Changes in the Hadley and Walker Circulations over the Maritime Continent

In this study we use a new method to investigate the Hadley and Walker circulations over the Maritime Continent. Our analysis is based on four reanalyses (ERA-Interim, NCEP2, MERRA and JRA). Among the important quantities calculated is the psi-vector, which is a generalized vector streamfunction defined in such a way as to objectively decompose three-dimensional divergent circulations into two circulations, projected onto zonal and meridional vertical planes. These circulations may be thought of as local Hadley and local Walker circulations. A great advantage of this method is that the overturning circulation in the meridional direction and the overturning circulation in the zonal direction are not defined by zonal averaging, and that the pair of two-dimensional overturning circulations can be added to give the original three-dimensional circulation. We present a climatology of the zonally and meridionally overturning circulations based on the psi-vector and show how these circulations change during El Nino and La Nina years. Additionally, the trends are calculated for the zonally and meridionally overturning circulations over the Maritime Continent to determine how they have changed between 1979 and 2009.