G4 Flight in Support of FASTEX IOP 18 (prepared by Bob Gall) Date February 22, 1997 Takeoff Time: 7:55 GMT (Shannon) Landing Time: 14:21 GMT (Goose Bay, Labrador) Flight Duration: 6 hr 26 min Purpose A major cyclone was expected to develop in mid Atlantic during the night of Feb 22 and this cyclone would pass through the northwest edge of the MAS on February 23. MSA operations with the P3 were being planned for the 23rd. A Lear flight had already occurred starting at 0000 GMT on February 22 to sample upstream targets for this low which was being referred to as L44. Early precursors of this system had a low with very cold air behind it coming out of Labrador under a very strong jet aloft. At the time of takeoff, this low was located directly south of Greenland and east of Labrador with a cold air trough moving southward to its west and along the Labrador coast. There was a 300 mb trough in mid atlantic with a 50 ms jet from the southwest to its east. A open frontal wave L42B was southwest of Ireland moving northeast. The flight could be thought of as consisting of three parts. The first part west of 30 W was designed to capture low level objective targets identified by singular vector or adjoint techniques. The middle part was primarily for constructing a high resolution across a prominent PV feature associated with the low including a strong tropopause fold. There were also some objective targets in this region but they required much lower sonde density than the subjective targets. The last part of the flight was for further objective targets, this time higher level targets and for further cross sections through the cold feature on the west side of the developing low. This was to be the first part of an over and return flight with quick turn around in Goose Bay. On the return we were to again sample the same system, now in mid Atlantic. The report of the return is given as a separate report. The MSA mission was in fact flown the next day as planned with the P3 supplying both radar and dropsonde support. Description of the Flight. On takeoff we passed through scattered low clouds and the ground was visible for the first 15 min or so. After that, heading directly west, we were flying over a continuous low cloud layer. Subsequently, the cirrus at flight level gradually increased until we were flying in thick cirrus by 9:30 GMT and 24 W. Still on the anticyclonic side of the jet we encountered fairly strong bumps. At 25 W we passed through the jet core and into strong cyclonic shear and the turbulence was clearly less than on the anticyclonic side. We passed out of the cirrus at a sharp edge at 27 W at 9:40 GMT with scattered clouds below. The flight was conducted at 27, 000 ft throughout and all drops were from this level. Our first drop occurred at 30 W at 10:00 GMT and we continued to drop with a spacing equivalent to about 1.5 degrees of latitude until 44 W. The first turn point at 32 W was reached at 10:15 after which the heading was toward the southwest. The purpose of the drops along this leg was to sample low level objective targets. This track took us along nearly constant surface pressure as indicated by the sondes and through the leading edge of the jet coming off Labrador. Wind speeds increased rapidly during the first half of the leg in spite of the oblique angel of our track with respect to the jet axis. After reaching the jet axis with speeds of nearly 70 ms, flight level winds were nearly constant until the turn point at 44W. Along this leg we were flying over layered clouds and were in cirrus near the end though the sun was visible. The turn point was reached at 11:42 GMT. At this point we doubled the sonde frequency with a spacing of better than the equivalent of 1 degree of latitude. During the first part of this leg we were flying in cirrus but after 10 min we suddenly broke into clear air with cirrus above us and altocumulus below. A sharp edge to the cirrus was visible ahead of the aircraft. We passed under this edge at 50.8 N 44 W. When we entered the clear air with cirrus above us, the dewpoint at flight level dropped dramatically. At this point we passed through the first of two wind maxima with speeds just short of 80 ms. Wind dropped off about 10 ms then rose to about 80 ms again about two thirds of the way along this leg. Theta remained constant at flight level until we passed the second wind max. After the second max, winds dropped off rapidly to the turn point with speeds near 20 ms. Winds backed slowly along this leg from west to southwest and we never reached the low center at flight level. Clouds along the remainder of this leg were in layers then mostly uniform stratoform clouds below the aircraft. The turn point was reached at 12:29 GMT. After the turn point drops continued at the same frequency with a spacing equivalent to one degree of latitude. Winds at flight level slowly increased to 80 ms from the west. Clouds along this leg were broken to continuous and all below the aircraft. At 13:02 and at 54.3 N 51.4 W we were suddenly flying in clear air all the way to the sea with clouds visible all around us. It took us about five min to cross this clear area (which was apparently visible in satellite imagery) and we dropped a sonde on its western edge at 13:12. The sondes proceeding this one this one showed fairly constant surface temperatures, while the succeeding ones showed a very sharp drop in temperature to the west. Surface winds were strong but did not show a vortex signature. After passing over this "hole" in the clouds we passed through clouds to flight level and then were in clear air until we landed. The approach to Goose bay was into a very strong head wind so ground speeds were very slow. On landing in Goose Bay, surface winds were very light and surface temperature was -21 C. Assessment of the Flight. All targets were successfully sampled including both objective and subjective targets. It would have been nice if we could have had a higher flight level on the south-north leg to get above the jet but the cross section produced looked very good. We got a good cross section through the cold air feature on the west side of the low south of Greenland. Sonde success rate was excellent. We dropped a total of 30 sondes, only 3 failed and they were immediately replaced.