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Interhemispheric Coupling Study by Observations and Modelling (ICSOM)
  • +26
  • Kaoru Sato,
  • Yoshihiro Tomikawa,
  • Masashi Kohma,
  • Ryosuke Yasui,
  • Dai Koshin,
  • Haruka Okui,
  • Shingo Watanabe,
  • Kazuyuki Miyazaki,
  • Masaki Tsutsumi,
  • Damian Murphy,
  • Chris Meek,
  • Yufang Tian,
  • Manfred Ern,
  • Gerd Baumgarten,
  • Jorge L. Chau,
  • Xinzhao Chu,
  • Richard L. Collins,
  • Patrick Joseph Espy,
  • Hiroyuki Hashiguchi,
  • Andrew John Kavanagh,
  • Ralph Latteck,
  • Franz-Josef Luebken,
  • Marco Milla,
  • Satonori Nozawa,
  • Yasunobu Ogawa,
  • Kazuo Shiokawa,
  • M. Joan Alexander,
  • Takuji Nakamura,
  • William Edmund Ward
Kaoru Sato
University of Tokyo

Corresponding Author:[email protected]

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Yoshihiro Tomikawa
National Institute of Polar Research
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Masashi Kohma
University of Tokyo
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Ryosuke Yasui
Meteorological Research Institute, Japan Meteorological Agency
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Dai Koshin
The University of Tokyo
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Haruka Okui
The University of Tokyo
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Shingo Watanabe
Japan Agency for Marine-Earth Science and Technology
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Kazuyuki Miyazaki
Jet Propulsion Laboratory
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Masaki Tsutsumi
National Institute of Polar Research
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Damian Murphy
Australian Antarctic Division
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Chris Meek
Institute of Space and Atmospheric Studies, University of Saskatchewan
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Yufang Tian
Institute of Atmospheric Physics,Chinese Academy of Sciences
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Manfred Ern
Forschungszentrum Jülich
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Gerd Baumgarten
Leibniz-Institute of Atmospheric Physics at the Rostock University
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Jorge L. Chau
Leibniz-Institute of Atmospheric Physics at the University of Rostock
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Xinzhao Chu
University of Colorado Boulder
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Richard L. Collins
University of Alaska Fairbanks
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Patrick Joseph Espy
Norwegian University of Science and Technology
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Hiroyuki Hashiguchi
Research Institute for Sustainable Humanosphere, Kyoto University
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Andrew John Kavanagh
British Antarctic Survey
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Ralph Latteck
Leibniz-Institute of Atmospheric Physics (LG)
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Franz-Josef Luebken
Leibniz-Institute of Atmospheric Physics (LG)
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Marco Milla
Pontificia Universidad Católica del Perú
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Satonori Nozawa
Institute for Space-Earth Environmental Research, Nagoya University
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Yasunobu Ogawa
National Institute of Polar Research
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Kazuo Shiokawa
Institute for Space-Earth Environmental Research, Nagoya University
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M. Joan Alexander
NorthWest Research Associates, CoRA Office
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Takuji Nakamura
National Institute of Polar Research
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William Edmund Ward
University of New Brunswick
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Abstract

An international joint research project, entitled Interhemispheric Coupling Study by Observations and Modelling (ICSOM), is ongoing. In the late 2000s, an interesting form of interhemispheric coupling (IHC) was discovered: when warming occurs in the winter polar stratosphere, the upper mesosphere in the summer hemisphere also becomes warmer with a time lag of days. This IHC phenomenon is considered to be a coupling through processes in the middle atmosphere (i.e., stratosphere, mesosphere, and lower thermosphere). Several plausible mechanisms have been proposed so far, but they are still controversial. This is mainly because of the difficulty in observing and simulating gravity waves (GWs) at small scales, despite the important role they are known to play in middle atmosphere dynamics. In this project, by networking sparsely but globally distributed radars, mesospheric GWs have been simultaneously observed in seven boreal winters since 2015/16. We have succeeded in capturing five stratospheric sudden warming events and two polar vortex intensification events. This project also includes the development of a new data assimilation system to generate long-term reanalysis data for the whole middle atmosphere, and simulations by a state-of-art GW-permitting general circulation model using reanalysis data as initial values. By analyzing data from these observations, data assimilation, and model simulation, comprehensive studies to investigate the mechanism of IHC are planned. This paper provides an overview of ICSOM, but even initial results suggest that not only gravity waves but also large-scale waves are important for the mechanism of the IHC.