Spectral radiance and its temporal dependence on incident and azimuth angle plays an important role for radiative transfer because all other radiative quantities may be derived from the spectral radiance. It depends on time, wavelength, incident angle, azimuth angle, height and geographic location as well as polarization. The modeling of spectral radiance is therefore the goal of many investigations. In practice, however, spectral radiance can often not be determined by calculation due to the absence of the necessary input parameters. In Antarctica the albedo of snow can reach 100%, so that nearly all incoming radiation is reflected back in the visible and UV range. This extremely high reflectance changes the spatial distribution of spectral radiance significantly. We found for example that the zenith radiance in Antarctica near the horizon can be up 16 times higher than at the zenith in the red part of the spectrum.

For the measurement of the spectral radiance traditional techniques and instruments are too slow to capture the rapid changes mainly caused by varying cloudiness. A newly developed advanced multidirectional spectroradiometer (AMUDIS) is capable of measuring spectral radiance from the UV to NIR with more than 100 directions within seconds. The presentation will demonstrate metrological, meteorological, medical and biological challenges and how to overcome these. Since turning of the input optics would change its sensitivity new methods for the calibration and characterization of instrument AMUDIS have been developed and tested.

References

EEAP. 2019. Environmental Effects and Interactions of Stratospheric Ozone Depletion, UV Radiation, and Climate Change. 2018 Assessment Report. Nairobi: Environmental Effects Assessment Panel, United Nations Environment Programme (UNEP) 390 pp. https://ozone.unep.org/science/assessment/eeap

Seckmeyer G., Lagos Rivas L., Gaetani C., Heinzel J.W., Schrempf M.: (2018) Biologische und medizinische Wirkungen solarer Strahlung (Biological and medical effects of solar radiation), in Promet, Heft 100, Strahlungsbilanzen, chapter 13, Deutscher Wetterdienst (DWD), 2018

Seckmeyer G., Bais A., Bernhard G., Blumthaler M., Lantz K., McKenzie R.L., Kiedron P., Drüke S., Riechelmann S. (2010): Instruments to measure solar ultraviolet radiation, part 4: Array Spectroradiometers, 43 pages, WMO-GAW report 191, TD 5038

Tobar Foster M., Luiz Weide E., Niedzwiedz A., Duffert J., Seckmeyer G.: Characterization of the Angular Response of a Multi-Directional Spectroradiometer for measuring spectral Radiance, EPJ Techniques and Instrumentation, https://doi.org/10.1140/epjti/s40485-021-00069-4, 28 July, 2021

Niedzwiedz A., Duffert J., Tobar M., Quadflieg E., Seckmeyer G.: Laboratory calibration for multidirectional spectroradiometers, Measurement Science and Technology, https://doi.org/10.1088/1361-6501/abeb93, March, 2021

How to cite: Seckmeyer, G., Wiegand, H., Ruttanawongchai, S., Kaur, K., and Atsegha, B.: Measuring the sky spectral radiance within seconds , EMS Annual Meeting 2025, Ljubljana, Slovenia, 7–12 Sep 2025, EMS2025-253, https://doi.org/10.5194/ems2025-253, 2025.

The incoming surface solar radiation is an essential climate variable as defined by GCOS. Long term monitoring of this part of the earth’s energy budget is required to gain insights on the state and variability of the climate system.

The EUMETSAT Satellite Application Facility on Climate Monitoring (CM SAF) generates and distributes high quality long-term climate data records (CDR) of energy and water cycle parameters, which are freely available.

The CM SAF CLARA and SARAH data records will be extended and updated in their next releases. Especially the latter will become a quasi-global data record in its upcoming edition - SARAH-4. Five geostationary orbits will be processed, and the consideration of snow on the ground will be further improved. Furthermore, the usage of daily varying aerosol information is explored for SARAH-4. Finally, the successor of the METEOSAT SEVIRI instrument, FCI, is already in orbit and will be used for a consistent near-realtime data processing.

