In 2023, the global mean temperature soared to almost 1.5°C above the preindustrial level, surpassing the previous record by about 0.17°C. Previous best-guess estimates of known drivers, including anthropogenic warming and the El Niño onset, fall short by about 0.2°C in explaining the temperature rise. This gap persisted in 2024, during which the stronger El Niño contribution resulted in an even higher global annual-mean temperature, exceeding the symbolic 1.5°C threshold. Using satellite and reanalysis data, we identified a record-low planetary albedo as the primary factor bridging this gap. The decline is apparently caused largely by a reduced low-cloud cover in the northern mid-latitudes and tropics, in continuation of a multiannual trend. Further exploring the low-cloud trend and understanding how much of it is due to internal variability, reduced aerosol concentrations, or a possibly emerging low-cloud feedback will be crucial for assessing the present and expected future warming.

How to cite: Goessling, H., Rackow, T., and Jung, T.: Recent global temperature surge intensified by record-low planetary albedo, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15920, https://doi.org/10.5194/egusphere-egu25-15920, 2025.

Incoming solar radiation drives the Earth’s climate system. Long-term surface observations of solar radiation reaching the surface have shown decreasing or increasing trends in different regions of the world in the past several decades, indicating the change of atmospheric components that reflect and/or absorb the solar radiation. This study investigates the roles of aerosols and climate change in determining the surface radiation trends through the change of anthropogenic emission, aerosol-radiation interaction, and aerosol-cloud interactions. With a series of model simulations and analysis of ground-based observations and satellite-derived data products, we will 1) estimate the relative importance of aerosols, clouds, and other radiatively active atmospheric trace gases on the surface radiation budget, 2) compare the relative magnitudes of effects from atmospheric components (aerosols, clouds, and trace gases) and atmospheric processes (aerosol-radiation interactions and aerosol-cloud interactions) in determining the surface radiation trends, and 3) assess the consequences of climate change and anthropogenic emission trends in the change of surface radiation in different regions of the world.

How to cite: Chin, M., Bian, H., Wild, M., Barahona, D., Yu, H., Qian, Y., Darmenov, A., Stackhouse, P., Loeb, N., Pinker, R., and Zhang, Y.: Multi-Decadal Trends of Solar Radiation Reaching the Surface Determined by Aerosol-Cloud-Radiation Interactions, Climate Change, and Anthropogenic Emissions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4577, https://doi.org/10.5194/egusphere-egu25-4577, 2025.

Observations have recorded significant decadal changes in the global surface solar radiation (SSR) over the past, a phenomenon known as the ‘global dimming’ and ‘brightening’. Many studies suggest that changes of SSR are dominated by aerosols, clouds, and other influences at the atmosphere. However, due to the lack of suitable data and methodology, there are few global evaluations and quantitative work that reveal the relative importance of impacting factors on the SSR trends. In this study, a linear regression method is used to investigate the driving factors of global SSR and to quantify their contributions to the long-term change and distribution of SSR. Based on a reanalysis dataset, from 2000 to 2023, the distributions and trends of SSR can be well explained by the linear regression model, with crucial variables such as aerosol optical depth (AOD), cloud radiative effect and water vapor as predictors. The model performs particularly well at low and middle latitudes. We find that under all sky condition, cloud radiative effect causes approximately 70% of the variation in SSR, which has the strongest influence on SSR among the other predictors. In addition, all-sky SSR also shows very high sensitivity to water vapor and AOD.

How to cite: Xiao, H., Huang, Y., Yu, Q., and Peng, Y.: Contributions of Driving Factors to Variations in Global Surface Solar Radiation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12299, https://doi.org/10.5194/egusphere-egu25-12299, 2025.

