A Synoptic Investigation of Anomalous Warmth in the Mid and Upper Troposphere During February 1964

Abstract

A case study is made of a period of exceptional warmth in the mid and upper troposphere over the Carib-bean from 19–21 February 1964. The case is a good example of intense winter interaction of mid-latitude and tropical circulations during which lateral forcing from higher latitudes appears to play a prominent role. For example, at 500 mb, temperatures of −1 to −2C which exhibited spacial and temporal continuity on the synoptic scale were noted. These values were more than three standard deviations warmer than monthly mean values and occurred in association with a strong low-latitude polar jet along the Gull Coast of the United States. Isentropic trajectories document average 12-hr descent rates of up to 2 cm sec−1 in the vicinity of 15N in association with the warmth area. Criteria for inertial instability is satisfied over a portion of the anti-cyclonic flank of the strong jet stream leading to a speculative case for a transverse thermally indirect circulation such that a persistent anticyclone north of Puerto Rico is strengthened. Reed and Vleck's hypothesis on the annual temperature cycle of the tropical lower stratosphere is examined on a limited basis with daily data both directly and indirectly with rather inconclusive results.