The demonstrational CM SAF HANNA data set will be introduced. HANNA stands for “High resolution EuropeAN Surface Solar RadiationN dAta record” and is the first CM SAF data set using the SEVIRI HRV channel. The data set has been generated for a two-year test period (2019/2020) and contains the global radiation in 1 km spatial and 15 min temporal resolution for Europe.      

The presentation will give an overview of the status quo of CM SAF’s surface solar radiation data records and will give insights into the latest developments. Intermediate results of the SARAH-4 data records under development will be shown. The demonstrational HANNA data set will be introduced incl. the results of some validation activities. 

How to cite: Pfeifroth, U., Eller, J., Kremmling, B., Sharma, V., Tetzlaff, A., and Trentmann, J.: Satellite-based surface solar radiation data records from the CM SAF – present and future, EMS Annual Meeting 2025, Ljubljana, Slovenia, 7–12 Sep 2025, EMS2025-73, https://doi.org/10.5194/ems2025-73, 2025.

The Earth’s radiation balance fundamentally determines the climatic conditions on our planet. While the radiation balance at the Top-of-Atmosphere (TOA) determines the overall heat uptake in the climate system, the radiation balance at the surface governs the thermal changes in our environments, and defines the energy that drives the evaporative flux and with it the global water cycle.

The present study investigates the representation of the global mean radiation balance components in 10 atmospheric reanalyses, and  compares their magnitudes with independent reference estimates as well as the ones simulated by the latest generation of climate models from the 6^th phase of the coupled model intercomparison project (CMIP6).

Despite the assimilation of comprehensive observational data in reanalyses, we find that the spread amongst the magnitudes of their radiation balance components generally remains substantial, up to more than 20 Wm^-2 in some quantities, and their consistency is typically not higher than amongst the much less observationally constrained CMIP6 models. A comparison of reanalysis runs in full assimilation mode with corresponding runs constrained only by sea surface temperatures reveals marginal differences in their global mean radiation balance components. This indicates that discrepancies in the global radiation balance components caused by the different model formulations amongst the reanalyses are hardly alleviated by the imposed observational constraints from the assimilation process. Similar to many climate models, reanalyses overestimate the global mean surface downward shortwave radiation and underestimate the surface downward longwave radiation by 3 - 7 Wm^-2. While reanalyses are of tremendous value as references for many atmospheric parameters, they may not yet be suited to serve as references for the magnitudes of the global mean radiation balance components.

Parts of the results of this study have been published in Wild, M. and Bosilovich, M., 2024: The Global Energy Balance as Represented in Atmospheric Reanalyses, Surveys in Geophysics, 45, 1799–1825. https://doi.org/10.1007/s10712-024-09861-9.

How to cite: Wild, M.: The representation of the Earth radiation budget in reanalyses, EMS Annual Meeting 2025, Ljubljana, Slovenia, 7–12 Sep 2025, EMS2025-83, https://doi.org/10.5194/ems2025-83, 2025.

A new quality-checked and homogenised dataset of total cloud cover (TCC) series over Italy for the period 1951–2018 is presented and the variability and trends of the obtained regional series are discussed (https://doi.org/10.1016/j.atmosres.2023.106625). The diurnal cycle highlights the important role of convection induced by solar radiation that, as expected, is more relevant at middle and high altitudes and in summer. In parallel, the annual cycle shows a strong minimum in July and a maximum in winter for southern Italy, while it shows a more complex behaviour with strong differences between low and high altitudes in northern Italy. Moreover, the seasonal and annual TCC series are characterised by a significant negative trend over the whole period considered, mainly due to the period 1951–1990. Although small differences can be observed between northern and southern Italy, the two regions show a coherent behaviour both for the long-term trends and for the decadal time-scale variability, suggesting that the causes of variability and trends of the Italian TCC records are more related to large-scale factors rather than to local scale changes. Indeed, the comparison with sea level pressure and 500-hPa geopotential height data highlights that large-scale atmospheric circulation explains a relevant fraction of the signal of the Italian TCC records. In particular, they show an opposite behaviour highlighting the same rate of decrease/increase especially during the 1970s and 1980s, where the most significant decrease/increase in TCC/SLP and 500-hPa geopotential height is concentrated. Moreover, TCC seems more linked to SLP during winter, spring and autumn while TCC seems more linked to 500-hPa geopotential height during summer, therefore, more linked to higher temperatures. Finally, the new TCC dataset shows that the long-term evolution of sunshine duration (https://doi.org/10.1002/2014JD022560) and surface solar radiation (https://doi.org/10.5194/acp-16-11145-2016) in Italy is only partially influenced by changes in TCC: if TCC would not have been changed over the investigated period, probably the rather weak dimming, due to the increase in the aerosol concentrations before about 1980 (https://doi.org/10.1016/j.atmosenv.2019.116861) would have been stronger, whereas the following rather strong brightening would have been weaker determining a more similar strength of the changes in the dimming and the brightening periods.

