Recent research has highlighted that radiative feedbacks — and thus climate sensitivity — are not constant in time but depend sensitively on sea surface temperature patterns. I will discuss three implications of this realization.

First, I will show how coupled climate models fail to reproduce observed surface warming patterns and global mean top of the atmosphere (TOA) radiation trends. I use large initial condition ensembles to compare observations to account for internal variability and model mean-state biases. For certain periods, not a single ensemble member can reproduce observed values of surface temperature trends and TOA radiation trends. Models which more greatly underestimate the observed local sensitivity of surface and TOA, and models with a weak variability in the Equatorial Pacific surface temperatures tend to have a higher equilibrium climate sensitivity. Despite these astonishing observation-model discrepancies their global-mean temperatures are simulated well which points to a common model problem in surface heat fluxes and ocean heat uptake.

Second, I will discuss the relevance of the pattern effect for climate change projections. Given that problems coupled models have in reproducing observed warming patterns, we should doubt their pattern evolution in projections. I will introduce “surface warming pattern storylines” starting from the observations and bridging to simulated future patterns in standard scenarios. I show that (CMIP) coupled climate models used ubiquitously for climate change projections underestimate the uncertainty of possible global-mean temperature evolutions due to their surface warming patterns throughout the 21st century.

Third, I will introduce how a feed-forward convolutional neural network (CNN) can be trained to learn the pattern effect and predict global-mean TOA radiation from surface warming patterns. I use explainable artificial intelligence methods to visualize and quantify that the CNN draws its predictive skill for physically meaningful reasons. Remarkably and different from traditional approaches, I can predict radiation under strong climate change from training the CNN on internal variability alone. This out-of-sample application works only when feedbacks are allowed to be non-linear or equivalent, changing in time, which is another, independent manifestation of the relevance of the pattern effect.

How to cite: Rugenstein, M.: The pattern effect: How radiative feedbacks depend on surface warming patterns and influence near-term projections , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12777, https://doi.org/10.5194/egusphere-egu24-12777, 2024.

The effective radiative forcing (ERF) is a robust predictor of future equilibrium warming. It is generally assumed that the ERF depends only on changes in atmospheric constituents and is independent of the background climate state. Building on recent work demonstrating that, in contrast, the instantaneous radiative forcing (IRF) for CO₂ is strongly state-dependent, we show that the ERF for CO₂ also increases in warmer climate states. 

We analyse a 4×CO₂ atmosphere-only forcing in both control and warmer climate states in eight CMIP6-era models. Four models participated in the Cloud Feedback Model Intercomparison Project (CFMIP) which used pre-industrial SSTs in its control state and SSTs from near the end of the same model’s coupled abrupt-4×CO₂ run in its warm state. In the other four models we used an AMIP climatology as the control state and a uniform increase in SSTs of 4 K above this AMIP climatology in the warm state. All eight models show an increase in 4×CO₂ ERF, ranging from 0.1-0.5 W m^-2, translating to a relative increase of 0.02-0.09 W m^-2 K^-1 or 0.2-1.1 % K^-1. The increase is statistically significant in five of the eight models.

Our findings have implications for derivation of simplified relationships of climate warming, for instance in the calculations of global warming metrics and in economic models, from which future climate change risks being underpredicted without a temperature adjustment.

We also run aerosol forcing experiments under the +4 K climate, for which there is less agreement between models, but some show large changes in aerosol ERF under the warmer climate state, with potential implications for our ability to discern transient warming even with a more accurate understanding of present-day aerosol forcing. 

How to cite: Smith, C., Watson-Parris, D., Kramer, R., Andrews, T., Gjermundsen, A., Mutton, H., Feng, J., Paynter, D., Chadwick, R., Douville, H., and Roehrig, R.: Robust increase in CO2 effective radiative forcing in warmer climates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8223, https://doi.org/10.5194/egusphere-egu24-8223, 2024.

The top of the atmsophere (TOA) instantaneous long wave radiative forcings resulting from increasing greenhouse gases such as CO2, CH4, N2O and various halogenated gases were found by solving the equation of transfer.  The observed altitude dependence of the greenhouse gas concentrations was used as well as the standard midlatitude temperature profile.  The calculations used the line intensities or absorption cross sections from the HITRAN database and also considered the effect of scattering by a cloud layer.  Various cloud properties were considered including altitude, optical depth and single scattering albedo for both isotropic and forward scattering.  The results show that a cloud layer reduces the TOA radiative forcing from its clear sky value.  The incremental forcing is even negative for an optically thick high altitude cloud.  This occurs because the temperature increases with altitude in the stratosphere.

