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    Air–Sea Heat Exchanges Characteristic of a Prominent Midlatitude Oceanic Front in the South Indian Ocean as Simulated in a High-Resolution Coupled GCM

    Source: Journal of Climate:;2009:;volume( 022 ):;issue: 024::page 6515
    Author:
    Nonaka, Masami
    ,
    Nakamura, Hisashi
    ,
    Taguchi, Bunmei
    ,
    Komori, Nobumasa
    ,
    Kuwano-Yoshida, Akira
    ,
    Takaya, Koutarou
    DOI: 10.1175/2009JCLI2960.1
    Publisher: American Meteorological Society
    Abstract: An integration of a high-resolution coupled general circulation model whose ocean component is eddy permitting and thus able to reproduce a sharp gradient in sea surface temperature (SST) is analyzed to investigate air?sea heat exchanges characteristic of the midlatitude oceanic frontal zone. The focus of this paper is placed on a prominent SST front in the south Indian Ocean, which is collocated with the core of the Southern Hemisphere storm track. Time-mean distribution of sensible heat flux is characterized by a distinct cross-frontal contrast. It is upward and downward on the warmer and cooler flanks, respectively, of the SST front, acting to maintain the sharp gradient of surface air temperature (SAT) that is important for preconditioning the environment for the recurrent development of storms and thereby anchoring the storm track. Induced by cross-frontal advection of cold (warm) air associated with migratory atmospheric disturbances, the surface flux is highly variable with intermittent enhancement of the upward (downward) flux predominantly on the warmer (cooler) flank of the front. Indeed, several intermittent events of cold (warm) air advection, whose total duration accounts for only 21% (19%) of the entire analysis period, contribute to as much as 60% (44%) of the total amount of sensible heat flux during the analysis period on the warmer (cooler) flank. This antisymmetric behavior yields the sharp cross-frontal gradient in the time-mean flux. Since the flux intensity is strongly influenced by local magnitude of the SST?SAT difference that tends to increase with the SST gradient, the concentration of the flux variance to the frontal zone and cross-frontal contrasts in the mean and skewness of the flux all become stronger during the spinup of the SST front. Synoptically, the enhanced sensible heat flux near the SST front can restore SAT toward the underlying SST effectively with a time scale of a day, to maintain a frontal SAT gradient against the relaxing effect of atmospheric disturbances. The restoration effect of the differential surface heating at the SST front, augmented by the surface latent heating concentrated on the warm side of the front, represents a key process through which the atmospheric baroclinicity and ultimately the storm track are linked to the underlying ocean.
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      Air–Sea Heat Exchanges Characteristic of a Prominent Midlatitude Oceanic Front in the South Indian Ocean as Simulated in a High-Resolution Coupled GCM

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    contributor authorNonaka, Masami
    contributor authorNakamura, Hisashi
    contributor authorTaguchi, Bunmei
    contributor authorKomori, Nobumasa
    contributor authorKuwano-Yoshida, Akira
    contributor authorTakaya, Koutarou
    date accessioned2017-06-09T16:29:29Z
    date available2017-06-09T16:29:29Z
    date copyright2009/12/01
    date issued2009
    identifier issn0894-8755
    identifier otherams-68821.pdf
    identifier urihttp://onlinelibrary.yabesh.ir/handle/yetl/4210421
    description abstractAn integration of a high-resolution coupled general circulation model whose ocean component is eddy permitting and thus able to reproduce a sharp gradient in sea surface temperature (SST) is analyzed to investigate air?sea heat exchanges characteristic of the midlatitude oceanic frontal zone. The focus of this paper is placed on a prominent SST front in the south Indian Ocean, which is collocated with the core of the Southern Hemisphere storm track. Time-mean distribution of sensible heat flux is characterized by a distinct cross-frontal contrast. It is upward and downward on the warmer and cooler flanks, respectively, of the SST front, acting to maintain the sharp gradient of surface air temperature (SAT) that is important for preconditioning the environment for the recurrent development of storms and thereby anchoring the storm track. Induced by cross-frontal advection of cold (warm) air associated with migratory atmospheric disturbances, the surface flux is highly variable with intermittent enhancement of the upward (downward) flux predominantly on the warmer (cooler) flank of the front. Indeed, several intermittent events of cold (warm) air advection, whose total duration accounts for only 21% (19%) of the entire analysis period, contribute to as much as 60% (44%) of the total amount of sensible heat flux during the analysis period on the warmer (cooler) flank. This antisymmetric behavior yields the sharp cross-frontal gradient in the time-mean flux. Since the flux intensity is strongly influenced by local magnitude of the SST?SAT difference that tends to increase with the SST gradient, the concentration of the flux variance to the frontal zone and cross-frontal contrasts in the mean and skewness of the flux all become stronger during the spinup of the SST front. Synoptically, the enhanced sensible heat flux near the SST front can restore SAT toward the underlying SST effectively with a time scale of a day, to maintain a frontal SAT gradient against the relaxing effect of atmospheric disturbances. The restoration effect of the differential surface heating at the SST front, augmented by the surface latent heating concentrated on the warm side of the front, represents a key process through which the atmospheric baroclinicity and ultimately the storm track are linked to the underlying ocean.
    publisherAmerican Meteorological Society
    titleAir–Sea Heat Exchanges Characteristic of a Prominent Midlatitude Oceanic Front in the South Indian Ocean as Simulated in a High-Resolution Coupled GCM
    typeJournal Paper
    journal volume22
    journal issue24
    journal titleJournal of Climate
    identifier doi10.1175/2009JCLI2960.1
    journal fristpage6515
    journal lastpage6535
    treeJournal of Climate:;2009:;volume( 022 ):;issue: 024
    contenttypeFulltext
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