How to cite: Manara, V., Brunetti, M., Wild, M., and Maugeri, M.: Total cloud cover over Italy (1951-2018): variability and trends, EMS Annual Meeting 2025, Ljubljana, Slovenia, 7–12 Sep 2025, EMS2025-180, https://doi.org/10.5194/ems2025-180, 2025.

Solar surface Radiation and Temperature Trends:

• Between 2001 and 2020, we explored the hypothesis that the measured increase in solar surface radiation might explain the observed temperature rise at 2 meters above ground in De Bilt.
• To investigate this, we combined solar surface radiation and temperature data from the Royal Netherlands Meteorological Institute (KNMI) with satellite measurements of radiation and cloud cover at the top of the atmosphere from the CERES satellite.
• By analyzing the energy and radiation balance of the atmosphere and considering partial balances at both the surface and the top of the atmosphere, we established connections between the components.
• The study solved for surface temperature, solar radiation reflection fraction, and solar radiation absorption fraction using balance equations.
• Energy balance calibration involved:
• Adjusting the temperature difference between the surface and the 2-meter height temperature to match observed temperature differences.
• Tuning the balance-calculated ratio of total forcing differences to temperature differences (ΔΣFi/ΔT) per season to align with the derivative of the Stefan-Boltzmann radiation law (R^2: 0.9992).
• Interestingly, we found that the atmosphere’s near surface emissivity could be well approximated by a power function of season dependent cloud cover.
• Additionally, the reflection and absorption fractions of solar radiation strongly correlated with cloud cover (R^2 > 0.90).

Key findings and best estimates related to solar surface radiation and its impact on temperature trends in De Bilt, Netherlands, over the period from 2001 to 2020 at a 95% confidence interval:

Surface Warming Contributions:

• Approximately 74% [43-100] of the surface warming is attributed to an increase in solar surface radiation.
• The remaining 26% [0-56] results from an increase in downward thermal radiation  from the atmosphere near the surface.
• No contribution from downward thermal radiation cannot be ruled out.

Atmospheric Warming at 2 Meters Height:

• The warming of the atmosphere at 2 meters height is influenced by several factors:
• Reduced reflection at the top of the atmosphere, contribution 39% [-2-80].
• Increased upward thermal radiation, contribution 29% [6-52].
• Enhanced latent heat and convection, contribution 28% [-6-63].
• Notably, the strong correlation between reflection fraction and cloud cover suggests that the surface-level atmospheric warming is also influenced by decreasing cloud cover.

Discussion about the Energy and Radiation Balance Analysis:

• Unmeasured variables can be inferred from balance equations.
• Observed warming can be explained by changes in energy and radiation components.
• Due to the high variability of the yearly data, the propagation of errors leads to high confidence intervals indicating that the true contribution could plausibly range anywhere from small negative to nearly the complete warming considered.

In summary, Energy and Radiation Balance Analysis indicates that the solar surface radiation  significantly impacts (> 43%) recent warming trends in De Bilt.

How to cite: Overmars, B.: Solar surface radiation and its impact on measured recent temperature increase in De Bilt, Netherlands, EMS Annual Meeting 2025, Ljubljana, Slovenia, 7–12 Sep 2025, EMS2025-657, https://doi.org/10.5194/ems2025-657, 2025.