How to cite: van Wijngaarden, W. and Happer, W.: Instantaneous Radiative Forcings of Greenhouse Gases  , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1295, https://doi.org/10.5194/egusphere-egu24-1295, 2024.

We assess the effect of uncertainty in water vapor continuum absorption on CO₂ forcing F, longwave feedback λ, and climate sensitivity S at surface temperatures T_s between 270K and 330K. We calculate this uncertainty using a line-by-line radiative-transfer model and a single-column atmospheric model, assuming a moist-adiabatic temperature lapse-rate and 80% relative humidity in the troposphere, an isothermal stratosphere, and clear skies. Emulating continuum uncertainty in observations, we hold total continuum absorption fixed at room temperature, but change its components: We assume a 10% decrease in self continuum absorption, which comprises interactions between water molecules, and a spectrally varying increase in foreign continuum absorption, which comprises interactions between water and non-water molecules. We find that continuum uncertainty mainly affects S through its effect on λ. Continuum uncertainty primarily impacts the surface feedback at T_s<290K and the atmospheric feedback at T_s>290 K. Under present-day conditions, those two effects have opposite signs and thus largely cancel each other, therefore the effect of continuum uncertainty on S is negligible (0.02K). At T_s>300K, however, the effect on S is much stronger (>0.2K). This is because at those T_s, the effects on λ of decreasing the self continuum and increasing the foreign continuum have the same sign. These results highlight the importance of a correct partitioning between self and foreign continuum to accurately determine the temperature dependence of Earth’s climate sensitivity.

How to cite: Roemer, F. E., Buehler, S. A., Kluft, L., and Pincus, R.: Effect of Uncertainty in Water Vapor Continuum Absorption on CO2 Forcing, Longwave Feedback, and Climate Sensitivity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1782, https://doi.org/10.5194/egusphere-egu24-1782, 2024.

Surface warming is directly associated with the surface energy balance, where downwelling longwave radiation is a critical factor influencing and reflecting surface temperature variations. Accurately identifying various forcing and feedback mechanisms is essential to making more realistic predictions about future climate change. Spectrally-resolved radiance measurements play an important role in this pursuit by leveraging the distinctive absorption features of atmospheric compositions. Only recently, the availability of comprehensive, long-term records of spectrally resolved radiation and atmospheric properties has enabled us to observe and quantify the forcing and feedback factors, such as the cloud feedback characterized by its high uncertainty.

This study initiated by homogenizing the 23-year record of downwelling longwave radiance (DLR) observed by the Atmospheric Emitted Radiance Interferometer (AERI) at the Southern Great Plains site. A detailed DLR record for diverse sky conditions was obtained, enabling the determination of long-term trends in both clear-sky and all-sky scenarios. These trends reveal distinct spectral signals associated with various meteorological variables, forming the basis for further climate change signal attribution analysis.

Subsequently, we develop and validate a novel spectral fingerprinting method tailored to constrain surface forcings and feedbacks from long-term DLR trends. Our analysis identifies positive CO₂ and negative O₃ surface forcings in both clear-sky and all-sky conditions. Moreover, we observe that changes in temperature and water vapor concentration over the 23-year period contribute to an increase in downwelling longwave radiation. Significantly, our study discovers a negative cloud feedback that offsets the increase in downwelling longwave radiation resulting from elevated CO₂, water vapor, and atmospheric temperature. These attributions of radiation changes, derived from AERI observations using the fingerprinting method, are validated against the kernel method and compared with the simulations of Global Climate Models.

How to cite: Huang, Y., Liu, L., and Gyakum, J.: Climate change signals of radiative forcing and feedback unveiled from long-term trends of spectrally resolved surface longwave radiation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4120, https://doi.org/10.5194/egusphere-egu24-4120, 2024.

Climate feedbacks over the historical period have been investigated in a 47 member ensemble of atmosphere-ocean general circulation model (AOGCM) simulations. Here, the model response to historical forcing, as well as individual forcing constituents such as aerosol and greenhouse gases separately, has been analysed. The analysis addresses the cause of differing feedbacks across the ensemble, the disparity between feedbacks seen in these AOGCM simulations and atmosphere-only GCM (AGCM) experiments prescribed with observed SSTs, and the different forcing efficacies of the respective forcing agents. It is found that much of the spread in feedbacks across ensemble members and different experiments can be explained through varying SST patterns. The level of polar amplification is shown to strongly control the amount of sea ice melt per degree of global warming, a mechanism responsible for the spread in shortwave clear sky feedback and a large contributor to the different forcing efficacies seen across the different forcing agents. The spread in feedbacks across the historical ensemble is also shown to be caused by both the level of tropical surface temperature warming, due to its influence on longwave clear sky feedback, and the response of  cloud feedbacks to local surface temperatures and large scale changes in tropospheric temperature. It is also shown that each of these processes discussed are partly responsible for the disparity in feedbacks seen between AOGCM simulations and  AGCM experiments prescribed with observed SSTs.

