New posts on TTL cirrus, Southern Ocean clouds, and an Aleutian marine cold air outbreak
Cold air outbreak over the Aleutians at seen in Worldview, 21st October 2014
Where in the world is this stratocumulus deck?
The subtropical deck extends 2000 km from east to west, It looks like it should be lying over the southeastern Pacific (SEP), but this deck extends from 130-160 W, where the average daytime stratocumulus cover is 25% (see below), compared with 50% over the SEP.
Here, we can see a cold air outbreak in this GOES-13 animation, using visible (day) and near-IR (night). This particular event shows offshore flow emerging from the NE US and Eastern Canada on the 6th March. The cold air floods over almost the entire North Atlantic region, eventually passing over the Azores (ARM ENA site, 39N, 28W) on the 8th March. The cold air outbreak is mared by open cellular convection in the low clouds. During the time that the cold air outbreak is over the Azores, the concentration of cloud condensation nuclei drops to lower than 50 /cm3, after the precipitation associated with the low clouds removes particles by coalescence scavenging. The event can also be seen on NASA Worldview.
This video depicts the albedo field from two LES simulations of a ship track. In the upper panel, the background cloud condensation nuclei concentration is approximately 10-15 /cm3, while in the lower panel, it is 100-150 /cm3. The ship track aerosol perturbation applied to the high background aerosol case is 10x as large as the low background aerosol case in order to make a visible signature, as the weaker perturbation used in the low aerosol case has a much weaker impact under conditions of high background aerosol.
Animation courtesy of Andy Berner