Physics
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmos51d1074n&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #OS51D-1074
Physics
1635 Oceans (1616, 3305, 4215, 4513), 4215 Climate And Interannual Variability (1616, 1635, 3305, 3309, 4513), 4522 Enso (4922), 4572 Upper Ocean And Mixed Layer Processes
Scientific paper
Heat balance in the surface mixed layer is examined at the eastern equatorial Pacific Ocean (0¢ª 140¢ªW) from 1999 La Nina to 2002 El Nino. Observational data from TAO/TRITON moored buoy are used for analysis of heat balance. The result shows that the interannual variation of eddy heat flux due to the tropical instability waves slows down the transition from La Nina to El Nino. This slow transition is known in the previous study as the pausing period of the ENSO cycle, i.e., El Nino does not appear in spite of deepened thermocline. Analysis of the heat balance shows that vertical heat advection and surface heat flux warm the mixed layer from 1999 to 2002. This warming anomaly is associated with deepening of the thermocline related to the recharge process, and is positive force from La Nina to El Nino transition. In contrast, the horizontal heat advection shows cooling anomaly, which reduces the warming anomaly and slows down the transition from La Nina to El Nino. In the horizontal heat advection terms, the eddy heat flux anomaly significantly contributes to the cooling anomaly. This eddy heat flux anomaly would be caused by weakened high-frequency variability less than 50 days period, i.e., weakened tropical instability wave. During the transition phase from La Nina to El Nino, the meridional shear between SEC and NECC is weakened due to the eastward current anomaly on the equator (i.e. weakened SEC) associated with relaxing zonal tilt of the thermocline. The weakened shear would cause the weakened tropical instability wave. Our results suggest that the synoptic scale processes in the tropical ocean effectively works in the basin scale variability to slow down the transition from La Nina to El Nino.
Ando Kazuma
Mizuno Keiju
Nagura Maki
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