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第 195 回 大気海洋物理学・気候力学セミナー のおしらせ

日　時： 7月 9日(木) 午前 09:30
場　所： 低温科学研究所 3階 講堂 Auditorium, Institute of Low Tem. Sci.

発表者：堀之内 武 \\Takeshi Horinouchi (地球環境科学研究院 Faculty of Environmental Earth Science)
題　目：自発的なハドレー循環？\\Spontaneous Hadley circulation?

発表者：Prescilla Kurien (Course in atmosphere-ocean climate dynamics DC3)
題　目：Mesoscale variability along the east coast of India in spring and fall revealed in satellite data and OGCM

発表者：正木 登 \\Noboru MASAKI (地球圏科学専攻 M2)
題　目：森林粗度層における乱流の空間スケールに関する観測的研究(修士論文所信表明)

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自発的なハドレー循環？\\Spontaneous Hadley circulation? (堀之内 武 \\Takeshi Horinouchi) 発表要旨 :

  
 ハドレー循環は，低緯度ほど高い SST による直接循環として理解され 
 ている．その基本的な枠組みは Held and Hou (1980) により与えられ，発展 
 してきた．ところが，大気GCMによる数値実験により，SST が一様，つまり 
 Held-Hou理論ではハドレー循環が発生しえない状況でも，あたかもハドレー循 
 環のような循環が発生しうることが明らかになった．積雲対流は内部の力学で 
 位置を変えられるためである．しかし，それだけでは特定の緯度に集中する必 
 然性がない．多数の数値実験により，循環の強さは積雲と結合した非定常擾乱 
 (MJOなど)の強さと密接な関係があることがわかってきた． 
  

Mesoscale variability along the east coast of India in spring and fall revealed in satellite data and OGCM (Prescilla Kurien) 発表要旨 :

 Since mesoscale meanders have great importance in nourishing coastal 
 fisheries, satellite data analyses and a numerical modeling study were 
 carried out for the east coast of India during spring inter-monsoon 
 time (March-May), when biological productivity is high. The East India 
 Coastal Current (EICC) system appears as a northward flowing western 
 boundary current of a seasonal subtropical gyre in Bay of Bengal. A 
 relatively clear sky permits satellite remote sensing of sea surface 
 temperature and Chlorophyll-a, whose patterns were verified against 
 geostrophic velocity in altimeter data: i.e., phytoplankton grows in 
 colder and richer water bounded by the seaward meanders. Progression 
 of meanders in the EICC was revealed and compared with an 
 eddy-resolving OGCM, which is capable of modeling wind-driven general 
 circulation and the meander growth. The numerical solutions provided 
 the following results, in a reasonable agreement with the linear 
 stability theory and numerical solutions using a three layer 
 quasi-geostrophic model. Baroclinic instability plays a key role, 
 while meanders in the EICC are initiated by isolated mesoscale 
 rotations propagating westward. The baroclinically unstable meanders 
 have a wavelength of 500~700 km, grow in one month and propagate 
 downstream of the EICC at several kilometers per day. From fall to 
 winter (September-January), in which a cyclonic wind stress curl could 
 provide a coastal current and consequent meanders, no persistent 
 meander is observed in altimeter data and OGCM. Both hydrographic data 
 and OGCM proved that the southward current has a narrow (100 km) core 
 in the upper 100-m layer and prevents instability. 
  

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