Inhomogeneities in the sunshine duration (SSD) observational series, caused by non-climatic factors like China’s widespread transition from manual to automatic SSD recorders in 2019 or station relocations, have hindered accurate estimate of near-surface solar radiation for the analysis of global dimming and brightening as well as related applications, such as solar energy planning and agriculture management. This study compiled raw SSD observational data from 1961 to 2022 at more than 2,200 stations in China and clearly found that the improved precision from 0.1 hour to 1 minute following the instrument update in 2019 led to a sudden reduction in the frequency of zero SSD from 2019 onwards, referred to as the day0-type discontinuity. For the first time, we systematically corrected this known day0-type discontinuity at 378 stations (17%) in China, resulting in an SSD series with comparable frequencies of zero value before and after 2019. On this base, we constructed a homogenization procedure to detect and adjust discontinuities in both the variance and mean of daily SSD from 1961 to 2022. Results show that a total of 1,363 (60%) stations experienced breakpoints in SSD, of which ~65% were confirmed by station relocations and instrument replacements. Compared to the raw SSD, the homogenized SSD was more continuous to the naked eye for various periods, and presented weakened dimming across China from 1961 to 1990 but a non-significant positive trend by a reduction of 60% in the Tibetan Plateau, suggesting that the homogenized SSD tends to better capture the dimming phenomenon. The northern regions continued dimming from 1991 to 2022 but the southern regions of China brightened slightly. The implementation of the Action Plan for Air Pollution Prevention and Control since 2013 contributed to a reversal of SSD trend thereafter, which was better reflected in the homogenized SSD with a trend shift from -0.02 to 0.07 hours·day^-1/decade from 2013 to 2022 in China, especially in heavily polluted regions. Besides, the relationships of cloud cover fraction and aerosol optical depth with SSD were intensified in the homogenized dataset. These results highlight the importance of the homogenized SSD in accurately understanding the dimming and brightening phenomena. The homogenized SSD dataset is publicly available for community use at https://yanyihe-rad.github.io/files/homog-daily-ssd-China-v1.0.mat.

How to cite: He, Y., Wang, K., Yang, K., Zhou, C., Shao, C., and Yin, C.: Homogenized daily sunshine duration over China from 1961 to 2022, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14211, https://doi.org/10.5194/egusphere-egu25-14211, 2025.

The Central India (CI), wherein synoptic-scale disturbances (monsoon lows and depressions) frequently pass through during the monsoon season, is identified as a monsoon core zone where detailed long-term atmospheric measurements of convection, clouds, precipitation, and radiation are overdue.

Considering the importance of observational and analytical research in this area, an Atmospheric Research Testbed in Central India (ART-CI) is established by the Ministry of Earth Sciences, Government of India. ART-CI is a huge permanent observational facility envisioned as a national research testbed with multiple laboratories (aerosol, radiation, cloud and precipitation measurements) and scientific user facilities similar to the international Atmospheric Radiation Measurement (ARM) site, USA.

Our climate system is largely determined by the Earth’s Radiation Budget, and is significantly influenced by drastic changes in clouds, aerosols, and greenhouse gases. Hence, to have long-term surface observations for monitoring the changes/trends in the Surface Radiation Budget, important for climate monitoring and prediction, Atmospheric Radiation Laboratory (ARL) is established in August 2023, as a part of the major research facility ART-CI. At ARL, a suite of radiation sensors was installed for continuous measurements of all components of solar and terrestrial radiation (such as total, direct and diffuse shortwave, long-wave, net and UV radiations) co-located with all other atmospheric data instrumentation.

Thus, this unique facility will have an extensive set of state-of-the-art observational systems that will provide continuous observations of land surface properties and surface energy budget. Site description, instrumentation and science plan of this new facility with initial results will be presented.

How to cite: PadmaKumari, B., Vasudevan, A. K., Sahoo, U. K., Victor, J., Lian, Y., Tr, L., Nikam, M., Kalgutkar, S., and Govindan, P.: Atmospheric Radiation Laboratory (ARL) in Monsoon core zone: A unique research facility in Central India, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-633, https://doi.org/10.5194/egusphere-egu25-633, 2025.

Accurate solar irradiance measurements are critical for optimising solar energy systems, understanding atmospheric processes, and advancing climate research. Pyrheliometers, which provide Direct Normal Irradiance (DNI) measurements over a broad spectral range, are widely used due to their simplicity, cost-effectiveness, and ease of deployment. However, they cannot provide detailed spectral information, which limits their application in advanced studies requiring wavelength-specific insights. In contrast, the Bi-Tec Sensor (BTS) spectroradiometer system measures spectral solar irradiance from 300 nm to 2150 nm with high spectral resolution, covering almost ~96.5% of the solar spectrum, and is traceable to the International System of Units (SI). This detailed spectral data enables in-depth studies of solar energy distribution across different wavelengths but excludes approximately 3.5% of the total solar spectrum in the infrared region (2150–5000 nm).

To overcome this limitation and enable full-spectrum comparisons, this study utilized libradtran, an atmospheric radiative transfer model, to extend the BTS spectral range, whereas due to the requirement of computational resources and expertise, A comparatively simpler functional model was developed based on libradtran simulations, focusing on critical parameters such as solar zenith angle, water vapor, and aerosol properties. This function closely matched the results from libradtran and achieved high precision with a mean value of 96.52% and a standard deviation of  0.20% that can be used to accurately extend the BTS measurements to cover the full spectrum. The comparison between pyrheliometer and BTS spectroradiometer yields a mean ratio of 0.9897 with a standard deviation of 0.0149, achieving a good correlation with pyrheliometer data while maintaining precise spectral details.

The results confirm that BTS spectroradiometers, combined with the spectral extension model, provide an effective and detailed alternative for solar irradiance monitoring. Unlike pyrheliometers, BTS instruments deliver wavelength-specific data crucial for advanced solar energy studies and atmospheric research. Moreover, integrating the extension model into BTS systems simplifies data processing, making high-quality measurements accessible for non-expert users and resource-limited regions.

This approach bridges the gap between the spectral detail of BTS systems and the broad range of pyrheliometers, offering a reliable solution for comprehensive solar irradiance measurements. These findings mark a step forward in solar energy research and environmental monitoring, with the potential to address global data gaps in cost-effective and scalable ways.

How to cite: Jaine, D. and Gröbner, J.: Comparison of solar spectral irradiance measurements with pyrheliometer total solar irradiance data., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6703, https://doi.org/10.5194/egusphere-egu25-6703, 2025.

The ecRad scheme is the latest radiative transfer scheme provided by the European Centre for Medium-range Weather Forecast (ECMWF), and is notably operational in the ECMWF’s Integrated Forecasting System (IFS) since 2017. Recent developments of ecRad enable it both to run using ecCKD high resolution gas-optics models and to produce surface shortwave spectral fluxes. The combination of both features allow ecRad to produce fine surface shortwave spectral fluxes, e.g., over a 310–315 nm spectral band.

We assessed this capability after embedding ecRad (v1.5.0) in the MAR (Modèle Atmosphérique Régional) regional climate model (v3.14). For this purpose, we used ground-based spectral observations captured by the Royal Belgian Institute for Space Aeronomy at Uccle (Belgium; 50.797° N, 4.357° E) from 2017 to 2020, in the 280–500 nm range and with a precision of 0.5 nm. After carefully tuning both MAR and ecRad and configuring fine spectral bands over the 280–500 nm range, we ran a MAR simulation over Belgium for the same period as the Uccle spectral observations.

After integrating the spectral observations on the same bands as configured in our MAR/ecRad simulation, we compared both time series of spectral fluxes at Uccle. Our evaluation yielded correlation coefficients ranging from 0.9 to 0.93 for all bands above 295 nm and low biases for all bands. As our spectral fluxes cover the ultraviolet (UV) range, we tried to predict UV indices with MAR/ecRad spectral fluxes. The UV index is a metric used to inform the public about how much harmful ultraviolet radiation reaches the Earth’s surface at a given time, and consists of a weighted integral of spectral fluxes over the UV range. Our model-based and observations-based UV indices are in very good agreement, though the former falls short of finding the highest UV indices of the latter, due to the ozone mixing ratios in MAR not varying on a daily basis.

Author's note: this research work is detailed in the paper "Inclusion of the ECMWF ecRad radiation scheme (v1.5.0) in the MAR model (v3.14), regional evaluation for Belgium and assessment of surface shortwave spectral fluxes at Uccle" currently available on EGUsphere in preprint (awaiting topic editor decision after referee comments and subsequent revision).

How to cite: Grailet, J.-F., Hogan, R. J., Ghilain, N., Bolsée, D., Fettweis, X., and Grégoire, M.: Evaluation of surface shortwave spectral fluxes at Uccle produced by the ECMWF ecRad radiation scheme (v1.5.0) embedded in the MAR regional model (v3.14) and prediction of UV indices, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17633, https://doi.org/10.5194/egusphere-egu25-17633, 2025.

The response of the Earth system to radiative perturbations is governed by a combination of fast and slow feedbacks.  Slow feedbacks are typically activated in response to changes in ocean temperatures on decadal timescales and often manifest as changes in Earth-system state with no recent analogue.  On the other hand, fast feedbacks can be activated in response to rapid atmospheric physical processes on timescales of weeks and are already operative in the present-day weather system. This distinction implies that the physics of fast radiative feedbacks is present in the historical reanalyses that have served as the training data for many of the most successful recent machine-learning-based emulators of weather.  In addition, these feedbacks are functional under the historical boundary conditions pertaining to the top-of-atmosphere radiative balance and sea-surface temperatures.    We discuss our work using historically trained weather emulators to characterize and quantify fast radiative feedbacks without the need to retrain for prospective Earth system  conditions.

How to cite: Collins, W. and Mahesh, A.: Examining fast radiative feedbacks using machine-learning-based emulators of weather, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13923, https://doi.org/10.5194/egusphere-egu25-13923, 2025.

