Flight summary, DC-8 flight 18 - Yokota-Kona -
04/04/2001 (arr. 04/03/2001).
Take-off time 8:39 am local (2239Z); flight duration 9.1 hours
Title: High-altitude Asian outflow and sunset MBL chemistry Objectives: (1)
To sample the warm conveyor belt associated with a frontal passage
over Japan; (2) to sample high-altitude biomass burning outflow
and subsiding Asian pollution over the central Pacific; (3) to
characterize MBL chemistry across sunset; (4) to conduct a MOPITT
validation experiment.
Execution: We flew a straight track from Yokota to Kona with a
dog leg to the south towards the end for the sunset MBL experiment. A
series of vertical profiles from cruise altitude (33-37Kft) down
to 0.5 Kft were conducted, in coordination with the P-3 (flying
the same track) to obtain a curtain of atmospheric composition. The
sunset MBL chemistry experiment was done in background tropical
air from (24N, 173W) to (22N, 166W), and consisted of a sequence
of two 1Kft legs on both sides of sunset with a 20-min 10Kft leg
in between.
Results: The MOPITT validation experiment had to be scrapped because
of clouds. The other objectives were met. Coordination
with the P-3 worked well and we achieved a high degree of complementarity
in sampling along the flight track. Climbing out of Yokota
we encountered a stratospheric intrusion between 18 and 28Kft (behind
the front located east of Japan). Heading south we sampled two
principal Asian outflow features: a high-altitude outflow above
20Kft with increasing biomass burning signature as we got further
south, and a low-altitude outflow below 8Kft of dominantly industrial
origin and which appeared to be due to recirculation of pollution
around the western Pacific High. Crossing the dateline on
a 1-hour leg at 31Kft we observed a transition into a highly polluted
layer beginning at 177W (CO up to 240 ppbv, ozone 110 ppbv, HCHO
160 pptv, non-volatile aerosol, high CH3CN, high C2Cl4);
this layer could be attributed from the forecasts to biomass burning
in SE Asia although the high C2Cl4 is not
consistent with this explanation. The first 1 Kft leg of
the sunset MBL chemistry experiment indicated extremely high concentrations
of carbonyls and methylhydroperoxide, dropping with altitude. Concentrations
of HNO3 were puzzlingly high (150 pptv). The second
1Kft leg had higher wind speeds (14 vs. 3 knots). Going
back up to cruise altitude before reaching Kona revealed several
high-ozone layers, some correlated with CO while others of stratospheric
origin.
Meteorological Summary DC-8 Yokota to Kona Transit 4
April 2001
Relevant Flow Features:
Surface-Two
frontal systems affected the weather along the flight track. A
developing wave cyclone was centered near 50N, 150E, with a cold
front extending southward. This front had passed through
Yokota during the previous afternoon, bringing abruptly cooler
temperatures and light rain. The second system was a deeply
occluded low just west of Alaska. Although its trailing cold front
influenced the eastern third of the flight track, this southern
portion of the front was very weak. Major surface anticyclones
were located near 40N, 170E and 40N, 145W
Middle
Troposphere-Troughs were located just east of Japan and along 175W,
in association with the surface lows described above. A well
developed subtropical high was centered near 20N, 160E, while a
weaker high was located north of Hawaii, near 35N, 155W. A
weak middle level low was developing southwest of Hawaii. Middle
level winds were predominately westerly over the flight track.
The only exception was northwest of Hawaii where southerly and
easterly winds were occurring.
Upper
Troposphere-The axis of the jet stream was near 30N over the western
two-thirds of the flight track, but extended farther north over
the eastern third of the track. The jet stream was not as
intense as during earlier flights. Winds had a strong westerly
component over the entire flight track.
Cloud Features and Other Goodies:
The
flight track was relatively cloudy. Major comma shaped cloud
patterns were associated with each of the major wave cyclones described
above. The flight track of the DC-8 traversed the extensive
area of multiple layered clouds associated with the westernmost
system. Mid and high level clouds prevented a MOPITT evaluation
between 150-160E. Flight track clouds associated with the
eastern feature were not nearly so widespread. The region
between the two systems-near the date line-was relatively cloud
free.
Stratospheric
air was encountered at relatively low levels (~17,000 ft) during
the climbout from Yokota, i.e., behind the cold front described
above. This area was in the entrance region of the jet stream.
Weaker stratospheric air was encountered just west of Kona.
The
first boundary layer run (near 0025Z) had multiple layered clouds
providing overcast conditions. Winds at 500 ft were from
170 deg at 36 kt-stronger than encountered on most previous runs. The
sea surface exhibited well developed white caps. This run
occurred on the warm side of the westernmost cold front. The
second boundary layer run (near 0217Z) had broken stratocumulus
with bases ~3500 ft and tops ~4500 ft, as well as scattered cirrus. The
third boundary layer run (near 0442Z) contained a variety of cumulus,
altocumulus, and cirrus, yielding a broken ceiling. Some cumulus
reached as high as 15,000 ft, providing rain showers in the area.
The chemical effects of these showers were observed during the
subsequent leg at 10,000 ft. The trade wind inversion near
6,500 ft was observed during the ascent/descent of the 3rd run.
Sunset
occurred near 0432Z. Some clouds were present during the
fourth boundary layer run (near 0554Z); however, the darkness prevented
a good observation of them.