Tropical cyclones are among the deadliest and costliest natural disasters on the planet, yet the factors that determine when and where they develop are not entirely clear. The requisite atmospheric and oceanic conditions, as well as the fundamental mechanism that couples the two and allows for intensification, are all well established. By redistributing enormous amounts of heat and moisture both from the oceans to the atmosphere and from the tropics to the extratropics, these storms are a major factor in the earth's synoptic weather systems as well as in its climate.
The source of the incipient vortices that do intensify to tropical cyclone strength is an area of active research which hopes to elucidate fundamental physical mechanisms of certain cases of genesis and may even prove useful in the predictability of the location and timing of the genesis of tropical storms and cyclones. We expand on one particular pathway to genesis in which one tropical cyclone excites another via eastward energy dispersion via equatorial Rossby waves.
Historically, synopticians have been aware of the phenomenon of one tropical cyclone forming a certain distance in the wake of a recent storm. Estimates vary as to the frequency of such an event, but this occurs frequently enough to be an important aspect of the summer seasons in each hemisphere. We start with the dispersion relation that results from the Laplace tidal equations adjusted with a Doppler-shifting term. We offer a novel physical interpretation of this term, namely that a background atmospheric vertical or horizontal shear would favor the occurence of such an event. While using an admittedly simplified model of the atmosphere (the shallow water model on the sphere), we succesfully model the observed phenomenon, the results of which roughly agree with the analytical predictions.
Predictions can be made regarding the necessary atmospheric conditions for this phenomenon to occur, and we employ a climatological dataset to test our various interpretations of the Doppler-shifting mechanism. The results in and of themselves don't prove or disprove any proposed mechanism or necessary conditions of the atmosphere, but that the horizontal shear interpretation is on average more accurate.
|Subjects||Meteorology; Atmospheric sciences|
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