Analysis And Comparison Of Cloud And Weather Radar Data

According to satellite observations and surface observations from the International Satellite Cloud Climatology Program(ISCCP),different shapes and scales of clouds filling the global air cover more than 60% of the sky.The researches on the macro-micro spatial and temporal characteristics of clouds and their effects on weather and climate have been the hot topic and focus of meteorology and atmospheric science.The cloud mainly affects the radiation budget of the earth-atmosphere system by reflecting the solar radiation and absorbing the earth's infrared radiation,hence radiative heating / cooling caused by the vertical distribution of single-layer or multi-layer clouds has important influences on the aerodynamics,thermodynamics and water circulation.In recent years,researches on cloud-aerosol-radiation interaction,remote sensing inversion of cloud parameters and parameterization of cloud radiation properties have been deepened.At present,the main means of cloud macro and micro parameters detection are airborne instruments,microwave radiometers,microwave radar,satellite passive and remote sensing inversion,ceilometers and radiosonde.Millimeter-wave radar is more sensitive to cloud particles and has higher spatial resolution and penetrating ability than the infrared and visible light detection instruments;therefore it is suitable for detecting non-precipitation clouds.Radiosonde is one of the most important means of meteorological observation.It can obtain the vertical distribution of temperature,humidity,air pressure,wind direction and wind velocity from the ground to ~ 30 km altitude.Clouds generally correspond to high atmospheric relative humidity,so relative humidity profiles can be used for cloud detection.The zero degree bright band refers to the phenomenon where radar reflectivity sharply increases,due to particles above the zero degree layer falling into and down the layer,with snowflake and ice crystal particles melting and thus covering the radar surface with water film.It affects the quality control of radar data,and causes the overestimation of precipitation nearby and the underestimation of ice crystals and snowflakes above the bright band.Weather radar is mainly used to monitor rainstorm,tropical cyclone and convective weather.The observation products provide guarantee for flood prevention,disaster reduction and important social activities' decision.The millimeter wave cloud radr and centimetre wave weather radar can both detect the bright bands of the precipitation in stratiform clouds by using the "reflectivity vertical profile method",which is prepared for the correction of the bright band.In this dissertation,a comprehensive observation and analysis is conducted on the macro parameters of clouds and the features of the bright band during stratiform cloud precipitation.The clouds detection capability of 8mm cloud radar and other observing devices is compared and analyzed.The observation data(8mm cloud radar and radiosonde)was conducted by the Institute of Atmospheric Physics,Chinese Academy of Sciences in Baochang Town,Taipusi Qi,Xilin Gol League,and Inner Mongolia Autonomous Region from July 17 to August 10,2013.Another set of the observation data(8mm cloud radar and C-band weather radar)was conducted by the College of Electronic Engineering,Chengdu University of Information Technology in Nyingchi,Tibet Autonomous Region from July to August,2015.By using these two sets of data,analyzing the cloud top and bottom heights(CTH and CBH)in summer in Inner Mongolia,summarizing a credibility criterion for identifying cloud boundaries(expressed as CBH and CTH)by 8mm cloud radar,analyzing the features of the bright band in stratiform cloud precipitation in summer in Nyingchi,Tibetan Plateau,verifying that C-band weather radar and 8mm cloud radar can both detect bright band.The main conclusions are as followings:(1)8mm cloud radar?s reflectivity can be directly obtained CBH and CTH,non-meteorological echo and other clutter can be removed by linear depolarization ratio(LDR).In general,CBH and CTH got by 8mm cloud radar and radiosonde match well,both the deviations are about 300 m.(2)Cloud boundary deviations from 8mm cloud radar and radiaosonde include the influence of "dry layer" below the cloud bottom which is caused by dry air from the northwest,the horizontal drift of the radiosonde sounding balloon,the detection error of the radiosonde humidity sensors caused by increasing height.(3)By calculating and comparing the temporal and spatial change rates of reflectivity at cloud bottom and top,a credibility criterion for identifying cloud boundaries by 8mm cloud radar is summarized.(4)The echo of C-band weather radar in Nyingchi area is seriously obscured,but the average reflectivity vertical profile of all unobstructed sectors in all elevation layers can still be used to identify the bright band in stratiform cloud precipitation.(5)The ?Vertical Profile of Reflectivity Method? is also suitable for 8mm cloud radar,which can identify the bright band in Nyingchi area.(6)The heights of top,bottom and peak value of reflectivity in bright bands identified by 8mm cloud radar are 120.5m,108 m and 80.5m lower than those identified by C-band weather radar.