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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 (∆F) and efficiency (∆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 (Sentinel5P 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 ∆F of the volcanic aerosols being greater than that of the dust events (associated with the larger aerosol load present), the ∆F E f f was found to be lower. The spectral ∆F E f f values at 440 nm ranged between −1.9 and −2.6 Wm−2nm−1AOD−1 for the mineral dust and mixed volcanic and dust particles, and between −1.6 and −3.3 Wm−2nm−1AOD−1 for the volcanic aerosols, considering solar zenith angles between 30◦ and 70◦, respectively. The authors also acknowledge the support of ACTRIS, Ministerio de Ciencia e Innovación of Spain, through the projects SYNERA: PID2020-118793GA-I00 and RT2018- 097864-B-I00, and Junta de Castilla y León grant N◦. VA227P20.

Ponencia presentada en: XVIII Congreso de la Asociación Española de Teledetección celebrado en Valladolid del 24 al 27 septiembre 2019. [ES]Este trabajo se centra en comparar los productos de vapor de agua integrado (IWV) de varios satélites respecto a un conjunto de datos en tierra obtenidos de GPS en nueve estaciones de la Península Ibérica. Los instrumentos satelitales son: Global Ozone Monitoring Instrument (GOME-2), Moderate-Resolution Imaging Spectroradiometer (MODIS), Ozone Monitoring Instrument (OMI), Spining Enhanced Visible and InfraRed Imager (SEVIRI), Atmospheric Infrared Sounder (AIRS), y Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY). Los productos de estos satélites muestran una buena correlación con respecto al producto de GPS (R2 ~ 0.7). Todos los satélites muestran cierta tendencia a sobrestimar los valores bajos de vapor de agua y a subestimar los altos. Además, la precisión, medida mediante el rango intercuartílico (IQR) también disminuye rápidamente al aumentar el IWV. Por otro lado, otro factor importante es el ángulo solar zenital (SZA) que influye en el rendimiento de los instrumentos satelitales, especialmente aquellos que dependen de la radiación solar. Al aumentar el SZA acercándose a 90°, los instrumentos pierden rendimiento aumentando la sobrestimación y el IQR. Sin embargo, a valores de SZA mayores de 90° (esto es, la noche) los índices calculados no tienen grandes dependencias con el SZA. [EN]This work focuses in the comparison of several integrated water vapor (IWV) from several satellites with respect to a dataset from ground-based GPS IWV, in nine stations at the Iberian Peninsula. The satellite instruments are Global Ozone Monitoring Instrument (GOME-2), Moderate-Resolution Imaging Spectroradiometer (MODIS), Ozone Monitoring Instrument (OMI), Spinning Enhanced Visible and InfraRed Imager (SEVIRI), Atmospheric Infrared Sounder (AIRS), and Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY). The products of this instruments show a fair correlation with respect to GPS product (R2 ~ 0.7). All satellites show a certain tendency to overestimation of low IWV values, while underestimating large IWV values. Moreover, the precision is studied using the inter-quartile range (IQR), which also decreases quickly when IWV increases. Another important factor is the solar zenith angle (SZA), which affects the performance of satellite instruments, especially those that are dependent on solar radiation. When SZA increases, going closer to 90°, the instruments had worse performance, increasing overestimation and IQR. Nevertheless, for SZA larger than 90° (that is to say, the night), the indexes do not show large dependencies on SZA.

