Imprint of Greenhouse cooling in Lidar observed stratospheric thermal structure over a sub-tropical station Mount Abu (24.5N, 72.7E, MSL height 1.7 Km)

In recent years there has been great concern of greenhouse effect in the atmosphere due to increased anthropogenic activities and its consequences in the global climate. The consequences for the middle/upper atmosphere, due to the increased concentration of trace gases, were examined using a global mean model and reported cooling in middle and upper atmosphere. Stratosphere is relatively stable/quiet but 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, Lidar has become a dynamic atmospheric probe for providing height profile of density/temperature in the middle atmospheric region. A Nd: YAG laser based Rayleigh Lidar was installed, 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 five years from 1997 to 2001. 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) and satellite observed temperatures. Below the stratopause, model and satellite 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. Atmospheric feature, like the double stratopause structure around 40-52 km has also been observed. For the study of long term changes in the thermal structure of the Stratosphere, consistently good data series for 1997-2008 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 layers 30-35, 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 signature of seasonal, QBO and solar cycle variability, a linear decreasing temperature trend (cooling) in stratospheric temperature has been found using the data from 1997-2008. In this talk, observed stratospheric cooling at Mount Abu over a period of 11 years, operative processes and their implication on lower/middle atmosphere will be discussed.

Datum

26.07.2010

Uhrzeit

11:00 Uhr

Ort

Bundesstr. 53, room 022/023
Seminar Room 022/023, Ground Floor, Bundesstrasse 53, 20146 Hamburg, Hamburg

ReferentIn

Som Kumar Sharma, Space & Atmospheric Sciences Division, Physical Research Laboratory, Ahmedabad, India

Chair


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