NAME =  Masamichi OHBA  
ORGANIZATION =  University of Tsukuba  
ADDRESS =  Tsukuba, Ibaraki 305-8572  
COUNTRY =  Japan  
PHONE =  +81-29-853-5692  
FAX =  +81-29-853-5692  
E-MAIL =  s0430256@ipe.tsukuba.ac.jp  
POSTER_ONLY =  no  
THEME =  T3  
DATE =  02-Aug-04-16:28:19  
ABSID = T3MO02Aug04162819 
TITLE = A Triggering Process of Indian Ocean Basin-wide Warming in Relation to ENSO forcing. 
AUTHOR_1 = Masamichi Ohba 
INSTITUTION_1 = University of Tsukuba  
PRESENTER = AUTHOR_1 
AUTHOR_2 = Hiroaki Ueda 
ABSTRACT =   The physical process of the Indian Ocean (IO) basin-wide warming is investigated using NCEP/NCAR reanalysis data and 1.5 layer ocean model experiments. Composite analysis of six warm episodes of the El Nino illustrates that the reversed Walker circulation (RWC) associated with El Nino-Southern Oscillation (ENSO) modulate the surface atmospheric circulation over the IO. During the autumn, the enhanced easterly wind anomalies and reduction of wind velocity are remarkable over the equatorial IO. This modulation of atmospheric circulation can be explained by the RWC, which effectively weaken the climatological westerly wind (Wyrtki Jet). 
  To elucidate how remote El Nino forcing influences the underlying SST, we conduct sensitivity experiment. The anomalous zonal wind, assuming the general remote forcing from the El Nino, is used during the boreal autumn, while climatological wind are used during the other season of year in the experiment. As a result of this experiment, the basin-wide warming in the equatorial IO is reproduced in the succeeding winter through the reduction of evaporative cooling. Thus, a coupling process between the RWC associated with the El Nino events and the monsoon circulation during the boreal autumn has a sufficient potential to trigger the IO basin-wide warming. 
  Furthermore, from the output of auxiliary experiment, we reveal that the easterly wind anomalies due to the RWC during the boreal summer result in the east-west asymmetric structure of SST. In view of this, a seasonal coupling process between the RWC and monsoon circulation is an important factor that regulates the SST variation in the IO.