Clearing of 19 July (0800Z to 1000Z) and Catalina Eddy Development Jodi Beattie

Coast and ship track Time period of clearing

Motivation Image seen An eddy does appear with-in 6hrs of us leaving the area.

Requirements for Eddy Formation Offshore Northerlies Along shore Southerlies Amplifying subtropical ridge moving closer toward coast 500mb trough Though not crucial for formation Coastal Mountains appear to be the initiating mechanism They create a lee trough forms a low that helps reverse the along coast pressure gradient, forcing the southerly flow. This area is slightly warmer and drier due to subsidence.

Results from SAIL data as we sailed from marine stratus to clear skies Wind speed drops 7m/s Pressure drops ~1.5mb Supports idea of lee troughing T and Td increase (RH decreases) Also supports lee troughing Long wave Radiation decreases Proving it is becoming clear Paper has these figures attached, not here for brevity.

Goleta, CA Profiler Shows the vertical profile of winds and temperature (note time from right to left) Concentrate on 700m+ winds want them from the north in order to establish the lee trough

020718 profiler Here we see the MBL is diurnal and quite high in the am local time See northerlies establish, 700-1500m layer…looking at weak low winds…ideal

020719 profiler See Northerlies continure into the 19th until about 0500-0600 (2100-2200 local) Still thru the 700-1500m layer Again can see diurnal fluctuations of the MBL

Development of the Eddy Satellite images used See clear skies we experienced turn into region of eddy development (arrow is where we were at the time) Observe offshore winds from NNW to WNW and along coast winds from SSE Notice the cyclonic rotation of the eddy

Surface Wind Analysis See the winds, NW offshore and S alongshore, with vectors Look near Goleta/Santa Barbara see cyclonic circulation Note: doesn’t move SW like eddy Winds near Goleta agree with profiler

Conclusions The clearing we experienced was the pre-cursor to the eddy It was a typical Catalina Eddy If our transit had been a few hours later we could have gone right into the eddy

Questions