SUMMARY OF COAST FLIGHTS 23-27
We have flown five flights in the past four days as part of the activities concluding the COAST summer field program. Reports for these flights are as follows:
COAST Flight 23 was flown on August 28, 2001. Measurements were made of the structure of the lower 1km of the atmosphere to assess diurnal variations in the atmosphere over the COAST region. The two subsequent flights (24 and 25, see below) were flown in a similar fashion. Measurements during this flight (Flight 23) were made between 1730 and 1915 PDT.
Flight 23 began with a straight and level leg at 150m from 43-35N 124-28W to 44-35N 124-18W. This line parallels the coastline at a distance of about 20 km from shore. We wanted to see if we could detect a systematic increase in the strength of the northerly winds on this line from north to south. We did see a clear change, from about 18 knots near the northern end of this line to about 23 knots in the south.
Line 4 was flown at 150m to measure low-level winds, and six AXBTs were deployed. The line was flown an additional 40km to the west of its normal end point to gather wind data. A vertical E-W section was then flown at the latitude of the Newport NOAA meteorological buoy (the buoy's position is 44-37.3N 124-31.7W, just 3nm south of the Line 4). Three sawtooth cycles were flown from 60m to 1km on this line, extending from about 100 km from shore to close to the coastline. Winds were moderately strong from the north with a jet-like structure, and a well defined atmospheric temperature inversion was seen. Measurements were concluded with a profile up from 60m to 1.5km. Stratus clouds covered much of the area.
COAST Flight 24 was flown on August 29, 2001. Measurements were again made of the structure of the lower 1km of the atmosphere as part of our effort to assess diurnal change. Measurements were made between 0845 and 0950 PDT on the E-W line at 44-37N. (A slight change in the flight line was made because of some military aircraft activity in the Warning Area that this line passes through. The western half of the line was flown on a heading of about 250T instead of 270T to keep clear of this area.) No AXBTs were deployed.
Three sawtooth cycles from 60m to 1km were made heading offshore on this line, and a level line at 60m was flown on the return to shore. Winds were seen to be moderate and from the north, and a marine layer inversion and wind jet were observed. Stratus clouds covered the entire line, with very low ceilings (ca. 50m) near the shoreward end of the line.
COAST Flight 25 was flown on August 29, 2001. This was the last in the short series of three flights made to observe diurnal changes. The flight was flown in the same sequence as Flight 23 (see above), including six AXBT deployments on Line 4. Measurements were made between 1730 and 1920 PDT. Winds were again from the north at moderate speeds. Stratus clouds were still present and lowest near the coastline. On the north-south line we again saw evidence of stronger northerly winds on the southern portion of the line.
I am reluctant to try to make comparisons among the three flights' observations here based on our views of the data as they came into the aircraft during flight. A careful post-flight analysis will be the better approach.
COAST Flight 26 was flown on August 30, 2001. This flight was made to deploy six AXBTs next to the R/V Wecoma in order to gather calibration data for the BTs. We met the Wecoma near the end of Line 5, and conditions were perfect for this task. Winds were light, seas were nearly flat, and the water depth at this location was much greater than the depth range of our BTs. We dropped three Hermes AXBTs (the 12" canister units) and three Sippican AXBTs (36" canister units), each on a different run past the ship. Data were collected between about 1330 and 1500 PDT.
COAST Flight 27 was flown on August 31, 2001. This flight covered the Big Box from south to north. AXBTs were deployed as follows:
Line 2: 6 AXBTs
Line 4: 6 AXBTs
Line 6: 7 AXBTs
Line 8: 7 AXBTs
Measurements were made of: SST, subsurface ocean temperature, and upper-ocean color; atmospheric temperature, humidity and horizontal winds. Although the winds had been moderate and from the north for the previous 2-3 days, the SST field and subsurface temperatures did not show much cool water near the coast from upwelling. Offshore, we saw SSTs near 20C, the highest surface temperature values observed from the aircraft this summer.
The atmosphere during this flight was relatively quiet, with winds in the lower 1000m below 10 knots. A slight temperature inversion was observed near 900m.
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
September 01, 2001