Wildfires and open biomass burning emit climate-warming gases and particles into the atmosphere (IPCC, 2021).     Light absorbing carbonaceous aerosols (LACs) emitted by such biomass burning events are a mixture of black carbon (BC) particles and other absorbing species, such as soluble light-absorbing organic molecules and tarballs (Corbin et al., 2019). In addition to the relative concentration of each particle type, the role of the mixing-state of these species among themselves and with non-absorbing species is also a crucial factor driving the particles light absorption (Cappa et al., 2019).

To constrain the role of aerosol particles released into the atmosphere by biomass burning, a laboratory experiment was carried out during summer 2024 at the Northern Forestry Center in Edmonton, Canada. Fuel types characteristic of Canadian wildfires and domestic heating were burned, including, grass, ponderosa pine, peat, mulch and mixtures mulch with

To be able to provide an accurate description of the mixing-state of the particles and its role on the absorption properties, highly-detailed measurements are essential. We have chosen mass-resolved measurements as they are related to the absorption through the mass absorption cross-section, a less complicated paradigm than using size and morphology. To this end, we have followed the method described by Naseri et al. (2024) where a centrifugal particle mass analyzer (CPMA, Cambustion Ltd.; Olfert and Collings, 2005) is used in tandem with a single-soot photometer (SP2-XR, Droplet Inc.). The aerosol light absorption is measured with a traceably calibrated dual-wavelength photo-thermal interferometer (PTAAM-2λ, Haze Instruments d.o.o.; Drinovec et al., 2022). To detect the relevance of tarballs, sampling on Transmission Electron Microscopy (TEM) grids was performed for every fuel 

We measured over 40 samples, of which we were able to perform 18 mass-segregated absorption measurements. We found a large variation of the coating in fresh smoke from different fuel types, with some samples, such as grass, containing highly coated particles. Figure 1 shows that for grass samples, there was a high level of coating, with a group of particles with BC mass m_rBC of around 10^-1 fg and particle mass m_p of around 4 fg, and another one with m_rBCof 2 fg and m_p of 7 fg. The coating of the BC particles with these aerosols can result in an enhancement of the absorption by a factor of 3 at the UV and a factor of 2 at the infrared, with an increasing enhancement as the fraction of coating vs BC increases (Zhang et al., 2018).

Figure 1. Particles counts of refractory BC mass (m_rBC) in fg measured by the SP2-XR vs the mass selected (m_p) by the CPMA for a grass-burning sample.

How to cite: Yus-Díez, J., Drinovec, L., Corbin, J. C., Olfert, J. S., Sipkens, T. A., Moallemi, A., Marshall, G. A., Zhao, R., Abbatt, J., and Močnik, G.: Laboratory transformations of black carbon from fresh biomass burning: changes in coating and mass absorption efficiency , EMS Annual Meeting 2025, Ljubljana, Slovenia, 7–12 Sep 2025, EMS2025-192, https://doi.org/10.5194/ems2025-192, 2025.

Mineral dust significantly impacts the Earth's climate, representing 75% of global aerosol mass and 25% of aerosol optical depth (Kinne et al., 2006). Black Carbon (BC) is the most influential short-lived climate-warming forcer, while Mineral Dust (MD) contributes to atmospheric heating and cooling through absorption and scattering (IPCC, 2021). The effects of BC and MD on atmospheric heating depend, among other factors, on their mixing state, which is not well-known presently.

             We present in situ surface measurements of dust and BC during dusty and non-dusty days. Measurements were conducted between February 12 to September 20, 2019, at three measuring stations, part of the EGAR monitoring and ACTRIS networks: Barcelona (BCN), Montseny (MSY), and Montsec (MSA), and from May 27 to August 27 at the MSA site. We will compare fine and coarse particles (BC and MD) at the three stations to understand the background environment and how dust particles affect aerosol light absorption in urban, remote, and continental sites.

