POC formation SSW of Tasmania

We have a nice case of pocket of open cell formation today SSW of Tasmania. Helpfully (and somewhat atypically), this transition occurs during daylight hours, meaning we should be able to get quality microphysical retrievals for this case. The morning Terra pass has no sign of a disturbance, while the afternoon Aqua pass has a small but well defined POC. It should be possible to use cases like this to observationally constrain the threshold for transition from closed to open cells.

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Distinguishing clouds over ice surfaces

The MODIS channel 3-6-7 blend available on Worldview is very effective at distinguishing clouds over ice surfaces. In this Worldview scene near Antarctica (1st Feb 2013; 73S, 103W), in the MODIS 3-6-7 channel blend (image below), one can see open ocean (black), surface sea/land ice (red), and clouds overlying them both (whiter hues). In visible imagery (image at bottom), it is often difficult to distinguish between clouds and sea ice. It is interesting that some of these clouds are so optically thin that one can see the outline of the ice edge through them.

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Clouds looking for a model to host them

Worldview shows the Southern Ocean clouds that climate models struggle and strive to represent. Almost exclusively found poleward of the storm track, these extensive layer clouds are constructed from multiple and single layers, frequently decoupled from the surface. Surprisingly, sometimes convection seems to be present, making one wonder whether the layers may sometimes be fed by cumulus detrainment. Much of their optical thickness appears to be attributable to supercooled liquid water.

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In Worldview’s 3-6-7 channel blend (primarily indicating microphysical differences), the convective elements can be seen in orange/red, penetrating the yellow/whiter stratiform layers:

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Martian cloudscape over the Southern Ocean

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It looks like Mars, but this surface is the top of layer clouds over the Southern Ocean (Southern Pacific sector, 69S, 150W) as seen by MODIS in Worldview. There is great variability in the cloud heights across this scene (mostly shallow and mid-topped, with some high clouds). This is clearly seen in the variability in MODIS-derived cloud top temperature.

And here is the scene in MODIS channels 3-6-7:

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This is a location where CALIPSO indicates clouds with tops at multiple levels:

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CALIOP 532 nm backscatter. Region corresponding to MODIS image at far left (65-70S)

Plume to POC in the Southern Ocean: Island effects and ACI?

A plume of thicker cloud, originating near the South Orkney Islands, transitions to a pocket of open cells (located at -54.0 N, -43.386 E), presumably following drizzle-induced aerosol scavenging and dynamical transition. The image was taken around 1230 UTC, May 17, 2014
A plume of thick cloud, originating near the South Orkney Islands, transitions to a pocket of open cells (located at -54.0 N, -43.4 E), presumably following drizzle-induced aerosol scavenging and dynamical transition. The image was taken around 1230 UTC, May 17, 2014

In this case from the Southern Ocean, the 3-6-7 channel image from MODIS on Terra, taken during the day pass on May 17, 2014, clearly shows a plume of thick, closed-cell MSc cloud transitioning to open-cell convection. HYSPLIT trajectories indicate that the flow in the boundary layer during the preceding 24 hours was from the south. What is the source of the mystery plume?

Backing up a day, the Terra pass on May 16 is difficult to interpret, but the Aqua pass is the key to the mystery:

A cloud tail behind Coronation Island under southerly flow on May 16, 2014
A cloud tail behind Coronation Island under southerly flow on May 16, 2014

It seems that under southerly flow, given the background environment, Coronation Island (located at -60.571 N, -45.676 E) generated a cloud tail in the MSc deck with elevated LWP. The trajectory analysis reveals that flow in the boundary layer took roughly 21 hours to advect north to where the distinct change in microphysics and dynamics becomes obvious. This is a unique example of a mechanically forced LWP perturbation in boundary layer cloud driving aerosol-cloud-precipitation feedbacks and triggering a downstream change in boundary layer structure.