Flight summary, DC-8 Hong Kong local 4 - 03/13/2001.
Title: Aged Asian outflow
Objectives: (1) to sample aged Asian outflow slowly transported
southeastward in the lower troposphere over the western Pacific
around a weak high pressure system, (2) to sample strongly subsiding
air with stratospheric influence capping this Asian outflow, (3)
to sample upper tropospheric outflow from biomass burning in southeast
Asia.
Execution: We flew an extended wall from HK east to (22N,
136E) with extensive low-altitude sampling on the eastern half
of the wall . On the return we extended the wall south to
(18N, 114E), with focus on high altitudes, in order to sample the
biomass burning outflow.
Results: The flight was a success. Aged Asian pollution
was consistently observed below 5Kft on the extended wall; this
pollution was characterized by CO up to 190 ppbv, O3 up to 70 ppbv,
high C2Cl4, high PAN, high sulfate (but low SO2), moderately high HCHO. Above
5 Kft the aircraft sampled strongly subsiding air with occasional
evidence of stratospheric influence and some aged pollution layers
at altitudes below 15 Kft (though not as strong as below 5 Kft). On
the return the aircraft sampled combustion plumes in the upper
troposphere (31-39 Kft) with high and correlated CO (up to 140
ppbv), CO2, O3, and aerosol (including a large non-volatile component);
these plumes were probably of biomass burning origin although no
confirmation of this was available from the flight data.
Meteorological Summary DC-8 Hong Kong Local # 4
Relevant Flow Features
Surface-A
high pressure area was centered over South Korea. No fronts were located
within the flight area. Most of the flight track experienced easterly
or northeasterly low-level flow.
Middle
troposphere-Westerly flow dominated the flight track by the 500
mb (~18,000 ft) level. A short wave trough was located just
east of Japan, and a closed anticyclone was located near Southeast
Asia.
Upper
troposphere-A major subtropical anticyclone was located near 15N,
155W. A short wave trough was located near Japan. The polar
jet stream was better defined than on most previous missions-it
extended over northern Asia. The subtropical jet stream stretched
across southern Asia. The two jets merged east of Japan. The
DC-8 traversed the southern portion of the jet streak east of Japan. Westerly
flow covered the entire flight area.
Relevant Cloud Patterns
Abundant
low level clouds blanketed the flight track. They typically
had bases near 3000 ft and tops near 5,000 ft. Middle and upper
level clouds were virtually absent over the area.
Southeast
Asia had been experiencing scattered deep convection over the past
several days, and this continued today. The Indonesia area
also exhibited convection. Trajectories indicated that upper
level outflow from these storms had been transported toward the
DC-8 flight track.
Water
vapor imagery denoted an area of dry middle tropospheric air over
the northeast portion of the flight area. This dry air probably
was associated with subsidence due to the jet streak and the surface
anticyclone in the area. In situ data showed that the dry
air extended as low as 5400 ft. Other portions of the flight
track were relatively humid in the middle levels.