Low-level cool air over the midlatitude oceans in summer

Teruhisa Shimada, Yuki Kanno, Toshiki Iwasaki

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1 Citation (Scopus)


The climatology of low-level cool air over the midlatitude oceans in summer is presented based on an isentropic analysis. This study focuses on isentropic surfaces of 296K to analyze an adiabatic invariant referred to as the negative heat content representing the coldness of the air layer below the threshold isentropic surface. This approach allows a systematic analysis and a quantitative comparison of the cool air distribution and a diagnosis of diabatic heating of the air mass. The cool air covers most of the subarctic oceans and extends equatorward over the coastal upwelling regions in the east of the ocean basins. In these regions, the genesis of the cool air is diagnosed. The loss of the cool air occurs over land and the subtropical oceans, particularly on the offshore side of the coastal upwelling regions. In the Pacific sector and the Indian Ocean sector of the Southern Ocean, another large loss of the cool air occurs along the oceanic frontal zone including the Agulhas Return Current. Over the zonally extended region where the cool air is generated in the Southern Hemisphere and the coastal upwelling regions, it is suggested that diabatic cooling associated with low-level clouds overcome heating by turbulent surface heat fluxes. The genesis of the cool air over the subarctic oceans in the Northern Hemisphere in the warm season switches into the loss of the cold air in the cool season on a basin scale. Meanwhile, over the oceans in the Southern Hemisphere, there is no basin-scale seasonal switch.

Original languageEnglish
Pages (from-to)2075-2090
Number of pages16
JournalJournal of Climate
Issue number5
Publication statusPublished - 2018 Mar 1


  • Atmosphere-ocean interaction
  • Atmosphere-ocean interaction
  • Climatology
  • Isentropic analysis
  • Summer/warm season

ASJC Scopus subject areas

  • Atmospheric Science


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