A Method for Retrieving Vertical Air Velocities in Convective Clouds over the Tibetan Plateau from TIPEX-III Cloud Radar Doppler Spectra  
[PERSON]  
1 Plateau Atmosphere and Environment Key Laboratory of Sichuan Province, School of Atmospheric Sciences, Chengdu University of Information Technology, Chengdu 610225, China; [EMAIL_ADDRESS] (J.Z. ); [EMAIL_ADDRESS] (K.Z. ); [EMAIL_ADDRESS] (B.W) 1  
[PERSON]  
2 State Key Lab of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing 100081, China 2  
weather prediction models. As a kinetic factor, vertical air motion plays an important role during the formation and evolution of convective cloud processes. However, due to the rapid change and complicated dynamic structure of convective clouds, accurate and high-resolution measurements of vertical air velocity obtained by remote sensing equipment are still lacking and challenging to apply. Moreover, convective clouds over the TP have certain characteristics, such as ice phases, weaker intensities, smaller scales, and shorter life cycles, which will worsen the retrieval difficulty: In meteorological research, retrieval of vertical air velocity would help us to better understand the dynamical processes of clouds during their lifetimes, and it would promote the parameterization of physical mechanisms within models at many scales. Millimeter-wave Doppler radar (generally dubbed \"cloud radar\") has been extensively developed over the last 20 years, becoming a major tool for the observation of clouds and light precipitation because of its high sensitivity and resolution. Cloud radars operate mainly in the Ka-band (\(\sim\)35 GHz, with a wavelength of 8 mm) and W-band (\(\sim\)94 GHz, with a wavelength of 3 mm), and their excellent performance in cloud detection has been demonstrated by many studies [12; 13; 14; 15; 16]. When an antenna is pointed vertically, cloud radar can measure the vertical motions of cloud particles in the atmosphere. However, the returned Doppler velocities consist of both particle terminal velocities and air motions [17]. Moreover, for convective clouds, radar-measured Doppler velocities can be influenced by small-scale turbulence and wind shear within the sampling volume [18]. Thus, the deviation of the vertical air velocity in convective clouds from oriented cloud radar measurements is difficult. In several early studies, meteorologists tried to establish an explicit relationship between radar reflectivity (\(Z\)) and mean fall velocity of particles (\(V_{t}\)) in quiet air, because both \(Z\) and \(V_{t}\) are proportional to hydrometeor diameter (D). The relationship was produced by theoretical derivations and practical observations [19; 20; 21; 22]. Using this relationship, vertical air velocity can be deduced by subtracting \(V_{t}\) estimated by radar-measured \(Z\) from the radar-measured mean Doppler velocity. However, the prerequisites of this method are knowledge of the particle size distribution and an accurate \(V_{T}-D\) equation, which are complicated and currently undefined for convective ice clouds. For a received radar signal, the Fast Fourier Transform, or other spectrum analysis algorithms, can be utilized to obtain the cloud radar Doppler spectra, which contain a wealth of information about cloud properties, vertical air motion, and turbulence. Under specific sets of conditions, cloud radar spectra can provide more reliable source data for the retrieval of vertical air velocity. During strong precipitation, W-band cloud radar will suffer from Mie scattering owing to its very short wavelength, and the signature of the observed spectra (modulated by the backscattering function that oscillates between fixed maxima and minima in the Mie regime) can be used as a reference point to retrieve the air velocity. This processing methodology was first mentioned by [PERSON], and it has been verified and applied by [PERSON] to derive the updrafts and downdrafts in strong convective precipitation [18; 23].