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Fig. 6 TMI SST anomalies in degree Celsius of the 11 case composite AB cycle for pentads -2to?5. At 0
pentad, SST is maximum over north Bay of Bengal and to its east and west. Note the minimum SST over the
same area at pentad ?4
Fig. 7 Surface wind anomaly (Quikscat) July and August as mean of El Ni˜os 2002, 2004 and 2009 minus
mean of non El Ni˜ o years 2000, 2001, 2003, 2005, 2006, 2007 and 2008
scale cyclonic wind stress curl north of the LLJ axis is hypothesised to generate a large area
of shallow MLD there. During the AB cycle, this area warms rapidly and causes the active
phase convection to shift there from west of 120E before moving to the equatorial Indian
ocean, thus prolonging the duration of the AB cycle. In the tropics, it is found that areas of
warmest SST attract moisture convergence, increase both the convection and the vertically
integrated moisture content of the atmosphere there. Available Argo data of Mixed Layer
Depth (MLD) and Quikscat surface wind data support the hypothesis made. Figure 7 gives
the surface wind anomaly of July and August as a composite of the latest 3 El Ni ˜os (2002,
2004 and 2009). The cyclonic wind area between longitudes 120E and 180E has shallow
MLD during the monsoon season of recent El Ni ˜o years as shown by ARGO data.
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