Record high solar irradiance in Western Europe during first COVID-19 lockdown largely due to unusual weather

Spring 2020 broke sunshine duration records across western Europe. The Netherlands recorded the highest surface irradiance since 1928, exceeding the previous extreme of 2011 by 13 %, and the diffuse fraction of the irradiance measured a record low percentage (38 %). The coinciding irradiance extreme and a reduction in anthropogenic pollution due to COVID-19 measures triggered the hypothesis that cleaner-than-usual air contributed to the record. Based on analyses of ground-based and satellite observations and experiments with a radiative transfer model, we estimate a 1.3 % (2.3 W m$^{-2}$) increase in surface irradiance with respect to the 2010-2019 mean due to a low median aerosol optical depth, and a 17.6 % (30.7 W m$^{-2}$) increase due to several exceptionally dry days and a very low cloud fraction overall. Our analyses show that the reduced aerosols and contrails due to the COVID-19 measures are far less important in the irradiance record than the dry and particularly cloud-free weather.Comment: 21 pages, 12 figures, submitted to Communications Earth and Environmen

Análisis de la trazabilidad en los valores del AOD obtenidos a partir de las medidas de las redes AERONET-CIMEL y GAW-PFR durante el período 2005-2015 en el Observatorio Atmosférico de Izaña

Las dos grandes redes mundiales de fotómetros terrestres para la medida de las propiedades ópticas del aerosol en la columna atmosférica con las AERONET-CIMEL y GAW-PFR. Dado que ambas son diferentes en cuanto a tipos, características, número y localización de fotómetros utilizados, así como a metodologías, procedimientos de calibración y algoritmos de cálculo empleados en la evaluación de datos, resulta conveniente comparar los productos similares suministrados por las dos redes y así determinar en qué medida son homogéneos o equivalentes. El objetivo de este trabajo es analizar las diferencias que existen en una propiedad óptica, fundamental para conocer y caracterizar el contenido en columna de los aerosoles atmosféricos, que es el espesor óptico de aerosoles (AOD) obtenido para diferentes longitudes de onda por cada una de las dos redes. El análisis se estructura en tres capítulos. En el capítulo 1, se expone el concepto de trazabilidad y se explica en qué se basa la definición y cuáles son sus implicaciones. Posteriormente, se aplica a las series de AOD y se muestran los resultados. En el capítulo 2, se analizan las principales causas que pueden dar lugar a diferencias no trazables de AOD para cada una de las parejas de series comparadas en cada longitud de onda. Finalmente, el capítulo 3, recoge las conclusiones y recomendaciones para mejorar, en la medida de lo posible, la trazabilidad y la homogeneidad de estos productos.Los autores agradecen a PMOD/WRC y AERONET los datos proporcionados y utilizados en este trabajo así como las calibraciones de los fotómetros Cimel por parte de AERONET-Europe TNA en el marco del proyecto europeo FP7 ACTRIS nº262254. Este trabajo forma parte de las actividades del “WMO-CIMO Testbed for Aerosols and Water Vapor Remote Sensing Instruments (Izana, Spain)”

Spectral aerosol optical depth from SI-traceable spectral solar irradiance measurements

Spectroradiometric measurements of direct solar irradiance traceable to the SI were performed by three spectroradiometer systems during a 3-week campaign in September 2022 at the Izaña Atmospheric Observatory (IZO) located on the island of Tenerife, Canary Islands, Spain. The spectroradiometers provided direct spectral irradiance measurements in the spectral ranges 300 to 550 nm (QASUME), 550 to 1700 nm (QASUME-IR), 300 to 2150 nm (BiTec Sensor, BTS), and 316 to 1030 nm (Precision Solar Spectroradiometer, PSR), with relative standard uncertainties of 0.7 %, 0.9 %, and 1 % for QASUME/QASUME-IR, the PSR, and the BTS respectively. The calibration of QASUME and QASUME-IR was validated prior to this campaign at Physikalisch-Technische Bundesanstalt (PTB) by measuring the spectral irradiance from two spectral irradiance sources, the high-temperature blackbody BB3200pg as a national primary standard and the tuneable laser facility TULIP

Aerosol optical depth comparison between GAW-PFR and AERONET-Cimel radiometers from long-term (2005–2015) 1 min synchronous measurements

