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Posted by Nikos
on November 17, 2010, 11:57 pm, in reply to "Re: La Niña Configuration"
114.108.222.208
hi gus,
actually the seasonal cold "Siberian HPA", the source of NE monsoon, appears to be present. however its ridge is the one restricted by the more dominant -thanks to La nina - "Semipermanent North Pacific HPA" (source of the trade winds). What we're seeing this time are the almost "flattened isobars" (i mean almost parallel to latitude lines) in the batanes and taiwan area. This situation favored a strong convergence between amihan and the trade winds indicated by the "stationary front" in sir Mike's t2k satellite analysis. The amihan flow is pushed to the west.
[note: refer to current JMA maps and animate for visual aids]
The visible formation zone of midlatitude lows (Low) (shortwave troughs) are usually to the west over the eastern himalayas and Myanmar. They move approx. north-northeastward and by the time they reach the vicinity of eastern China and Taiwan they form fronts. then, as the Low intensify and move further eastward their fronts become more established and elongated. Usually this is also the time that the ridge of the cold HPA intensify in unison behind the cold front. by the time the Low is NE of Taiwan, the ridge has extended further south and we get a surge of cool amihan (ie,pagasa issues a "tail-end of cold front advisory"). Of course, this ridge eventually detaches from its parent HPA and becomes a shallower subtropical HPA moving East and sometimes it intensifies and merges with the North pacific HPA.
Now, i think the case is different:
The Lows (midlatitude) develop much further East at approx NE of Luzon. Then, they quickly move NNE'ward into the higher latitudes. So by the time they form fronts their much further away and the HPA behind the front produces a ridge that propagates more eastward instead of southward. The absence of low pressure system genesis over the Eastern himalayas is compensated, i think, by the warm low over the Philippines and south china sea. Thus, Tropical Cyclone formation is favorable there but die off quickly due to proximity to land. Hmmm... i think that makes sense. La Nina also promotes the "warm pool" over south china sea care of the strong easterlies (trade winds). Hmmm...
hope this helps.
nikos
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