Characteristics and dynamic aspects of Chilean coastal jet

The Navy mesoscale model, COAMPS, had been applied to the Southeast Pacific (SEP) region to provide real-time forecasts during the field observational period of VOCALS (VAMOS Ocean-Cloud-Atmosphere-Land Study) from 20 October to 30 November, 2008. The forecasted surface winds compare favorably with available observations. The objective of this study is to advance our understanding of the structure, characteristics and dynamics of the low-level jet offshore of the Chilean Coast (CCLLJ) using the 40-day COAMPS real-time forecasts. Additional higher-resolution simulations and sensitivity simulations have been conducted for two strong CCLLJ events to further investigate the roles of synoptic forcing, topography, and differential heating between land and sea in the formation of CCLLJ.

According to this study, CCLLJ is very sensitive to the location of the SEP high pressure center; a wide and strong jet is present between 40o and 25o S when the SEP high center is located to east of 100oW, and the low-level jet becomes narrower, weaker, and shorter in length (between 32o-25o S) when the SEP high pressure center is far away from the coast (west of 100o W). The interaction between Andes and the SEP high pressure system results in the formation of a mesoscale pressure ridge to the south of CCLLJ and a mesoscale coastal low to the north of CCLLJ, and consequently this north-pointing pressure gradient force tends to enhance CCLLJ. CCLLJ, which is largely in geostrophic balance at the marine boundary layer top level, is proportional to the cross-shore baroclinicity. The Andes significantly weakens the low-level zonal flows in the coastal area and helps to anchor a baroclinic zone, and therefore, the low-level jet along the coast. In general, differential heating between land and sea tends to enhance the CCLLJ through strengthening the cross-shore temperature gradient in the lower atmosphere along the Chilean Coast.