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The present work proposes a new model based on a convolutional neural network (CNN) to retrieve solar shortwave (SW) irradiance via the estimation of the cloud modification factor (CMF) from daytime sky images captured by all-sky cameras; this model is named CNN-CMF. To this end, a total of 237,669 sky images paired with SW irradiance measurements obtained by using pyranometers were selected at the following three sites: Valladolid and Izaña, Spain, and Lindenberg, Germany. This dataset was randomly split into training and testing sets, with the latter excluded from the training model in order to validate it using the same locations. Subsequently, the test dataset was compared with the corresponding SW irradiance measurements obtained by the pyranometers in scatter density plots. The linear fit shows a high determination coefficient ( R 2 ) of 0.99 . Statistical analyses based on the mean bias error (MBE) values and the standard deviation (SD) of the SW irradiance differences yield results close to − 2 % and 9 % , respectively. The MBE indicates a slight underestimation of the CNN-CMF model compared to the measurement values. After its validation, model performance was evaluated at the Antarctic station of Marambio (Argentina), a location not used in the training process. A similar comparison between the model-predicted SW irradiance and pyranometer measurements yielded R 2 = 0.95 , with an MBE of around 2 % and an SD of approximately 26 % . Although the precision provided by the SD at the Marambio station is lower, the MBE shows that the model's accuracy is similar to previous results but with a slight overestimation of the SW irradiance. Finally, the determination coefficient improved to 0.99 , and the MBE and SD are about 3 % and 11 % , respectively, when the CNN-CMF model is used to estimate daily SW irradiation values. [ABSTRACT FROM AUTHOR]

During the months of February–March (FM) of the 2020–2022 period, several intense dust intrusions from northern Africa affected Europe. The frequency of dust events was exceptional, considering that wintertime is the season with minimum dust activity in the Mediterranean, and some episodes displayed a duration and/or intensity never recorded before, affecting large areas of the western Euro-Mediterranean (WEM) region. The main objective of this work is to construct a catalogue of FM dust events over the WEM for the 2003–2022 period based on satellite aerosol retrievals and to analyse their atmospheric drivers at the synoptic and large scales, paying special attention to the recent 2020–2022 period of high dust activity. Overall, our results indicate large intraseasonal and interannual variability in the occurrence of wintertime dust events over the WEM. Dust events of FM 2020–2022 were characterized by enhanced dust concentration and high maximum altitudes in comparison with those of previous years (2003–2019). WEM dust events are associated with enhanced activity of high-pressure systems over the Euro-Atlantic sector, which favour the obstruction of the westerlies and the occurrence of cut-off lows at subtropical latitudes. However, these high-pressure systems can exhibit a large variety of configurations, including meridional dipole blocking patterns with poleward shifted jets or Mediterranean subtropical ridges with an intensified mid-latitude jet. The former is the dominant favourable pattern for WEM dust occurrence, but the latter was relatively common during the 2020–2022 period. [ABSTRACT FROM AUTHOR]

During the winters of the 2020–2022 period, several intense North African dust intrusions affected Europe. Some of them displayed a duration never recorded before. They were referred to as exceptional by several international operational and research institutions considering that wintertime is the season with minimum dust activity in the Mediterranean and Europe. These anomalous winter events with origin in North Africa largely affected western Mediterranean. The main objective of the present work is to analyse the atmospheric drivers (synoptic and large-scale environments) of wintertime (from January to March) dust events over the region covering North Africa, the Western Mediterranean and the Euro-Atlantic during the period 2003–2022. Overall, our results indicate large interannual variability over the study period. A dust catalogue of dust events identified by aerosols retrievals from satellite and aerosol reanalysis products shows a very irregular record and large differences between winter months. The analyses demonstrate a positive anomaly in dust concentration and maximum altitude during the dust events of 2020–2022 in comparison with those of previous years (2003–2019). Winter dust events over western Mediterranean are associated with enhanced blocking activity over the Euro-Atlantic sector, which favours the obstruction of the westerlies and the occurrence of cut-off lows at subtropical latitudes. However, these high-pressure systems can exhibit a large variety of configurations, including meridional dipole blocking patterns with poleward shifted jets or Mediterranean subtropical ridges with an intensified mid-latitude jet. The former was more frequent during the reference 2003–2019 period, whereas the latter was relatively common during the anomalous 2020–2022 period. [ABSTRACT FROM AUTHOR]

