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

• Published in: Journal of climate 2008-11, Vol.21 (22), p.5960-5975
• Main Authors: Kobashi, Fumiaki, Xie, Shang-Ping, Iwasaka, Naoto, Sakamoto, Takashi T.
• Format: Article
• Language: English
• Subjects: Atmospheric effects; Atmospheric moisture; Atmospherics; Baroclinic instability; Baroclinic mode; Baroclinity; Climatology. Bioclimatology. Climate change; Curl; Cyclonic winds; Data assimilation; Earth, ocean, space; Electric power; Exact sciences and technology; External geophysics; General circulation models; High seas; Humidity; Low pressure; Low pressure systems; Marine; Meteorology; Meteors; Oceanography; Oceans; Physics of the oceans; Precipitation; Remote sensing systems; Satellite observation; Sea level; Sea surface; Sea surface temperature; Sea-air exchange processes; Seasonal variations; Storm tracks; Storms; Studies; Surface temperature; Surface wind; Troposphere; Velocity; Vertical profiles; Water vapor; Water vapour; Wind; Wind stress; Wind stress curl; Wind velocity
• ISSN: 0894-8755; 1520-0442
• DOI: 10.1175/2008jcli2311.1

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.