Spectral direct UV-Visible normal solar irradiance (DNI) measured with an EKO MS-711 spectroradiometer at the Izaña Atmospheric Observatory (IZO, Spain) has been used to determine aerosol optical depth (AOD) at several wavelengths (340, 380, 440, 500, 675 and 870 nm) between April and September 2019 that have been compared with synchronous AOD measurements from a reference Cimel-AERONET (Aerosol RObotic NETwork) sunphotometer. The EKO MS-711 has been calibrated at Izaña Observatory using the Langley-Plot method during the study period. Although this instrument has been designed for spectral solar DNI measurements, and therefore has a field of view (FOV) of 5° that is twice that recommended in solar photometry for AOD determination, the AOD differences compared against the AERONET Cimel reference instrument (FOV ∼ 1.2°), are fairly small. The comparison results between AOD Cimel and EKO MS-711 present a root mean square (RMS) of 0.013 (24.6 %) at 340, and 380 nm, and 0.029 (19.5 %) for longer wavelengths (440, 500, 675 and 870 nm). However, under relatively high AOD, near forward aerosol scattering might be significant because of the relatively large circumsolar radiation (CSR) due to the large EKO MS-711 FOV, resulting in a small but significant AOD underestimation in the UV range. The AOD differences decrease considerably when CSR corrections, estimated from LibRadtran radiative transfer model simulations, are performed, obtaining RMS of 0.006 (14.9 %) at 340 and 380 nm, and 0.005 (11.1 %) for longer wavelengths. The percentage of 2-minute synchronous EKO AOD–Cimel AOD differences within the World Meteorological Organization (WMO) traceability limits were ≥ 96 % at 500 nm, 675 nm and 870 nm with no CSR corrections. After applying the CSR corrections, the percentage of AOD differences within the WMO traceability limits increased to > 95 % for 380, 440, 500, 675 and 870 nm, while for 340 nm the percentage of AOD differences showed a poorer increase from 67 % to a modest 86 %. AERONET Sun photometers at Izaña have been calibrated within the AERONET Europe TNA, supported by the European Union Horizon 2020 research and innovation program under grant agreement no. 654109 (ACTRIS-2). This research benefited from the results of the project funding by MINECO RTI2018-097864-B-I00.

Integrated water vapor (IWV) data from Global Navigation Satellite Systems (GNSS) and radiosounding (RS) are compared over four sites (Lindenberg, Ny-Ålesund, Lauder and Sodankylä), which are part of the Global Climate Observing System (GCOS) Reference Upper Air Network (GRUAN). Both datasets show an excellent agreement, with a high degree of correlation (R2 over 0.98). Dependences of GNSS-RS differences on several variables are studied in detail. Mean bias error (MBE) and standard deviation (SD) increase with IWV, but in relative term, these variables decrease as IWV increases. The dependence on solar zenith angle (SZA) is partially related to the distribution of IWV with SZA, but the increase of SD for low SZA could be associated with errors in the humidity sensor. Large surface pressures worsen performance, which could be due to the fact that low IWV is typically present in high pressure situations. Cloud cover shows a weak influence on the mentioned MBE and SD. The horizontal displacement of radiosondes generally causes SD to increase and MBE to decrease (increase without sign), as it could be expected. The results point out that GNSS measurements are useful to analyze performance to other instruments measuring IWV. Support from the Junta de Extremadura (Research Group Grants GR15137) is gratefully acknowledged. Work at Universidad de Valladolid is supported by project CMT2015-66742-R.

Ponencia presentada en: XVIII Congreso de la Asociación Española de Teledetección celebrado en Valladolid del 24 al 27 septiembre 2019. [ES]En este trabajo presentamos casos de estudio sobre la atenuación de la irradiancia directa espectral medida con el espectrorradiómetro EKO-MS 711 debido a la presencia de nubes altas (tipo cirros) en el Observatorio de Izaña (IZO; 2400 m s.n.m.) en la isla de Tenerife (Islas Canarias, España). Para identificar este tipo de nubes hemos utilizado como herramientas auxiliares las imágenes de la cámara de todo cielo (SONA) y la evolución temporal de la señal corregida en rango medida con el LiDAR. Además hemos utilizado el modelo de transferencia radiativa LibRadtran para simular la irradiancia sin la presencia de nubes, dando como parámetros de entrada el espesor óptico de aerosoles (AOD), el vapor de agua y la columna total de ozono medidos en IZO. Los resultados muestran que la irradiancia directa en el rango visible (400-800 nm) y en el rango espectral completo de medida del espectrorradiómetro (300-1100 nm) disminuye dependiendo del tipo de nubes altas. Así para el caso de cirros la disminución es del 10%, mientras que para cirrostratos la disminución es menor al 5%. [EN]In this work we present the attenuation of spectral direct irradiance performed with the EKO MS-711 spectroradiometer due to the presence of high-level clouds (cirrus type) at the Izaña Observatory (IZO; 2400 m a.s.l.), Tenerife Island (Canary Islands, Spain). Auxiliary images from the sky camera (SONA) and the temporal evolution of the LIDAR range-corrected signal have been used to identify this type of clouds. We have also used the LibRadtran radiative transfer model to simulate the irradiance without the presence of clouds, giving as input parameters the aerosol optical depth (AOD), water vapour and total ozone column measured at IZO. The results show that the spectral direct irradiance in the visible range (400-800 nm) and the full spectral range of the spectroradiometer (300-1100 nm) decreases depending on the type of high-level clouds, 10% for cirrus while the decreased observed for cirrostratus is less than 5%.

