A Rayleigh lidar study of the atmospheric temperature structure over Mt. Abu, India

Abstract

A Nd-YAG laser based Rayleigh Lidar was set up at Guru Shikhar, Mount Abu (24.5° N, 72.7° E, altitude 1.7 km) by the Physical Research Laboratory to study the temperature structure in the altitude region of 30-75 km at tropical latitudes. Temperature profiles are derived from relative density measurements, following the method described by Hauchecorne & Channin (1980). Photon counts are averaged over one hour (2 hour during the later phase) in time and 480 m in altitude. Measurements were made for about 5 nights of each month around new moon except the monsoon season (June-August). Temperature profiles obtained on 109 nights during the period November 1997 to November 2001 are used to derive average temperature profile for each month (September to May) and are compared with the CIRA-86 model. Observed temperature profiles are in good agreement with CIRA-86 below 50 km but are higher by up to 10 K above 50 km. The agreement is better during winter months. The temperature profiles are also compared with the equatorial model for the Indian region (Sasi & Sengupta 1979) based on rocket and balloon measurements. Day to day variability is less than ± 5 K for altitudes below 50 km and up to ± 10 K around 70 km. The variability is the least around 40-50 km. The mean values of the stratopause level and temperature are found to be 48 km and 271 K respectively over the measurement site. Seasonal variation of the temperature below 60 km shows equinoctial and summer maxima whereas above 70 km winter maximum with equinoctial minima are seen.