The MJO and Hurricanes
by Eric Maloney
Could MJO Predictions Help Forecast Periods of Enhanced
Hurricane Activity?
Motivation
The MJO produces a strong modulation of tropical cyclone activity in
many regions of the tropics, including the Atlantic Ocean, Gulf of Mexico,
and east Pacific Ocean. The MJO is associated with variations in
sea surface temperature, organized precipitation, low-level winds, vertical
wind shear, and atmospheric humidity and temperature, important factors
in tropical cyclone formation and maintenance. Forecasts of the
MJO at 2-3 week lead times might aid in forecasting periods of enhanced
tropical cyclone formation.
Research Summary
Tropical cyclogenesis preferentially occurs during certain phases of
the MJO. Figure 1 shows the composite eastward propagation of Northern
Hemisphere summer velocity potential and tropical cyclone genesis locations
associated with the MJO during 1979-1997 (adapted
from Higgins and Shi [2001]). Green areas indicate anomalous upper
level divergence, where precipitation is enhanced and tropical cyclogenesis
preferentially occurs. Brown areas indicate anomalous upper level convergence,
where precipitation and tropical cyclogenesis are suppressed. One notable
feature is the enhancement of tropical cyclogenesis in the Americas
during periods of enhanced upper level divergence and enhanced precipitation
(e.g. Day 0 and Day +5 of Figure 1). For example, an analysis during
1949-1997 indicates that the MJO strongly modulates Gulf of Mexico
and Caribbean Sea hurricanes and tropical storms (Figure 2, adapted
from Maloney and Hartmann 2000). Gulf of Mexico and Caribbean Sea hurricanes
are four times more likely to occur when the MJO is producing enhanced
precipitation and divergent upper level winds than when precipitation
is suppressed and upper level winds are convergent. The modulation
of major hurricanes (Categories 3-5) by the MJO is even more pronounced.
Similarly, when the divergent (convergent) phase of the MJO is located
over the Indian or west Pacific Ocean, typhoon activity in increeased
(decreased).
Implications
Given the evidence that the MJO is predictable with 2-3 week lead-times,
periods of enhanced or suppressed hurricane activity may be predicted
at similar lead times. Such knowledge would have implications for public
safety, energy production, recreation/tourism, among other interests.
Future Work
Two avenues of further investigation include: 1) understanding how the
MJO modulates hurricane activity, and 2) determining whether 2-3 week
predictions of the MJO can be used to predict periods of enhanced tropical
cyclone activity.
Selected References
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Bessafi, M., and M. C. Wheeler. 2006: Modulation of south Indian Ocean tropical cyclones by the Madden–Julian Oscillation and convectively coupled equatorial waves. Mon. Wea. Rev., 134, 638–656.
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Hall, J. D., A. J. Matthews and D. J. Karoly. 2001: The Modulation of tropical cyclone activity in the Australian region by the Madden–Julian oscillation. Mon. Wea. Rev., 129, 2970–2982.
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Higgins, W and W. Shi, 2001: Intercomparison of the principal modes of interannual and intraseasonal variability of the North American monsoon system. J. Climate, 14, 403-417.
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Liebmann, B., H. H. Hendon, and J. D. Glick, 1994: The relationship between tropical cyclones of the western Pacific and Indian Oceans and the Madden-Julian oscillation. J. Meteor. Soc. Japan, 72, 401-411.
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Maloney, E. D., and D. L. Hartmann, 2000: Modulation of hurricane activity in the Gulf of Mexico by the Madden-Julian Oscillation. Science, 287, 2002-2004
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Mo, K. C., 2000: The association between intraseasonal oscillations and tropical storms in the Atlantic basin. Mon. Wea. Rev., 128, 4097–4107.