Contrail cirrus is regarded to be the largest contributor to aviation induced global warming based on classical radiative forcing and exceeds the corresponding climate impact of accumulated air traffic CO₂ emissions. However, recent studies indicate that the leading role of contrail cirrus declines when using more advanced climate metrics, such as the effective radiative forcing, or even disappears when considering the induced surface temperature change. 

Here we present results from climate model simulations to derive a fully self-consistent set of classical radiative forcings, effective radiative forcings and corresponding surface temperature changes for a contrail cirrus and CO₂ perturbation. The simulations were extensively evaluated by feedback analysis in order to determine the origin of the reduced efficacy of contrail cirrus to warm Earth’s surface. When switching from classical radiative forcing to effective radiative forcing the impact of contrail cirrus decreases by 45% relative to CO₂. Feedback analysis revealed a reduced formation of natural cirrus as the major reason, as contrail cirrus formation removes large parts of available ambient humidity. When looking at surface temperature change, the efficacy of contrail cirrus turned out to be reduced, even more, by 79% relative to CO₂. Again, cloud feedbacks were found to be the major reason for the different behavior between the contrail cirrus and CO₂ perturbation, however, in this case mainly triggered by decreasing low- and mid-level clouds in the CO₂ simulation. The efficacy reduction is also supported by a larger negative lapse rate feedback (change of the vertical temperature slope) which is the result of a temperature dipole formed by contrail cirrus, with strongest warming rates directly below the contrail cirrus cloud base and decreasing strength towards surface.

How to cite: Bickel, M., Ponater, M., Burkhardt, U., Righi, M., Hendricks, J., and Jöckel, P.: The important role of feedback processes for contrail cirrus climate impact, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19022, https://doi.org/10.5194/egusphere-egu25-19022, 2025.

Recent decades have seen significant changes in land surface phenology, with earlier leaf development in northern ecosystems and diverse changes in autumn senescence, primarily attributed to climate change. These phenological changes feed back to Earth’s climate system by altering biogeochemical and biogeophysical processes at the land surface. However, little is known about the strength of these diverse effects on the Earth's energy balance, and whether their combination results in a net positive (warming) or negative (cooling) feedback to global warming.

Using a fully-coupled Earth system model (ESM) with an interactive global carbon cycle, we investigate the effects of land phenological changes on the Earth's energy balance and the subsequent biogeophysical and biogeochemical feedbacks. We prescribe transient shifts in leaf area index (LAI) in the ESM based on remote sensing estimates of phenological spring advancement (2.1 days per decade) and autumn delay (1.8 days per decade). Note these shifts are only prescribed for extratropical northern ecosystems, where robust phenological changes have been observed, however, the effect in the ESM is global including local and non-local effects. Our results provide a first quantification of the impact of these phenological changes on the processes affecting the Earth’s energy balance, namely, shortwave radiation through changes in surface albedo, surface sensible and latent heat fluxes, longwave surface emissions, ground heat flux, longwave radiation balance through greenhouse gases, and the overall radiative fluxes through cloud properties and planetary albedo.

We find that autumn LAI shifts have a stronger net effect than spring LAI shifts on the Earth's energy balance, and that these effects can compensate each other when they co-occur in the same year. Our simulations also reveal compensating effects between outgoing longwave and outgoing shortwave radiation at the top of the atmosphere, where the former points to a positive and the latter to a negative radiative forcing. Altogether, we report an average negative radiative forcing of 0.17 ± 0.1 W m^-2 for a 10-day lengthening of the growing season, resulting in a global mean surface temperature cooling of 0.1 ± 0.03 °C. The effect is more pronounced in simulations when spring advancement and delay in senescence are prescribed separately in the ESM, amounting to a negative radiative forcing of 0.24 ± 0.21 W m^-2 and 0.32 ± 0.25 W m^-2 for a 10-day lengthening of the growing season, respectively. These simulations suggest that phenological changes triggered by global warming result in a net negative feedback to global warming. Future research is needed to confirm this first quantification and to investigate the saturation of phenological responses to global warming, which could weaken this cooling feedback effect in the future.

How to cite: Winkler, A. J. and the PhenoFeedBacks Team: Phenology's Net Cooling Effect as Feedback to Global Warming, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19629, https://doi.org/10.5194/egusphere-egu25-19629, 2025.

