Estimating daily average net radiation in Northern Mongolia

ABSTRACT

Net radiation is a key component of surface radiation balance and has a strong influence on hydrological processes via evapotranspiration. In this study, daily average net radiation (Rn_mean) for all-sky conditions was investigated as a function of the estimated daily average global radiation (GR_mean) during the summers of 2011 and 2012 (128 days total) in the Sugnugur Valley of Northern Mongolia. We present a simple alternative remote sensing approach that considers factors such as topography, cloud fraction, cloud optical thickness and surface albedo. First, a geometric model for the simulation of daily average global radiation (GR_CS:mean) for clear-sky conditions was applied on a daily basis. It considers topographical effects, such as slope, azimuth and elevation. GR_mean was then derived for all-sky conditions by coupling the averaged atmospheric products of MODIS. Finally, Rn_mean was obtained as a function of the simulated GR_mean using the linear regression parameters found at a permanent observation site. The results were validated with the data from a nearby temporary observation site. The root mean square errors (RMSE) were 44 and 52 Wm⁻² for GR_mean and 18 and 25 Wm⁻² for Rn_mean at the two different sites. This methodology requires few observations and offers a simple means for estimating GR_mean with high spatial (30 m) and temporal (daily) resolution under any sky conditions in the absence of ground measurements. Furthermore, Rn_mean can be modeled from the simulated GR_mean at regional or watershed scales where ground observations exist at one site at least.

KEYWORDS:

• Net radiation
• global radiation
• albedo
• all-sky conditions
• complex terrain

Acknowledgement

The authors thank Gansukh Yadamsuren for his support with the albedo calculation and Matthias Stork for his critical discussions and comments. Munkhdavaa Munkhjargal received funding from the Federal Ministry of Education and Research (BMBF) through the German Academic Exchange Service (DAAD) during the preparation of this manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

The author contributions

Munkhdavaa Munkhjargal analyzed the data, designed the study and wrote the manuscript. Lucas Menzel designed the observational network, helped with the field work and supervised the study.

Notes on contributors

Munkhdavaa Munkhjargal is a Ph.D candidate at the Department of Geography, Heidelberg University. His particular research interest is to understand the water balance and the impacts of wildfire on hydrological regimes in the discontinuous permafrost region of northern Mongolia. http://www.geog.uni-heidelberg.de/hydro/munkhjargal.html

Lucas Menzel holds a full professorship in Hydrology and Climatology at Heidelberg University since 2009. http://www.geog.uni-heidelberg.de/hydro/menzel.html

ORCID

Munkhdavaa Munkhjargal http://orcid.org/0000-0001-8160-2182