How to cite: Mutton, H., Andrews, T., Hermanson, L., Seabrook, M., Smith, D., Ringer, M., Jones, G., and Webb, M.: Efficacies, pattern effects & radiative feedback in a large ensemble of HadGEM3-GC3.1-LL historical simulations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5679, https://doi.org/10.5194/egusphere-egu24-5679, 2024.

In recent years, radiative feedbacks in the earth system have been strongly tied to the spatial pattern of sea surface temperatures (SSTs). This “pattern effect” has been strongly tied to the strength of cloud radiative feedbacks driven by atmospheric stability changes. SST patch Green’s functions experiments have revealed that the ratio of warming in deep convective tropical regions, versus outside, drives significant changes in atmospheric stability. These Green’s functions can be used to reconstruct feedbacks from given warming patterns. However, it remains unclear how different warming patterns arise. Different Green’s functions, prescribing surface heat fluxes in atmosphere-ocean coupled models instead of temperature changes in fixed SST experiments, may answer this question by showing how energy inputs translate into temperature changes.

Using a simplistic set of patches of applied surface heat fluxes in CESM2-CAM6 and HadCM3, we find that heat input into the tropics results in strongly negative radiative feedbacks from enhanced warm pool warming. This results in a small climate sensitivity to this tropical forcing. Conversely, heat fluxes input into the extratropics cause significantly less negative feedbacks that result in greater climate sensitivity to extratropical forcing.Furthermore, the response to tropical forcing occurs rapidly, with equilibrium roughly achieved within a few years both in slab ocean and fully coupled models. The response to extratropical forcing, by contrast, induces near-zero feedbacks in the first few years, followed by significantly weaker negative feedbacks than seen under tropical forcing, which leave this simulation far from equilibrium after 150 years in the fully coupled model.

These outcomes of forcing, from within the tropics and outside, can be combined to explain the early changes in feedbacks in response to global uniform forcing, or near-uniform global forcings such as from CO₂. Reconstruction of the uniform case by summing the tropical and extra-tropical cases gives a good fit, except for an apparent temperature dependence in CESM2, and shows that extra-tropical component of surface forcing is driving the long-term feedbacks in the uniform forcing scenario.

Understanding the process of how the pattern of forcing results in different temperature change patterns may be key to comprehending future temperature changes, given that the pattern of future forcing evolves with the changing mix of anthropogenic forcing agents. Furthermore, exploring how models vary in their conversion of forcing into temperature change, even within the simple experimental design of this study, may highlight significant model feedback differences and contribute to narrowing the range in model predictions of future warming.

How to cite: Salvi, P., Gregory, J., and Ceppi, P.: Assessing the Impact of Surface Energy Inputs on Radiative Feedbacks in Tropical and Extra-tropical Regions: Strength, Evolution, and Timescales, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8514, https://doi.org/10.5194/egusphere-egu24-8514, 2024.

Accurate diagnosis of regional atmospheric and surface energy budgets is a critical component for understanding the spatial distribution of the Earth’s Energy Imbalance (EEI). This contribution reviews frameworks and methods for consistent evaluation of key quantities of those budgets using observationally constrained data sets. It thereby touches upon assumptions made in data products which have implications for these evaluations. We evaluate 2001-2020 average regional total (TE) and dry static energy (DSE) budgets using satellite-based and reanalysis data. Uncertainties of the computed budgets are assessed through inter-product spread and evaluation of physical constraints. Furthermore, we infer fields of net surface energy flux by combining top-of-atmosphere radiative fluxes from satellites with reanalysis-based atmospheric TE budget terms (i.e., divergence and storage of energy). Results indicate biases <1 W/m² on the global, <5 W/m² on the continental, and ~15 W/m² on the regional scale. Inferred surface energy fluxes exhibit reduced large-scale biases compared to surface flux data based on remote sensing and models. We use the DSE budget to infer atmospheric diabatic heating from condensational processes. Comparison to observation-based precipitation data indicates larger uncertainties (10-15 Wm^-2 globally) in the DSE budget compared to the TE budget, which is reflected by increased spread in reanalysis-based fields. Continued validation efforts of atmospheric energy budgets are needed to document progress in new and upcoming observational products, and to understand their limitations when performing EEI research.