Monitoring the Earth Energy Imbalance (EEI) is of prime importance for a predictive understanding of climate change. Furthermore, monitoring of the EEI gives an early indication on how well mankind is doing in implementing the Paris Climate Agreement. EEI is defined as the small difference between the incoming energy the Earth receives from the Sun and the outgoing energy lost by Earth to space. The EEI is cumulated in the Earth climate system, particularly in the oceans, due to their substantial heat capacity, and results in global temperature rise. Currently the best estimates of the absolute value of the EEI, and of its long term variation are obtained from in situ observations, with a dominant contribution of the time derivative of the Ocean Heat Content (OHC). These in situ EEI observations can only be made over long time periods, typically a decade or longer. In contrast, with direct observations of the EEI from space, the EEI can be measured at the annual mean time scale. However, the EEI is currently poorly measured from space, due to two fundamental challenges. The first fundamental challenge is that the EEI is the difference between two opposing terms of nearly equal amplitude. Currently, the incoming solar radiation and outgoing terrestrial radiation are measured with separate instruments, which means that their calibration errors are added and overwhelm the signal to be measured. To make significant progress in this challenge, a differential measurement using identical intercalibrated instruments to measure both the incoming solar radiation and the outgoing terrestrial radiation is needed. The second fundamental challenge is that the outgoing terrestrial radiation has a systematic diurnal cycle. Currently, the outgoing terrestrial radiation is sampled from the so-called morning and afternoon Sun-synchronous orbits, complemented by narrow band geostationary imagers. Recently the sampling from the morning orbit was abandoned. The sampling of the diurnal cycle can be improved, for example, by using two orthogonal 90° inclined orbits which give both global coverage, and a statistical sampling of the full diurnal cycle at seasonal time scale. For understanding the radiative forcing – e.g. aerosol radiative forcing - and climate feedback – e.g. ice albedo feedback - mechanisms underlying changes in the EEI, and for climate model validation, it is necessary to separate the Total Outgoing Radiation (TOR) spectrally into the two components of the Earth Radiation Budget (ERB), namely the Reflected Solar radiation (RSR) and Outgoing Longwave Radiation (OLR) and to map them at relatively high spatial resolution. The Earth Climate Observatory (ECO) mission concept was recently selected by the European Space Agency as one of the 4 candidate Earth Explorer 12 missions, that will be further studied in Phase 0 until mid 2026. The current paper provides a broad overview of the ECO mission objectives, the mission requirements, and the key elements of a baseline mission concept. During Phase 0, the ECO mission concept will be further elaborated in two parallel industrial studies, which may or may not adopt or refine the elements of the baseline concept.

How to cite: Dewitte, S., Mauritsen, T., Meyssignac, B., August, T., Schifano, L., Smeesters, L., Roca, R., Brindley, H., Russell, J., Clerbaux, N., Hollmann, R., Megner, L., Haberreiter, M., Gumbel, J., Marotzke, J., Riedi, J., Riihela, A., Trent, T., and Wendisch, M.: The Earth Climate Observatory space mission concept for the monitoring of the Earth Energy Imbalance., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12847, https://doi.org/10.5194/egusphere-egu25-12847, 2025.

The Earth’s radiation budget is a crucial part of climate and its evolution. Being part of this budget, the outgoing longwave radiation (OLR) has been extensively studied, especially in the context of climate-change and anthropogenic greenhouse gases emissions modifying the Earth’s radiative equilibrium.

In this study we present a new line-by-line radiative code RadForcE, we have developed to compute the global OLR and radiative forcing over a 10-year period. Based on a backward longwave Monte Carlo method, RadForcE uses line-by-line spectroscopic data for several molecular gases (CO₂, H₂O, CH₄ and O₃) from high-resolution databases GEISA and HITRAN, as well as different continua. The clouds’ vertical distributions are taken into account with a vertical overlap subgrid parameterization that is sampled "on the fly" for each optical path along vertical atmospheric profiles. Those profiles are sampled over a 10-year period all over the globe, either from GCM outputs or from ERA5 reanalysis, to compute the unbiased global OLR at a very small computational cost (~10 minutes on a laptop).

We this new method we are also able to directly compute any greenhouse gas radiative forcing, and present estimates of the radiative forcing for a doubling of CO₂. The Monte Carlo approach allows us to identify, for each outgoing optical path at the top of the atmosphere, the emitting species as well as the altitude of emission. By doing so, we can visualize the profile of altitude of emission for each species, as well as how some gases can screen other species’ emission or the surface’s emission. We can also visualize, for a doubling of CO₂, the increase of stratospheric emission by CO₂, and its screening of the surface’s emission and water vapor tropospheric emission.

How to cite: Jean-Louis, D., Raphaël, L., Yaniss, N.-P., Richard, F., and Stéphane, B.: Using line-by-line Monte Carlo to compute the Earth’s outgoing longwave radiation and CO2’s radiative forcing, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16594, https://doi.org/10.5194/egusphere-egu25-16594, 2025.

