G4 Flight in support of FASTEX IOP 4 (prepared by Bob Gall) Date January 17, 1997 Takeoff Time (approx): 9:00 GMT Return Time (approx): 15:40 GMT Flight Duration: 6 hr 40 min Purpose The FASTEX scientists had been tracking a cold air circulation from the vicinity of Greenland and Iceland around a large scale cyclonic circulation that was generally centered to the south of Iceland. Precursors of this system had been the subject of an intensive observation period from the mid Atlantic ships with observations being taken every 90 min. The satellite imagery in the morning of the 17th showed a distinct circulation centered near 45 N 30 W with a cloud head off toward the northeast of this location. The purpose of this flight was to sample the cloud head and the circulation feature with the G4 dropsonde system. This was to be a follow up of the intensive observations by the ships and to further document the evolution of the system prior to turboprop observations of the system late on the 17th. Because later forecasts of this system indicated that it would the be in a decaying stage at the time the turboprops could get there and because of apparent opportunities the next day, the turboprop observations of this system were eventually canceled. Since the G4, prior to this flight, had never been flown on a research mission, this flight also had the added purpose of validating the G4 systems, particularly the dropsonde system, and to give the scientists some experience with the aircraft. There also was a need to calibrate the wind sensor system on the aircraft so a racetrack pattern was planned for late in the flight to remove wind bias errors. Description of the Flight. With the exception of the race track patterns that were executed after the last sonde drop, the entire flight was executed according to the preplanned track. All preplanned way points were reached and all sondes were dropped near to the preplanned locations. Sondes were released at a regular interval of 10 min. On leaving Shannon, the flight proceeded directly to 50 N 20 W where the first sonde was released just after 10:00 GMT. Roughly 10 min before the first release, we entered the northern edge of the cirrus associated with the cloud head. The flight then proceeded directly south with regular sonde releases to 43 N 19 W, reaching this point at 11:00 GMT. At about half way to this point we came out of the cloud head and could see the sea. In the southern portion of leg, there were scattered small convective clouds a few extending to flight level.. The course was then toward the northwest with regular sonde drops up to 50N 25W, reaching that point at 12:00 GMT. During this leg, flight level winds increased to over 50 m/s at the mid portion of the leg (from the southwest), then dropped off and switched to the northeast at the end of the leg. The cloud head was again entered about midway through the leg. The third leg was directly south, starting within the cloud head, crossing out of the cloud edge at mid leg, and entering, at that point, a region that resembled a large eye, with few clouds below the aircraft, and higher clouds surrounding the region. After passing through the southern band of higher clouds (which was narrow), there were only scattered convective clouds below the flight level. Winds along this leg were first from the east to northeast and switched to southwest in the eyelike region. The southern point was reached just before 13:00 GMT The last leg was toward the northeast over scattered convective clouds and flight level winds were strong from the southwest. The cloud edge was at the northern edge of the reserved box (at 50N ) and its southern edge had an impressive display of mammatus. A strong line of convection was visible on radar within the cloud head. At this point a series of race track like patterns were executed in the clear air to the south of the cloud head. After completing the race track patterns, the flight proceeded in a northeast direction through the cloud head and leaving it about 45 min before landing. Overall Assessment of the Flight A total of 30 sondes were released. Of these 19 provided complete soundings with winds temperature and humidity from flight level to the sea. There were three partial soundings; two had complete temperature, humidity and pressure but winds at only some levels and one started considerably below flight level but had complete winds, temperature, humidity and pressure from that level on down. Eight sondes failed completely. Overall the flight was considered successful with a good distribution of sonde data throughout the circulation system.