Implementation of the Bessel's method for solar eclipses prediction in the WRF-ARW model

• Published in: Atmospheric chemistry and physics 2016-01, Vol.2016 (1), p.1
• Main Authors: Montornès, A, Codina, B, Zack, J. W, Sola, Y
• Format: Article
• Language: English
• Subjects: Analysis; Eclipses (Astronomy); Meteorological research; Methods; Numerical weather prediction; Radiation (Physics); Solar energy; Solar energy industry; Technology application; Weather
• ISSN: 1680-7316; 1680-7324

Solar eclipses are predictable astronomical events that abruptly reduce the incoming solar radiation into the Earth's atmosphere, which frequently result in non-negligible changes in meteorological fields. The meteorological impacts of these events have been analyzed in many studies since the late 1960s. The recent growth in the solar energy industry has greatly increased the interest in adding additional detail to the modeling of solar radiation variations in Numerical Weather Prediction (NWP) models for use in solar resource assessment and forecasting applications. The recent partial and total solar eclipses that occurred in USA (October 23, 2014) and Europe (March 20, 2015), respectively, are showing the necessity for including these astronomical events on the current solar parameterizations, beyond the purely meteorological interest. Although some studies added solar eclipse episodes within NWP codes in the 1990s and 2000s, they used eclipse parameterizations designed for a particular case of study. In contrast to these earlier implementations, this paper documents a new package for the Weather Research and Forecasting -- Advanced Research (WRF-ARW) model that can simulate any partial, total or hybrid solar eclipse for the period 1950 to 2050 and is also extensible to a longer period. The algorithm computes analytically the trajectory of the Moon's shadow and the degree of obscuration of the solar disk at each grid-point of the domain based on the Bessel's method and the Five Millennium Catalog of Solar Eclipses provided by NASA, with a negligible computational time. Then, the incoming radiation is modified accordingly at each grid-point of the domain. This contribution is divided in two parts. First, we present a description of the implementation of the Bessel's method within the WRF-ARW model together with a validation for the period 1950-2050 of all solar eclipse trajectories with respect to NASA values. Second, we analyze the model response in four total solar eclipse episodes: 1994-11-03 (South America), 1999-08-11 (Europe), 2006-03-29 (North Africa) and 2009-07-22 (Eastern Asia). The second part includes a validation of the simulated global horizontal irradiance (GHI) with measurement data from selected Baseline Surface Radiation Network sites within the area affected by each event as well as an analysis of the impact of the GHI changes in surface temperature and wind speed.