitivity of the Earth climate system. The main goal of this study is to seek a general explanation for the quasi-linear OLR-T_S relation that does not require the narrowing of “atmospheric window” of planetary thermal radiation. The physical understanding on the quasi-linear OLR-T_S relation and its slope is gained from observation analysis, climate simulations with radiative-convective equilibrium and general circulation models, and a series of online feedback suppression experiments.

The observed quasi-linear OLR-T_S relation manifests a climate footprint of radiative (such as greenhouse effect) and non-radiative processes (poleward energy transport). The former acts to increase the meridional gradient of surface temperature and the latter decreases the meridional gradient of atmospheric temperatures, causing the flattening of the meridional profile of the OLR. Radiative processes alone can lead to a quasi-linear OLR-T_S relation that is more steeply sloped. The atmospheric poleward energy transport alone can also lead to a quasi-linear OLR-T_S relation by rerouting part of the OLR to be emitted from the warmer place to colder place. The combined effects of radiative and non-radiative processes make the quasi-linear OLR-T_S relation less sloped with a higher degree of linearity. In response to anthropogenic radiative forcing, the slope of the quasi-linear OLR-T_S relation would be further reduced via stronger water vapor feedback and enhanced poleward energy transport.

How to cite: Cai, M., Sun, J., Ding, F., Kang, W., and Hu, X.: The quasi-linear relation between planetary outgoing long wave radiation and surface temperature: a climate footprint of radiative and non-radiative processes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1078, https://doi.org/10.5194/egusphere-egu23-1078, 2023.

Theoretical models suggest that ∼55% of the outgoing longwave radiation from Earth is within the far-infrared region, 100-666 cm⁻¹. Nevertheless, the top-of-atmosphere radiation spectrum in this region has never been measured, something that will change with ESA’s Far-infrared Outgoing Radiation Understanding and Monitoring (FORUM) mission, launching in 2027. Studies have indicated that absorption within this region is dominated by tropospheric water vapour, significantly impacting Earth’s radiation budget. Quantifying these concentrations plays a vital role in estimating its radiative effects and associated feedbacks.

The Infrared and Microwave Sounding (IMS) retrieval scheme developed at RAL Space is an optimal estimation scheme currently using channels within the mid- and near-infrared as well as the microwave region to obtain simultaneous retrievals of the vertical atmospheric profile and cloud properties. Current retrievals using this scheme have been performed on observations from Infrared Atmospheric Sounding Interferometer (IASI), Microwave Humidity Sounder (MHS) and the Advanced Microwave Sounding Unit (AMSU) onboard the MetOp satellites. Temperature and water vapour retrievals using this framework have been validated against radiosonde data with biases within 1 K and 10% of the reference respectively.

This work seeks to extend IMS into the far-infrared and exploit the known sensitivity of upwelling radiation within this region to improve current retrievals of water vapour. This would enhance our understanding of the spatial and temporal variations of water vapour within the atmosphere, and its role in Earth's radiation budget. Unique clear-sky airborne measurements will be used to analyse channel sensitivity within this region and maximise the information content for the retrieval. This retrieval capability would be the first of its kind to be thoroughly validated in this way and would be available for use on FORUM observations.

How to cite: Panditharatne, S., Brindley, H., Cox, C., and Siddans, R.: Optimising water vapour retrievals by exploiting sensitivity within the far-infrared: A study in support of the ESA FORUM mission., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2384, https://doi.org/10.5194/egusphere-egu23-2384, 2023.

The Libera Mission, named for the daughter of Ceres in Roman mythology, will provide continuity of the Clouds and the Earth’s Radiant Energy System (CERES) Earth radiation budget (ERB) observations from space. Libera’s attributes enable a seamless extension of the current 23-year ERB climate data record from CERES. Libera will acquire spectrally integrated radiance over the CERES FM6-heritage broad spectral bands in the shortwave (0.3 – 5 μm), longwave (5 – 50 μm) and total (0.3 – beyond 100 μm) and adds a split-shortwave band (0.7 – 5 μm) to provide deeper insight into shortwave energy deposition. Libera leverages advanced detector technologies using vertically aligned black-carbon nanotubes with closed-loop electrical substitution radiometry to achieve radiometric uncertainty of approximately 0.2%. Libera will also employ a wide field-of-view camera to provide scene context and accelerate the development of the split-shortwave angular distribution models.

Libera’s stewardship of the ERB record begins in the latter part of this decade, at an important juncture in the monitoring of climate trends. Libera is currently slated for a launch aboard JPSS-3 in December 2027, when the probability of a CERES data gap will be approaching 50%. The Libera science objectives associated with continuity and extension of the ERB data record are to identify and quantify processes responsible for ERB variability on various times scales. Beyond data continuity, Libera’s new and enhanced observational capabilities will advance our understanding of spatiotemporal variations of radiative energy flow in the visible and near-infrared spectral regions in addition to facilitating the rapid development of new angular distribution models for near-infrared and visible radiance-to-irradiance conversion.

This talk provides an overview of the Libera’s observational strategy, its measurements, science goals and objectives. We discuss the importance of climate data record continuity in the context of the current climate state and anticipated changes over the next decade and beyond.

How to cite: Pilewskie, P., Hakuba, M., and Stephens, G.: The Future of Earth Radiation Budget Observations Beyond CERES: Libera and Continuity of the ERB Climate Data Record, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17097, https://doi.org/10.5194/egusphere-egu23-17097, 2023.