Flight summary, Hong Kong Local 1 03/07/2001.
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.