Climate anomalies north of 55 °N associated with tropical climate extremes

✍ Scribed by Joachim Klaßen; Andreas Hense; Ulrich Römer

• Publisher: John Wiley and Sons
• Year: 1994
• Tongue: English
• Weight: 986 KB
• Volume: 14
• Category: Article
• ISSN: 0899-8418
• DOI: 10.1002/joc.3370140802

✦ Synopsis

Abstract

The relationship between extremes in tropical climate phenomena, e.g. ENSO and Indian summer monsoon, and the lower tropospheric temperature north of 55 °N is examined. For this purpose we carry out a dynamic statistical analysis applied to the data set of monthly mean 500–1000 hPa thickness from January 1949 to December 1991 (German Weather Service (DWD) analyses). To test the null hypothesis of identical horizontal mean distributions of the polar temperature field in irrespective of the sign of extreme tropical episodes a multivariate significance test is performed and the level of recurrence is estimated. In order to improve the signal‐to‐noise ratio, the data are projected onto the eigenmodes of an advection‐diffusion model. Comparing composites of warm versus cold ENSO events, the model indicates a significant difference in the winter lower tropospheric temperature pattern in northern latitudes. This pattern contains a warmer lower troposphere over the northern North American continent in winter, corresponding to other studies. The multivariate analysis further shows that the Indian summer monsoons with deficient rainfall are preceded by a strong cold anomaly in the lower troposphere over the northern Asian continent early in the year, corresponding to the known hypothesis of Asian‐snow—monsoon coupling.