John D'Alessandro - March 19

Convective Meteorology (Mesoscale Dynamics) Seminar

Characterizing the occurrence and spatial heterogeneity of liquid, ice and mixed phase clouds over the Southern Ocean using in situ observations

John D’Alessandro

Friday, March 19^th

3:00pm

Join Google Meet

https://meet.google.com/ksh-txvg-kni

Low level clouds over the Southern Ocean are an essential component controlling the energy budget over the region, having an annual mean spatial fraction around 80%‒90%. Weather and climate models often fail to capture the observed radiative fluxes over the Southern Ocean, in part because they generally produce lower cloud fraction and less supercooled liquid water than observed. However, studies have relied heavily on satellite retrievals due to a lack of in situ measurements in the region.

Recently, the Southern Ocean Clouds, Radiation, Aerosol Transport Experimental Study (SOCRATES) took airborne in situ observations over the Southern Ocean outside of Hobard, Tasmania. A suite of cloud instrumentation was available, of which three probes’ observations were combined to classify each cloud sample as liquid phase, ice phase or mixed phase (liquid and ice particles within the same sample volume). A large frequency of liquid phase samples is observed between -20° and 0°C, consistent with previous satellite observations. A quantitative approach is introduced to discern the spatial heterogeneity of cloud phase, which reveals the liquid phase is the most spatially homogeneous and the mixed phase is the most spatially heterogeneous within boundary layer clouds.

In addition, the vertical structure of boundary layer clouds is examined and compared between single and multi-layered cloud regimes. A strong correlation is found between cloud condensation nuclei and cloud droplet number concentrations at cloud top for single layer cases, suggesting significant cloud droplet nucleation near cloud top.