970209H IOP12 (Flight 8) on Low 34a and Cold Frontal Rainband
Aircraft Involved: P-3, Electra, UK C-130, and G-IV
(Note: the G-IV had to abort its planned pass on Low 34b due to electrical problems. The Electra couldn't launch from Shannon).
Summary Description of Mission:
The planned primary mission was a "systematic survey" of the cyclone associated with Low 34a. The UK C-130 and P-3 were to join up on a survey of the low center around 1530 UTC and perform a survey with ~400 km legs of the low center and warm frontal precipitation to the north of the center, which should be near 58.5N, 24.5W. After two such "lawnmower" flight legs, which the P-3 about 25 km north of the C-130 track, both aircraft will switch to "survey" of the cold frontal region extending south from the low center, and will be met by the Electra which will join in two of the survey legs. The Electra would then break off to perform phenomena relative flight patterns along the cold front, while the P-3 and C-130 completed their suvey legs down the front.
On the intial approach to pt. 1 (57 22N, 19 53W) the P-3 observed what appeared to be the cold front running approximately north-south near 20.5W. The P-3 and C-130 executed their first two east-west legs in a highly time-coordinated fashion from about 1530 UTC to about 1800 UTC. During that time the P-3 completed 11 "perl" patterns in strong precipitation. The P-3 cuts its leg 2 a bit short (near 22W) to save time for legs 3 and 4. Those legs were also cut about 25 nm short to insure enough time to complete a pass parallel to the narrow cold frontal rainband.
The Ops Center notified us at 1605 UTC that the Electra can not fly today. Sid and I came to the conclusion that the low center and bent-back region were of more interest than the cold frontal band of the initial plan, so we added two additional flight legs to continue the survey of the cyclone. Those legs were completed by 1950 UTC. The aircraft apparently mapped the circulation associated with the bend-back region well, and the sonde info from the C-130 indicated stratospheric descent to the west of the low center. Following the completion of the 4 survey legs, the P-3 then tracked to the bouy to find the cold front. At 2041 we completed a perl at the buoy and tracked south just to the west of the narrow cold frontal rainband. The rainband was the most intense convective feature we've seen so far in FASTEX, with a 3-km wide core of 45-50 dBZ somewhat continuous for over 100 nm. We tracked band-relative 5-10 nm to the west of the precip core of the band and were generally embedded in stratiform precip with the convective core to our left. The radial velocity structure was what would be expected for a shallow convective line. Strong convergence ahead of the line, and a pronounced "rear-inflow". The line was apparently propagating rapidly eastward as we had trouble maintaining a constant distance to the line, having to correct multiple times eastward. We completed the band-relative part of the flight pattern by 2144 UTC. The UK C-130 made dropsondes through our region on its ferry to Lyneham. We landed SNN at 2230 UTC for about a 9.5 hour mission duration
Communications and Coordination:
1. No problems with VHF. The Sat Comm e-mail system on the C-130 worked well in getting information from the Ops Center concerning the low and narrow cold frontal rainband positions. No trouble was encountered in adding the two additional flight legs when the Electra couldn't launch.
P-3 Equipment Problems Encountered:
1. C-130 reported trouble with its new GPS sondes. Maybe only a 30% success rate. The P-3s radar data system froze up intermittently during the flight. No significant data was lost.
Recommendations & Evaluation:
1. This mission is certainly the best organized low center mission with sfc pressure estimates as low as 953 mb. Excellent data was gathered on the low center structure and precip maximum north of the center. The narrow cold frontal rainband was the strongest reflectivities we've seen so far too. Excellent data was gathered on our hour-long run to the south just behind the narrow cold frontal rainband.
--Dave Jorgensen & Yvon Lemaitre