We will report on the simulation of a Type #1 case (anticyclone remains over the Pacific Ocean offshore of Chile) in which cold air damming east of the Andes is negligible and a Type #2 case (anticyclone builds eastward across Chile into southern Argentina and cold air damming ensues) that eventually turns into a Type #4 case (cold air damming occurs east of the southern Brazilian Highlands along the immediate coast). We will distinguish between the role of large-scale dynamical processes and orographic forcing in our results.
Our results to date indicate that the Type #1 case is distinguished by a moderately amplified large-scale flow regime with a ridge centered to the west of Chile with a downstream trough and northwesterly flow across central South America (SA). This flow configuration ensures the presence of a lee trough to the east of the Andes. A nose of high pressure builds across southern SA behind a weak cold front associated with weak cyclogenesis near the coast of Argentina. Cold air damming is minimized because the low-level flow in southern SA is directed eastward away from the Andes. The Type #2 case features dynamic anticyclogenesis over southern SA in a highly amplified flow regime. With the flow aloft directed due equatorward a 1030+ hPa anticyclone builds eastward across the Andes and becomes associated with a southerly wind surge that reaches the equator. The surface anticyclone eventually splits into two centers. One center moves equatorward along the Andes and drives the cool surge while a second center moves northeastward and results in cold air damming east of the southern Brazilian Highlands as the flow pattern gradually deamplifies.
Oral presentation preferred Presenter: Bosart (bosart@atmos.albany.edu)
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