970202H IOP9 (Flight 5) on Low 27

Aircraft Involved: P-3, Electra

Summary Description of Mission:

The planned primary mission was a "systematic survey" low 27 center and cloud head region plus a leg or two (with dropsondes) over the Electra investigation region along the occluded frontal precip band farther to the east. The P-3 was to take off about 4 hours ahead of the Electra in order to conduct a dropsonde survey of the cloud head and low region (which was centered near 60N and 24W) which was out of range of the Electra. Four 250 nm long east-west flight legs were planned at 20-25 kft centered on the cloud head region. The low center was moving toward 050 (from the UKMO LAM forecast), but the precip associated with the cloud head looked to be moving north at about 30 knots. Dropsondes were planned to be deployed about every 63 nm along each of the four flight legs.

At the first dropsonde point at 61 7N, 20 9W, the aircraft lost the sonde signal about a minute after the launch. Subsequent sondes also lost signals, indicating a reception problem on the P-3. On the southbound leg to pt 3, following the failure of sonde 5, we decided to continue the next leg (which should have been right through the middle of the cloud head region) at 5k ft to optimize the Doppler data collection and not waste any more sondes. Executed a spiral (sounding) descent at pt 3 from 21k ft to 5k ft. Following the conclusion of leg 2 another sonde deployment was executed after the aircraft had spiraled up to 15k ft at pt 4. That sonde also lost its signal, and the sonde system was secured for the rest of the flight. The P-3 then returned to 5k ft for the continuation of the Doppler legs. Because of large headwinds (the P-3 went around the low center clockwise, thus always encountering a headwind) and the extra fuel expended at the low altitude, leg 3 had to be terminated early (aircraft went as far west as 23 30W). Lowest surface pressure was 883 mb which matched the UKMO LAM forecast for 21 UTC. Communications with the Electra was established at 2147 UTC, and radar information was relayed concerning the north-south precipitation band north of 58N along about 20W.

Communications:

1. No problems with VHF. HF didn't work at all again.

P-3 Equipment Problems Encountered:

1. Sonde system failed totally, probably due to a bad antenna. 7 sondes were deployed (and lost).

Coordination Problems

1. Due to the endurance limitation of the P-3, no coordinated patterns could be set up with the Electra, although information was passed to them concerning precip location.

Evaluation:

1. Very good Doppler work was performed on the cloud head region. 4 "perls" were executed in very active precip regions. Interesting banded structure was seen in the cloud head.

--Dave Jorgensen & Frank Roux