Preliminary Estimation of Specific Humidity Profiles with Wind Profile Radar

As a new type of detection instrument, wind profile radar (WPR) can detect meteorological factors such as wind profiles, spectral width, and refractive index structure constant and so on. The special detecting ability of WPR decides its broad application in atmospheric science research, meteorological operation application, climate research, aviation security and many other areas. With the advances of detection, a new specific humidity profiles retrieving method with WPR is proposed.Based on the turbulent backscattering theory, the method of estimating specific humidity profiles using boundary layer wind profile radar characteristics of clear-air echoes is devised. A retrieving test of specific humidity profiles are carried out with the data of observational campaign conducted from 15 Aug to 10 Sep in 2011 at a meteorological station of Dali, Yunnan Province, analyzing the main factors of retrieving accuracy. In the low atmosphere the refractive index gradient (M) is mainly influenced by three factors: dq/dz by 80.39%, the atmospheric temperature (T) by 12.75%, and the specific humidity q by 6.86% on average, respectively. Obviously, the dq/dz item is the most important factor, namely, there is a close relationship between the refractive index gradient and specific humidity.It is the measurement of refractive index gradient that turns out to retrieve specific humidity profiles with the help of WPR. The volume reflectivity (η) of turbulence echoes can indicate the fluctuation of atmosphere specific humidity due to the good correlation with M. Another factor that matters is the atmospheric turbulence dissipation rate which is under the influence of the signal spectral width observed by WPR. Radio Acoustic Sounding System (RASS) provides virtual temperature in retrieving of specific humidity profiles with the measurement of acoustic speed; PWV from GPS provides a method to obtain the initial boundary specific humidity; estimation of specific humidity profiles comparing with radiosonde data at the same time is conducted with WPR, RASS and GPS data.Results show that WPR can successfully retrieve specific humidity profiles with a certain degree of error. Among many factors that affect the retrieving accuracy, the determining of the sign of M, the refractive index structure constant and turbulence spectral width plays the key role, while the temperature and pressure are not so important. This new method can retrieve specific humidity profiles simply with the remote sensing instruments. The specific humidity retrieving from WPR, temperature profilers and initial boundary specific humidity from radiosonde shows the same trend comparing with which observed by radiosonde. The mean deviation and standard deviation turns out to be 0.75 g·kg^-1 and 0.8 g·kg^-1 respectively, both showing an increasing trend with height. With the assistance of WPR, GPS/PWV and RASS data, the retrieving mean deviation and standard deviation of specific humidity is 0.64 g·kg^-1 and 0.85 g·kg^-1 comparing with the observation of radiosonde.