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| Titel |
Investigation on the variability of East Asia Boreal Summer Front Frequency and Linkage between Tropical Air Temperature |
| VerfasserIn |
Eunho Choi, Gyu-Ho Lim |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250124230
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| Publikation (Nr.) |
 EGU/EGU2016-3629.pdf |
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| Zusammenfassung |
| Summer time front is one of the most significant phenomena over East Asia including China,
Korea and Japan. Many efforts have been established to understand the nature of
front.
However, there was no research conducting identifying East Asia summer time fronts
objectively. We have established objective front recognition method. The method follows next
procedures : 1) We calculate vorticity on 850-hPa surface. 2) Any grid point that have
horizontal gradient of equivalent potential temperature (EPT hereafter) on 850-hPa surface
less than 4 ‘c / 100km set to zero. 3) Next, we smooth this field using 9-point smoothing
technique. 4) Finally we extract the main axis of closed contour correspond to vorticity of 1.5
10-5s-5. Voronoi diagram used to extract this axis. We define this axis as front on 850-hPa
pressure surface.
We have applied the method on 1981-2010 ERA-Interim dataset. From the result, front
frequency maximums are in around of East China Sea (34N, 122E), north (38N, 136E) and
south (34N, 140E) of main island of Japan. Below 30N and above 40N, front frequency tends
to decrease maybe due to decrease in the magnitude of gradient of EPT and the frequency of
cyclonic weather disturbance.
Two main regions affect the variability of East Asia Front Frequency. One is equatorial
positive region especially over Taiwan (25N, 120E). The other one is East Sea next to Korea
(40N, 135E). Humid warm air transported from southern China (20N-30N, 100E-110E) and
dry cold air transported from northern China (30N-40N, 100E-110E) compressed by
clockwise high system over Taiwan and counter-clockwise low system over East Sea). This
compressed precipitation-making system or front moves by extratropical westerly and
transported out to north-western Pacific.
It looks like geopotential over Taiwan affected by tropical activity, especially vertical
integration of temperature (VIT hereafter) over tropical region (30S-30N). When VIT is
higher than normal, geopotential over Taiwan also higher than normal with correlation
coefficient of 0.5 (1981-2010). Therefore, we can conclude that when VIT is higher than
normal, front frequency is higher than normal. VIT is significantly related with ENSO
variability. We will investigate how the tropical region activity affects the front frequency
over East Asia. |
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