CLOUDSYMP Comparisons of Rainfall and Snowfall Microphysical Characteristics between the Southeastern Tibetan Plateau and Low-Altitude Areas

Climate and weather models are challenged by biases and uncertainties in representing microphysical characteristics of rainfall and snowfall over Tibetan Plateau (TP). The low air pressure and density over the TP may affect the microphysical characteristics of precipitation. In order to bridge the gaps in our understanding of microphysical characteristics of precipitation on the TP, an integrated and systematic measurements are conducted on the southeastern Tibetan Plateau (SETP) during 2022–2023. The major objective of this campaign was to collect cloud microphysical properties including, fall velocity, aspect ratio, and particle size distribution (PSD). PSD on the SETP are studied using a two-dimensional video disdrometer (2DVD), a micro rain radar (MRR) and a microwave radiometer and compared with that in low-altitude areas.

The results show that the particle number concentration of snowfall is less than 10³ mm⁻¹·m⁻³, which is one to two orders of magnitude smaller than that reported in low-altitudes in eastern China. The shape parameter μ is mainly in the range 0–4 and the slope parameter λ is mainly in the range 3–7 mm⁻¹, exceeding the values for eastern China. In heavy snowfall processes (snowfall rate (SR) exceeding 2 mm/h), the collision-coalescence process between snowfall particles is enhanced, and the number concentration of small particles decreases with SR, whereas that of large particles increases. A negative correlation was observed between the aspect ratio and the diameter of snowfall particles.

The falling speed of raindrops on the SETP is higher than that in low-altitude areas. Under different rainfall rate categories, the number concentration and the maximum diameter of raindrops on the SETP are smaller than those in low-altitude region. The convective rainfall on the SETP is more maritime-like because the South Asian summer monsoon brings water vapor from the ocean here. The number concentrations of small raindrops for stratiform and convective rainfall on the SETP are higher than those in low-altitude areas. Compared with stratiform and convective rainfall in low-altitude regions of China, the mass-weighted mean diameters (Dm) on the SETP is the smallest. The generalized intercept parameter (Nw) of stratiform rainfall is balanced at a low rainfall rate, while that of convective rainfall is balanced at a high rainfall rate. Furthermore, for a given μ (the shape parameter of Gamma distribution) value, the λ (the slope parameter of Gamma distribution) value on the SETP is the highest.

The microphysical characteristics derived from these analysis will be used to improve the microphysical scheme and evaluate the representation of precipitation in the climate model.