Flight summary, DC-8 flight 11 Hong Kong - Okinawa 2 - 03/17/2001.
Title: MOPITT validation and China outflow Objectives: (1) to
conduct a MOPITT validation experiment in a relatively uniform
column (away from major Asian influence); (2) to sample China outflow
forecast in the lower free troposphere at 25-30N.
Execution: We flew from HK SE to (20N, 123E) for the MOPITT validation
experiment, which consisted of two successive spirals above the
same point bracketing in time the satellite overpass. We
then went E and NE to (30N, 139E) to sample a forecast gradient
of increasing China outflow going north, and then W and S into
Okinawa (26N, 128E), to remain in that outflow. As usual,
extensive in-progress vertical profiling was conducted.
Results: The objectives were met and the flight yielded some surprises.
The MOPITT validation spot was in clear sky with only a few scattered
low clouds; the spiral extended from 0.5 to 33Kft. CO was
flat at 90 ppbv above 10Kft, and was enhanced below 10Kft with
values of typically 130 ppbv (max. 150 ppbv). On vertical
profiles for the rest of the flight we consistently encountered
at 23-28Kft a "mystery layer" with high ozone (80-100
ppbv), flat CO, depressed CO2, and high PAN. At
30N this mystery layer had ozone up to 120 ppbv with flat but relatively
high CO (160 ppbv), depressed CO2, high benzene, nitriles,
PAN, low HNO3. relatively high NO. Our best
guess was that this mystery layer represented African biomass burning
outflow, but it could have been a soup of different tropical influences. Below
20Kft Asian pollution outflow was observed, with maximum in free
troposphere and increasing with latitude. This Asian outflow
contained high PAN, high C2Cl4, high N2O,
only modest O3 enhancement (60 ppbv), and little HCHO
enhancement. A possible source, on the basis of the chemical
forecasts, is outflow from the high-elevation Szechuan Basin in
central China. At our NE waypoint (30N, 139E) the CO concentration
reached 330 ppbv and CO2 reached 386.4 ppmv, the
highest observed in the mission so far. The strong Asian
influence extended down to the surface, an unexpected result in
view of the forecast onshore flow there. At 2.5 km the depolarization
of the lidar return signal indicated the presence of high concentrations
of non-spherical particles.
Meteorological Summary DC-8 Transit from Hong Kong to Kadena
AFB Henry Fuelberg
Relevant Flow Features
Surface-A developing wave cyclone was located near Shanghai. An
anticyclone was centered just east of Tokyo. The wave cyclone
intensified during the day and moved eastward. Its associated
cold front also swept toward the east, passing Kadena between 0700
- 0800 Z-just before our landing. Surface winds over most
of the area were from the south or east. However, winds behind
the front were from the north.
Middle troposphere-The subtropical high was located over the
northern Philippines. A short wave trough was just west of the
Yellow Sea. Westerly winds dominated the flight area.
Upper troposphere-Westerly flow continued over the flight area.
The polar and subtropical jet streams continued to be clearly separated
over the area. The axis of the polar jet stream passed over
northern Japan. The subtropical jet stream was located near
30N. Its area of maximum speeds (the jet streak) was over
the Shanghai area. This location is somewhat farther west
than on the previous several days.
Relevant Cloud Features
The MOPITT validation area near 20N, 123E was virtually cloud
free. Only isolated small cumulus were present. Some cirrus
were located south of the spiral points, but these clouds never
were overhead.
The boundary layer run near 0411 Z had only scattered cumulus
clouds with bases of 1800 ft and tops of 2400 ft.
Clouds increased greatly shortly after the third boundary layer
run. During the ascent, a deep cloud layer with tops near
15,000 ft was encountered. Some of the clouds appeared convective
shortly after our turn to the west near 0615 Z. A few isolated
tall towers were noted near 0652 Z. These towers probably were
associated with the surface position of the cold front.