On 19 September 2021, a volcanic eruption began on the island of La Palma (Canary Islands, Spain). The eruption has allowed the assessment of an unprecedented multidisciplinary study on the effects of the volcanic plume. This work presents the estimation of the spectral direct radiative forcing (Δ F) and efficiency (Δ F E f f ) from solar radiation measurements at the Izaña Observatory (IZO) located on the island of Tenerife (∼140 km from the volcano). During the eruption, the IZO was affected by different types of aerosols: volcanic, Saharan mineral dust, and a mixture of volcanic and dust aerosols. Three case studies were identified using ground-based (lidar) data, satellite-based (Sentinel-5P Tropospheric Monitoring Instrument, TROPOMI) data, reanalysis data (Modern-Era Retrospective Analysis for Research and Applications, version 2, MERRA-2), and backward trajectories (Flexible Trajectories, FLEXTRA), and subsequently characterised in terms of optical and micro-physical properties using ground-based sun-photometry measurements. Despite the Δ F of the volcanic aerosols being greater than that of the dust events (associated with the larger aerosol load present), the Δ F E f f was found to be lower. The spectral Δ F E f f values at 440 nm ranged between −1.9 and −2.6 Wm − 2 nm − 1 AOD − 1 for the mineral dust and mixed volcanic and dust particles, and between −1.6 and −3.3 Wm − 2 nm − 1 AOD − 1 for the volcanic aerosols, considering solar zenith angles between 30 ∘ and 70 ∘ , respectively. [ABSTRACT FROM AUTHOR]

A comprehensive comparison of more than 70000 synchronous 1-minute aerosol optical depth (AOD) data from three Global Atmosphere Watch-Precision Filter Radiometer (GAW-PFR) and 15 Aerosol Robotic Network-Cimel (AERONET-Cimel) radiometers was performed for the four nearby wavelengths (380, 440, 500 and 870nm) in the period 2005-2015. The goal of this study is to assess whether, despite the marked differences between both networks and the number of instruments used, their long term AOD data are comparable and consistent. AOD traceability established by the World Meteorological Organization (WMO) consists in determining the percentage of synchronous data within specific limits. If, at least, 95% of the AOD differences of an instrument compared to the WMO standards lie within these limits, both data populations are considered equivalent. The percentage of traceable data is 92.7% (380nm), 95.7% (440nm), 95.8% (500nm) and 98.0% (870nm). When small misalignments in GAW-PFR sun-pointing were fixed (period 2010-2015), the percentage of traceable data increased. The contribution of calibration related aspects to comparison outside the 95% traceability limits is insignificant in all channels, except in 380nm. The simultaneous failure of both cloud screening algorithms might occur only under the presence of cirrus, or altostratus clouds on the top of a dust-laden Saharan air layer. Differences in the calculation of the optical depth contribution due to Rayleigh scattering, and O3 and NO2 absorption have a negligible impact. For AOD >0.1, a non-negligible percentage (≈1.9%) of the AOD data outside the 95% traceability limits at 380nm can be partly assigned to the different field of view of the instruments. The comparison of the Angström exponent (AE) shows that under non-pristine conditions (AOD >0.03 and AE <1) the AE differences remain <0.1. The excellent traceability in this study has been obtained using well calibrated Master instruments. [ABSTRACT FROM AUTHOR]

