| The abruptly recurving tropical cyclones over the Western
North Pacific Ocean Basin during El Niño and La Niña events are
studied. Temporal and spatial variations of these anomalous tracks under
different phases of ENSO are shown. The anomalies of the pressure field in
relation to ENSO circulation for the occurrence of the abruptly recurving
cyclone tracks are investigated using fuzzy method. These are supplemented
by wind field analyses. It is found that the occurrence of recurving-left
(RL) and recurving-right (RR) tropical cyclones under the modification of
the steering currents, including the re-adjustment of the westerly trough,
the expansion or contraction of the sub-tropical high pressure, the
intensifying easterly flow and the strengthening of the cross-equatorial
flow, can be in El Niño or La Niña events. Evidently, there is a
higher chance of occurrence of anomalous tropical cyclone trajectories in El
Niño rather than La Niña events, but there is not any pronounced
spatial pattern of anomalous tropical cyclone tracks. By analyzing the
pressure-field, it is seen RL (RR) tropical cyclones tend to occur when the
subtropical high pressure is weak (strong) in El Niño and La Niña
events. More importantly, how the internal force of tropical cyclones
changed by the steering current, which relies upon the relative location of
tropical cyclones to the re-adjustment of the weather systems, shows when
and where RL and RR tropical cyclones occur in El Niño and La Niña
events. |