Real-Time Monitoring and Prediction of Modes of Coherent Synoptic
to Intraseasonal Tropical Variability
Matthew Wheeler and Klaus M. Weickmann
2001: Monthly Weather Review, 129, 2677-2694.
Abstract
A technique of near real-time monitoring and prediction of various
modes of coherent synoptic to intraseasonal zonally-propagating tropical
variability is developed. It involves Fourier filtering of
a daily-updated global dataset for the specific zonal wavenumbers
and frequencies of each of the phenomena of interest. The filtered
fields obtained for times before the end of the dataset may be
used for monitoring, while the filtered fields obtained for times
after the end-point may be used as a forecast. Tests of the
technique, using satellite-observed outgoing longwave radiation
(OLR) data, reveal its skill for monitoring. For prediction, it
demonstrates good skill for the Madden-Julian oscillation (MJO),
and detectable skill for other convectively coupled equatorial modes,
although the decaying amplitude of the predictions with time is a
characteristic that users need to be aware of.
The skill for the MJO OLR field appears to be equally as good as that
obtained by the recent empirical MJO forecast methods developed by
Waliser et al., and Lo and Hendon, with a useful forecast
out to about 15 to 20 days. Unlike the previously-developed
methods, however, the current monitoring and prediction technique
is extended to other defined modes of large-scale coherent
zonally-propagating tropical variability. These other modes are
those that appear as equatorial wave-like oscillations in the OLR.
For them, the skill shown by this empirical technique,
although considerably less than that obtained for
the MJO, is still deemed to be high enough for the
technique to be sometimes useful, especially when
compared to that of a medium-range global numerical
weather prediction (NWP) model.
