G4 Flight in support of FASTEX IOP 17 
 Low 41: the Fastex Cyclone
 Part I: Far upstream targetting flight
 Date: February 17, 1997
 (prepared by Jean-Pierre Cammas and 
               Gwenaelle Hello)
 
 Ferry flight to Saint-Johns (New Foundland):
 Take-off Time Shannon (approx): 0800Z
 Landing Time Saint Johns (approx): 1245Z
 Flight duration: 4 hr 45 mn
 
 Targetting flight nearby Saint-Johns: 
 Take-off Time (approx): 1500Z
 Landing Time (approx):  2030Z
 Flight duration: 5hr 30 mn
 
 Scientists: Jean-Pierre Cammas (LA/CNRS), 
             Gwenaelle Hello (METEO-FRANCE), 
             Melvin Shapiro (NOAA/ETL), 
             Tom Rosemond (NRL), 
             Diana Bartels (NOAA/NSSL)
 
 
 Purpose:
 
 The first flight was a ferry from Shannon to Saint-Johns. After 
 landing and refueling, a first scientific flight was designed 
 to target the far upstream sensible areas of Low 41 which was expected 
 to explosively deepen in the MSA region the day after. The targets
 were designed as follow, verifying time 0219 00Z and target time 0217 18Z.
 Duration of this flight (5hr 30mn) was fixed upon the constraints of 
 the maximum daily crew duty time, taking-off the day after as soon as 
 1530Z, a flight centered around 1800Z for data assimilation purposes.
 
 Some far upstream targets were shown to be east of St Johns according to 
 adjoint and singular vectors computations both from Arpege (Meteo-France) 
 and NOGAPS (NRL) models. Scheduled way-points were: St-Johns, WP1 
 50.0N-52.0W, WP2 48.0N-40.0W, WP3 44.0N-40.0W, WP4 40.0N-55.0W, St-Johns.
 The first leg cuts some upper level structures (other parts of its
 could be assessed by the US land soundings). The second leg sampled is 
 devoted to low level features following maximum axis and the third leg
 cuts some maximum of the low level targets. The last waypoint is in fact
 in the north part of the deepening area.
 The area sampled is roughly north-east of the incipient surface low 
 (approx 37N-62W) and its upper-level precursor (approx 41N-68W). Aloft 
 the general situation involves a very strong zonal upper-level jet stream 
 whom the axis is a few degrees south of St Johns. At the surface, 
 the pressure field involves a saddle area between the parent low south of 
 Iceland, the incipient low 41 south of St Johns, and two anticyclones 
 over the eastern United States and over the Azores. 
 
 Description of the flight:
 
 A total of 22 dropsondes were launched, all successfully except for a few 
 missing and bad winds. A first part of the flight plan was flown at FL270 
 (approx 365 hpa) involving the first ten dropsondes. Entering the NY ATC 
 area (west of 40.0 W), authorization was got to fly at FL 410 (approx 165 
 hPa), then at FL 450 (approx 150 mb) until the last dropsonde 
 (46.0N-53.3W). 
 
 Though the flight plan was entirely builded to follow targetting objectives, 
 some interesting mesoscale structures have been sampled. Relatively to high 
 levels, legs from WP1 to WP3 and from WP4 to St Johns involve two 45-degrees 
 oriented cuts across the cyclonic shear side of the upper-level jet stream 
 and the associated gradient of tropopause height (geopotentiel on the 2 PVU 
 surface). The leg between WP3 and WP4 was along the jet-core with very strong 
 winds ahead. The highest winds recorded with the dropsondes were about to 170 
 knots during the last leg to St Johns (approx 44.3N-53.7W). Relatively to the 
 surface, the flight plan encompasses first the north-westerly winds in the 
 cold air outbreak east of St Johns (approx 1018 hPa), then a region of higher 
 surface pressure (approx 1028 hPa) before to enter the easterly winds 
 downstream of the incipient low (approx 1012 hPa). 
 Very clear transitions were observed between two different boundary layers 
 in the cold air outbreak east of St Johns and over the Gulf Stream south of 
 St Johns. 
 
 Flying above the upper-level jet core at FL 410 and FL 450, wind measurements 
 by the aircraft have been found questionable because they were greater than 
 the maxima observed with the dropsondes.  


 Overall Assessment of the Flight:

 Very successful flight. The target areas have been sampled as scheduled.
 Three dropsondes were analysed by the Arpege model in real time at 1800Z. The
 complete structure of the objective targets could be studied as the Lear Jet
 did a flight nearly in the same area but 6 hours later.
 Interesting actual structures have been documented, among which are found the 
 cyclonic shear side of a very strong zonal upper-level jet, clear transitions 
 between different boundary layers.