9702019H IOP17 (Flight 11) on Low 41

Aircraft Involved: P-3, UK C-130

Summary Description of Mission:

The planned primary mission was a combination of a warm frontal pass with a small "systematic survey" of the circulation center and bent back region of Low 41 using the P-3 and UK C-130. The wave cyclone was expected to develop near the center of the MSA and move very rapidly to the northeast (system motion: 040/20 m/s). The plan called for the C-130 and P-3 to have virtually identical tracks to insure that dropsondes were collected within the 100 km wide swath of dual-Doppler data. The first leg would be a north-south pass through the warm front along longitude 12.8W.

Shortly after departure from Shannon the P-3 and C-130 met at the inital point of 54.9N, 12.8W for their run to the north. Although the initial P-3 altitude was 5,000 ft, strong turbulence associated with the low-level jet to the east of the low center (90 knots) forced the P-3 to ascend to 7,000 ft in order to get the radar systems working properly. During this leg the Ops Center requested that the pattern be shifted northward by 30 miles. Strong stratiform precipitation was encountered during the leg through the warm front and north of the occlusion zone. The third leg went though the bent-back region. The last two legs were not very useful for the P-3, as they were flown in clear air. Repeated requests to the Ops Center to allow the P-3 to break off the last leg to make a run through the bent-back region were denied. The P-3 attempted a quick return to the cold frontal region on the fourth leg by climbing to 15,000 ft to get a favorable tailwind, by the cold front was largely gone/moved eastward by the time the aircraft got to 11W.

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.

P-3 Equipment Problems Encountered:

1. The P-3 radar system had a hard time coming up. The TA transmitter/receiver had to be changed. During the latter part of the flight, the LF receiver quit.

2. The P-3s GPS navigation system became unreliable soon after takeoff. The P-3s primary navigation source was switched to INE #1. Apparently the GPS antenna was not repaired after the last flight.

Recommendations & Evaluation:

1. Very good coordination on what appeares to be a good FASTEX case. First 3 legs through the warm front/bent back occlusion region were very good. The last 2 legs were a waste since the P-3 was largely in clear air. Some data was collected near Ireland on the cold front as the P-3 returned to base.

2. 15 "perl" patterns were completed by the P-3 in moderate to heavy precipitation associated with the warm front/occlusion zone.

--Dave Jorgensen & Frank Roux