A new parameterization of the effective cloud fields
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ORIGINAL PAPER
A new parameterization of the effective cloud fields Marius Paulescu 1
&
Andreea Sabadus 1 & Alexandru Dumitrescu 2 & Viorel Badescu 3,4
Received: 1 April 2020 / Accepted: 15 July 2020 # Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract With all the progress made in atmospheric modeling, the cloud field parameterization is still a critical issue. The present study proposes a new model for the probability of a clear-line-of sight (PCLOS). The great benefit of the proposed model is in the estimation of the effective cloud field parameters (namely, the cloud aspect ratio and cloud factor) from radiometric data. The sophisticated numerical procedures used in previous approaches are reduced to simple algebra. The model verification shows that the relationship between the cloud shade and point cloudiness computed using the estimated cloud field parameters accurately recovers the typical relationship derived from measurements. Keywords Cloud field . Cloud aspect ratio . Cloud fraction . Sunshine number . Radiometric data
1 Introduction Clouds reflect solar radiation and cool the atmosphere, but they also trap the upward thermal radiation, thus heating the atmosphere and ground. The diversity of clouds and their random spatial and temporal distribution strongly affect the Earth’s radiation budget. The energy budget plays a key role in establishing the climate. The cloud fields are different and complex in both morphological and microphysical properties. The inclusion of cloud fields in atmospheric models has been documented for decades as a major source of uncertainty in climate modeling (Randall et al. 2003). Despite the huge effort paid and the significant achievements, appropriate cloud parameterization schemes are still critical issues in modeling the atmosphere (Hunerbein et al. 2014). The present study deals with the morphological properties of a cloud field, such as the ratio of vertical to horizontal * Marius Paulescu [email protected] 1
Faculty of Physics, West University of Timisoara, V. Parvan 4, 300223 Timisoara, Romania
2
Department of Climatology, Meteo Romania (National Meteorological Administration), 97 Sos. Bucuresti-Ploiesti, 013686 Bucharest, Romania
3
Candida Oancea Institute, Polytechnic University of Bucharest, Spl. Independentei 313, 060042 Bucharest, Romania
4
Romanian Academy, Calea Victoriei 125, 010017 Bucharest, Romania
dimensions of individual clouds and their spatial distribution. Here we report a simple parameterization of the effective cloud fields on the basis of time series of radiometric data. The relationship between the state-of-the-sky and solar irradiance was investigated for a long time and from many perspectives. Because clouds control the level of solar irradiance at ground level, many equations were developed for estimating solar irradiance based on various quantifiers of the state-of-the-sky. The most famous equation was proposed a hundred years ago (Ångström 1924). It adjusts the estimates of clear sky solar irradiance to the
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