Editorial Type:
Article
Article Type:
Research Article

Deep Atmospheric Response to the North Pacific Oceanic Subtropical Front in Spring

Fumiaki Kobashi Faculty of Marine Technology, Tokyo University of Marine Science and Technology, Tokyo, Japan

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Shang-Ping Xie International Pacific Research Center, and Department of Meteorology, University of Hawaii at Manoa, Honolulu, Hawaii

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Naoto Iwasaka Faculty of Marine Technology, Tokyo University of Marine Science and Technology, Tokyo, Japan

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Takashi T. Sakamoto Frontier Research Center for Global Change, Japan Agency for Marine-Earth Science and Technology, Kanagawa, Japan

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Print Publication:
15 Nov 2008
DOI:
https://doi.org/10.1175/2008JCLI2311.1
Page(s):
5960–5975
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Abstract

The North Pacific subtropical front (STF) is a zone of high sea surface temperature (SST) gradients located around 25°N in the western basin and is most pronounced in spring. The STF’s atmospheric effects are investigated using satellite observations and an atmospheric reanalysis. During April–May along the STF, surface wind stress curl turns weakly cyclonic in the general background of anticyclonic curls. Atmospheric column-integrated water vapor displays a pronounced meridional maximum along this surface trough, suggesting a deep vertical structure. Cyclonic wind curls occur intermittently at intervals of a few days along the STF in subsynoptic low pressure systems accompanying larger, synoptic highs in the main storm track to the north. In the subsynoptic surface lows, convective rain takes place with deep upward motion moistening the entire troposphere. The lows are enhanced by condensational heating, leading to the formation of weak cyclonic wind curls. The lows display vertical structure characteristic of baroclinic instability, suggesting that they are triggered by the passage of synoptic migratory highs and grow on the baroclinicity anchored by the SST front. The cyclonic wind curls appear to be related to a cloud/rainband associated with the so-called pre-baiu/meiyu front in May.

Corresponding author address: Fumiaki Kobashi, Tokyo University of Marine Science and Technology, Faculty of Marine Technology, Etchujima 2-1-6, Koto-ku, Tokyo 135-8533, Japan. Email: kobashi@kaiyodai.ac.jp

Abstract

The North Pacific subtropical front (STF) is a zone of high sea surface temperature (SST) gradients located around 25°N in the western basin and is most pronounced in spring. The STF’s atmospheric effects are investigated using satellite observations and an atmospheric reanalysis. During April–May along the STF, surface wind stress curl turns weakly cyclonic in the general background of anticyclonic curls. Atmospheric column-integrated water vapor displays a pronounced meridional maximum along this surface trough, suggesting a deep vertical structure. Cyclonic wind curls occur intermittently at intervals of a few days along the STF in subsynoptic low pressure systems accompanying larger, synoptic highs in the main storm track to the north. In the subsynoptic surface lows, convective rain takes place with deep upward motion moistening the entire troposphere. The lows are enhanced by condensational heating, leading to the formation of weak cyclonic wind curls. The lows display vertical structure characteristic of baroclinic instability, suggesting that they are triggered by the passage of synoptic migratory highs and grow on the baroclinicity anchored by the SST front. The cyclonic wind curls appear to be related to a cloud/rainband associated with the so-called pre-baiu/meiyu front in May.

Corresponding author address: Fumiaki Kobashi, Tokyo University of Marine Science and Technology, Faculty of Marine Technology, Etchujima 2-1-6, Koto-ku, Tokyo 135-8533, Japan. Email: kobashi@kaiyodai.ac.jp

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