The rains of February 2004: Forcing from the tropics? | The Meteorological Society of New Zealand

The rains of February 2004: Forcing from the tropics?

G.N. Kiladis
M.J. Revell

February 2004 weather was unusual. Normally a settled period for the North Island of New Zealand, the monthly rainfall for February 2004 was four to six times average from the Waikato down to Wellington and in the Wairarapa. It was also very cold and it was the windiest month over the North Island since monitoring started in 1941, in marked contrast to January 2004. We show that the change in the tropical mean circulation between January and February 2004 had many features in common with the canonical circulation change associated with the two phases of the Madden Julian Oscillation (MJO). Associated with these tropical changes, through Rossby wave propagation and the setting up of teleconnections, there are also changes in the higher latitude circulation. We show the correlation between these higher latitude circulation changes and the MJO is weaker than that for tropical regions, but nevertheless it is significant. The low frequency component of a series of synoptic scale rainfall events over 1-2 month periods, such as was observed for instance during February 2004, showed a relatively weak but statistically significant relationship with negative outward longwave radiation (OLR) anomalies over Indonesia and northern Australia. Lagged relationships confirmed that the tropical convective signal propagated eastward much in the same way as the evolution of OLR within the composite MJO.

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