A comprehensive comparison of more than 70 000 synchronous 1 min aerosol optical depth (AOD) data from three Global Atmosphere Watch precision-filter radiometers (GAW-PFR), traceable to the World AOD reference, and 15 Aerosol Robotic Network Cimel radiometers (AERONET-Cimel), calibrated individually with the Langley plot technique, was performed for four common or “near” wavelengths, 380, 440, 500 and 870 nm, in the period 2005–2015. The goal of this study is to assess whether, despite the marked technical differences between both networks (AERONET, GAW-PFR) and the number of instruments used, their long-term AOD data are comparable and consistent. The percentage of data meeting the World Meteorological Organization (WMO) traceability requirements (95 % of the AOD differences of an instrument compared to the WMO standards lie within specific limits) is >92 % at 380 nm, >95 % at 440 nm and 500 nm, and 98 % at 870 nm, with the results being quite similar for both AERONET version 2 (V2) and version 3 (V3). For the data outside these limits, the contribution of calibration and differences in the calculation of the optical depth contribution due to Rayleigh scattering and O3 and NO2absorption have a negligible impact. For AOD >0.1, a small but non-negligible percentage (∼1.9 %) of the AOD data outside the WMO limits at 380 nm can be partly assigned to the impact of dust aerosol forward scattering on the AOD calculation due to the different field of view of the instruments. Due to this effect the GAW-PFR provides AOD values, which are ∼3 % lower at 380 nm and ∼2 % lower at 500 nm compared with AERONET-Cimel. The comparison of the Ångström exponent (AE) shows that under non-pristine conditions (AOD >0.03 and AE <1) the AE differences remain <0.1. This long-term comparison shows an excellent traceability of AERONET-Cimel AOD with the World AOD reference at 440, 500 and 870 nm channels and a fairly good agreement at 380 nm, although AOD should be improved in the UV range.The Federal Office of Meteorology and Climatology MeteoSwiss International Affairs Division, Swiss GCOS Office, has funded the project “The Global Atmosphere Watch Precision Filter Radiometer (GAW-PFR) Network for Aerosol Optical Depth long term measurements”, and specifically the GAW-PFR program at the Izaña Observatory. AEMET has funded the AERONET programme at the Izaña Observatory. Some of the AERONET-Cimel radiometers have been calibrated at Izaña Observatory by the AERONET Europe Calibration Service, financed by specific European Community programmes for integrating activities: Research Infrastructure Action under the Seventh Framework Programme (grant no. FP7/2007-2013) and ACTRIS (grant no. 45 262254). This research has received funding from the European Union's Horizon 2020 Research and Innovation Programme (grant no. 654109) (ACTRIS-2). Funding from MINECO (grant no. CTM2015-66742-R) and Junta de Castilla y León (grant no. VA100P17) is also gratefully acknowledged. Much of this study has been performed in the frame of the WMO CIMO Izaña test bed for aerosols and water vapour remote-sensing instruments funded by AEMET

Aerosol Optical Depth comparison between GAW-PFR and AERONET-Cimel radiometers from long term (2005–2015) 1-minute synchronous measurements [Discussion paper]

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.The work was supported by the project “The Global Atmosphere Watch Precision Filter Radiometer (GAW-PFR) Network for Aerosol Optical Depth long term measurements” supported by Bundesamt für Meteorologie und Klimatologie MeteoSchweiz – GCOS Swiss Office. Part of the AERONET-Cimel radiometers have been calibrated at Izaña Observatory by AERONETEUROPE Calibration Service, financed by the European Community specific programs for Integrating Activities: Research Infrastructure Action under the Seventh Framework Programme (FP7/2007-2013), ACTRIS grant agreement No. 262254, and Horizon 2020 Research 25 and Innovation Program, ACTRIS-2 grant agreement No. 654109. This research has received funding from the European Union’s Horizon 2020 Research and Innovation Programme under grant agreement No. 654109 (ACTRIS-2).The funding by MINECO (CTM2015-66742-R) and Junta de Castilla y León (VA100P17) is also gratefully acknowledge

Aerosol optical depth retrieval at the Izaña Atmospheric Observatory from 1941 to 2013 by using artificial neural networks [Póster]

Póster elaborado para el International Symposium CLIMA-ES 2015, Tortosa, Spain, 11-13 March 2015.A 73-year time series of the daily aerosol optical depth (AOD) at 500 nm has been reconstructed from 1941 to 2013 at the subtropical high-mountain Izaña Global Atmospheric Watch (GAW) Observatory (IZO) located in Tenerife Island (The Canary Islands, Spain ; 28º 18’ N, 16º 29’W, 2.367 ma.s.l) For this purpose, we have combined AOD estimates from Artificial Neuronal Networks (ANNs) from 1941 to 2001, and AOD measurements directly performed with Precision Filter Radiometer (PFR) between 2003 and 2013. Theanalysis is limited to cloud-free conditions (Oktas=0) and to the summer season (JAS), where the largest aerosol load is observed at IZO (Saharan mineral dust particles). In order to account for the observed AOD inter-annual/decadal variations, we have done a preliminary study about the relationship between AOD time series and the large-scale climatic indexes, such as the Atlantic Multidecadal Oscillation (AMO), obtaining a significant anti-correlation.This work was developed under the Specific Agreement of Collaboration between the Meteorological State Agency (AEMET)of Spain and the University of Valladolid. Financial supports from the Spanish Ministry of Economy and Competitiveness (MINECO)and from the “Fondo Europeo de Desarrollo Regional” (FEDER)forprojectsCGL2011-23413,CGL2012-33576andCGL2012-37505 are gratefully acknowledged

Aerosol optical depth retrievals at the Izaña Atmospheric Observatory from 1941 to 2013 by using artificial neural networks

