1 research outputs found
In situ observations of wintertime lowâaltitude clouds over the Southern Ocean
<div>Cloud droplet concentration (Nd), effective radius (reff) and liquid water content (LWC) measured by a DMT CAPS and an SEA WCMâ2000 of wintertime lowâaltitude clouds over the Southern Ocean (SO) are presented for 20 flights taken over 3 years (JuneâOctober, 2013â2015). Such clouds have been reported to have the lowest Nd on record (10â40 cmâ3) from the Southern Ocean Cloud Experiment (SOCEX I) field campaign in 1993. Of the total 20 357 oneâsecond records spent in cloud, 38.5% were found to contain ice crystals, primarily in mixedâphase clouds (36.7%). Ice was observed at some point during 19 of the 20 missions. The droplet spectra and temperature range suggest these clouds were often ideal for the HallettâMossop ice multiplication process.</div><div><br></div><div>The average Nd and reff for liquid clouds were 28 (±30) cmâ3 and 12.5 (±2.9) ”m, which are consistent with those from SOCEX I. Fortyânine percent of all liquid cloud samples were observed to be drizzling with an average drizzle rate of 0.733 mm hâ1. As drizzle samples were commonly in the neighbourhood of mixedâphase or nonâdrizzling clouds, it was rare to observe solid patches of drizzle of greater than 10 s. On average, drizzling clouds had lower Nd and greater reff and LWC than those of nonâdrizzling clouds. Distinct observations of nonâdrizzling clouds with relatively high Nd (âŒ89 cmâ3), small reff (âŒ8.5 ”m) and low LWC (âŒ0.173 g kgâ1) were noted for two flights. An initial examination of the local environment and synoptic meteorology for these flights failed to identify any particular forcing that may have led to these unique microphysical properties, although these were the only observations of closed mesoscale cellular convection. This research highlights that greater variability exists in the microphysics of wintertime clouds over the SO, when a wider range of synoptic meteorology is investigated.</div