Abstract
Abstract. Daily net surface radiation fluxes are estimated for Indian land mass at spatial grid intervals of 0.1 degree. Two approaches are employed to obtain daily net radiation for four sample days viz., November 19, 2013, December 16, 2013, January 8, 2014 and March 20, 2014. Both the approaches compute net shortwave and net longwave fluxes, separately and sum them up to obtain net radiation. The first approach computes net shortwave radiation using daily insolation product of Kalpana VHRR and 15 days time composited broadband albedo product of Oceansat OCM2. The net outgoing longwave radiation is computed using Stefan Boltzmann equation corrected for humidity and cloudiness. In the second approach, instantaneous clear-sky net-shortwave radiation is estimated using computed clear-sky incoming shortwave radiation and the gridded MODIS 16-day time composited albedo product. The net longwave radiation is obtained by estimating outgoing and incoming longwave radiation fluxes, independently. In this, MODIS derived surface emissivity and skin temperature parameters are used for estimating outgoing longwave radiation component. In both the approaches, surface air temperature data required for estimation of net longwave radiation fluxes are extracted from India Meteorological Department’s (IMD) Automatic Weather Station (AWS) records. Estimates by the two different approaches are evaluated by comparing daily net radiation fluxes with CERES based estimates corresponding to the sample days, through statistical measures. The estimated all sky daily net radiation using the first approach compared well with CERES SYN1deg daily average net radiation with r2 values of the order of 0.7 and RMS errors of the order of 8–16 w/m2.
Highlights
Net surface radiation is the balance of energy between incoming and outgoing shortwave and longwave radiation fluxes at landatmosphere interface
The daily maximum, minimum and dew point temperature data required for estimation of net longwave radiation are extracted from India Meteorological Department’s (IMD) Automatic Weather Station (AWS) records
2.2.3 Daily Net Surface Radiation Flux: The net radiation at surface essentially follows the shape of the diurnal variation of the land surface temperature during day-time
Summary
Net surface radiation is the balance of energy between incoming and outgoing shortwave and longwave radiation fluxes at landatmosphere interface. Point measurements of incoming shortwave may be extended to a much larger area if atmospheric scattering and absorbing properties are assumed to be uniform over the region (Blad et al, 1998) Radiative transfer model such as MODTRAN is useful for estimating incoming conditions; its computational complexity makes it unsuitable for estimating the global surface radiation flux directly. Many GCMs have simplified land surface emissivity and considerable differences exist between model outputs and satellite derived products (Liang et al, 2012). Sensed data is found more useful for estimation of reflected and emitted radiation (outgoing components) from different types of surfaces and at various spatial scales. Net surface radiation products are generated for Indian land mass at spatial grid intervals of 0.1 degree for four sample days of November 19, 2013, December 16, 2013, January 8, 2014 and March 20, 2014
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