Take-off time 8:36 am local (2336Z on 0326); flight duration 9.4 hours  Title: Convective outflow and stratospheric influence  

Objectives: (1)  to sample high- and mid-level outflow from intense convective activity and convergence developing over SE Asia and China; (2) to sample a tropopause depression wrapped around the jet stream; (3) to sample dust outflow from northern China.  

Execution: The DC-8 conducted two extended walls along the Asian coast, one at 133-139E and one at 125E.  After take-off from Yokota (36N, 139E), we flew SW to (23N, 133E) for our first wall to sample outflow from deep convection and convergence over Asia, and from there headed W to (25N, 125E) where we set up the second wall headed north into the Yellow Sea (37N, 125E).  The purposes of this second wall were to sample convective outflow at all levels south of 30N, a depression of the tropopause around the jet stream at 30-32N, and dust outflow further north.  We then backtracked to (33N, 125E), returning to Yokota around Korea and through the Sea of Japan.  

Results: The objectives were in general met and the flight yielded some surprises.  The first wall SW out of Yokota showed considerable Asian outflow at all levels as well as stratospheric filaments at the higher levels.   Above 10Kft the outflow appeared to be of convective and mainly biomass burning origin (up to 200 ppb CO, high CH₃CN, low C₂Cl₄, low SO₂). Below 10Kft the outflow was mostly industrial (up to 300 ppb CO, high C₂Cl₄) and appeared to reflect post-frontal boundary layer outflow as well as weak convergent lifting over eastern Asia.  Ozone showed complicated correlations with CO and CO₂ in these profiles.  During the W leg at our southernmost point we saw boundary layer outflow up to 5 Kft capped by clean tropical air; climbing up for a leg at 33Kft at (24N, 132E) we sampled outflow from a nearby marine thunderstorm (NO up to 600 pptv, high CH₃OOH/H₂O₂, low ozone, high methylnitrate, low aldehydes, etc) superimposed first on clean tropical air but then later on biomass burning outflow.  On our wall heading north at 125E we saw considerable outflow at all levels south of 30N and then ran a constant-altitude leg at 33Kft where we observed the sharp stratospheric intrusion at 30-32N forecast from the models.  Profiling down to the boundary layer over the Yellow Sea yielded considerable outflow structure, again as forecast, with pollution layers in the free troposphere (convergent lifting over eastern China). This pollution outflow in the free troposphere over the Yellow Sea was in contrast to previous flights in the region where the pollution was confined to the boundary layer and was strongly capped by clean subsiding air.  Flying back to Yokota we observed additional pollution layers as well as a dust layer at 10-15Kft over Japan.   Boundary layer air over Yokota was highly polluted, with over 400 ppm CO₂.  

Meteorological Summary DC-8 Yokota Local # 3  27 March 2001

Relevant Flow Patterns
         Surface-Twin low pressure areas were centered over extreme southeastern Russia and over extreme northeastern Japan.  A surface cold front extended southeast to near 30N 160E and then west to near Taiwan. The Siberian anticyclone was well defined, with a weaker high over South Korea.  A weak low was developing just south of Taiwan.  Surface winds were from the northeast or east over most of the flight area.

         Middle troposphere-Closed low pressure was just northwest of Japan. The subtropical high was just east of the Philippines.  Westerly flow covered the flight track.  On a broader scale, a sharp ridge was over central Asia, while more zonal flow was south of about 35N.  The effects of this split flow were evident in the backward trajectories.

         Upper troposphere-The jet stream had strengthened considerably just south of Japan.  A zone of winds exceeding 160 kt extended eastward from near Shanghai to ~155E.  The split flow described above continued.

Relevant Cloud Patterns

         On the broad scale, an extensive cloud band was associated with the wave cyclone and frontal system described above.  Details along the flight track are described below.

         As we headed south from Yokota, clouds rapidly increased at all altitudes.   The first boundary layer run (near 0130Z) had overcast clouds at multiple layers.  Occasional light rain occurred, and the ceiling was ragged, with some scud at flight level.  As we ascended, we appeared to pass through the frontal boundary at ~6,000 ft, where a sharp chemical transition was observed.

The second boundary layer run (near 0315 Z) also was overcast, with fog.  The southerly winds at this point suggested that we were near the surface position of the old front.  Clouds were at multiple levels. At the beginning of the segment, light rain occurred.  However, as the segment continued, the rain became very heavy (near 0424Z).  Considerable sharp turbulence was encountered.  As we ascended, cloud tops were ~ 33,000 ft.  Stratospheric air was encountered at 33,000 ft beginning near 0440 Z.

          The Yellow Sea had broken to overcast clouds at multiple levels. Winds at 2,000 ft (3rd boundary layer run) were from the east-contrasting with the westerly winds encountered there on previous flights.  The fourth boundary layer run (near 0613ZZ) had overcast stratocumulus with bases near 5,000 ft.  Finally, the fifth boundary layer run in the Sea of Japan (near 0733Z) had an overcast deck of altostratus near 18,000 ft.