Title: China outflow and frontal crossing   

Objectives: (1) to sample fresh pollution advected to the western Pacific from China in the boundary layer behind a cold front, (2) to cross the front and sample lifted pollution and clean air ahead of the front.   

Execution: Both aircraft went around Taiwan and headed north.  The P-3 remained close to the China coast, on a track extending up to 28N and returning along the same track.  The DC-8 headed north to (31N, 125E) and from there east to (30N, 140E) to cross the front; it then returned to Hong Kong on a SW track, remaining ahead of the front.   

Results: The objectives were met.  (1) High levels of fossil fuel and biomass burning pollution were sampled extensively behind the front, both in the boundary layer and in free tropospheric layers presumably lifted over China ahead of the front.  Strong pollution outflow was observed from 17Kft to 28Kft at 30N, with CO levels in excess of 270 ppbv.  Very dry subsiding layers were also observed.  The DC-8 crossed the front and sampled clean air ahead of the front, with isolated pollution layers in the free troposphere again from frontal uplift.  Air ahead of the front south of 24N was consistently clean.   P-3B observations included upper tropospheric conditions (15Kft) representative of tropical air to begin the flight (CO-70s, O3-20s). Polluted conditions were first encountered around 10Kft at 22N (CO-300s, O3-90s).  In the frontal region, cloud modulation of composition was recorded with changes in CO of 75% and doubling of NOy in and out of convective cells.  CO values to the north behind the front were in the high 200-300 range.  On the return to Hong Kong a well defined pollution layer only 1000 ft in thickness was encountered at 9Kft.  Values in this layer for CO were double those encountered in the boundary layer and ozone values were almost quadrupled compared to BL values.  On the last boundary layer leg, a ship plume was encountered that lasted 15 seconds with enhancements in NOy, particles, SO2, and CO2 as well as a significant titration of ozone.

Meteorological Summary DC-8 Hong Kong Local # 1

Relevant Flow Patterns
         Surface--A low pressure area was centered near 40N 140E.  A cold front extended southwest to ~ 25N, 110E.  A high pressure area was located near 25N, 150W.  Flow ahead of the front was mostly from the southwest. Behind the front, there was brisk northerly flow.  South of Hong Kong, there was onshore flow.

         Middle troposphere-A low pressure area was centered between Korea and Japan.  Subtropical highs stretched across the western Pacific, centered near 20N.  There was westerly flow over the entire flight area.

         Upper troposphere-The subtropical jet was just north of the Hong Kong area.  It merged with the polar jet stream near Japan.  A jet streak extended from the coast of Asia, across Japan, and into the western Pacific.  The DC-8 flew through the entrance (western) portion of this jet streak, encountering winds as strong as 157 kt.  There was westerly flow over the entire flight area.

Relevant Cloud Patterns
         Prior to reaching the cold front, clouds mostly were patchy, with areas of broken cumulus and cirrus.  The top of the haze layer near Hong Kong was ~10,500 ft.

         The first descent to the boundary layer was near 22N, 123E.  There were a few scud at 1,800 ft, with the main cloud base at 2,400 ft, and most tops at 5,000 ft.  A few stratus were near 6,500 ft.

         The DC-8 intersected the surface position of the front near 24N,125E.  Extensive clouds were behind the front.

The second descent to the boundary layer occurred near the northern point of the flight.  This was an area of extensive deep, multi-layered clouds that extended to near 20,000 ft.  The boundary layer run was shortened due to poor visibility and strong turbulence which persisted throughout the climb out.

         The DC-8 crossed the surface frontal position a second time near 30N, 134W.  Clouds rapidly diminished east of the front.  The aircraft remained on the warm side of the front throughout the remainder of the flight.  There was much less cloud cover in the warm air than the cold air.  Only scattered clouds were encountered during the remainder of the flight-usually scattered, but sometimes broken.  Very dry middle tropospheric air was encountered during middle portion of the southward leg.  This was due to subsidence associated with the subtropical highs. There was some enhanced cirrus as the aircraft approached Hong Kong.