Flight summary, DC-8 flight 20 - Kona-Dryden - 0409.
Take-off time 7:15 am local (1715Z); flight duration 6.8 hours
Title: Aircraft intercomparison, stratus chemistry, and jet stream transport Objectives: (1)
To conduct an extensive intercomparison with the P-3; (2) to
examine chemical processing in stratus clouds; (3) to sample Asian pollution
transported in the jet stream around the east Pacific ridge and southward
over California.
Execution: We flew from Kona (20N, 156W) to (22.5N, 151.5W) for
the intercomparison, which consisted of a 20-min leg at 17Kft,
a descent to 1Kft at 500fpm, and a 20-min leg at 0.5Kft. We
then did a 20-min leg in stratus (6Kft) and headed to Dryden
(35N, 118W) with a spiral followed by a climb to 39Kft along
the way.
Results: The intercomparison was a success; all instruments were
on-line and the aircraft flew within 200-400 ft from each
other most of the time. Steady concentrations were observed
on both the 17Kft and the 1Kft intercomparison legs. The
stratus deck extended from 3 to 7 Kft. The 20-min leg
at 6Kft following the intercomparison was conducted in almost-continuous
stratus. No particularly strong pollution layers were observed
in the flight; there were layers at 5-15Kft with CO up to 240 ppbv,
and the boundary layer was enhanced in CO and CO2 also (typically 170
ppbv CO, 377.2 ppbv CO2, 56 ppbv O3). The atmosphere was
featureless above 15Kft and did not reveal any structure
that would be associated with jet stream transport of Asian
pollution. Approaching California we flew a long leg
in the stratosphere (39Kft) and sampled a major stratospheric intrusion
extending down to 20Kft and capping thunderstorm activity over southern
California.
Meteorological Summary DC-8 Kona to Dryden Transit 9 April
2001
Relevant Flow Features:
Surface-A
strong anticyclone was centered near 40N, 145W. A weak surface low was
passing over southern California. Although not strong at the surface,
this low was better defined aloft and associated with a strong short wave trough. Due
to these pressure systems, surface winds were from the east on the western
part of the flight track and mostly northerly on the eastern part of the track.
Middle troposphere-The
high northeast of Hawaii, and the low over southern California persisted
into the middle levels. Easterly winds continued along the westerly
portion of the track and northerly winds along the western portions.
Upper troposphere-Due
to the closed anticyclone, the polar jet stream was displaced far to the
north of most of the flight track. However, the jet plunged southward along
the California Coast. The subtropical jet stream extended from south
of Hawaii to Baja California. The flight track was north of this jet. Winds
along the western portion of the track were from the west, but from the northwest
over eastern portions.
Backward
trajectories at all levels showed considerable circular transport over much
of the flight track. This was due to the persistent anticyclone noted
above. Only near California did the trajectories show well defined
transport from Asia. This air had traveled around the strong anticyclone
located farther west.
Relevant Cloud Patterns and Other Goodies:
Most of the
flight track was devoid of middle and high clouds. The only exception was near
California-in association with the low pressure described above. However,
much of the flight track was blanketed by broken layers of cumulus and stratocumulus.
The area
of the DC-8/P-3 intercomparison had only broken cumulus and stratocumulus
clouds At 17,500 ft, the winds were from 087deg at ~25 kt. During
the descent to 500 ft, two major cloud layers were observed. Stratocumulus
had bases of 5100 ft and tops of 7250 ft. The tops were uniform, and
this level marked the trade wind inversion. A cumulus deck was below,
with bases of ~3700 ft and varying tops that occasionally reached ~7000 ft. Some
of these clouds produced light rainshowers. The intercomparison leg
at 500 ft had winds from ~ 070 deg at ~27 kt-stronger than many runs at this
altitude. The cloud level run at ~6000 ft remained in the clouds at
most times, but some breaks did occur.
The second
boundary layer run ( near 2129Z) had an almost overcast cover of stratocumulus. Bases
were near 3500 ft and tops near 5100 ft. A broken layer of cumulus
was below, with bases near 2600 ft. The winds at this run were somewhat
weaker than in the previous run, ~20 kt here. The direction was northeasterly
at the beginning of the run, but shifted to northerly by the end.
The stratosphere
was entered near 2225Z as the DC-8 was passing 35,700 ft for 39,000 ft. We
remained in the stratosphere until the descent into Dryden. A line
of weak thunderstorms was located off the California Coast and near Dryden
.