Sortie De-brief Flight B052
15th September 2004.
Mission Scientist: Dr Jonathan P Taylor.
Campaign: EAQUATE – European AQUA Thermodynamic Experiment.
The aim of the sortie was to under-fly two overpasses of the Aqua satellite within the
swath of the AIRS instrument in cirrus cloud conditions. Unfortunately the Proteus
was unable to fly due to fuel pump problems.
Take off was at 0930Z with a long transit to a position 58N 7deg W as this region
would be under AIRS overpasses at 1225Z (Western edge of swath) and 1403Z
(Eastern edge of swath).
For the majority of the transit there were clear skies above with scattered cumulus
below, transit was at FL280. Ozone levels were very high at FL280 with peaks of
156ppb. A profile was flown from FL280 to 100ft in to the operating area. Cirrus
clouds were overhead which appeared to be thickening to the North and West. East of
Benbecula there was significant low level cloud but West between Benbecula and St
Kilda the low level cloud was much more patchy <1/8 and at around 2500 to 4000ft.
A run was then flown on a northeasterly heading at 100ft below the cirrus, SST was
around 13.8degC but low cumulus built up along this run with drizzle encountered at
north eastern end. The best cirrus and least cumulus was to the west so a profile from
100ft to FL267 was flown. Two orbits at 45deg bank angle were flown at FL267
immediately below the cirrus layer. A profile was then flown up into the cirrus layer
to FL320 winds were 307/44m.s-1 and ice crystals were small (less than 200um) and
low number densities of 50 to 100/litre. This was typical of all cirrus clouds flown in
during the entire sortie. At the end of the profile a run was flown in a northerly
direction within this cirrus sheet for the first AIRS overpass at 1225Z. A sonde was
dropped at 121701Z from within the cirrus so its profile will be coincident with the
AIRS overpass. A few minutes before the overpass we broke out of the cirrus clouds
so turned on a reciprocal heading to get back in cloud for the overpass. A second
sonde was launched at exactly overpass time when we were in the cirrus clouds – the
downward video suggested that there was some patchy cu/sc below the cirrus during
the overpass time.
After the overpass run a climb to FL350 was made to try and get above the cirrus
clouds. A run was then flown over the cirrus but we passed over the edge before the
end of the run. The cirrus cloud was very variable both in thickness and horizontal
extent. There appeared to be a major area of cirrus west of 10W (outside our
NOTAM area) and another layer orientated roughly north-south close to the Scottish
coast. In some parts we were flying in cirrus at FL350.
At this stage it was decided that for fuel reasons we should reposition to a point 56N
8degW for the second AIRS overpass to allow us time to make measurements in the
vicinity of the overpass before heading back to Prestwick. This would move our
operating area in to NOTAM area F which we had cleared allowing further dropsonde
operations. In the original area the cirrus was being advected rapidly over land and
outside of the AIRS swath. A transit to the new way point was flown at FL350.
Once in the new overpass area runs were flown at FL350 first on a heading of 319
degrees and then a reciprocal on 142 degrees. During this run the aircraft was right
in the tops of a thin cirrus layer with only the occasional sign of a wisp of Ci
overhead. Two sondes were launched bracketing the overpass time of 1404Z with
ARIES and SWS making nadir views during the overpass. Following the overpass a
profile descnet was flown through the cirrus showing the cirrus base to be at FL310
i.e. only 4000ft thick. Droplet concentrations were low (100/litre) with small ice
crystal sizes of less than 200um. Once below the cirrus layer it was evident that there
was little or no low level clouds below the cirrus in the vicinity of the second satellite
overpass.
A rapid descent was then flown in to Prestwick for a refuel, after refuel a transit back
to Cranfield was flown. SWS made some further cal measurements and possibly
cirrus views.
Summary
A successful sortie, the first AIRS overpass saw the 146 in cloud but there were
patches of cu/sc below. The second overpass was over a different area of cirrus but
the 146 was above a thin cirrus layer with no other cloud layers below, this overpass
should make a very useful case study for the impact of very thin cirrus.
Note that on many occasions the 146 was making contrails and these will be of
interest for the Defence project. Logs of times when contrails were formed were kept
by the Flight Manager.
Dr Jonathan P Taylor
15/09/04