9702015H IOP15 (Flight 9) on Low 38
Aircraft Involved: P-3, UK C-130, and G-IV
(The G-IV completed a dropsonde "figure 4" pattern over the low center several hours before the departure of the P-3 from Shannon)
Summary Description of Mission:
The planned primary mission was a series of 4 radial legs normal to the orientation of various frontal features of the LOW 38. The P-3 and C-130 flew stacked legs (although differing often by minutes in time), starting from an Initial Point that was the northern buoy (56N, 14.2W). The first leg was through the warm front and cold front. The warm front was seen near 55N 17W, about where it was predicted to be by the UKMO LAM model near 0900 UTC. Farther along on that first leg, both aircraft encountered precipitation bands that may have been associated with the cold front. At the P-3's flight level the winds turned slightly from southerly to southesterly and the ambient termperature dropped 4-5 C as the band was crossed. An extensive warm tougue was seen in the equiv. potential temperature pattern at 5k ft. The next leg focused on the occlusion zone northeast of the low center. Extensive precipitation was noted north of about 57N, and many "perl" patterns were completed by the P-3. Another leg through the occlusion band farther west was completed by both aircraft by 1300 UTC, at which time the P-3 headed southwest to line up for a westbound run through the "bent back" frontal region, and the C-130 continued to track southbound for a run through the low pressure center. The data from the P-3s leg to the westnorthwest through the bent back region exhibited a dramatic wind shift and temperature drop. Flight level winds (5 k ft MSL) shifted in a few minutes from southeasterly at 30 knots to northerly to northeasterly at 20 knots. Complicated shear patterns were also seen in the radar radial velocity display. Following the completion of the leg to pt. 7 (57N, 38W) the P-3 climbed to 10k ft for fuel economy and tracked to the northern buoy. Extensive precipitation was seen during most the 1.6 hour leg. Following a run over the buoy at 10k ft, the P-3 returned to SNN and landed at about 1700 UTC, for a mission duration of 9.7 hours.
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 froze a couple of times in inopportune moments.
2. The P-3s GPS navigation system became unreliable after about 0915 UTC. Poor reception of the signals. The P-3s primary navigation source was switched to INE #1.
Recommendations & Evaluation:
1. Very good mature cyclone case. Excellent coordinated data on frontal transects. Sondes on C-130 apparently worked much better than previous IOP. Fascinating structures seen in the "bent-back" region on the radial velocity display on the P-3.
2. 8 "perl" patterns were completed by the P-3 in moderate to heavy precipitation associated with the occluded front.
3. 47 sondes were deployed by the C-130
--Dave Jorgensen & Frank Roux