Evidence of Long Period Modulations in Spectral Aerosol Optical Depths Over Central Himalayas

In this study, large scale modulations in Aerosol Optical Depths (AOD) observed by sun photometer over Manora Peak, Nainital (29.4 N; 79.2 E; 1957 AMSL) in central Himalayan region (free troposphere site) are investigated. Earlier studies from this location showed some intriguing results of the aerosol concentration and also forenoon and afternoon asymmetry. However, the short scale and large modulations has not been studied yet. In view of this, it is thought to study the large scale modulations affecting AODs thereby leading to atmospheric forcing and subsequent heating in the atmosphere. Power spectrum analysis showed significant quasi-6.5, quasi -16 and also 25-45 day oscillations during the observational period. Amplitudes of these modulations are quite dominant contributing to the diurnal and seasonal variation of AODs. The morphological characteristics and the plausible generation mechanism of aerosol particles at this site are discussed which ultimately affect overall Earth's radiation budget. Preliminary results obtained will be discussed in the light of current understanding of aerosol dynamics and related energy budget.