An observational study of diurnal and seasonal variations, and macroscopic and microphysical properties of clouds and precipitation over Mount Lu, Jiangxi, China

The Mount Lu (Lushan) observational station of clouds and fog was restarted in 2015. Characteristics of clouds and precipitation are investigated based on observations collected at Mount Lu station from November 2015 to February 2018, including microphysics properties of clouds/fog and precipitation of 15 months in cold and warm seasons. Statistical results suggest that heavy precipitation over the Mount Lu is frequent in summer with maximal daily precipitation exceeding 100 mm. Clouds and fog occur frequently in autumn, winter and spring. The maximum number of clouds and fog reaches 25 days per month with the lowest visibility of about 20 m. Affected by radiative effects of clouds and fog in the morning, the minimum temperature in the diurnal variation of temperature occurs at about 09:00 (local sun time), right before the dissipation of clouds and fog. Based on analysis of radar data, stratiform precipitation, stratiform precipitation with embedded convection and convective precipitation account for 29%, 44% and 27% of the total precipitation in the autumn and winter, respectively; convective precipitation and stratiform precipitation with embedded convection account for 83% and 17% of the total precipitation in the spring and summer, respectively. Compared with precipitation in urban areas, more small and medium size raindrops are found for precipitation over Mount Lu. Compared with that in urban areas, clouds and fog over Mount Lu are characterized by smaller number concentration, more significant bimodal feature and wider spectra. As the precipitation within clouds increases, both the number concentration and the size of raindrops increase, which makes it easier to initiate the collision and aggregation process, leading to reduction in cloud droplets smaller than 11 μm and larger than 30 μm. As a result, the peak at 11 μm becomes more significant. During snowing period, small cloud droplets are abundant, and the solid-phase precipitation consumes large freezing cloud droplets through the riming process.