## 2 Materials and Methods  
### Experiment, Instrument, and Measurements  
In the summer of 2013, the Chinese Academy of Meteorological Sciences (CAMS) and several other research institutes launched the TIPEX-III experiment, which is the newest and largest meteorological experiment on the TP, with a duration of ten years. One purpose of this experiment is to use multi-wavelength radars, microwave radiometers, disdometers, and other ground-based equipment to construct a three-dimensional observation system for clouds and precipitation. The first-stage mission of this experiment was achieved in the summers of 2014 and 2015 [28]. The primary instrument is a vertically pointing millimeter-wave cloud radar, deployed at Naqu in the Tibet autonomous region (latitude: 32\({}^{\circ}\)19\({}^{\prime}\) N; longitude: 92\({}^{\circ}\)04\({}^{\prime}\) E; altitude: 4507 m), to detect the vertical profiles of clouds and weak precipitation. This radar was developed by CAMS and the 23 rd Institute of China Aerospace Science and Technology Corporation. To better adapt to the hostile environment of the plateau and to ensure a long-term operating capacity, the radar uses a solid-state transmitter and is equipped with an independent container. The radar operates at 33.44 GHz (a wavelength of 8.9 mm) with a peak power of over 100 W. The primary aim of using the Ka-band is to obtain as much backscattered energy as possible under the Rayleigh scattering mechanism, while reducing the attenuation effects of air and precipitation particles. A 2-m-diameter Cassegrain antenna was used to achieve a 53-dB gain and to form a 0.3-degree beamwidth, so that the radar's horizontal resolution is only 26 m at 5 km (above ground level (AGL)). The transmitted pulse width is 0.2 us, corresponding to a vertical resolution of 30 m. Thus, the radar can provide fine-resolution mapping of cloud structures and boundaries. The radar measurements include the initial Doppler spectrum, reflectivity (Z, dBZ), mean Doppler velocity (MV, m\(\cdot\)s\({}^{-1}\)), spectrum width (\(\sigma_{\rm v}\), m\(\cdot\)s\({}^{-1}\)), linear depolarization ratio (LDR, dB), skewness (S\({}_{\rm k}\), unitless), and kurtosis (K\({}_{\rm t}\), unitless). For the Doppler spectrum, a positive velocity represents downward motion of the targets (toward to radar antenna), and negative velocity means upward motion of targets (away from radar antenna). However, for MV and retrieval of vertical air velocity (\(\omega\), m\(\cdot\)s\({}^{-1}\)), the signs are opposite. The major technical and operational parameters of the radar are summarized in Table 1.  
For the radar system, the key performance indicators, such as its sensitivity, detectable range, unambiguous velocity, and velocity resolution, are a compromise. So, to meet the requirements for cloud and precipitation observation over the TP at different heights and with different intensities, three operational modes were designed for this radar: the boundary mode (BL), the cirrus mode (CI), and the precipitation mode (PR). The three modes were configured with different pulse widths and coherent and incoherent integration numbers. BL and PR are used mainly to observe clouds and light precipitation in the low and middle levels. Short pulses ensure a small blind range for both modes, while the minimum detectable reflectivity is relatively large. The major difference between BL and PR is that the BL mode performs four times more coherent integrations, which reduce the minimum detectable reflectivity by 6 dB, decrease the Nyquist velocity by a factor of 4, and increase the velocity resolution by a factor of 4. CI is used for cloud detection in the middle and upper levels, where clouds are characterized by high altitude and small or moderate reflectivity and vertical motion. For this purpose, pulse compression (with a wide pulse of 12 us) and twice as much coherent integration are used to decrease the minimum detectable reflectivity by 20 dB.