Proyecto de Investigación: ESTUDIO EXPERIMENTAL DEL EFECTO DE LAS NUBES BAJAS EN EL PERFIL VERTICAL DE RADIACION
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RTI2018-097332-B-C21
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Cirrus-induced shortwave radiative effects depending on their optical and physical properties: Case studies using simulations and measurements
(Elsevier BV, 2020-12-01) Córdoba Jabonero, C.; Gómez Martín, L.; Del Águila, A.; Vilaplana, Jose Manuel; López Cayuela, M. A.; Zorzano, María-Paz; Agencia Estatal de Investigación (AEI); European Research Council (ERC); Ministerio de Economía y Competitividad (MINECO); 000-0002-6655-7659; 0000-0002-4492-9650; 0000-0002-8825-830X; 0000-0003-4859-471X; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
Cirrus (Ci) clouds play an important role in the atmospheric radiative balance, and hence in Climate Change. In this work, a polarized Micro-Pulse Lidar (P-MPL), standard NASA/Micro Pulse NETwork (MPLNET) system, deployed at the INTA/El Arenosillo station in Huelva (SW Iberian Peninsula) is used for Ci detection and characterization for the first time at this site. Three days were selected on the basis of the predominantly detected Ci clouds in dependence on their cloud optical depth (COD). Hence, three Ci cloud categories were examined at day-times for comparison with solar radiation issues: 19 cases of sub-visuals (svCi, COD: 0.01-0.03) on 1 October 2016, 7 cases of semitransparents (stCi, COD: 0.03-0.30) on 8 May 2017, and 17 cases of opaques (opCi, COD: 0.3-3.0) on 28 October 2016. Their radiative-relevant optical, macro- and micro-physical properties were retrieved. The mean COD for the svCi, stCi and opCi groups was 0.02 +/- 0.01, 0.22 +/- 0.08 and 0.93 +/- 0.40, respectively; in overall, their lidar ratio ranged between 25 and 35 sr. Ci clouds were detected at 11-13 km height (top boundaries) with geometrical thicknesses of 1.7-2.0 km. Temperatures reported at those altitudes corresponded to lower values than the thermal threshold for homogenous ice formation. Volume linear depolarization ratios of 0.3-0.4 (and normalized backscattering ratios higher than 0.9) also confirmed Ci clouds purely composed of ice particles. Their effective radius was within the interval of 9-15 mu m size, and the ice water path ranged from 0.02 (svCi) to 9.9 (opCi) g m(-2). The Cirrus Cloud Radiative Effect (CCRE) was estimated using a Radiative Transfer (RT) model for Ci-free conditions and Ci-mode (Ci presence) scenarios. RT simulations were performed for deriving the CCRE at the top-of-atmosphere (TOA) and on surface (SRF), and also the atmospheric CCRE, for the overall shortwave (SW) range and their spectral sub-intervals (UV, VIS and NIR). A good agreement was first obtained for the RT simulations as validated against solar radiation measurements under clean conditions for solar zenith angles less than 75 degrees (differences were mainly within +/- 20 W m(-2) and correlation coefficients close to 1). By considering all the Ci clouds, independently on their COD, the mean SW CCRE values at TOA and SRF were, respectively, -30 +/- 26 and -24 +/- 19 W m(-2), being the mean atmospheric CCRE of -7 +/- 7 W m(-2); these values are in good agreement with global annual estimates found for Ci clouds. By using linear regression analysis, a Ci-induced enhancing cooling radiative effect was observed as COD increased for all the spectral ranges, with high correlations. In particular, the SW CCRE at TOA and SRF, and the atmospheric CCRE, presented COD-dependent rates of -74 +/- 4, -55 +/- 5, -19 +/- 2 W m(-2) tau(-1), respectively. Additionally, increasing negative rates are found from UV to NIR for each Ci category, reflecting a higher cooling NIR contribution w.r.t. UV and VIS ranges to the SW CCRE, and being also more pronounced at the TOA w.r.t. on SRF, as expected. The contribution of the SW CCRE to the net (SW + LW) radiative balance can be also potentially relevant. These results are especially significant for space-borne photometric/radiometric instrumentation and can contribute to validation purposes of the next ESA's EarthCARE mission, whose principal scientific goal is focused on radiation-aerosol-cloud interaction research.
Comparison of global UV spectral irradiance measurements between a BTS CCD-array and a Brewer spectroradiometer
(European Geosciences Union, 2022-07-15) González, Carmen; Vilaplana, Jose Manuel; Bogeat Sánchez-Piqueras, José Antonio; Serrano, Antonio
Spectral measurements of UV irradiance are of great importance for protecting human health as well as for supporting scientific research. To perform these measurements, double monochromator scanning spectroradiometers are the preferred devices thanks to their linearity and stray-light reduction. However, because of their high cost and demanding maintenance, CCD-array-based spectroradiometers are increasingly used for monitoring UV irradiance. Nevertheless, CCD-array spectroradiometers have specific limitations, such as a high detection threshold or stray-light contamination. To overcome these challenges, several manufacturers are striving to develop improved instrumentation. In particular, Gigahertz-Optik GmbH has developed the stray-light-reduced BTS2048-UV-S spectroradiometer series (hereafter “BTS”). In this study, the long-term performance of the BTS and its seasonal behavior, regarding global UV irradiance, was assessed. To carry out the analysis, BTS irradiance measurements were compared against measurements from the Brewer MK-III #150 scanning spectrophotometer during three campaigns. A total of 711 simultaneous spectra, measured under cloud-free conditions and covering a wide range of solar zenith angles (SZAs; from 14 to 70∘) and UV indexes (from 2.4 to 10.6), were used for the comparison. During the three measurement campaigns, the global UV spectral ratio BTS / Brewer was almost constant (at around 0.93) in the 305–360 nm region for SZAs below 70∘. Thus, the BTS calibration was stable during the whole period of study (∼ 1.5 years). Likewise, it showed no significant seasonal or SZA dependence in this wavelength region. Regarding the UV index, a good correlation between the BTS and the Brewer #150 was found, i.e., the dynamic range of the BTS is comparable to that of the Brewer #150. These results confirm the quality of the long-term performance of the BTS array spectroradiometer in measuring global UV irradiance.