Ponencia presentada en: XVIII Congreso de la Asociación Española de Teledetección celebrado en Valladolid del 24 al 27 septiembre 2019. [ES]Este trabajo se centra en comparar los productos de vapor de agua integrado (IWV) de varios satélites respecto a un conjunto de datos en tierra obtenidos de GPS en nueve estaciones de la Península Ibérica. Los instrumentos satelitales son: Global Ozone Monitoring Instrument (GOME-2), Moderate-Resolution Imaging Spectroradiometer (MODIS), Ozone Monitoring Instrument (OMI), Spining Enhanced Visible and InfraRed Imager (SEVIRI), Atmospheric Infrared Sounder (AIRS), y Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY). Los productos de estos satélites muestran una buena correlación con respecto al producto de GPS (R2 ~ 0.7). Todos los satélites muestran cierta tendencia a sobrestimar los valores bajos de vapor de agua y a subestimar los altos. Además, la precisión, medida mediante el rango intercuartílico (IQR) también disminuye rápidamente al aumentar el IWV. Por otro lado, otro factor importante es el ángulo solar zenital (SZA) que influye en el rendimiento de los instrumentos satelitales, especialmente aquellos que dependen de la radiación solar. Al aumentar el SZA acercándose a 90°, los instrumentos pierden rendimiento aumentando la sobrestimación y el IQR. Sin embargo, a valores de SZA mayores de 90° (esto es, la noche) los índices calculados no tienen grandes dependencias con el SZA. [EN]This work focuses in the comparison of several integrated water vapor (IWV) from several satellites with respect to a dataset from ground-based GPS IWV, in nine stations at the Iberian Peninsula. The satellite instruments are Global Ozone Monitoring Instrument (GOME-2), Moderate-Resolution Imaging Spectroradiometer (MODIS), Ozone Monitoring Instrument (OMI), Spinning Enhanced Visible and InfraRed Imager (SEVIRI), Atmospheric Infrared Sounder (AIRS), and Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY). The products of this instruments show a fair correlation with respect to GPS product (R2 ~ 0.7). All satellites show a certain tendency to overestimation of low IWV values, while underestimating large IWV values. Moreover, the precision is studied using the inter-quartile range (IQR), which also decreases quickly when IWV increases. Another important factor is the solar zenith angle (SZA), which affects the performance of satellite instruments, especially those that are dependent on solar radiation. When SZA increases, going closer to 90°, the instruments had worse performance, increasing overestimation and IQR. Nevertheless, for SZA larger than 90° (that is to say, the night), the indexes do not show large dependencies on SZA.

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, 2373ma.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. The IZA BSRN program has benefited from results obtained within POLARMOON project funded by the Ministerio de Economía y Competividad from Spain, CTM2015-66742-R.

The aim of this paper is to analyze the suitability of the high-mountain stations Mauna Loa and Izaña for Langley plot calibration of Sun photometers. Thus the aerosol optical depth (AOD) characteristics and seasonality, as well as the cloudiness, have been investigated in order to provide a robust estimation of the calibration accuracy, as well as the number of days that are suitable for Langley calibrations. The data used for the investigations belong to AERONET and GAW-PFR networks, which maintain reference Sun photometers at these stations with long measurement records: 22 years at Mauna Loa and 15 years at Izaña. In terms of clear sky and stable aerosol conditions, Mauna Loa (3397m a.s.l.) exhibits on average of 377 Langleys (243 morning and 134 afternoon) per year suitable for Langley plot calibration, whereas Izaña (2373m a.s.l.) shows 343 Langleys (187 morning and 155 afternoon) per year. The background AOD (500nm) values, on days that are favorable for Langley calibrations, are in the range 0.01-0.02 throughout the year, with well defined seasonality that exhibits a spring maximum at both stations plus a slight summer increase at Izaña. The statistical analysis of the long-term determination of extraterrestrial signals yields to a calibration uncertainty of ~0.2-0.5%, being this uncertainty smaller in the near infrared and larger in the ultraviolet wavelengths. This is due to atmospheric variability that cannot be reduced based only on quality criteria of individual Langely plots. 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 10 by MINECO (CTM2015-66742-R) and Junta de Castilla y León (VA100P17) is also acknowledged.

