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.