Upper tropospheric humidity (UTH) is a diagnostic of the atmospheric water cycle and strongly contributes to climate sensitivity. Therefore, it is important to understand UTH variability and how this is represented by global climate models. Here, infrared and microwave brightness temperature observations and satellite simulations based on ECMWF Reanalysis v5 (ERA5) and the Hadley Centre Global Environment Model version 3 (HadGEM3) Atmospheric Model Intercomparison Project (AMIP) data are used to evaluate and characterise UTH variability since 1979. UTH satellite observations have been simulated using a radiative transfer code (RTTOV) from ERA5 and HadGEM3 to provide a more direct comparison of the model and reanalysis to observations.

We present results on the sensitivities of water vapour brightness temperatures. There are competing influences of temperature and specific humidity on the brightness temperatures. The effect of these is such that fluctuations can be considered as a proxy for relative humidity. Despite this, a spurious increase in UTH of up to 1% is identified for a 1K increase in profile temperature when relative humidity remains constant.

How to cite: Stevens, T., Allan, R., Hegglin, M., Bodas-Salcedo, A., and John, V.: Investigating trends, variability in observed and simulated upper tropospheric humidity and outgoing longwave radiation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4221, https://doi.org/10.5194/egusphere-egu25-4221, 2025.

Water vapour (WV) is one of the most significant greenhouse gases and plays a critical role in the majority of the thermodynamic processes that occur within the atmosphere. Thus, it significantly influences the radiative budget and cloud formation mechanisms, being of paramount importance in weather forecasting. Therefore, accurate and detailed characterisation of its spatial and temporal distribution is of undoubtedly great interest. However, measurement techniques often struggle with its variability both in space and time, making it challenging to obtain regular and reliable measurements. 

Although high resolution height-resolved profiles of water vapour mixing ratio are currently being acquired by lidar systems and providing powerful information, such instruments usually suffer from overlap issues in the lower hundred meters, precisely where greater concentrations of water vapour appear. This issue, together with the reduced global representativity due to the scarce number of operative lidar systems, hinders the use of this technique for continuous monitoring of water vapour near the ground. In contrast, other passive and active remote sensing techniques like Microwave Radiometers (MWR), Sun Photometers (SP) or Global Navigation Satellite System (GNSS) are well established and have been globally proven as a feasible and trustworthy alternative for continuous measurements of the total vertical column water vapour concentration (IWV). 

This study addresses the characterisation of IWV over Granada, a city in southern Spain, using remote sensing techniques (MWR, SP and GNSS). These techniques are first validated against in situ data collected from over 70 radiosondes (RS). The study then investigates the IWV evolution over Granada for a 14-year period. The daily, seasonal and annual cycles are described together with the statistical behaviour of the data series in search of tendency changes.

Reanalysis data from Numerical Weather Prediction (NWP) models such as MERRA-2 (Modern-Era Retrospective Analysis for Research and Applications, version 2) and ERA5 (fifth generation of European Centre for Medium-Range Weather Forecasts reanalysis) are also validated against remote sensing measurements and then considered to expand the study period to more than 40 years, allowing the climatological study of water vapour in the area. Seasonal decomposition and a Mann-Kendall statistical test discovered an increasing tendency in IWV. Analogous analysis for the temperature in the region also found a positive increase, accentuated since the beginning of the 21st century and reinforcing the results of climate change studies. The relationship between both magnitudes indicates a possible contribution of increased water vapour concentrations to the observed increased temperatures.

How to cite: Naval Hernández, V. M., del Águila Pérez, A., Díaz Zurita, A., Rodríguez Navarro, O., Muñiz Rosado, J., Pérez Ramírez, D., Neil Whiteman, D., Alados Arboledas, L., and Navas Guzmán, F.: Long-Term Integrated Water Vapour (IWV) analysis in Southern Spain using remote sensing techniques and reanalysis models, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12571, https://doi.org/10.5194/egusphere-egu25-12571, 2025.

Many trace gases throughout Earth’s atmosphere are known to have a large potential to impact the radiation budget. The HITRAN database provides spectroscopic parameters and supplementary data in the form of line-by-line lists, absorption cross sections, collision induced absorption, water vapor continuum, and aerosol properties that enable molecular absorption to be modeled, which allows the radiation budget and radiative forcing to be determined. For HITRAN2024, in addition to increasing the number of molecules with line-by-line lists to 61, the absorption cross sections are receiving a substantial update. The update of cross sections makes use of many newly available experimental data and results in the addition over 100 molecules to the large number of molecules already represented as absorption cross sections in HITRAN2020 (Gordon et al. 2022). The absorption cross section update will also expand the range of experimental conditions available (i.e., temperatures, pressures, broadening gases, and resolutions) for many molecules that are present in Earth’s atmosphere. The new cross-sections have been a subjected to a validation process prior to being added to the database. This talk will showcase the absorption cross sections in HITRAN, and will highlight major updates for the 2024 compilation.

