G4 Flight in support of IOP-10 (prepared by Bob Gall) Date: February 3, 1997 Takeoff Time: 15:30 Z (St Johns, Newfoundland) Landing Time: 21:15 Z (Shannon) Flight Duration: 5 hr 45 min Purpose Forecast guidance was suggesting that there would be a secondary cyclone forming on a front that extended out of a deep low south of Iceland. This secondary low, would be referred to as L28 and was expected to pass through the MSA on Feb 4. A second low L30 was also expected to follow behind L28 and reach the MSA on Feb 5th . The objective of the flight on Feb 3 was to first sample 48 hour adjoint targets that would be just east of Newfoundland for forecasts of L30 in the MSA lat on the 5thand early on the 6th then proceed east to survey the region around the precursor to L28 in mid Atlantic. Both L28 and L30 were well sampled by aircraft in the MSA on 5th and the 6th. Description of the Flight The entire flight was conducted at 26000 ft. The initial Leg of the flight was first east and then east-southeast over the adjoint targets for L30. First drops started at 50 W and continued at a separation distance equal to about one degree of latitude until 45 N 40 W, the first turning point. This point was reached at 1637 Z. During this leg we were flying in clear air over low stratocumulus clouds. At one point the stratocumulus was characterized by long lines with a very regular spacing (near 46.7 N 44.3 W). After the turning point the course was directly north and the drop frequency was increased so that the distance between them was equal to about to about half degree of latitude. This track took us from a point somewhat north of the surface front, as suggested by the surface temperatures revealed by the sonde at the southern point of this leg, across the jet core to a point near a weak surface low that was forming in a thermal trough northeast of Newfoundland. The jet core was encountered at about 46N with strong anticyclonic shears to the north. The sondes were indicating strong southwest winds in the southern portion of this leg, switching to weak southerly winds north of 50N. Temperatures at the surface were around 11 C at the southern end of the leg and 6 C at the northern end. Clouds along this leg consisted of several layers with views of the sea occasionally available. There were some convective clouds with moderate vertical development. Sonde success rate on this leg was excellent and a very good cross section of the jet and related frontal features under it was obtained. We reached the turning point at 52 N 40 W at 1735 Z. From here the direction was toward the southeast and a point 40 N 35 W. On this leg, sonde drop separation distance remained equivalent about a half degree of latitude. The jet was again crossed at 50 N with a shear profile similar to that on the previous leg. Surface winds were initially from the southeast with a very rapid shift to southwest as we moved south. The shift occurred again near 50 N. There were no inversions in the sounding neear the surface just north of the wind shift. Temperatures in this region were increasing with each sonde but not significantly more rapidly as the wind shift line was passed. On the south end of the leg temperatures increased to about 14 C and winds remained out of the southwest and strong. It is not clear whether we reached a point south of the surface front. Clouds along this section consisted of broken middle level clouds under the aircraft. High cirrus could be seen well to the south and distinct convective clouds appeared to the east of the flight track during the last half of this leg. From a point at 47.3 N 36.4 W at 1814 Z a strange very bright cirrus cloud appeared to the right and ahead of the aircraft. It was an elongated, elliptical shape and appeared much bigger than a contrail. The turn point at 45 N 35 W was reached at 1821 Z. Time series of flight level wind along the two legs so far indicated that the western leg was in a confluent region of a small jet core and the leg toward the southeast was passing through the difluent region of the jet. From the turn point the direction was toward the northeast and 52 N 30 W. The track took us again across the jet maximum. Surface winds were strong from the southwest at the southern end, switching to southeast north of 48 N. At the northern most part of this leg, surface winds were from the east and the temperature was about 7 C. Along this leg, it was getting dark but the convective region observed on the southeastward leg was still visible to our left. We were flying over scattered clouds in two layers. We made the turn at 1927 Z and it was dark by 1937 Z. Drop frequency along this leg was a distance equal to about a degree of latitude. The final leg was nearly east, or directly toward home. Drops continued separated by a distance equal to about a degree of latitude and continued to 15 W. At flight level we again crossed the jet maximum and at the surface winds were first easterly, then northerly and we again crossed the surface front near 18 W. To the east of the surface front surface winds were from the southwest.. The surface temperature on the final sonde was 14 C., about 3 C warmer than the air just to the west of the front. On landing in Shannon we passed through some snow at flight level and it was raining lightly at the airport. Overall Assessment of the Flight Sonde success was unusually high so with four crosses of the jet axis we were able to obtain an exceptional view of the jet structure all across the Atlantic including a clear small scale jet core. The precursors of L 28 were probably contained in this section at about mid Atlantic. The flight was considered to have been very successful.