MMCR-based characteristic properties of non-precipitating cloud liquid droplets at Naqu site over Tibetan Plateau in July 2014

Abstract

Microphysical properties of low level liquid clouds at the Naqu site over the Tibetan Plateau (TP) are characterized using empirical regression algorithms based on ground-based millimeter cloud radar (MMCR) boundary mode observations in July 6–31, 2014. Monthly averaged temperature profiles measured over the Naqu site by radiosondes at Beijing local time 8:00 and 20:00 and diurnal variation of microwave radiometer (MWR) temperature profiles indicate a 0°C layer above 1.2km. Only clouds below 1.2km are examined in this study and they are assumed as pure liquid in phase. The parameters used in the regression equations have been scaled based on MWR liquid water path when there are only low non-precipitating liquid clouds and MWR measurements are available. Statistically, the characteristic properties of liquid clouds show a single mode distribution for cloud droplet effective radius (re) with most frequent values around 5–7μm, and for cloud liquid water content (LWC) with most frequent values below 0.2g/m3. The diurnal distribution shows weak variation with slightly low values in the morning and evening time; and the vertical distribution shows increasing cloud droplet re and LWC with height. Especially, cloud droplet re increases from approximately 4–6μm to 8–12μm with height. The monthly mean cloud droplet re and LWC are approximately 5.7μm and 0.07g/m3 in July 2014. The liquid cloud properties characterized here have been shown comparable to those obtained from MODIS satellite observations, which has an average value of 5.1μm for the same observation period.