How to cite: Mayer, M., Kato, S., Bosilovich, M., Bechtold, P., Mayer, J., Schroeder, M., Behrangi, A., Kobayashi, S., Roberts, B., and L'Ecuyer, T.: Assessment of atmospheric and surface energy budgets using observation-based data products, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12901, https://doi.org/10.5194/egusphere-egu24-12901, 2024.

In the context of global warming, the radiation balance in the Tibetan Plateau region is closely linked to changes in the cryosphere, such as glacier retreat, reduced snow cover, and degradation of permafrost. The abnormal changes in radiation balance further impact the East Asian circulation and global climate change. In this study, based on 23 years (2000-2022) of data from the Clouds and the Earth's Radiant Energy System (CERES) for atmospheric and surface radiation fluxes, the temporal and spatial characteristics of solar radiation reflection at the top of the atmosphere (TOA) over the Tibetan Plateau (TP) and its components, including cloud, atmospheric, and surface components, were analyzed. The results showed that the average TOA solar radiation reflection over the TP was 128.5 W m^-2, with cloud component contributing approximately 60.3 %, clear-sky atmospheric component contributing approximately 18.4 %, and surface component contributing approximately 21.3%. From 2000 to 2015, there was a significant decreasing trend in TOA solar radiation reflection over the TP, with a Sen's slope of -1.59 W m^-2 10a^-1. The interannual variability intensity (i.e., standard deviation of anomalies) was approximately 1.44 during this period. However, from 2016 to 2022, the interannual variability intensity increased to 3.62. The changes in interannual variability of TP solar radiation reflection were closely related to the changes in cloud, atmospheric, and surface parameters. Further analysis is needed to understand the reasons for the changes in radiation balance over the TP. This study plans to explore the impacts and contributions of various atmospheric circulation factors on the interannual changes in TP solar radiation reflection and its components using reanalysis meteorological data and synthesis analysis, aiming to reveal the possible mechanisms behind the abrupt change in interannual variability intensity around 2015.

How to cite: Jian, B. and Li, J.: Investigating the Causes of Interannual Variation in Solar Radiation Reflection at the Top of the Atmosphere over the Tibetan Plateau, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4595, https://doi.org/10.5194/egusphere-egu24-4595, 2024.

Asian large-scale orography profoundly influences circulation in the North Hemisphere. Considerable spring top-of-the-atmosphere (TOA) radiative cooling over Southeast China (SEC) is very likely related to upstream orography forcing. Here we investigate the mechanical and thermal forcings of Asian large-scale orography, particularly the Tibetan Plateau (TP), on downstream East Asian cloud amount and atmospheric radiation budget during March-April using the Global Monsoons Model Intercomparison Project simulations. The thermal forcing drives significant surface heating and a low-level cyclone over the TP, pumping low-level air to the middle troposphere. Ascent and water vapor convergence triggered by the thermal forcing favor air condensation, low-middle clouds, and resultant strong spring cloud radiative cooling over SEC. Moreover, the thermal forcing moves the position of cloud radiative cooling westward towards the TP. The TP’s blocking role weakens low-level westerlies over SEC, but its deflecting role increases downstream high-level westerlies, dynamically favoring cloud formation over SEC and the eastward ocean. In addition, the TP can force ascent and increase cloud amounts over the western and central TP. The thermal forcing contributes to 57.1% of total cloud amount and 47.6% of TOA cloud radiative cooling induced by the combined orography forcing over SEC while the mechanical one accounts for 79.4% and 95.8% of the counterparts over the ocean to the east of SEC. Our results indicate that Asian large-scale orography shapes the contemporary geographical distribution of spring East Asian cloud amount and atmospheric radiation budget to a large extent.

How to cite: Li, J.: Mechanical and thermal forcings of Asian large-scale orography on spring cloud amount and atmospheric radiation budget over East Asia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6888, https://doi.org/10.5194/egusphere-egu24-6888, 2024.

How to cite: Della Fera, S., Fabiano, F., Libois, Q., Leonarski, L., Masiello, G., Raspollini, P., Ridolfi, M., von Hardenberg, J., and Cortesi, U.: Climate evolution in the spectral signatures of simulated and observed radiances, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10684, https://doi.org/10.5194/egusphere-egu24-10684, 2024.

We describe a technique, singular vector decomposition (SVD), that can identify the spatial patterns that best describe the temporal variability of a global satellite dataset. These patterns, and their temporal evolution are then correlated with established climate indices. 
We apply this technique to datasets of cloud properties and radiative  fluxes over three decades ((A)ATSR/SLSTR, MODIS, IASI and CERES), but it can be more generically used to extract the pattern of variability of any regular gridded dataset such as different parameters from satellite retrieval and models.
Leading singular vector for independent global data sets on both cloud properties (cloud fraction, cloud-top height) 
and TOA radiative fluxes, from polar orbiting satellites, covering different time periods is strongly correlated with ENSO index.
SVD approach can provide incites into the underlying causes of observed changes in a particular dataset and provide a new tool in using global satellite observations in assessing global climate model (GCM) performance.

