Atmospheric boundary layer structure obtained by lidar from years 1997 to 2002 at the observatory for Atmospheric Radiation Research at Sri Samrong, Changwat Sukhothai

Abstract

Atmospheric Boundary Layer (ABL) is the lowest atmospheric layer of great concern to all of human being activity. Especially, top of ABL is very important to estimate precipitable water vapor content and cloud circulation. Since ABL structure rapidly varies spatially and temporaly, continuously observation instrument such as lidar is extremely useful for monitoring ABL structure. Lidar is an active remote sensing instrument that emits laser beam to the atmosphere and receive backscattering signals from atmospheric particles which enable us to evaluated atmospheric particle concentration and the altitude. High backscattering signal layer has been defined as the ABL because of higher aerosol and water vapor concentration than atmospheric layer above. The objective of this study is to monitor ABL structure with particular interest on ABL top height, ABL diurnal variation and related factors for ABL variation. We used lidar data observed at the Observatory for Atmospheric Radiation Research at SriSamrong, Sukhothai, Thailand together with other reference data also observed in the same area. The data analysis has been done in two ways, one is to overview monthly lidar data to see ABL variation throughout the year and the other to combine lidar data with surface meteorological and radiosonde data. As a result, ABL could be divided into three periods, namely, Period A,B and C. Period A is in cold season, ABL depth varies in accordance with subsidence of air mass from ridge of high pressure that moves to cover the study area. ABL top height is almost constant at about 2 km. For Period B, ABL varies due to the influence of high surface temperature and lateral wind. ABL top height varies from 2.5 km in earier part of this period to 4.5 km in later part of this period. Aerosol concentration in ABL is high in these two periods. For Period C, ABL may be identified at the cloud base which continuously increases from morning to next day morning and a new ABL appears at surface. Aerosol concentration is very low in this period probably due to the influence of south-west monsoon.