Remote-sensing Of Atmospheric Temperature And Humidity Profiles Based On Microwave Radiometer In Semi-Arid Area Of Northwest China

Using the data of air sounding over Yuzhong station (52983), in Gansu Province from2004to2013and the microwave radiometer measured at the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL) from2007to2013, the characteristics of temperature, Relative Humidity (RH), water vapor mixing ratio, vapor density and liquid water content vertical distribution and diurnal variation were analyzed. Then, the comparison between the retrieval data and sounding detections was made and the effects of height, seasons and weather conditions were discussed. Then the temperature profile correction of retrieval was given. In addition, the vertical distribution and temporal evolvement characteristics of temperature, relative humidity, water vapor mixing ratio, vapor density and liquid water content were analyzed in a precipitation process and a sand-dust weather process. The main conclusions are as follows:(1) The temperature lapse rate at20:00was slightly larger than at8:00. The temperature inversion was strongest in winter and weakest in summer. The diurnal range showed a reducing tendency with height. The shape of diurnal temperature variation curves was "U" type from2to6.5km and inverted "U" type above8km.The retrieval temperature from the microwave radiometer observations had a similar tendency with the air sounding data below7km. The retrieval effect of microwave radiometer was better in summer and autumn. The retrieval results at14:00were reliable. The effect of temperature profile correction was significant.(2) The maximum RH of sounding data appeared on the surface at08:00and approximately1.5km at20:00. While the high value zone of the retrieval RH generally appeared approximately4.75km. The water vapor mixing ratio and vapor density also showed a reducing tendency with height. Liquid water content first increased and then decreased with height. Water vapor mixing ratio, vapor density and liquid water were all biggest in summer and least in winter. The RH had an opposite trend with temperature and the diurnal range reached10%at4.5km. The diurnal variation of water vapor density and liquid water content delayed1-2h.The liquid water content fluctuated above3km. The retrieval RH from the microwave radiometer observations had a similar tendency with the air sounding data below2.5km and the bias was less than10%. Compared with temperature, the retrieval RH had a large deviation and poor correlation.(3) In the precipitation process, the temperature near the surface had been decreasing approximately12.0K. The temperature was higher in the precipitation process than before and after precipitation above4km. The RH maintained a high value in the whole layer. The water vapor mixing ratio reached a maximum value before precipitation. The continuous time of high value zone contained the whole ground rainfall duration and after4hours. Vertical thickness of liquid water content accumulation zone extending to the ground was more consistent with the time duration of precipitation. During the precipitation process, the integrated liquid water content began to increase rapidly in half an hour. While at the end of precipitation, there would be a significant reduction. High values area of integrated water vapor content and integrated liquid water content had a good consistency with the ground precipitation duration.(4) Before the sandstorm occurred, the temperature in low layer increased significantly and the temperature lapse rate was large. Atmospheric water vapor was low; the RH was less than30%; the water vapor mixing ratio was less than2g·kg-1; the water vapor density was less than2.5g·m-3and the liquid water content was less than0.02g·m-3. In high layer, the temperature drastically decreased with low atmospheric moisture as well. The weather condition with warm and dry air in low layer and cold and dry in high layer provided advantages for the occurrence of this sand-dust weather process. During the process, the temperature near the surface decreased first and then increased; the water vapor content was slightly larger than before; the integrated water vapor content was less than lcm.