Journal of Oceanography, Vol. 63 (No. 4), pp. 561-572, 2007

Upper Ocean Heat Content and Atmospheric Anomaly Fields in the Off-Equatorial North Pacific Related to ENSO

Takuya Hasegawa¹* and Kimio Hanawa²

¹Oceanographic Research Department, Meteorological Research Institute, Nagamine, Tsukuba, Ibaraki 305-0052, Japan
²Department of Geophysics, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan

(Received 18 March 2006; in revised form 22 December 2006; accepted 16 February 2007)

Abstract: We have investigated interannual-scale variations of oceanic and atmospheric anomaly fields, such as upper ocean heat content (OHC), sea surface temperature (SST), latent heat flux (LHF) through the sea surface, sea level pressure (SLP) and wind stress curl (WSC) in the tropical Pacific and their relationships to El Niño/Southern Oscillation (ENSO) events. The results reported here show that the OHC and SST anomalies are almost in phase and lead LHF anomalies in the western tropical Pacific (WTP) region, which are preferable to the generation of subsequent atmospheric anomalies in the WTP. We also describe linear relationships between the amplitudes of these variables in the WTP. In addition, the results show that the both WSC and LHF anomalies are in phase with the temporal trend of OHC anomalies in the WTP, and suggest a combined effect of the local WSC and LHF anomaly in the WTP and ENSO-related, off-equatorial, westward propagating OHC anomaly to generate a large OHC anomaly in the WTP. In contrast to the WTP, OHC and SST anomalies are not in phase to the east of the WTP. The results also indicate that OHC anomalies in the WTP have a potential effect on the generation of an equatorial OHC anomaly via both a reflection of waves at the western boundary and atmospheric variations, which force the enhancement of western equatorial OHC anomaly. Therefore, the WTP is a key region where ENSO events are significantly modulated, and OHC anomalies in the WTP play an important role in the subsequent ENSO event.