White clouds, dirty skies

Today (Sunday June 16) morning was my turn. Birgit invited me to fly with her. Conditions were excellent: high stratocumulus with some holes, almost no wind, no conflict with other aircrafts. Our Romeo-Oscar took off at 09:50 and climbed west of the island to make a sounding. I doubt, whether many Graciosa inhabitants had ever a chance to see the whole island from above. We had :).



Beautiful Graciosa, a home of ENA observatory and today’s clouds above.

On the way up, several interesting things happened. First, we could not notice aerosol in the boundary layer. Second, we passed through a thin stratocumulus deck capped with a weak 1 K inversion and again were in absolutely clean air. However, at ~1600 m and up we reached a second, much stronger (4 K) inversion and haze. The situation was reverse to normal: clear boundary layer and dirty free troposphere! What a chance to get unusual data!
We felt a strong push to do the best: collect as much information as possible to understand this phenomenon.
We started horizontal legs north of the island: probing free troposphere, the strong inversion, and then the weak inversion just above the stratocumulus top to characterize aerosols in various layers above the clouds. Then we let ACTOS to fly through the cloud to measure cloud droplets. Finally, we made several porpoises to study the vertical structure of the cloud deck.
I was a bit anxious, since yesterday one of our two fast temperature senor broke and we had no time to replace it. A failure of the second sensor would be a disaster...
Wen we passed down through the stratocumulus deck we noticed beautiful patterns of cumulus clouds in between the sea surface and stratiform cloud base. Waves at the sea surface suggested wind convergence in the surface layer below the cumulus cloud street. We had to check these clouds! The helicopter was flying just above their tops, sometimes touching them with the landing gear. ACTOS was patiently doing his job inside white cloud blobs.


A cumulus cloud street we sampled. See the sea surface below.

Unfortunately, the tank of Romeo-Oscar has a limited capacity. After a few minutes in clouds we had to come back to GRW. On the way back we collected more aerosol data from cumulus base level. After ACTOS and HELIOS safely landed, I had one second to shot ARM-ENA site from a very short distance. I hope that their remote sensing data will be even more valuable when we support them with our in situ measurements. Remote sensing is always guessing: what could scatter photons which got into the detectors? With in-stitu data from ACTOS there is no need to guess. We provide real information about scattering particles, crucial to check and calibrate lidars and radars there.


ENA ARM site shot just before landing.

On ground I found that our temperature sensor made a great job. We have to analyze the data and share our results. No excuse!



Mysterious Romeo-Oscar together with ACTOS on ground.

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