Atmospheric sampling of Supertyphoon Mireille with NASA ...

1854 NEWELL ET AL: DC-8 SAMPLING OF TYPHOON MIREILLE
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Figure 1. Track of Typhoon Mireille from September 13-28, 1991 [from Rudolph and Guard, 1992].
Positions of ground stations Kenting and Oki Island are noted.
Aeronautics and Space Administration, has carried out
atmospheric sampling in various regions of the world.
In the typhoon system, there is a substantial lateral
inflow of air in the lower troposphere to compensate for
Measurements are used here from flights through a
typhoon during the Pacific Exploratory Mission-West A
(PEM-West A) NASA DC-8 deployment to the western
the rising convective motions and outflow aloft, and these
quasi-horizontal flows are also important in redistributing
trace constituents. An opportunity to carry out an
Pacific in September-October 1991. The instrumentation experiment to check this redistribution was presented when
carded on the DC-8 is described by Hoe# et al. [this issue] Typhoon Mireille approached an area to the south of Japan
and the background meteorology by Bachmeier et al. [this which could be accessed from Tokyo. Air emering the
issue]. Sampling was plmmed in two separate seasons: one typhoon in the surface boundary layer, in the eye itself,
toward the end of the summer monsoon and the other emerging from the eye and surrounding wall cloud region
toward the end of the winter monsoon. The summer in the upper troposphere, was sampled.
monsoon of the tropical western Pacific always includes a Typhoon Mireille was first noted on the weather maps
number of typhoons; five occurred during the 6 weeks of as a significant system on September 13, 1991, when
the first PEM-West deployment. The large-scale positioned at 12øN, 172øE moving westward (see Figure 1)
manifestation of atmospheric convection that these [from Rudolph and Guard, 1992] and qualified as a
typhoons represent could be important in the redistribution typhoon, with 1-min sustained winds exceeding 32 ms 'l,
of atmospheric trace constituents. In some previous on September 16 while at 15øN, 157øE. By September 22
it had turned toward the northwest and winds had increased
discussions of typhoons, there was debate as to why the air
mass in the eye was apparently different from the to 67 ms -1, qualifying Mireille as a "super typhoon." After
surrounding air mass. Bergeron [1954], referring to the September 23, Mireille began to slowly weaken, although
work of others, noted that "The two air masses are its size, as measured by the diameter of its outermost
separated by a boundary zone which sometimes has been closed isobar, continued to increase. On September 26,
taken for the tmpopause itself, sucked down from its Mireille turned northward, then northeastward, and made
normal height .... " In Bergeron's view, "It is more land in western Kyushu at about 0600 UT on September
plausible that this boundary zone has been formed by a 27. During the evening of September 27 it passed over the
similar process within the tropospheric air itself." In the Sea of Japan and gradually lost force, passing over
present experiment, ozone, a good stratospheric tracer, was northern Honshu and southern Hokkaido early on
measured to test these ideas.
September 28.