Second G4 Flight in support of FASTEX IOP 18
 
Takeoff: 16:24 GMT (Goose Bay, Labrador)

Landing: 21:23 GMT (Shannon)

Duration: 5 hr



Purpose

This flight immediately followed the previous G4 flight that took off in
Shannon in the morning. This flight, in spite of the fact that it was
basically a return to Shannon, constitutes a separate mission.  The purpose
was to essentially redo the subjective and objective targets that were
sampled on the first mission but catch the targets in mid Atlantic.  L44 was
traveling very fast and it was necessary to turn around immediately at
Goose Bay rather than lay over to the next day when it would have been
too late.  L44 was expected to be in the MSA by then.  Leaving
immediately meant that the storm would not be really in mid Atlantic but
this was the best compromise.

At the time of mid flight, forecasts had the low southeast of the tip of
Greenland and still east of Labrador with a central pressure of 978, down
from 983 on the outbound of the two missions.  The jet off Labrador was
of course still there and the jet on the eastern side of the Atlantic had
moved somewhat to the east with the surface wave center just east of the
Ireland Coast.

Since we made a decision on the outbound mission to conserve sondes, we
expected to have enough left as we approached the Irish coast to try a cross
section across the dramatic jet we passed on the way out.  The number
would depend on the failure rate and the need to replace the failures on the
earlier legs.  In fact by the time we reached 25 W on the return we had
almost 14 sondes left and a total of 11 were use to create this cross section. 
In addition we expected to be able to drop from high levels and in fact did
from 37,000 ft on this one cross section.



Description of the Flight.

The turn around in Goose Bay went well with the refueling and we left the
service area on time.  We were however, delayed in taking off by ATC by
about half an hour due to concerns about the dropsondes.  This delay
required a modification in the original flight plan which would have taken
us to 52 N 30 W and instead we had to go from 57 N 45 W to 53 N 25 W
and then directly to Shannon.  There had been some hope of getting as far
south as 50 N at 30 W to better sample objective targets but the late
takeoff and crew duty day considerations required the more direct route.

After takeoff, we climbed to 26,000 (or 27,000:  notes not clear) and all
drops before 25 W were from this altitude.  First part of the flight was in
clear skies with beautiful views of the snow covered Labrador, the ice at
the edge of the coast and the ice flows off shore.  By 17:07 GMT we
could see towering convective clouds ahead (52.1 N 51.1 W).  First drop
occurred after 50 W around an 17:15 GMT.  The first three drops to the
turn point were separated by about the equivalent of 1.5 degrees of
latitude.  At 51.6 N and 48.3 W we passed over what appeared to be a
semi-circular hole in the clouds with higher convective clouds to north,
west and south and none to the east.  There were puffy cumulus and
stratocumulus below the aircraft. It was clear at flight level.  The turn point
was reached at 17:32 GMT.  During this leg we reached ground speeds of
about 600 knots due to an almost 80 ms tail wind that was parallel to our
track.

After the turn point the track was directly north again almost along the
same south-north leg we flew on the way into Goose Bay but one degree
further west.  The purpose was to again sample the strong PV feature in
this region.  Drop frequency was again increased to an spacing equivalent
to better than one degree of latitude.  This time as we flew north, we only
found a single jet that was very well defined with a very sharp cyclonic
shear to the north.  Slightly north of the jet we passed over a very strong
edge of the cirrus (which was below us) at 17:55 GMT and 53.6 N 45.0 W. 
To north of our position when we passed over the edge of the cirrus,
higher clouds could be seen that appeared to be associated with deep
convection.   At the northern end of the flight track, flight level winds
went to zero then switched into the east.  At the surface, as indicated by
the sondes, we remained west of the low center and lowest surface
pressure was 985 mb.  We reached the turn point at 18: 24.  

From the turning point at 57 N 45 W the track was east southeast toward
53 N 25 W.  From here the drop frequency was again reduced to the
equivalent of about 1.5 degrees of latitude.  This track took us just very
slightly to the north of the surface low at 56 N 36 W with a central
pressure of 975 mb (about what was forecast on the 12 hour prog).  Flight
level winds slowly veered first from the east and then to southwest by the
end of the leg.  Speeds slowly increased to about 40 ms.  It became dark
about two thirds of the distance along this leg and over the part that was in
sunlight, clouds included layers of stratocumulus and cirrus and some
towering cumulus scattered along the flight track.  Last sonde along this
track was at 30 W due to ATC considerations.  The purpose of these sonds
was to sample objective targets.

The turn point was reached at about 20:00 GMT at which point we
climbed to 37,000 feet for our final series of drops.   These drops were at a
frequency of the equivalent of better than one degree of latitude.  At flight
level (37,000) winds varied in speed only slightly and backed from west
southwest to southwest.   The sondes indicated we were clearly above the
jet level and cross sections indicate that we had a strong shear zone on the
cold side of the jet, with a nearly vertical front that extended from the jet
to the surface.  Final sondes indicated that they were east of the front with
northerly winds on one side and southerly on the other.

After the final sonde at 12 W and at 20: 59 GMT we descended for our
landing at Shannon.



Overall assessment of the Flight.

We were somewhat disappointed that we could not get as far south at 30
W as we originally planned.  This would have provided better coverage of
the objective targets.  The last cross section however was a bonus and
provided both verification of the surface wave and as well as targets for
this system that would verify after it was north of the MSA.  The south-
north section at 45 west was regarded as very successful in that we reached
the center of the upper level low and PV anomaly.

Sonde success rate was as high as the earlier mission.  We dropped a total
of 35 sondes and only 3 failed.  All three were replaced after failure.