Seasonal Net Shortwave Radiation of Bare Arable Land in Poland and Israel According to Roughness and Atmospheric Irradiance

Jerzy Cierniewski,Jean-Louis Roujean,Jarosław Jasiewicz,Sławomir Królewicz

doi:10.3390/rs13101897

Abstract

Tillage of arable fields, using for instance a smoothing harrow, may increase the magnitude of albedo of such soil surfaces depending on the location, the sun’s illumination and atmospheric components. As these soil surfaces absorb less shortwave radiation compared to plowed soils, the result is an atmospheric cooling and a positive effect on the Earth’s climate. This paper is the follow-on of a previous study aimed at quantifying the seasonal dynamics of net shortwave radiation reflected by bare air-dried arable land areas located in contrasting environments, i.e. Poland and Israel. Soil tillage includes a plow, a disk harrow, and a smoothing harrow. Previous work concentrated on the estimate of net shortwave radiation under clear-sky theoretical scenarios, whereas the present study deals with a realistic atmosphere throughout the year 2014. This latter is characterized by the observations of the Spinning Enhanced Visible and Infrared Imager (SEVIRI) instrument on board the Meteosat Second Generation (MSG). The variations of the net shortwave radiation for the selected bare arable land areas were assessed in combining observations from Landsat 8 images and digital maps of land use and soil, plus model equations that calculate the diurnal variations of the broadband blue-sky albedo with roughness inclusive. The daily amount of net shortwave radiation for air-dried bare arable land in Poland and Israel for the time their spatial coverage is the largest was found to be about 40–50% and 10% lower, respectively, in cloudy-sky conditions compared to clear-sky conditions.

Highlights

The broadband albedo of the Earth’s surface is a key parameter for modeling shortwave radiation exchanges with the atmosphere [1]
In Israel, the curve describing the annual arable land (Ad) distribution shows its highest values comprised between 2000 km2 and 2150 km2 at the turn of summertime and early fall between the DOY 195 and 290
The results of this study demonstrate that the measured daily shortwave radiation under changing cloud cover conditions over the year 2014 for both Poland and Israel was notably less than the theoretical estimates derived from ideal clear-sky conditions, i.e., without any atmosphere compounds

Summary

Introduction

The broadband albedo of the Earth’s surface is a key parameter for modeling shortwave radiation exchanges with the atmosphere [1]. Estimation of the albedo values of bare arable land at coarse scale are based on satellite observations as they are the only means to obtain routine observations in a coherent manner [3]. Observations over land occur under clear-sky conditions and at a given time of the day for LEO (Low Earth Observation) satellites. As the albedo changes with the solar zenith angle throughout the day, the daily average albedo is more representative than instantaneous albedo of the surface energy budget [4,5,6]. In clear-sky conditions, the albedo shows a U-shape curve, reaching its minimum at the local noon and its maximum when the sun rises and sets [7,8,9].

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Conclusion