How to cite: Carboni, E., Thomas, G., Siddans, R., and Kerridge, B.: Singular Vector Decomposition (SVD) of satellite datasets: relation between cloud properties, radiative fluxes and climate indices., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18872, https://doi.org/10.5194/egusphere-egu24-18872, 2024.

Earth radiation budget (ERB) satellite observations require conversion of the measured radiance, which is a remotely-sensed quantity, to a derived irradiance, which is the relevant energy balance quantity routinely used in modelling and analysis of the climate system. The state-of-the-art approach for radiance-to-irradiance conversion taken by the Clouds and the Earth's Radiant Energy System (CERES) benefits from the exhaustive sampling of radiance anisotropy by multiple CERES instruments across many years. Unfortunately, the CERES approach is not easily extended to new ERB spectral channels that lack previous sampling, such as the “split-shortwave” planned to be part of the next-generation ERB mission: Libera. As an alternative approach, the capability of a monochromatic, wide-field-of-view camera to provide dense angular sampling in a much shorter timeframe is assessed. We present a general concept for how this can be achieved and quantify the proficiency of a camera to provide rapid angular distribution model (ADM) generation for the new Libera ultraviolet-and-visible (VIS) sub-band. A single mid-visible camera wavelength (555 nm) is shown to be ideal for representing the VIS sub-band, requiring only basic scene stratification for 555 nm to VIS conversion. Synthetic camera sampling with realistic operating constraints also demonstrates that the angular radiance field of various scenes can be well populated within a single day of sampling, a notable advance over existing approaches. These results provide a path for generating observationally-based VIS ADMs with minimal lag time following Libera’s launch. Coupled with efforts to utilize a camera for scene identification, this may also pave the way for future ERB satellite systems to develop stand-alone irradiance products for arbitrary sets of spectral channels, opening up new measurement and science possibilities.

How to cite: Gristey, J. and Schmidt, S.: A Spaceborne Camera To Augment Future Earth Radiation Budget Satellite Observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14047, https://doi.org/10.5194/egusphere-egu24-14047, 2024.

The recent surge in rocket launch rates, including the proposal of large low earth orbit satellite constellations (LLC’s) has renewed interest into how space traffic may impact Earth’s climate. In the future.  The current annual mass flux from satellites vaporized in Earth’s middle atmosphere each year is ~0.4 Gg, well below the ~20 Gg/year natural mass emissions from meteor ablation. However, it is predicted that if all proposed LLC’s are implemented, the total number of satellites in low earth orbit (LEO) will balloon from ~5,000 to over 60,000 units. The corresponding annual emissions from satellite re-entry is also expected to increase and approach 10 Gg/yr. Although little is currently known about the composition of  aerosols released during satellite ablation, we assume a significant portion of the aerosol population is metallic aluminum that will convert to aluminum oxide (Al₂O₃). Here we present results from a study which focuses on the radiative impacts and atmospheric transport of hypothetical Al₂O₃ emissions from satellite re-entry. The WACCM6 global model coupled with the CARMA sectional model was run with a 10 Gg/year mass flux of alumina aerosol between 60 km and 70 km. We evaluate how aerosol size and latitude of emission may impact the overall transport, atmospheric burden, and radiative impacts from satellite re-entry.

How to cite: Rosenlof, K. and Maloney, C.: Potential impacts of launch and orbital debris re-entry emissions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12717, https://doi.org/10.5194/egusphere-egu24-12717, 2024.

Global ground heat storage is the second largest term of the Earth heat inventory only after the ocean, representing a 4-5% of the total heat storage within the climate system. Furthermore, determining the heat storage and heat flux in the land subsurface is necessary for closing the surface energy budget and quantifying the total energy exchange between the lower atmosphere and the shallow continental subsurface. Global long-term estimates of ground heat storage have been retrieved from geothermal data, with measurements from Eddy-covariance stations as a complement. Nevertheless, these two databases are biased towards northern extratropical latitudes, and there are not enough records to obtain a global average of ground heat storage after the year 2000. For this reason, ground heat storage for the period 2000-2020 consists in an extrapolation of the trend from the previous 30 years.

