Microphysical Properties of Generating Cells Over the Southern Ocean: Results From SOCRATES

Abstract

The bulk microphysical properties and number distribution functions (N(D)) of supercooled liquid water (SLW) and ice inside and between ubiquitous generating cells (GCs) observed over the Southern Ocean (SO) during the Southern Ocean Clouds Radiation Aerosol Transport Experimental Study (SOCRATES) measured by in situ cloud probes onboard the NCAR/NSF G‐V aircraft are compared. SLW was detected inside all GCs with an average liquid water content of 0.31 ± 0.19 g m−3, 11% larger than values between GCs. The N(D) of droplets (maximum dimension D < 50 μm) inside and between GCs had only slight differences. For ice particles, on the other hand, the mean concentration (median mass diameter) with D > 200 μm inside GCs was 2.0 ± 3.3 L−1 (323 ± 263 μm), 65% (37%) larger than values outside GCs. As D increases, the percentage differences became larger (up to ~500%). The more and larger ice particles inside GCs suggest the GC updrafts provide a favorable environment for particle growth by deposition and riming and that mixing processes are less efficient at redistributing larger particles. The horizontal scale of observed GCs ranged from 200 to 600 m with a mean of 395 ± 162 m, smaller than GC widths observed in previous studies. This study expands knowledge of the microphysical properties and processes acting in GCs over a wider range of conditions than previously available.

Simulating Observations of Southern Ocean Clouds and Implications for Climate

“…Cloud top was about 1.5 km for the whole layer, and cloud base at 1 km with some precipitation shafts extending lower. The cloud deck was solid on top, but thin with cellular structure (Wang et al, 2020). Figure 4 is a visible wing camera image of the cloud layer at 410 z just before turning north (58 • S), illustrating it was optically thick.…”

Phase Characterization of Cold Sector Southern Ocean Cloud Tops: Results From SOCRATES

“…Wang et al (2020) analyzed in situ measurements of cloud top generating cells during the SOCRATES field campaign and found that all cloud top generating cells sampled had SLW at cloud top even at CTTs as cold as −33°C. The ubiquitous presence of SLW at cloud top found in in situ data from Wang et al (2020) is consistent with the remote sensing results herein. Optically thick clouds fully attenuate the HSRL signal limiting phase retrievals beneath cloud top on the high-altitude flight legs, but the retrieval algorithm developed herein allowed for identification of CTP.…”

“…The RICE was also used to identify when SLW was present based on voltage changes. Periods with a voltage change of at least 2 mV s −1 indicated the presence of SLW (Cober et al, 2001; McFarquhar et al, 2013; Wang et al, 2020). Cloud liquid water measurements were made at a rate of 1 Hz and were linearly interpolated to 2 Hz to assign liquid water measurements to each column.…”

“…The differences between the HSRL beam and the HCR beam for a flight altitude of 5.5 km was 70 m 1 km below the GV, 245 m 3.5 km below the GV (boundary layer cloud top at 2 km), and 385 m 5.5 km (the ocean surface) below the GV (Schwartz et al, 2019). The average width of a cloud top generating cell sampled over the SO was 395 ± 162 m (Wang et al, 2020). If cloud top height in the lower boundary layer was ~2 km, for example, different parts of cloud top could be sampled simultaneously by the HCR and HSRL.…”

“…During SOCRATES, clouds most frequently had liquid-bearing cloud tops. Wang et al (2020) analyzed in situ measurements of cloud top generating cells during the SOCRATES field campaign and found that all cloud top generating cells sampled had SLW at cloud top even at CTTs as cold as −33°C. The ubiquitous presence of SLW at cloud top found in in situ data from Wang et al (2020) is consistent with the remote sensing results herein.…”