SUMMARY OF COAST FLIGHTS 14 and 15

Date: Wed, 25 Jul 2001 10:53:05 -0400
From: John Bane
Subject: COAST Flight Report - July 23 and 24

COAST Flight 14 was flown on July 23, 2001. This flight was to be the third in a time series of flights that would capture the system as it shifted from a period of weak and southerly winds to northerly winds. Throughout the morning we looked at satellite cloud imagery to determine if the rather extensive fog would clear enough to allow us to see the ocean surface well enough to make AXBT drops. We departed Corvallis about 1pm and transited to the southern portion of the Big Box, as the coast was clearing slightly there. We had hoped we might be able to fly under a low stratus cloud layer, if it still persisted. Upon reaching Line 8 we descended to 500 feet, but we were still in the cloud/fog layer and unable to see the surface. We flew above the shallow cloud layer to the North Bend airport and landed, where we waited about two hours to see if the fog would abate. Upon our departure at about 3:30 we saw no change to the extensive cloud/fog coverage, so we returned to Corvallis.

COAST Flight 15 was flown the next day, July 24. This time we were successful in covering the Big Box. The morning cloud/fog layer on this day did disappear over the region by early afternoon, allowing us to fly the planned survey. This provided the third realization in this time series [July 18 (weak winds), July 21 (moderate northerly winds), and July 24 (strong northerly winds)].

Measurements were made of: SST, subsurface ocean temperature, and upper-ocean color; atmospheric temperature, humidity and horizontal winds. Data were collected on all eight Big Box Lines, flying from south to north.

AXBTs were deployed as follows:

Line 2: 6 AXBTs
Line 4: 6 AXBTs
Line 6: 7 AXBTs
Line 8: 6 AXBTs

Vertical sections of meteorological variables were measured on lines 1, 3, 5 and 7, extending from 60 m to 1,000 m altitude. There was a well-defined temperature inversion at around 400 m, sloping upward toward the west. Winds were strong and northerly, with a jet structure seen at most locations in the marine layer. Peak winds were above the ocean surface, typically at around 200-400 m height, and maximum wind speeds were around 35 to 40 knots. A N-S gradient in wind speed was observed, wiht generally weaker winds in the north.

The SST field showed a change from the flight on July 21, with a more extensive cool water region along the coast. Some BT profiles showed the thermocline to be quite sharp, but the spatial distribution of this was not clear during the flight. It may be that the cases we saw of strong dT/dz were due to various BTs profiling through internal wave crests.

(Disclaimer - These descriptions are from looking at computer graphical displays while aboard the aircraft, and closer inspection of post-flight data products will provide more accurate conclusions, some of which may differ from statements here.)

Data products will be available from http://www.marine.unc.edu/cool/COAST or they may be retrieved from the real-time results or 4-days-plus results areas. All of these are buttons off of the main COAST site.

Submitted by:
John Bane
July 25, 2001