Seasonal Dependence of the MJO-ENSO Relationship
Harry H. Hendon, Matthew C. Wheeler, and Chidong Zhang
2007: J. Climate, 20, 531-543.
Abstract
Observations of the development of recent El Ni·o events suggest a pivotal
role for the Madden-Julian Oscillation (MJO). Attempts to uncover a
systematic relationship between MJO activity and El Ni·o, however, have
yielded conflicting results. Some earlier studies that failed to find a
relationship were either based on boreal winter data, when the MJO is
strongest but shifted into the Southern Hemisphere, or used all months
together that biased the results to boreal winter. By stratifying by season
and focusing on MJO activity in the equatorial western Pacific, we
demonstrate a robust lagged relationship between MJO activity in late spring
and El Ni·o in the subsequent autumn/winter for the period 1979-2005. Spring
is the season when the MJO is most focused near the equator and is most
sensitive to SST variations at the eastern edge of the warm pool. Enhanced
MJO activity in the western Pacific in spring is shown to be associated with
an eastward-expanded warm pool and associated westerly surface zonal wind
anomalies. These westerly anomalies in the western Pacific are hypothesized
to project most favourably onto a developing El Ni·o in spring.