Funding from NASA grant 80NSSC23K1596 is acknowledged.

Reference: Gordon, et al., JQSRT 277, 107949 (2022). https://doi.org/10.1016/j.jqsrt.2021.107949

How to cite: Hargreaves, R., Gordon, I., Hill, C., Kochanov, R., and Rothman, L.: Updating the experimental absorption cross sections for HITRAN2024, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20646, https://doi.org/10.5194/egusphere-egu25-20646, 2025.

Aerosol-cloud-interactions (ACI) is a leading uncertainty in estimates of their radiative forcing and hence for climate projection. The aerosol radiative forcing obtained from climate models is poorly constrained by observations, because the ACI signal is frequently entangled with noise of meteorological co-variability.

       The Iceland-Holuhraun volcanic eruption in Iceland in 2014 provided an unprecedented opportunity to examine ACI of marine low-level clouds and how well they are represented in climate models. Malavelle et al. (2017) used Collection 5 data from the MODIS Aqua satellite and provided an assessment of the impact of the large release of sulfur dioxide on cloud effective radius (r_eff) and cloud liquid water path (LWP), finding a considerable impact on the former, but no impact on the latter. We revisit this eruption with a considerably extended satellite record which includes new Collection 6 data from the Terra and Aqua satellite and additional years of data from 2015-2020. This tripling of satellite data allows using novel data-science approach for a more rigorous assessment of ACI, including the impacts not just on cloud micro-physical properties (r_eff and LWP), but also on the macro property cloud coverage (Chen et al., 2022).

These results show that cloud fraction is significantly increased by 10% and appears to surpass cloud brightening and to be the dominant factor in aerosol indirect radiative cooling. The ACI cooling effect via increasing of cloud cover is even more remarkable in tropics (Fig.1, upto 50%), as demonstrated by our recent study of Hawaii volcanic natural experiments (Chen et al., 2024). Climate models are unable to replicate such strong impacts on cloud cover. These results show that the ongoing debate about the cooling impact of aerosols is far from over while climate models continue to inadequately represent the complex macro- and micro-physical impacts of ACI. These researches point towards a direction and provide new constraints for improving model representation of ACI.

Figure 1. Aerosol-induced changes in cloud cover from volcano natural experiments. Source: Chen et al., (2024)

References:

Chen, Y., Haywood, J., Wang, Y., Malavelle, F., Jordan, G., Partridge, D., Fieldsend, J., De Leeuw, J., Schmidt, A., Cho, N., Oreopoulos, L., Platnick, S., Grosvenor, D., Field, P., and Lohmann, U.: Machine learning reveals climate forcing from aerosols is dominated by increased cloud cover, Nature Geoscience, 10.1038/s41561-022-00991-6, 2022.

Chen, Y., Haywood, J., Wang, Y., Malavelle, F., Jordan, G., Peace, A., Partridge, D. G., Cho, N., Oreopoulos, L., Grosvenor, D., Field, P., Allan, R., and Lohmann, U.: Substantial cooling effect from aerosol-induced increase in tropical marine cloud cover, Nature Geoscience, https://doi.org/10.1038/s41561-024-01427-z, 2024.

Malavelle, F., Haywood, J., Jones, A. et al. Strong constraints on aerosol–cloud interactions from volcanic eruptions. Nature 546, 485–491 (2017). https://doi.org/10.1038/nature22974

How to cite: Chen, Y., Haywood, J., Wang, Y., Malavelle, F., Jordan, G., Peace, A., Partridge, D., Cho, N., Oreopoulos, L., Grosvenor, D., Field, P., Allan, R., and Lohmann, U.: Observational evidence of strong aerosol fingerprints on clouds and effect on radiative forcing, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-27, https://doi.org/10.5194/egusphere-egu25-27, 2025.

Ozone is the third most important greenhouse gas, contributing a forcing of 0.47 W/m2 over the historical period. All assessments of ozone forcing so far have used the stratospheric-temperature adjusted radiative forcing (SARF) calculated by offline radiative transfer models. The two most recent IPCC reports have recommended the use of effective radiative forcing (ERF) as the preferred measure of forcing, but no calculations have been available.

For the first time we calculate the future ozone online ERF from six Earth system models and compare this to the SARF calculations. The future ozone calculations are for the SSP3-7.0 scenario for the year 2050. Only the ozone changes (and any consequent impacts on meteorology) are included in the radiative forcing calculations. We find an ERF of 0.27+/- 0.09 Wm-2  and an ozone column increase of 12 DU. Approximately half of the forcing change comes from ozone recovery following the decline in halocarbons.

