Flight summary, DC-8 flight 15 - Yokota local 3 - 03/27/2001.
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.