             We used a pair of Aethalometers AE33 (Drinovec et al., 2015) with PM1 and a virtual impactor (VI) inlets to determine the absorption coefficient for fine (PM1) and coarse fractions (Drinovec et al., 2020). We have quantified the absorption of dust and BC at different wavelengths using AAE values of 1.1 for BC and 2.88 for MD for the multi-wavelength apportionment model  (Massabo et al., 2015), and calculated the Heating Rate(HR) for MD and BC (Ferrero et al., 2021). Similarly, the Mass Absorption Cross-section (MAC) of MD was calculated using the method proposed by Drinovec et al.(2020), which assumes calcium constitutes about 12% of the total mineral dust mass.

           Our results show that during dusty days in summer, dust absorption is higher in the MSA site at 370 nm (2.29 ± 2.85 Mm^-1), with increases of 1.7 and 6 times compared to MSY (1.28 ± 1.22 Mm^-1) and BCN (0.33 ± 0.48 Mm^-1), respectively. The MAC values progressively increase from lower to higher altitudes, with values of MAC during dusty days in summer: BCN (77 m a.s.l) 0.11 ± 0.19 m²g^-1, to MSY (720 m a.s.l) 0.39 ± 0.82 m²g^-1, and at MSA (1600 m a.s.l) 1.05 ± 1.9 m²g^-1. These results show an increasing trend in dust MAC with altitude within our study area, where anthropogenic influence decreases at higher elevations. Finally, we will also present our results for the HR during dusty events, which show mean values of 0.13 ± 0.27 K day⁻¹ in the MSA and 0.066 ± 0.052 K day⁻¹ in the MSY for MD, and 0.29 ± 0.31 K day⁻¹ in the MSA and 0.53 ± 0.39 K day⁻¹ in the MSY for BC.

How to cite: Gautam, S., Pandolfi, M., Perez, N., Alastuey, A., Ivančič, M., Gregorič, A., Ježek, I., Rigler, M., Drinovec, L., Yus, J., and Mocnik, G.: Species-Separated Absorption Coefficient and Atmospheric Heating Rate for Black Carbon and Mineral Dust in the Western Mediterranean, EMS Annual Meeting 2025, Ljubljana, Slovenia, 7–12 Sep 2025, EMS2025-487, https://doi.org/10.5194/ems2025-487, 2025.

The cloud cover is a very important factor that influences many atmospheric processes and the Earth’s systems. The Antarctic Peninsula is located in the circumpolar low-pressure trough which results in high cyclonic activity and variable cloud cover. Despite its importance in planetary systems, the lack of cloud cover observations and instrumentations in Antarctica does not allow for detailed analysis of cloud radiative feedback. The gap in our knowledge is often filled by radiative transfer modelling, although its reliability needs to be verified as these models are usually calibrated outside of Antarctica. To study the influence of cloud cover and cloud types on the shortwave radiation (SR) flux, a summer experiment was conducted in the northeastern part of the Antarctic Peninsula. Ground-based observations were carried out at the J.G. Mendel station in the period from 26 January to 7 March 2025. The station is located in a coastal ice-free area with local albedo ranging between 0.2 (bare ground) and 0.9 (continuous snow cover). The SR intensity was measured using Kipp‌&Zonen CMP-11 pyranometer at 10-min interval and was used for estimation of the highest radiative flux and daily means. Sky camera was used for estimation of the cloud cover and cloud types using multicriterial analysis and processing of hemispherical images at 10-min interval. The total cloud cover and layer cloud amount were also observed manually. Furthermore, clear-sky SR flux was estimated using Bird and Hulstrom radiative transfer model. To further analyse the cloud radiative effect, we calculated a cloud modification factor. The model results were compared with manual cloud cover observations, sky camera imagery and ERA5 reanalysis data. SR flux for different cloud layers and cloud genera was examined for the most typical clouds, such as cirrus, cirrostratus, altostratus and altocumulus. Special attention was paid to the highest SR fluxes that occurred during clear-sky conditions, high-reflectance cloud layer or days with extreme radiative flux caused by multiple reflection between cloud cover and snow surface.

How to cite: Szymszová, S., Láska, K., Lupi, A., Frangipani, C., and Matějka, M.: Influence of cloud cover and cloud types on shortwave radiation flux at Mendel station, northern Antarctic Peninsula, EMS Annual Meeting 2025, Ljubljana, Slovenia, 7–12 Sep 2025, EMS2025-590, https://doi.org/10.5194/ems2025-590, 2025.

