G4 Flight in support of FASTEX IOP 15 Low 38: Primary cyclone Date: February 15, 1997 (report prepared by Jean-Pierre Cammas) Ferry flight to Saint-Johns (New Foundland): Take-off Time Shannon (approx): 1200Z, February 13, 1997 Landing Time Saint Johns (approx): 1700Z Targetting flight nearby Saint-Johns: Take-off Time Saint-Johns (approx): 2100Z, February 13, 1997 This flight was cancelled due to mechanical problems with the aircraft. Subjective flight from Saint-Johns to Shannon: Take-off Time Saint-Johns (approx): 0300Z, February 15, 1997 Landing Time Shannon (approx): 0930Z, February 15, 1997 Flight Duration: 6H30mn Scientists: Melvin Shapiro (NOAA), Ron Gelaro (NRL), Gerald Desroziers (METEO-FRANCE), Diana Baertels (NOAA), Jean-Pierre Cammas (LA/CNRS, not in the aircraft during this mission, proposed and designed the flight plan at Operations Center, Shannon) Purpose: The purpose of this flight was to document actual structures of a primary mature cyclone over the Central Atlantic, Low 38. The others MSA aircraft flights were scheduled to take-off right after the G4 landing in Shannon with flights focused on precipitation features in the occluded portion of the mature low on its northeastern part. In order to get the best coverage of the system, the G4 flight plan was designed to sample the northwestern back bent surface front, the low center and its southwestern part, the upper-level potential vorticity anomaly and the apex of the warm sector with surface frontal structures on the eastern part of the low. Description of the flight: The entire track has been flown at FL260. About 29 dropsondes were sent on the GTS. Seven dropsondes were launched across the north part of the bent back surface front, a nice easterly low level jet was observed (> 35 ms -1). With about 5 dropsondes, the next north-south leg sampled a cross-section across the low center, observed as a warm and humid core, as well as across the potential vorticity maximum aloft. Mid-tropospheric dryness is observed on the south part of this leg. The third leg involved 5 dropsondes in the northwesterlies south of the bent back surface front. Strong low level winds were observed (35-40 ms-1). The last zonal leg involved about 15 dropsondes across features east of the low center (dry intrusion, cold front, apex of warm air and warm front, southerly upper-level jet). Wind speeds in excess of 60 ms-1 were observed with the dropsondes (400 hPa) when crossing the jet core. The upper-level frontal zone and the surface cold front were well resolved by the dropsonde sampling. Overall assessment of the flight: Very good data on the mature phase of a primary cyclone. Focus was put first on the northhwestern bent back surface front, the surface low center and the lowest tropopause part. The flight ended with a nicely sampled cut across the dry intrusion, the cold front, the apex of warm air and the warm front, and the southerly upper-level jet.