Some observations of ocean thermal response to typhoon passage.

Abstract

The fact that typhoons cause a cooling of the upper oceanic layers during their passage is well documented. This case study establishes the magnitude of this cooling for 17 western Pacific super-typhoons during the period 1968 to 1972. Digitized bathythermograph (BT) records for the typhoons were screened to acquire points before and after typhoon passage that met selection criteria. The selected BT records were then assigned a weight that reflected the number of hours before or after the typhoon passed its closest point of approach (CPA). The resulting data file for the 17 typhoons was analyzed using several techniques. It was found that there is a positive correlation between the magnitude of mixed-layer cooling and the distance from the typhoon path, as well as with wind velocity at the BT site. Mean mixed- layer cooling near the storm path ranged from .70° to 2.0°C with a maximum cooling of 4.8°C. At the outer reaches of the storm's influence (300 nmi ) the mean mixed-layer cooling range was -.09°C to ,36°C. The results of the analysis compare favorably with single storm analyses in the Atlantic and a 14 storm analysis in the Pacific. Mixed-layer depth information was subjected to the same analysis as the mixed-layer cooling but the results were inconclusive.