Abstract
In the Himalayan region, aerosols received much attention because they affect the regional as well as local climate. Aerosol Optical Depth (AOD) observation from satellite are limited in the Himalayan region mainly due to high surface reflectance. To overcome this limitation, we have conducted a multivariate regression analysis to predict the AOD over the cryospheric portion of Nepalese Himalaya. Prediction using three meteorological variables from ERA-Interim: relative humidity, wind components (U10 and V10) were taken into account for model development as independent variables, while the longest time series AOD observation at Pokhara station is used as dependent variable. Model coefficients were found significant at 95 percent level with 0.53 coefficients of determination for daily values. Correlation coefficients between model output and AERONET observations were found to be 0.68, 0.73, 0.75, 0.83, and 0.82 at Lumbini, Kathmandu Bode (KTM-BO), Kathmandu University (KTM-UN), Jomson, and Pyramid laboratory/observatory (EVK2CNR) AERONET stations, respectively. Model overestimate AOD at Jomsom, and EVK2CNR AERONET stations while slightly underestimates AOD in Lumbini, KTM-UN, and KTM-BO AERONET station, respectively. Both model output and MODIS observation showed that the highest AOD over Nepal is observed during winter and pre-monsoon season. While lowest AOD is observed during monsoon, and post monsoon season. The result of this research supports that the use of linear regression model yields good estimation for daily average AOD in Nepal. The model that we have presented could possibly be used in other mountain regions for climate research.
Highlights
Aerosols are a focal point of climate research due to their role, and significant uncertainty, in atmospheric processes
We found that the altitudinal distribution follows a semi-logarithmic form with a slope and coefficient of determination of −0.135 and 0.899, respectively
We found that the disagreement between the simulated, and observed Aerosol Optical Depth (AOD) is due to the altitudinal dependencies (Figure 5), as it follows the topography
Summary
Aerosols are a focal point of climate research due to their role, and significant uncertainty, in atmospheric processes. These research showed that the aerosols over the Himalayan region are in increasing trend, which is mainly detected during the winter and postmonsoon seasons and are forced by the high anthropogenic emissions, composed of bio and fossil fuel combustions (Acharya and Sreekesh, 2013). Ramanathan and Carmichael (2008) state that aerosols ( black carbon) in the high Himalayas likely play significant role in the snow and glacier melt by increasing solar heating. Aerosol deposition and its transport over the Himalaya is attracting more attention due to its impact on the transformation of hydrological processes, and regional energy balance, affecting billions of people living downstream (Nepal et al, 2014)
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