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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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