Hydrological Signatures Relating the Asian Summer Monsoon and ENSO

Abstract

Using the NCEP–NCAR reanalysis for the 1950–2000 period, differences in the atmospheric hydrological cycle between the extremes of ENSO (i.e., La Niña minus El Niño) are examined. Zonal vertically integrated moisture transport (VIMT) across 100°E accounts for about half of the variability in net moisture convergence in the north Indian Ocean region between ENSO extremes when all ENSO events are considered. Changes in VIMT across 100°E are associated with large changes in the strength of the Pacific Ocean trade wind regime during ENSO. The bulk of the remaining VIMT anomalies are from the Arabian Sea and appear to be associated with sea level pressure variations in the northern and western parts of the Indian Ocean Basin. This initial analysis, therefore, suggests that the interaction between the monsoon and ENSO may be more complex than the direct modulation of VIMT by the Pacific Ocean trade winds alone. The analysis is refined further by comparing the differences of the Indian and Pacific Ocean... Abstract Using the NCEP–NCAR reanalysis for the 1950–2000 period, differences in the atmospheric hydrological cycle between the extremes of ENSO (i.e., La Niña minus El Niño) are examined. Zonal vertically integrated moisture transport (VIMT) across 100°E accounts for about half of the variability in net moisture convergence in the north Indian Ocean region between ENSO extremes when all ENSO events are considered. Changes in VIMT across 100°E are associated with large changes in the strength of the Pacific Ocean trade wind regime during ENSO. The bulk of the remaining VIMT anomalies are from the Arabian Sea and appear to be associated with sea level pressure variations in the northern and western parts of the Indian Ocean Basin. This initial analysis, therefore, suggests that the interaction between the monsoon and ENSO may be more complex than the direct modulation of VIMT by the Pacific Ocean trade winds alone. The analysis is refined further by comparing the differences of the Indian and Pacific Ocean...