By decomposing the radiative forcing into instantaneous (IRF), stratospheric-temperature adjusted (SARF) and effective (ERF) radiative forcing we gain insights into the adjustment processes causing the differences between the radiative forcing measures. The ERF is typically larger than the SARF. This is mostly due to positive non-cloud adjustments through increased water vapour (particularly in the stratosphere) and decreased surface albedo. Reductions in high and mid-level cloud increase the short-wave forcing, but decrease the long-wave forcing. The adjustments to the forcing depend on the altitude of the ozone change, with adjustments to ozone changes following reductions in ozone-depleting substances being more strongly positive than those following increases in ozone precursors.

How to cite: Collins, W., O'Connor, F., Byrom, R., Hodnebrog, Ø., Jöckel, P., Mertens, M., Myhre, G., Nützel, M., Olivié, D., Skeie, R., Stecher, L., Horowitz, L., Naik, V., and Murray, L.: Comparing radiative forcing measures for ozone, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11349, https://doi.org/10.5194/egusphere-egu25-11349, 2025.

How to cite: Deshmukh, A., Laakso, A., Mielonen, T., Gkouvousis, A., Arola, A., Kokkola, H., and Bergman, T.: Radiative forcing of anthropogenic Brown Carbon in EC-Earth3, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19921, https://doi.org/10.5194/egusphere-egu25-19921, 2025.

How to cite: Gao, C. and Gao, Y.: Dwindling Effective Radiative Forcing of Large Volcanic Eruption: The Compensation Role of Ocean Latent Heat Flux, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1674, https://doi.org/10.5194/egusphere-egu25-1674, 2025.

The land surface albedo is one of the key parameters of the global radiation budget, since it regulates the shortwave radiation absorbed by the Earth’s surface. The polar regions, in particular, a decrease in snow and ice cover results in a decrease of surface albedo and in the intensification of solar heating further reducing the snow and ice areas (ice-albedo feedback). In remote areas, where in-situ instruments are absent, satellites are crucial to measure surface albedo changes.

In this work, a comparison of satellite and in-situ measurements of broadband shortwave surface albedo is conducted. The area of interest selected is around the Thule High Arctic Atmospheric Observatory (THAAO) on the North-western coast of Greenland (76.5°N, 68.8°W), where the measurements of down-welling and up-welling shortwave irradiance have been started in 2009 and 2016, respectively (https://www.thuleatmos-it.it/).

Albedo determinations based on MODIS observations from both Terra and Aqua (MODIS MCD43A3 dataset), consisting of daily values with a spatial resolution of 500 m, have been compared with the ground-based measurements.

The analysis has been conducted for all-sky and clear-sky conditions with a focus on some events to better understand the behavior of MODIS data with respect to ground-based measurements, taking advantage of the additional information (meteorological parameters, cloudiness, precipitation) available at THAAO.

The results for the period 2016-2024 show an underestimation of the albedo measurements from satellite compared to the ground-based measurements at the THAAO over a large part of the period considered. The best agreement is found in the summer when there is no snow around the Observatory, and the mean measured albedo value is 0.1633 for cloud-free conditions and 0.1903 for all-sky conditions. The mean bias during this season is around -0.0074 for cloud-free conditions and 0.0067 for all sky conditions. In spring, when the in-situ albedo values are highly variable, between 0.350 and 1, the mean bias is around -0.0645 for cloud-free conditions and -0.0159 for all sky conditions.

The fast changes in surface albedo occurring after short snow precipitation or removal events are seldom captured by satellite observations.

How to cite: Tosco, M., Meloni, D., Calì Quaglia, F., Muscari, G., Di Iorio, T., Pace, G., Ciardini, V., and di Sarra, A. G.: Measurements of land surface albedo at the Thule High Arctic Atmospheric Observatory (THAAO) in Pituffik, Greenland and comparison with MODIS data., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17123, https://doi.org/10.5194/egusphere-egu25-17123, 2025.

How to cite: Shukla, S., Kleidon, A., Ghausi, S. A., and Chauhan, T. A.: Understanding altitudinal temperature variations using a surface energy balance approach , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11477, https://doi.org/10.5194/egusphere-egu25-11477, 2025.

How to cite: García-Pereira, F., González-Rouco, J. F., Meabe-Yanguas, N., Jungclaus, J., de Vrese, P., and Lorenz, S.: An insufficient subsurface depth biases the long-term surface energy balance in Land Surface Models , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13806, https://doi.org/10.5194/egusphere-egu25-13806, 2025.