This paper presents the reconstruction of a 73-year time series of the aerosol optical depth (AOD) at 500 nm at the subtropical high-mountain Izaña Atmospheric Observatory (IZO) located in Tenerife (Canary Islands, Spain). For this purpose, we have combined AOD estimates from artificial neural networks (ANNs) from 1941 to 2001 and AOD measurements directly obtained with a Precision Filter Radiometer (PFR) between 2003 and 2013. The analysis is limited to summer months (July–August–September), when the largest aerosol load is observed at IZO (Saharan mineral dust particles). The ANN AOD time series has been comprehensively validated against coincident AOD measurements performed with a solar spectrometer Mark-I (1984–2009) and AERONET (AErosol RObotic NETwork) CIMEL photometers (2004–2009) at IZO, obtaining a rather good agreement on a daily basis: Pearson coefficient, R, of 0.97 between AERONET and ANN AOD, and 0.93 between Mark-I and ANN AOD estimates. In addition, we have analysed the long-term consistency between ANN AOD time series and long-term meteorological records identifying Saharan mineral dust events at IZO (synoptical observations and local wind records). Both analyses provide consistent results, with correlations  >  85 %. Therefore, we can conclude that the reconstructed AOD time series captures well the AOD variations and dust-laden Saharan air mass outbreaks on short-term and long-term timescales and, thus, it is suitable to be used in climate analysis.The AERONET Cimel sun photometer at Izaña has been calibrated by AERONET-EUROPE Calibration Service, financed by the Aerosol Cloud and TRace gas InfraStructure (ACTRIS) European Research Infrastructure Action (FP7/2007-2013 no. 262254). Financial support from the Spanish Ministry of Economy and Competitiveness (MINECO) and from the “Fondo Europeo de Desarrollo Regional” (FEDER) for project CGL2012-33576 is gratefully acknowledged

Aerosol optical depth retrievals at the Izaña Atmospheric Observatory from 1941 to 2013 by using artificial neural networks [Discussion paper]

This paper presents the reconstruction of a 73-year time series of the aerosol optical depth (AOD) at 500 nm at the subtropical high-mountain Izaña Atmospheric Observatory (IZO) located in Tenerife (Canary Islands, Spain). For this purpose, we have combined AOD estimates from artificial neural networks (ANNs) from 1941 to 2001 and AOD measurements directly obtained with a Precision Filter Radiometer (PFR) between 2003 and 2013. The analysis is limited to summer months (July–August–September), when the largest aerosol load is observed at IZO (Saharan mineral dust particles). The ANN AOD time series has been comprehensively validated against coincident AOD measurements performed with a solar spectrometer Mark-I (1984–2009) and AERONET (AErosol RObotic NETwork) CIMEL photometers (2004–2009) at IZO, obtaining a rather good agreement on a daily basis: Pearson coefficient, R, of 0.97 between AERONET and ANN AOD, and 0.93 between Mark-I and ANN AOD estimates. In addition, we have analysed the long-term consistency between ANN AOD time series and long-term meteorological records identifying Saharan mineral dust events at IZO (synoptical observations and local wind records). Both analyses provide consistent results, with correlations  >  85 %. Therefore, we can conclude that the reconstructed AOD time series captures well the AOD variations and dust-laden Saharan air mass outbreaks on short-term and long-term timescales and, thus, it is suitable to be used in climate analysis.The AERONET Cimel sun photometer at Izaña has been calibrated by AERONET-EUROPE Calibration Service, financed by the Aerosol Cloud and TRace gas InfraStructure (ACTRIS) European Research Infrastructure Action (FP7/2007-2013 no. 262254). Financial support from the Spanish Ministry of Economy and Competitiveness (MINECO) and from the “Fondo Europeo de Desarrollo Regional” (FEDER) for project CGL2012-33576 is gratefully acknowledged

Quality Assurance of Spectral Ultraviolet Measurements in Europe Through the Development of a Transportable Unit (QASUME)

QASUME is a European Commission funded project that aims to develop and test a transportable unit for providing quality assurance to UV spectroradiometric measurements conducted in Europe. The comparisons will be performed at the home sites of the instruments, thus avoiding the risk of transporting instruments to participate in intercomparison campaigns. Spectral measurements obtained at each of the stations will be compared, following detailed and objective comparison protocols, against collocated measurements performed by a thoroughly tested and validated travelling unit. The transportable unit comprises a spectroradiometer, its calibrator with a set of calibration lamps traceable to the sources of different Standards Laboratories, and devices for determining the slit function and the angular response of the local spectroradiometers. The unit will be transported by road to about 25 UV stations over a period of about two years. The spectroradiometer of the transportable unit is compared in an intercomparison campaign with six instruments to establish a relation, which would then be used as a reference for its calibration over the period of its regular operation at the European stations. Different weather patterns (from clear skies to heavy rain) were present during the campaign, allowing the performance of the spectroradiometers to be evaluated under unfavourable conditions (as may be experienced at home sites) as well as the more desirable dry conditions. Measurements in the laboratory revealed that the calibration standards of the spectroradiometers differ by up to 10%. The evaluation is completed through comparisons with the same six instruments at their homes sites