Net Cloud Radiative Forcing at the Top of the Atmosphere in the Asian Monsoon Region

M. Rajeevan India Meteorological Department, Pune, India

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J. Srinivasan Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bangalore, India

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Abstract

Based on the data from Earth Radiation Budget Experiment (ERBE), many investigators have concluded that the net cloud radiative forcing at the top of the atmosphere is small in the deep convective region of the Tropics. This conclusion has been shown to be invalid for the Asian monsoon region during the period June–September. The ERBE data have been used to show that in the Asian monsoon region the net cloud radiative forcing at the top of the atmosphere is negative and its magnitude exceeds 30 W m−2 in 25% of the grids in this region. The large negative net cloud radiative forcing in the Asian monsoon region during June–September has been shown to be on account of the presence of large amount of high clouds and the large optical depth of these clouds. This combination of high cloud amount and high optical depth occurs in the Asian monsoon region only. In the other deep convective regions of the Tropics, high clouds with large optical depths are present, but they do not cover a large area.

* Additional affiliation: Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, India.

Corresponding author address: Dr. J. Srinivasan, Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bangalore 560012, India.

Email: jayes@caos.iisc.ernet.in

Abstract

Based on the data from Earth Radiation Budget Experiment (ERBE), many investigators have concluded that the net cloud radiative forcing at the top of the atmosphere is small in the deep convective region of the Tropics. This conclusion has been shown to be invalid for the Asian monsoon region during the period June–September. The ERBE data have been used to show that in the Asian monsoon region the net cloud radiative forcing at the top of the atmosphere is negative and its magnitude exceeds 30 W m−2 in 25% of the grids in this region. The large negative net cloud radiative forcing in the Asian monsoon region during June–September has been shown to be on account of the presence of large amount of high clouds and the large optical depth of these clouds. This combination of high cloud amount and high optical depth occurs in the Asian monsoon region only. In the other deep convective regions of the Tropics, high clouds with large optical depths are present, but they do not cover a large area.

* Additional affiliation: Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, India.

Corresponding author address: Dr. J. Srinivasan, Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bangalore 560012, India.

Email: jayes@caos.iisc.ernet.in

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