Assessing Radiometric Parameters at a Continental Global Atmosphere Watch (GAW) Station, Nagpur, in India

Article type: Research Article

Authors: Sarkar, Jayanta

Affiliations: India Meteorological Department, Pune-411005

Note: [] Corresponding author. E-mail: [email protected]

Abstract: Several radiometric parameters viz. direct solar irradiance, long wave radiation, Angstrom turbidity and transmission coefficient for Nagpur have been analyzed and discussed based on data for the period of 1989–1998. Solar irradiance at Nagpur is the highest in winter and amongst the winter months in January due to cloudless sky and good transparency of the atmosphere. It is the least during the monsoons due to increased moisture content of the atmosphere and extended cloudiness. Diurnal variation in direct solar irradiance shows that for all the months the peak is reached between optical air masses 1.5 FN and 1.5 AN with a maximum value of about 700 W/m^2 in January. Turbidity values show fluctuations on yearly basis. During the study period, the lowest value was observed to be 0.082 in 1990 and the highest was 0.108 in 1996. In a year, winter season experiences lowest turbidity while the post-monsoon season witnesses the highest. Diurnal variation of turbidity indicates that optical air mass 3.0 FN is less turbid for all the months in a year while the peak is reached in between air masses 1.5 FN and 1.5 AN. It is seen that transparency of the atmosphere over Nagpur decreases from winter till May. This is to be attributed to the increasing dust content of the atmosphere over Nagpur. The atmosphere transmits only 65% of the incident energy. At early morning and late afternoon hours, transparency is found to be higher when compared to higher solar elevations. Rather, the transparency decreases from morning till noon and later increases. This could be attributed to convective activity during the maximum temperature epoch of the day. Net long wave radiation is found to be the highest in pre-monsoon (64–65 W/m^2). With the monsoon onset, it goes on decreasing, with the lowest value of 42.6 W/m^2 in August. This is mainly due to the extensive cloud cover and high humidity conditions. After the monsoon withdrawal again it starts rising.

Keywords: Solar irradiance, turbidity, transmission coefficient, net longwave radiation

Journal: Asian Journal of Water, Environment and Pollution, vol. 5, no. 1, pp. 49-55, 2008