Open AccessClimatology of columnar aerosol properties and the influence of synoptic conditions: First‐time results from the northeastern region of India
Author(s) -
Gogoi Mukunda M.,
Krishna Moorthy K.,
Babu S. Suresh,
Bhuyan Pradip K.
Publication year - 2009
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2008jd010765
Subject(s) - angstrom exponent , aerosol , monsoon , environmental science , climatology , atmospheric sciences , mineral dust , arid , air mass (solar energy) , geology , geography , meteorology , physics , boundary layer , thermodynamics , paleontology
Six years of spectral aerosol optical depths (AODs), from the northeastern part of India (Dibrugarh), are used to evolve a climatology for this region. The results indicate that the seasonal mean AODs at 500 nm go as high as 0.45 ± 0.05 during premonsoon season (March to May), decrease gradually through the monsoon (June to September) to reach the lowest value of 0.19 ± 0.06 during the retreating‐monsoon season (October and November), and increase to 0.31 ± 0.04 in winter (December to February). The AOD spectra are generally flatter than those seen typically over continental sites of India (and elsewhere in the neighboring regions) with Ångström exponent α remaining below 1.0 during February through August, indicating a relatively low abundance of fine and accumulation mode aerosols. The columnar size distributions (CSD) retrieved from spectral AODs are, in general, bimodal with primary mode at ∼ 0.1 μ m and secondary mode at ∼ 1.0 μ m. High mass loading (∼309.5 ± 65.9 mg m −2 ) and effective radius (∼0.40 ± 0.09 μ m) occur during premonsoon and are attributed to significant abundance of coarse (natural) aerosols. Cluster analysis of air mass back trajectories indicate significant transport of mineral dust from the arid regions of west Asia and northwest India across the Indo‐Gangetic plains and marine aerosols advected from the Bay of Bengal contributing largely to the coarse mode aerosols during this season. On the other hand, the peculiar topography combined with the local conditions and the widespread rainfall lead to a more pristine environment during retreating‐monsoon season with quite low AODs and columnar loading.