Flight summary, Kona-Guam transit 02/27/2001.
Title: Asian pollution subsidence and MOPITT tropical validation
Objectives: (1) to sample aged Asian pollution subsiding in the
tropics, (2) to conduct a MOPITT tropical validation, (3) to intercompare
instruments on the DC-8 and P-3 aircraft.
Execution: The intercomparison, planned as a boundary layer run
out of Kona with the two aircraft flying parallel tracks, had to
be canceled because of lack of clearance. The DC-8 followed
a straight flight track from Kona to Guam, with extensive vertical
profiling. A MOPITT validation experiment was conducted at
(18N, 175W, 2235 UTC) with a spiral from 31Kft to 0.5Kft above
a broken cumulus deck (tops at 6Kft) in a strongly subsiding atmosphere.
Results: Our first two objectives were met. (1) We observed
and sampled repeatedly a layer of Asian pollution at 8-12Kft (CO
up to 210 ppbv, ozone up to 80 ppbv) with background air above
and below. This pollution was in a strongly subsiding layer
on top of the trade wind inversion, and appeared to contain both
fossil fuel and biomass burning influence. Through mapping with
DIAL it was determined to extend from 170W to 162E. The layer was
predicted in the chemical forecast where it was due to Asian outflow
transported rapidly to the central Pacific, and then strongly subsiding
and stagnating west of Hawaii, although the observed layer extended
further west than forecast. Formaldehyde was elevated (up
to 700 pptv), in contrast to the Asian plumes sampled on the Dryden-Kona
flight, reflecting presumably the stronger photochemical activity. (2)
the MOPITT validation experiment was a success. Skies were
100% clear above 6Kft. Although the aircraft ceiling was
31Kft, DIAL observations showed very clean air above. The
dominant feature of the profile was the strong layer of Asian pollution
at 8-12Kft.
Meteorological Summary DC-8 Kona to Guam
Relevant Flow Patterns
Lower troposphere-Subtropical
high pressure areas dominated the flight track. One center was near Hawaii,
while a second was located over the western Pacific Basin.
Middle troposphere-Subtropical highs continued to dominate the
area.
Upper troposphere-Continued high pressure over the area. The
jet stream was centered near 35oN-well north of the flight track.
Relevant Cloud Features
The flight
track mostly was devoid of middle and upper level clouds. However, scattered
to broken cumulus and/or stratus covered much of the flight area.
Water
vapor imagery showed that the flight area was quite dry in the
middle and upper troposphere. The dryness was associated
with widespread subsidence associated with the subtropical highs
described above. In situ soundings revealed classical subsidence-type
temperature/dew point profiles. Chemical data indicated that the
moisture and ozone/CO concentrations were consistently anti-correlated
with each other.
The
MOPITT evaluation area exhibited a scattered, thin layer of stratus
with tops ~6,000 ft. There also was a broken cumulus deck
with bases near 1500 ft, and tops reaching ~2500 ft. The
clouds in the MOPITT area today were not as uniform as encountered
yesterday.
Slight,
brief rain rainshowers were encountered near Guam.