We estimate ground heat storage from six remote sensing products provided by the Climate Change Initiative of the European Space Agency (ESA-CCI). The products consist in land surface temperatures derived from three single-sensor (ENVISAT, MODIS-Terra, and MODIS-Aqua) and three multi-sensor datasets (IRCDR, IRMGP, and SSMI-SSMIS), covering all land surface except Greenland and Antarctica. First, ground heat fluxes are derived from the satellite land surface temperatures using two different methods, and are then evaluated against in situ heat flux observations at Eddy-covariance stations from the FLUXNET, the Integrated Carbon Observation System (ICOS), and Ameriflux databases. The heat fluxes are accumulated to derive ground heat storage for each satellite product, and combined with the estimates from geothermal data to cover the period 1960-2020. This new estimate yields a heat storage of 20.9 ± 4.3 ZJ during the period 1960-2018, while previous estimates reached 24.0 ± 5.4 ZJ and 20.47 ± 0.19 ZJ for the same period. During the period without geothermal estimates, from 2000 to 2020, the new multi-satellite average reaches 10.5 ± 6.4 ZJ, a similar value to the one based on a linear extrapolation of geothermal values (10.18 ± 0.22 ZJ). Furthermore, satellite estimates provide spatial patterns of heat flux changes at the global scale with a high spatial (1 km) and temporal (monthly) resolutions, which will allow to perform analyses not possible with other, more coarse, datasets. Overall, these results reinforce the values obtained in previous analyses, while the methodology used here ensures the monitoring of global ground heat storage in the next decades.

How to cite: Cuesta-Valero, F. J. and Peng, J.: Ensuring the monitoring of ground heat storage with satellite data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5330, https://doi.org/10.5194/egusphere-egu24-5330, 2024.

Knowledge of the emissivity of the Earth’s surface is vital for understanding the Earth’s radiation budget. However, there is a lack of emissivity measurements in the far-infrared (wavenumbers less than 667 cm^-1 or wavelengths greater than 15 μm) despite studies showing that the surface emissivity in these regions can have a discernible impact on the outgoing longwave radiation. In-situ measurements of surface emissivity in the far-infrared are also needed to support the upcoming far-infrared satellite missions; the Polar Radiant Energy in the Far-InfraRed Experiment (PREFIRE) developed by NASA and due to launch in spring 2024, and the European Space Agency’s Far-infrared Outgoing Radiation Understanding and Monitoring (FORUM) mission due to launch in 2027.

To fill this observational gap, the Far INfrarEd Spectrometer for Surface Emissivity (FINESSE) was developed at Imperial College London. FINESSE has a spectral range of 400 to 1600 cm^-1 (6.25 to 25μm) and is designed for in-situ measurements of surface emissivity, particularly in cold climates.

In this presentation we present observations from the first deployment of FINESSE to the ALOMAR observatory in Northern Norway (69°16' N, 16° 0' E). We describe the campaign, the radiance measurements made by FINESSE and the auxiliary data taken. We then outline the method used to determine the surface temperature and emissivity and finally present the retrieved emissivity of the ice and snow surfaces.

How to cite: Warwick, L., Murray, J., Panditharatne, S., Brindley, H., Schuettemeyer, D., and Oetjen, H.: In-situ Measurements of the Emissivity of Ice and Snow surfaces in the Mid- and Far-infrared, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15022, https://doi.org/10.5194/egusphere-egu24-15022, 2024.

One of the most vulnerable regions to climate change is the NAMEE (North Africa Middle East Europe) domain, hosting a variety of aerosol species of both natural and anthropogenic origin. This is one of the reasons why NAMEE constitutes an ideal region for assessing the aerosol-induced direct radiative effects (DREs) within the Earth-Atmosphere system. The overarching goal of the present study is to estimate clear-sky shortwave DREs via a holistic approach involving spaceborne retrievals, radiative transfer simulations and aerosol/radiation observations. We emphasize on the importance and sensitivity of the aerosol-speciated lidar ratio (LR) on calculating DREs. Our main dataset consists of CALIOP-CALIPSO backscatter coefficient vertically resolved retrievals (Level 2, Version 4.20) extracted from the LIVAS (LIdar climatology of Vertical Aerosol Structure for space-based lidar simulation studies) database (2007-2020). Besides the CALIPSO aerosol optical depth (AOD) retrieval, the aerosol-speciated LRs based on the newly developed DeLiAn database, a collection of state-of-the-art ground-based measurements acquired by lidars operating at different regions of the world affected by various aerosol types, are also applied to the CALIPSO backscatter coefficient profiles for the calculation of a more representative AOD. Through a series of quality assurance filtering we conclude to 550 case studies collocated against ground-based AERONET stations characterized by either dust, marine, polluted continental/smoke, elevated smoke or clean continental aerosol layers according to the latest CALIPSO (V4) aerosol classification algorithm scheme. For the radiative transfer simulations, the libRadtran Radiative Transfer Model (RTM) is implemented for the spectral range of 250–5000 nm using a 4-stream plane parallel approximation. The CALIPSO aerosol-speciated AOD profiles at 532 nm along with lookup tables of spectrally resolved optical properties extracted from the AERONET almucantar retrievals make up the aerosol RTM inputs. For the surface inputs, the MODIS snow-free BRDF/albedo dataset and the libRadTran built-in IGBP albedo library are utilized. The columnar concentrations of ozone and water vapour are extracted from the MERRA-2 reanalysis. The simulated solar fluxes at TOA and at the surface are evaluated against satellite (CERES) and ground-based (BSRN) observations for cloudless conditions, respectively. Our key finding is that the consideration of the DeLiAn-based LR leads to more representative DREs and improves the simulated solar fluxes when mineral particles dominate.    

