signature=37192e339f304f4a29d30d77c6a7b958,Detection of long range transport of aerosols with elevat...

摘要：

An advanced version of Boundary Layer LiDAR system, termed as LiDAR for atmospheric measurement and probing (LAMP) has been operational, at Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital, a high altitude station (29.4°N, 79.5°E, ~1960 m above mean sea level), in central Himalayas, since October 2011. The site is at an altitude, which is well above the planetary boundary layer particularly during the night when observations are taken and thus, lies in the free troposphere. Also, there are no anthropogenic sources of aerosols nearby. However, from March to June, due to strong convection, the aerosols get transported to higher altitudes, up to 2 km or more, from the nearby urban and distant regions as well. Here, a case study of each long range transport and convectively driven elevated aerosol layers, observed with LAMP on 22 and 24 March 2012, has been presented. A normal profile observed on 28 March 2012 without any signature of elevated layer of aerosol is also discussed. The seven days back air mass trajectories over three altitude levels, viz. at 4.5, 3 and 1 km on 22 March; at 4.5, 2 km and 700 m on 24 March, and at 4.5, 2 km and 500 m on 28 March have been derived. The upper levels delineate that the possible origin of the multiple elevated aerosol layers on 22 and 24 March may be transported from far-off regions, such as the dry arid regions of North Africa and Saudi Arabia. To confirm the same, the observations were further substantiated with the TERRA satellite yielded aerosol optical depth (555 nm) obtained from the on board instrument Multi-angle Imaging Spectro Radiometer (MISR), which explicitly shows the high value of time averaged columnar aerosol optical depth (AOD) over Saudi Arabia and Red Sea during 18-23 March 2012 and an appreciable decrease during the period 25-29 March 2012, confirming the origin of long range transport. For the first time, such a high altitude aerosol layers (~4.5 km) are observed over this region. The lowest aerosol layer observed on 24 and 28 March 2012 in vertical aerosol backscatter profile is attributed to the transport from adjoining regions via boundary layer evolution and associated mixing.

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