Catching the waves at stratocumulus cloud top



We had some nice 'surfing' at the top of a layer of stratocumulus clouds this morning (July 9). Before the flight the kazr radar showed a thin stratocumulus layer with cloud base approximately 900 m, and this layer was just starting to break up when we started. Take off was at approximately 9:30 am. We made a vertical profile to 7000 feet. The profile revealed a strong inversion with a temperature increase of approximately 8 K occurring over less than 100 m. The cloud top was very well defined with isolated regions of nonuniformity where highly dynamic entrainment was taking place.

Here's a nice shot of cloud top as the helicopter flew toward Pico. Good thing I didn't drop my phone while taking this one! But apparently Alwin thought I did, so he opened the door to see if it was sitting on the cloud top!

We continued with a level flight leg with ACTOS inside the cloud. We observed liquid water contents of approximately 0.4 g/m^3. Then we made a level flight leg just above the cloud layer for aerosol measurements. Aerosol flight legs are a good opportunity to see cloud top... and here is a nice shot of the shadow of the helicopter surrounded by a glory.

Now the fun started... we went cloud surfing for the next 45 minutes or so. That consisted of porpoise dive maneuvers, with ACTOS going completely through the cloud layer, from just below cloud base to near the top of the inversion layer. Peak liquid water contents were approximately 0.7 or 0.8 g/m^3 in the thickest clouds. The cloud thickness was highly variable and sometimes there were breaks between the large regions of stratocumulus convection cells. 

In some places the cloud top was incredibly dynamic as the inversion layer was slowly eroded by turbulent entrainment. This video ends with a really nice shot of an evolving Kelvin-Helmholtz billow right next to the helicopter... wow!

On the way back we got a nice view of the ENA ARM site.


Finally, our fun was over, and we performed a final vertical profile, followed by a perfectly smooth ACTOS and helicopter landing at around 11:30 am. Thanks, Juergen and Alwin, for the nice surfing trip! 





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