Ponencia presentada en: XI Congreso de la Asociación Española de Climatología celebrado en Cartagena entre el 17 y el 19 de octubre de 2018. [ES]La observación del vapor de agua es un desafía de gran importancia, debido a que este es fundamental en el sistema climático. A pesar de la variedad de instrumentos que miden el vapor de agua, su alta variabilidad en los dominios temporal y espacial hace difícil dar mediciones completas. Las radiosondas (RS) permiten obtener el perfil vertical del vapor de agua, y están consolidadas como referencia. En las últimas décadas, los sistemas satelitales de navegación global (GNSS) proporcionan medidas de vapor de agua integrado (IWV), y se están implementando redes densas de receptores se están implementando gracias a su bajo coste, alta tasa de medidas, y su uso para otras aplicaciones en geofísica. Ambos instrumentos se compararon en la estación de Ny-Alesund, perteneciente a la red GRUAN, siendo RS la referencia, con un alto grado de correlación y un pequeño error sistemático (alrededor de 0.7 mm). Sin embargo, se observaron algunas dependencias: se han estudiado las dependencias con IWV, ángulo solar cenital (SZA) y presión en superficie. Un aumento en IWV lleva a un descenso del error medio (MBE) relativo, y de la desviación estándar (SD) relativa, mientras que los aumentos del SZA y la presión también empeoran el MBE, mientras que la SD se mantiene estable. [EN]Monitoring water vapor is a challenge of great importance because of its fundamental character in the climate system. Despite the variety of instruments to measure water vapor, its high variability in the spatial and temporal regimes makes it difficult to provide complete measurements. Radiosondes (RS) allow to retrieve the vertical profile of water vapor, and are consolidated as a reference. In the last decades, Global Navigation Satellite Systems (GNSS) provide integrated water vapor (IWV) measurements, and dense networks of receivers are being implemented because of their low cost, high measurement rate and use in other geophysics applications. Both instruments in Ny-Alesund GRUAN station are compared, being RS the reference, with a high degree of correlation, and a small, dry bias (around 0.7 mm). Nevertheless, some dependences are observed: IWV, solar zenith angle and surface pressure are studied. Increase in IWV lead to lower relative mean biased error (MBE, in %) and standard deviation (SD), while SZA and pressure increases also worsens both MBE, while SD is quite stable.

This work was supported by the Spanish Ministry of Economy and Competitiveness through project CGL2014-56255-C2. Support from the Junta de Extremadura (Research Group Grant GR15137) is gratefully acknowledged. Work at the Universidad de Valladolid is supported by project CMT2015-66742-R. Work at the Universidad de Granada was supported by the Andalusia Regional Government (Project P12-RNM-2409) and the Spanish Ministry of Economy and Competitiveness and FEDER funds under the projects CGL2016-81092-R and “Juan de la Cierva-Formación” program (FJCI-2014-22052). In this work, water vapor radiative effect (WVRE) is studied by means of the Santa Barbara's Disort Radiative Transfer (SBDART) model, fed with integrated water vapor (IWV) data from 20 ground-based GPS stations in Spain. Only IWV data recorded during cloud-free days (selected using daily insolation data) were used in this study. Typically, for SZA = 60.0 ± 0.5° WVRE values are around − 82 and − 66 Wm−2 (first and third quartile), although it can reach up − 100 Wm−2 or decrease to − 39 Wm−2. A power dependence of WVRE on IWV and cosine of solar zenith angle (SZA) was found by an empirical fit. This relation is used to determine the water vapor radiative efficiency (WVEFF = ∂WVRE/∂IWV). Obtained WVEFF values range from − 9 and 0 Wm−2 mm−1 (− 2.2 and 0% mm−1 in relative terms). It is observed that WVEFF decreases as IWV increases, but also as SZA increases. On the other hand, when relative WVEFF is calculated from normalized WVRE, an increase of SZA results in an increase of relative WVEFF. Heating rates were also calculated, ranging from 0.2 Kday−1 to 1.7 Kday−1. WVRE was also calculated at top of atmosphere, where values ranged from 4 Wm−2 to 37 Wm−2

A 7-year comparison study between measured and simulated LDR under cloud-free conditions has been performed at the BSRN Izaña. Results show an excellent agreement with a mean bias (simulated-measured)

This study presents a new zenith looking narrow-band radiometer based system (ZEN), conceived for dust aerosol optical depth (AOD) monitoring. Our results suggest that ZEN is a suitable system to fill the current observational gaps and to complement observations performed by sun-photometer networks in order to improve mineral dust monitoring in remote locations. AERONET sun photometers at Izaña have been calibrated within the AERONET Europe TNA, supported by the European Community-Research Infrastructure Action under the FP7 15 ACTRIS grant agreement no. 262254.