The cooperative German research unit C3SAR, started in summer 2024, aims at a unique and comprehensive combination of 3D-modelling and observation of clouds and their radiative effects that accounts for the 3D nature of cloud structure The initiative is working towards a physically-based correction of biases in climate modelling and cloud remote sensing, that have been a result from oversimplifications of the complex geometrical and microphysical nature of clouds in previous work.  Along this goal, characteristic 3D cloud structures for relevant cloud regimes from cloud resolving modelling and from synergistic satellite observations will serve as input to radiative transfer modelling of different complexity to quantify the consequences for cloud structure simplifications and to establish physically based cloud-radiation correlations. Long-term high-quality ground-based cloud and radiation observations over Germany provide the validation of these relations by means of radiative closure studies. Current and new generations of satellite sensors such as EarthCARE and Meteosat Third Generation will provide the corresponding closure at the top of the atmosphere. A large field campaign in summer 2026 in Lindenberg, Germany (C3SAR-X), will bring modelling, ground-based and satellite-based remote sensing and in-situ radiation measurements together in a synergetic closure study in order to validate our ability to observe, understand and model the cloud radiative effects and thus to reduce a major source of uncertainty in predicting the future climate. For the second phase of the research unit, it is planned to extend this approach to more globally distributed test-beds in the framework of large international observational networks, to improve the regime-based cloud-radiation relations and apply those to climate modelling and the new generations of satellite sensors. 

We will present methods and concepts of this research unit as well as first results from the initial phase including test case studies and first radiation closure experiments.

How to cite: Macke, A., Deneke, H., Hünerbein, A., Knist, C., Mayer, B., Schemann, V., Seckmeyer, G., Senf, F., Stengel, M., and Wacker, S. and the C3SAR research unit: Cloud 3D Structure And Radiation (C3SAR) - A joint initiative to account for 3d effects in climate modelling and remote sensing , EMS Annual Meeting 2025, Ljubljana, Slovenia, 7–12 Sep 2025, EMS2025-517, https://doi.org/10.5194/ems2025-517, 2025.

The current generation of geostationary satellites enables the retrieval of global horizontal irradiance (GHI) down to scales of 500 m.  GHI nowcasting products could benefit from this increase in spatial resolution. However, it also provides challenges. Satellite retrievals are almost exclusively based on one-dimensional (1D) radiative transfer where pixels are assumed to be plane parallel and independent from each other. Towards smaller spatial scales, the validity of the plane parallel assumption is expected to increase whereas the independence of pixels is less guaranteed.  This study quantifies the validity of these assumptions in synthetic satellite retrievals.  We use the newly developed Monte Carlo KNMI (MONKI) three-dimensional (3D) radiative transfer code. With MONKI, we simulate 3D as well as 1D top-of-atmosphere reflectances based on cloud fields modelled with the Large Eddy Simulation (LES) code MicroHH. These top-of-atmosphere reflectances are used to retrieve cloud properties and GHI at spatial resolutions ranging from 0.05 to 6.4 km.  Comparing retrieval results for these resolutions gives an indication of the plane parallel bias, while the validity of the independent pixel approximation is quantified by comparing the 1D and 3D based retrievals. For all retrievals, GHI calculated directly from the LES output with 3D radiative transfer serves as a reference. Preliminary results for a shallow cumulus case show that for spatial resolutions below 400 m, the probability density function of the 3D minus 1D reflectances has a clear bimodal distribution.  The two peaks correspond to the illuminated side of the clouds and the cloud-shaded areas.  At coarser resolutions, the bimodal distribution disappears.  

How to cite: Wiltink, J. I., Trees, V. J. H., Wang, P., van Heerwaarden, C. C., and Meirink, J. F.: The influence of spatial resolution and three-dimensional radiative effects on the accuracy of global horizontal irradiance retrievals, EMS Annual Meeting 2025, Ljubljana, Slovenia, 7–12 Sep 2025, EMS2025-518, https://doi.org/10.5194/ems2025-518, 2025.