The Baseline Surface Radiation Network (BSRN) was implemented by the World Climate Research Programme (WRCP) starting observations with 9 stations in 1992, under the auspices of the World Meteorological Organization (WMO). Currently, 59 BSRN stations submit their data to the WRCP. One of these stations is the Izaña station (Station: IZA, #61) that enrolled in this network in 2009. This is a high-mountain station located in Tenerife (Canary Islands, Spain; at 28.3° N, 16.5° W, 2373 m a.s.l.) and is a representative site of the subtropical North Atlantic free troposphere. It contributes with basic-BSRN radiation measurements, such as, global shortwave radiation (SWD), direct radiation (DIR), diffuse radiation (DIF) and longwave downward radiation (LWD) and extended-BSRN measurements, including ultraviolet ranges (UV-A and UV-B), shortwave upward radiation (SWU) and longwave upward radiation (LWU) and other ancillary measurements, such as vertical profiles of temperature, humidity and wind obtained from radiosonde (WMO, station #60018) and total column ozone from Brewer spectrophotometer. The IZA measurements present high quality standards since more than 98 % of the data are within the limits recommended by the BSRN. There is an excellent agreement in the comparison between SWD, DIR and DIF (instantaneous and daily) measurements with simulations obtained with the LibRadtran radiative transfer model. The root mean square error (RMSE) for SWD is 2.28 % for instantaneous values and 1.58 % for daily values, while the RMSE for DIR is 2.00 % for instantaneous values and 2.07 % for daily values. IZA is a unique station that provides very accurate solar radiation data in very contrasting scenarios: most of the time under pristine sky conditions, and periodically under the effects of the Saharan Air Layer characterized by a high content of mineral dust. A detailed description of the BSRN program at IZA, including quality control and quality assurance activities, is given in this work. [ABSTRACT FROM AUTHOR]

A 7-year (2010-2016) comparison study between measured and simulated longwave downward radiation (LDR) under cloud-free conditions has been performed at the Izaña Atmospheric Observatory (IZO, Spain). This analysis encompasses a total of 2062 cases distributed almost 50% between day and night. Results show an excellent agreement between Baseline Surface Radiation Network (BSRN) measurements and simulations with LibRadtran V2.0.1 and MODTRAN V6 radiative transfer models (RTM), similar for both models. Mean bias (simulated-measured) <1.1%, and root mean square error (RMSE) <1%, are within the instrumental error (2%). These results highlight the good agreement between the two RTMs, demonstrating to be useful tools for LDR measurement quality control and for detecting temporal drifts in field instruments. The standard deviations of the residuals, associated to the RTM input parameters uncertainties are rather small, 0.47% and 0.49% for LibRadtran and MODTRAN, respectively, at day-time, and 0.49% to 0.51% at night-time. The observed night-time difference between models and measurements is +5Wm-2, for precipitable water vapor (PWV)>10mm, indicating a scale change of the World infrared standard group of Pyrgeometers (WISG), which serves as reference for atmospheric longwave radiation measurements. [ABSTRACT FROM AUTHOR]

A 1-year intercomparison of classical and modern radiation and sunshine duration instruments has been performed at Izaña Atmospheric Observatory (IZO) located in Tenerife (Canary Islands, Spain) starting on July 17, 2014. We compare global solar radiation (GSR) records measured with a CM-21 pyranometer Kipp & Zonen, taken in the framework of the Baseline Surface Radiation Network, with those measured with a Multifilter Rotating Shadowband Radiometer (MFRSR), and a bimetallic pyranometer (PYR), and GSR estimated from sunshine duration performed by a Campbell-Stokes sunshine recorder (CS) and a Kipp & Zonen sunshine duration sensor (CSD). Given the GSR BSRN records are subject of strict quality controls (based on principles of physical limits and comparison with the LibRadtran model), they have been used as reference in the intercomparison study. We obtain an overall root mean square error (RMSE) of ~0.9 MJm2 (4%) for GSR PYR and GSR MFRSR, 1.9 MJm2 (7%) and 1.2 MJm2 (5%) for GSR CS and GSR CSD, respectively. Factors such as temperature, fraction of the clear sky, relative humidity and the solar zenith angle have shown to moderately affect the GSR observations. As application of the methodology developed in this work, we have re-evaluated the GSR time series between 1977 and 1991 obtained with two PYRs at IZO. By comparing with coincident GSR estimates from SD observations, we probe the high consistency of those measurements and their temporal stability. These results demonstrate that 1) the continuous-basis intercomparison of different GSR techniques offers important diagnostics for identifying inconsistencies between GSR data records, and 2) the GSR measurements performed with classical and more simple instruments are consistent with more modern techniques and, thus, valid to recover GSR time series and complete worldwide distributed GSR data. The intercomparison and quality assessment of these different techniques have allowed to obtain a complete and consistent long-term global solar radiation series (1977-2015) at Izaña. [ABSTRACT FROM AUTHOR]