HR: 0800h
AN: A21E-0787    [Abstracts]
TI: Rayleigh Lidar study of upper stratospheric thermal structure and long term trends over a sub-tropical station Mount Abu (24.5o N, 72.7o E, MSL height 1.7 Km)
AU: * Sharma, S
EM: somkumar@prl.res.in
AF: Physical Research Laboratory, Navrangpura, Ahmedabad, 380 009, India
AU: Jayaraman, A
EM: jraman@prl.res.in
AF: Physical Research Laboratory, Navrangpura, Ahmedabad, 380 009, India
AU: Chandra, H
EM: hchandra@prl.res.in
AF: Physical Research Laboratory, Navrangpura, Ahmedabad, 380 009, India
AU: Lal, S
EM: shyam@prl.res.in
AF: Physical Research Laboratory, Navrangpura, Ahmedabad, 380 009, India
AU: Acharya, Y
EM: yacharya@prl.res.in
AF: Physical Research Laboratory, Navrangpura, Ahmedabad, 380 009, India
AB: Stratosphere plays very vital role in deciphering various geophysical phenomena taking place in the Earth's atmosphere. It is also a well known reservoir of ozone which protects us from the hazard of the UV radiation emanating from the Sun. For more than two decades, Rayleigh Lidar has become a dynamic atmospheric probe for providing height profile of temperature in the middle atmospheric region. A Nd: YAG laser based Rayleigh Lidar was set up, at a high altitude observatory near Mount Abu (24.5o N, 72.7o E, altitude1.7 km), in the Indian sub-tropical region, to study the Earth's neutral atmospheric temperature structure. The system is transmitting pulses of 7 ns duration at a frequency of 10 Hz with average power about 350 mJ at 532 nm. For the study of temperature climatology in the stratosphere, we have used the Rayleigh lidar data collected for about seven years from 1997 to 2003. The temperature profiles are derived from photon count profiles followed by Hauchecorne and Chanin (1980). The systematic and statistical errors in deriving temperature are found to be less than ~1 K below 50 km. The monthly mean temperature profiles obtained are compared with three different model atmospheres (CIRA-86, MSISE-90 and Indian low latitude model). Below the stratopause, model temperatures are in agreement with the observed values. To study the year to year variability, mean monthly temperature profiles have been estimated for different years. The variability is least around 40-50 km with a value of 5 K. The mean stratopause height and its temperature are found to be 48 km and 270 K respectively. Interesting features, like the double stratopause structure around 40-52 km has also been found. For the study of long term changes in the thermal structure of the Stratosphere, consistently good data series for 1997-2006 has been investigated. Monthly mean temperature profiles for each month individually have been used to remove seasonal variability. A multivariable analysis is used to consider natural variability (Solar Cycle and QBO) and similarly the changes in stratospheric ozone concentration due to anthropogenic activity have also been taken into account in trends estimations. We have selected different height regions 36-40, 41-45 and 46-50 km for trends analysis. Linear Regression analysis is applied to calculate temperature trend in different altitude regions. Considering the imprints of seasonal, QBO and solar cycle variability, a linear decreasing temperature trend in stratospheric temperature has been found using the data from 1997-2006. In this paper, long term trends in temperature at a subtropical high altitude station will be presented and discussed.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting