## 2 Materials and Methods
### Introduction of Data Processing Methods
#### 2.2.2 Atmospheric Parameters  
To better understand the atmospheric characteristics of the Tibetan Plateau during the EAWM, especially in the precipitation (snow) environment, two types of parameters need to be considered. One is the direct product of the MWR, which mainly includes the vertical structure of atmospheric temperature, humidity, and water vapour density, and inverse products such as precipitable water. The other is the instability indices related to atmospheric thermodynamics, which can be used to investigate atmospheric dynamics and precipitation processes. Precipitable water can be quantified by precipitable water vapour (_PWV_) and liquid water content (_LWC_). _PWV_, also known as atmospheric water vapour content, represents the amount of precipitation formed by the condensation of water vapour in the whole atmosphere to the ground per unit area. Cloud liquid water content refers to the integral liquid water content from the cloud bottom to the cloud top.  
The stability and convection indices mainly contain the downdraft and standard convective available potential energy (_CAPE_), convective inhibition (_CIN_), and maximum vertical velocity (_MVV_). When the air mass near the ground rises along the insulation line due to vertical wind shear disturbance or terrain, the energy obtained by gas inclusions from the surrounding environment can be represented by the _CAPE_ value. _CAPE_ is the buoyancy potential energy, which represents the energy of the air in the surface boundary layer and is an important indicator to evaluate whether the vertical atmosphere is stable and whether convection easily develops. Downdraft _CAPE_ (_DCAPE_) denotes the maximum energy available in the downdraft process. _CIN_ represents the energy that prevents gas from rising from the ground to the level of free convection. _MVV_ refers to the maximum vertical velocity of the updraft that may produce convection. These stability and convection indices can be defined as follows [32].  
\[CAPE=R_{d}\int\limits_{P_{LC}}^{P_{L}}\left(T_{vp}-T_{ve}\right)d\left(\ln \frac{1000}{P}\right) \tag{3}\]  
\[DCAPE=R_{d}\int\limits_{P_{0}}^{P_{D}}\left(T_{vp}-T_{wb}\right)d\left(\ln \frac{1000}{P}\right) \tag{4}\]  
\[CIN=R_{d}\int\limits_{P_{0}}^{P_{LC}}\left(T_{vp}-T_{ve}\right)d\left(\ln \frac{1000}{P}\right) \tag{5}\]  
\[MVV=\sqrt{2(CAPE-CIN)} \tag{6}\]  
where \(R_{d}\) denotes the specific gas constant of dry air and can be taken as 287.05 J/(kg.K). \(T_{vp}\), \(T_{ve}\) and \(T_{wb}\) denote the virtual temperature of an air parcel, ambient environmental temperature, and wet-bulb temperature, respectively. \(P_{LFE}\), \(P_{EL}\), \(P_{D}\) and \(P_{0}\) denote atmospheric pressure at the level of free convection (_LFC_), equilibrium level (_EL_), depth of downdraft, and near-ground level, respectively. \(P\) denotes the specific pressure. All parcel heightsand stability indices can be calculated through skew T-log diagrams and the Complete Rawinsonde Observation Program [27; 28].  
For sounding observations used for instrument calibration, atmospheric temperature and relative humidity are provided by a sounding balloon twice a day (7:00 and 19:00, UTC+8), and the water vapour density should be calculated by the water vapour pressure atmospheric temperature as follows [33; 34].  
\[e=6.11 RH\exp\left(17.71\frac{T-273.16}{T+29.33}\right) \tag{7}\]  
\[VD=2.167\frac{e}{T} \tag{8}\]  
where \(e\) denotes the water vapour pressure in hPa, \(RH\) denotes relative humidity in %, \(VD\) denotes vapour density in g/m\({}^{3}\) and \(T\) denotes atmospheric temperature in K.