Acknowledgements: Authors acknowledge support by the Hellenic Foundation for Research and Innovation (H.F.R.I.) under the “2nd Call for H.F.R.I. Research Projects to support Post-Doctoral Researchers” (Project Acronym:  ATLANTAS, Project number:  544). Part of this work was supported by the COST Action Harmonia (CA21119) supported by COST (European Cooperation in Science and Technology)

How to cite: Moustaka, A., Korras-Carraca, M.-B., Papachristopoulou, K., Stamatis, M., Proestakis, E., Fountoulakis, I., Kazadzis, S., Amiridis, V., Tourpali, K., Solomos, S., Spyrou, C., Zerefos, C., and Gkikas, A.: Assessing lidar ratio impact on CALIPSO retrievals utilized for estimating aerosol shortwave direct radiative effects over the NAMEE domain, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16988, https://doi.org/10.5194/egusphere-egu24-16988, 2024.

Global Dimming and Brightening (GDB), which refers to the decrease/increase of incoming total solar radiation at the Earth's surface (or surface solar radiation, SSR) due to natural or anthropogenic composition changes of the Earth’s atmosphere, plays an important role in the Earth’s climate. According to the literature, the main drivers of the phenomenon are aerosols and clouds, contributing to GDB to different degrees depending on the world region and time period. This study aims, using a detailed spectral radiation transfer model (RTM), to identify and quantify the causes of GDB worldwide on a climatological scale. Specifically, it intends to determine their contribution to GDB as well as their spatio-temporal variability, performing detailed analyses on a monthly basis and a spatial latitude/longitude resolution of 0.5°x0.625°, all over the globe and for the 35-year period 1984-2018. The RTM required input data, such as those for cloud and aerosol optical properties, are taken from a synergy of satellite and reanalysis databases, namely the EUMETSAT’s CLARA-A2 and the NASA’s ISCCP-H and MERRA-2. Model runs, which are the main/base runs, are performed at the aforementioned spatial and temporal resolution and coverage to accurately calculate solar fluxes and GDB. Τhe contribution of clouds (cloud amount-CA and cloud optical thickness-COT of low, middle, high and total clouds), aerosol optical properties (aerosol optical depth-AOD, single scattering albedo-SSA and asymmetry parameter-AP), water vapor and ozone to GDB during the 35-year period 1984-2018 are calculated through RTM computations in which each parameter is kept ‘frozen’ at its initial conditions, namely the first year of the study period (namely 1984). Then, the contribution of a parameter P to the overall GDB is estimated from the difference between the GDB of the main RTM run, with all parameters being activated, and the GDB of the run with ‘frozen’ P parameter. In addition to the overall 35-year investigation, the study is also conducted on a decadal time scale, as well as on global, hemispherical, regional, and land/ocean spatial scales, in order to investigate the contribution of each parameter to GDB in more detail.

How to cite: Stamatis, M., Hatzianastassiou, N., Korras Carraca, M. B., Matsoukas, C., Wild, M., and Vardavas, I.: A comprehensive study on the causes of Global Dimming and Brightening using a radiative transfer model and satellite and reanalysis input data , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17894, https://doi.org/10.5194/egusphere-egu24-17894, 2024.

Photosynthetically active radiation (PAR) is one of the most important ecosystem steering factors. This study presents the results of 10-year (2013-2022) continuous measurements of incoming (PAR_d) and reflected (PAR_u) photosynthetically active radiation made at the Kopytkowo site (53°35′30.8′′ N, 22°53′32.4′′ E, 109 m ASL) within the Biebrza National Park in northeastern Poland.  The site represents a unique wetland ecosystem on a European scale. The assessment employed a PQS1 Quantum Sensor positioned at a height of 2.7 m AGL, capturing PAR with a time step of ten seconds. Subsequently, the data underwent averaging to establish a 5-minute time step used in the study. The results were expressed in photosynthetically active photon flux density (PPFD in µmol·m⁻²^-·s⁻¹^-).

