Flight summary, Guam-Hong Kong transit 03/04/2001.
Title: Asian outflow: frontal, convective, and South China Sea
Objectives: (1) to intercompare instruments on the two aircraft;
(2) to sample a variety of outflow patterns including post-frontal
boundary layer outflow off the China coast, biomass burning outflow
convected to the upper troposphere, and boundary layer outflow
to the South China Sea.
Execution: The intercomparison experiment was conducted in the
boundary layer out of Guam. The DC-8 and the P-3 flew parallel
to each other (separated by 2000') for 20 minutes at 0.5Kft and
then remained parallel as they climbed to 10Kft at a rate of 500'/min. The
P-3 then flew WNW from Guam to the strait between the Philippines
and Taiwan (20N, 121E) and conducted a southerly leg to (16N, 115E)
to sample outflow over the South China Sea. The DC-8 flew
NW to (27N, 126E) to cross a cold front moving across the western
Pacific, and then S to overfly the P-3 and provide DIAL coverage.
Results: All objectives were met. (1) The intercomparison
was successfully conducted, in clear skies with broken shallow
cumuli. The first half of the intercomparison was done in
a homogeneous air mass but the second half showed significant gradients
that will need to be investigated (aged ship plume?). (2)
Complex pollution outflow of biomass burning origin was observed
in the upper troposphere along the DC-8 NW leg. (3) The frontal
crossing experiment was successful, showing a sharp contrast in
the lower troposphere between clean air ahead of the front and
highly polluted air behind the front off the coast of China. The
polluted post-frontal boundary layer outflow was capped by a strong
subsidence inversion at 7Kft and filaments of stratospheric air
were observed at higher altitudes. (4) Strong northerly outflow
to the South China Sea was observed in a highly polluted layer
extending up to 8Kft.
Meteorological Summary DC-8 Guam to Hong Kong
Relevant Flow Patterns
At the surface,
a low pressure area was centered just north of Korea. A cold front extended
south of the low. Air ahead of the front was blowing from the south or
southeast. Behind, the front, winds were strongly out of the northwest. Surface
winds in the Hong Kong area were out of the northeast.
The
low pressure over Korea persisted throughout the vertical column. Winds
became more westerly with increasing altitude. The northeastly
low level flow near Hong Kong also became westerly by 15,000 ft. The
axis of the jet stream was located near 32oN. Our flight
track intruded on the right rear quadrant of the jet streak. Peak
winds encountered by the DC-8 were ~ 135 kt.
Relevant Cloud Features
The
area of P-3 and DC-8 intercomparison was virtually free of all
clouds. Only scattered cumulus and a few cirrus strands
were observed. Cloud bases of the cumulus were ~2000 ft, with
tops at ~4000 ft. A few isolated thin stratus were near 4,000
ft. The trade wind inversion in this area was located near
7,000 ft (moist air below and very dry air aloft).
The
DC-8 intersected the surface position of the cold front near 22oN,
132oE. This area had a rather uniform and solid deck of stratocumulus.
Fewer clouds were located behind the front.
The
descent area near the northern-most flight point was very hazy. Although
difficult to estimate due to the absence of landmarks, visibility
was ~ mile. The top of the haze layer was at ~8,000 ft. This
probably corresponded to the top of the cold air mass. There
were only isolated clouds in this area. Winds at 1000 ft
were from 310o at ~30 kt. There was considerable turbulence in
this flight segment.
The
descent area farther south also was very hazy. The top of
the haze layer again was ~8,000 ft. There were broken cumulus in
the area. Maximum cloud tops were ~3500 ft. Winds at 1,000
ft. were from the northeast. They shifted rapidly with height
to westerly near 8,000 ft.