Using observations from the ARM Eastern North Atlantic (ENA) site in the Azores, we find that clouds in the post-cold frontal regions display sensitivities to large-scale drivers such as surface winds, subsidence strength, inversion strength or environmental moisture, similarly to clouds in more quiescent conditions. However, the extratropical cyclones produce a dynamically active environment that causes clouds to be thicker and higher than their quiescent counterparts. Cloud base and top heights and temperatures show a strong correlation with the strength of the cold air advection, measured with the Marine Cold Air Outbreak parameter M, because of a strong sensitivity to both air-sea contrast in temperature, and inversion strength.
In order to generalize these results to the midlatitudes overall, we will present a similar analysis based on southern ocean observations. The site is located on Macquarie Island, around 50°S, an area where extratropical cyclones are ubiquitous. At this location, the storms are stronger, but the environmental moisture and temperature lower. Consequently, the clouds in post-cold frontal regions are colder than at the ENA site, while being supercooled a lot of the time.
We will discuss the implications for their representation in general circulation models.