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.