Central American Cold Surge: An Observational Analysis of the Deep SouthwardPenetration of North American Cold Fronts

摘要

The occurrence and structure of the Central American Cold Surge (CACS) isquantified using surface and upper air observations, GOES satellite imagery and satellite estimates of total precipitable water (TPW) and rain rate. A quantitative CACS definition, similar to established East Asian Cold Surge definitions, is developed and used to construct an eleven winter season climatology of CACS frequency and relative strength. Central America experiences between 11 and 21 CACS events each winter season, with a winter season average of 16 events. GOES imagery is analyzed to quantify the duration and southward penetration of CACS events. Each cold surge typically affects Central America for 3 to 6 days, but may persist for up to 13 days. The mean CACS southward penetration ranges from 12 deg N to 14 deg N, while the maximum southward penetration is approximately 7 deg N. Over 76% of CACS events penetrate south of 15 deg N and over 26% penetrate south of 10 deg N. CACS onset characteristics are described from Belize City, Belize surface observations. A wind shift to the north, sharp rise in sea level pressure and increase in low-level cloud cover are the best cold surge indicators. CACS events contribute from 70% to 90% of the winter season precipitation across Central America. Temporal cross sections of upper air data are constructed to quantify the vertical structural