Two distinct seasons corresponded to different PAR_d regimes in the Biebrza Basin. On average the first season (the warm part of the year) commences in the latter half of March and lasts until early October. Throughout this period, the development of convective cloudiness impacts daily photosynthetically active radiation values. The winter season, which lasts for the remainder of the year, is characterised by a higher proportion of cloudy days, influencing the reduced values of surveyed radiation. In general, the annual and daily PAR_d course reflects the incoming radiation on the top of the atmosphere and its attenuation in the atmosphere. On the contrary, the highest values of PAR_u manifest during the winter months, resulting from reduced vegetation development and snow cover present at the measurement site. Around mid-April values of PAR_u begin to drop due to vegetation growth and the assimilation of light.

Simultaneous measurement of PAR_d and PAR_u allowed the calculation of albedo in terms of photosynthetically active radiation, which was then used to trace changes in the growing season of plants and their growth dynamics in the study area. Research shows an average of about 210 days of increased absorption of photosynthetically active radiation per year, which falls during the vegetation development period (April to November). The first stage (rapid development) starts at the beginning of April and lasts until the middle of the month. It is characterized by a sharp decline in the proportion of PAR. This is followed by a period of stable expansion, which lasts until the end of May, after which the PAR_u/PAR_d ratio remains at a similar low level until mid-November. The highest values occur in January and February, due to the presence of snow cover, which increases the reflection of radiation, and due to reduced plant activity.

Acknowledgements: The National Science Centre, Poland provided funding for this research under project UMO-2020/37/B/ST10/01219 and the University of Lodz under project 4/IDUB/DOS/2021. The authors thank the authorities of the Biebrza National Park for allowing continuous measurements in the area of the Park.

How to cite: Górowski, J., Fortuniak, K., Siedlecki, M., and Pawlak, W.: Photosynthetically Active Radiation Dynamics in Wetland Ecosystem: A Decadal Study in the Biebrza National Park, Poland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3518, https://doi.org/10.5194/egusphere-egu24-3518, 2024.

Links between stratospheric ozone depletion, climate change and UV variability reaching the ground have been established already in a number of studies. Apart from ozone variability and among other factors, aerosol properties, surface reflectivity and clouds are critical for the modulation of the surface UV radiation levels.

In the first part of the study, we examine the evolution of these variables through the years, as derived from simulations by models participating in the 6^th Phase of the Coupled Model Intercomparison Project (CMIP6). The period of interest extends from the years before the peak of the ozone depletion (here we selected as reference period the years 1950-1960), up to the end of the 21^st century. For a better understanding of future UV radiation levels, we selected three of the IPCC Shared Socioeconomic Pathways (SSPs); SSP1–2.6 as the most sustainable, SSP3–7.0 with high amounts of GHGs and SSP5–8.5 as the most extreme.

In the second part of the study, we provide an overview of the surface UV changes around the globe, with radiative transfer model (RTM) simulations of solar irradiance using libRadtran version 2.0.3. Monthly mean data of ozone, aerosol optical depth (AOD) at 550 nm and surface reflectivity from CMIP6 models are used as input data for the RTM simulations. Here we present changes of the local noon UV-Index (UVI), after weighting the simulations with the Commission Internationale de l'Éclairage (CIE) erythemal action spectra.

Some key changes in drivers and UVI will be discussed. After the middle of the 21^st century there is an increasing trend of total ozone column, and more specifically over the Antarctic region, where the depletion is more pronounced, we find that ozone recovery is projected under SSP3–7.0 and SSP5–8.5, while this never fully occurs under SSP1–2.6. According to RTM simulations, reduction of UVI is expected due to the recovery of the ozone layer after the middle of the 21^st century. AOD increases over the areas with strong emissions under the three SSPs, which leads to more scatter of irradiance and consequently to lower surface UVI. Finally, surface reflectivity simulations for the end of the 21^st century show reductions under all SSPs, mostly over the high latitudes, mainly attributed to ice melt, resulting in decreases of surface UVI.

How to cite: Chatzopoulou, A., Tourpali, K., Bais, A. F., Karagkiozidis, D., and Braesicke, P.: Projecting the Surface UV Radiation from CMIP6 Models and how Factors Influencing it are Changing, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7893, https://doi.org/10.5194/egusphere-egu24-7893, 2024.