Lake breeze characteristics and high-resolution cloud products retrieved by wind profile radar in Nam Co, TP

Lake breeze systems can contribute substantially to the local climatic and hydrological variability by altering atmospheric boundary layer processes, such as the advection and convection of air flow, exchanges of turbulent latent and sensible heat fluxes, and the spatial heterogeneity of clouds and precipitation formation. However, the limited in situ measurements and the low spatiotemporal resolution of satellite products and reanalysis data has hindered our comprehensive and complete assessment of local atmospheric recirculation flows (i.e. lake breeze) over lake basins of the Tibetan Plateau. Here, based on the high-resolution wind profile radar measurements at Nam Co Station for one year (2022.6-2023.5), we analyzed the characteristics of lake breeze and clouds, and evaluated four popular reanalysis wind products (ERA5, MERRA-2, CSFv2, JRA55). The results showed that (1) The lake breeze had annual occurrence frequency of 29%, annual mean speed of 3.6 m/s, average onset 2-5 h after sunrise, annual mean duration of 4.8 h, and average vertical development height ranging from 300 m to 600 m. The lake breeze developed vigorously when the background wind was less than 6 m/s. Increased frequency, earlier onset time, and longer duration during May-September indicated lake breeze evident seasonal variation. (2) The diurnal variation of cloud frequency fluctuated around 0.5 from May-September, and the cloud frequency at night was higher than that during the day from October to April. (3) The wind direction deviation of 550hPa reanalysis data was large (RMSE > 60°, MAE: 43-48°), the wind field of 500hPa and above were in good agreement with the radar, and ERA5 had superiority.

Keywords: Tibetan Plateau, Nam Co, lake breeze, cloud base height, reanalysis data evaluation.