Flight summary, DC-8 flight 19 - Kona local - 04/06/2001.
Take-off time 8:56 am local (1856Z); flight duration 10.3 hours
Title: Subsidence over East Pacific and MOPITT transect Objectives: (1)
To characterize aged continental outflow subsiding around the East Pacific
High; (2) to conduct a MOPITT underpass spiral as well as an extensive transect
along the Terra orbit track to validate horizontal gradients seen by MOPITT. (It
was unfortunately not possible on this flight to sample Asian outflow traveling
in the jet stream, because of a persistent blocking ridge over the central
Pacific that deflected the jet stream north of 50N).
Execution: We flew from Kona (20N, 156W) straight E to (20N, 140W) for
a MOPITT underpass spiral at (21N, 140W). From there we flew NNE to
(37N, 136W), remaining in the MOPITT orbit track throughout and with extensive
vertical profiling up to 28Kft. We then headed straight back to Kona
along a SW track, again with extensive vertical profiling, and flew a series
of low-altitude legs near Kona to characterize the chemistry of oxygenated
organics in the MBL.
Results: The objectives were met. The MOPITT spiral (from 33Kft down)
was conducted over a solid stratus deck with a few breaks and cloud tops
at 6Kft. There were no higher-altitude clouds. Above cloud tops
the CO concentrations were relatively uniform at 120 ppbv with a moderate
pollution layer at 18-22Kft (CO up to 150 ppbv). In the MBL below
cloud top was aged polluted air (150 ppbv CO, 1890 ppbv CH4,
high C2Cl4, etc). Remarkably high concentrations of
carbonyls and methylhydroperoxide were observed in the MBL. Heading
NNE on the MOPITT transect we sampled a variety of air masses with a fair
degree of layering and latitudinal structure (CO ranged from 80 to 210 ppbv). Solid
stratus (tops 4-6Kft) with a few breaks and no higher-altitude clouds persisted
for the duration of the transect. The CO/CH4/CO2 ratios
varied quite a bit between pollution layers, and CH4/CO ratios
were low in the higher-altitude layers, perhaps providing an indication
of European vs. Asian origin. Heading back SW we encountered a few more
aged pollution layers against a clean background, and persistently high
concentrations of CO below 5Kft (typically 150 ppbv). Low-altitude
legs at the end of the flight sampled air below, within, and above the stratus
cloud deck.
Meteorological Summary DC-8 Kona Local 6 April 2001
Relevant Flow Features:
Surface-A
weak subtropical low was located near 30N 165W. This system had been
moving slowly northward during the previous several days, showing little change
in intensity. A major area of high pressure was near 45N 150W. Its
axis was oriented northwest to southeast. A weaker high was centered
just south of Hawaii. The intertropical convergence zone was becoming better
defined south of Hawaii along ~5N.
Middle
troposphere-The weak subtropical low was almost vertically stacked, extending
through all flight levels. The major high northeast of Hawaii extended
through 500 mb and then became a ridge line at higher levels. This
feature brought northerly winds to the eastern leg of the flight track. The
subtropical high south of Hawaii was evident at all altitudes.
Upper
troposphere-Westerly flow dominated the flight track in the upper levels. The
closed subtropical low northwest of Hawaii and the ridge line east of the
Islands caused some directional changes along the northern part of the
track. The primary jet stream was far north of the flight track. However,
a wind maximum just east of Hawaii brought flight level winds to ~95 kt
in that area. Elsewhere, winds generally were less than 50 kt-sometimes
much less.
Cloud Patterns and Other Goodies:
The subtropical
low produced a broad area of low, middle, and high clouds. This area
had a north-south axis, extending as far east as the central Hawaiin Islands. The
wind maximum south and east of Hawaii produced a band of cirrus. Much
of the flight track was covered by stratocumulus clouds that often reached
broken to overcast conditions.
The MOPITT
spiral point (21N 140W) had good cloud conditions. Only overcast stratocumulus
were present, with occasional small breaks. Bases were near 4800 ft and
tops near 6300 ft. A few stratocumulus were at ~3,000 ft. The
trade wind inversion was near 6300 ft, separating moist air below from
very dry air aloft. The ensuing boundary layer run beginning near 2031Z
had a few, very light rain showers. During the climbout, cloud tops were
somewhat lower than below--~5100 ft.
The second
boundary layer run (near 2211Z) had broken cumulus clouds, with bases near
2900 ft and tops near 3500 ft. The trade wind inversion was well
defined near 3500 ft. This height was considerably lower than during
the first boundary run. The temperature at 500 ft (~12.8C) was cooler than
at the first boundary run (17.3C). During he climbout beginning near
2241Z, the trade wind inversion was not well defined, with relatively humid
ir extending into the middle troposphere.
The initial
part of the third boundary layer run (near 0028Z) had a broken layer of
clouds with bases of 3100 ft and tops of 5100 ft. A scattered layer
was at 2500 ft. The clouds became less common during the run. Winds
initially were from the north, but changed to a more northeasterly direction
as the leg continued.
The fourth
boundary layer run (beginning at 0213Z) included segments within the clouds
and above the clouds. The clouds in the area had more vertical development
than during previous runs. A scattered stratus deck was between ~6500
- 7500 ft. A broken layer of cumulus had bases of ~2000 ft and maximum
tops of ~7500 ft. Some of the taller clouds produced light rainshowers The "above-cloud" segment
did pass through some clouds.