Spatial and temporal 850 hPA air temperature and sea-surface temperature covariances in the Mediterranean region and their connection to atmospheric circulation

摘要

The spatial and temporal covariability between the lower troposphere and sea surface temperatures (SSTs) are studied in the Mediterranean basin for the period 1958-98. Monthly air temperature anomalies for the 850 hPa pressure level (T-850hPa) at 2.5°* 2.5°grid points and SST anomalies in 5°* 5°grid boxes are utilized. As a first step, factor analysis is applied on both sets of data in order to reduce their dimensionality. Then, canonical correlation analysis is applied and this leads to one statistically significant pair of canonical variates for winter and to two pairs for summer. In winter, a teleconnection (see-saw) between western Europe and the eastern Mediterranean at the 850 hPa level is revealed, and a corresponding weaker one between the areas of central-west and eastern Mediterranean for SST. The correlation between T-850hPa and SST appears higher over the eastern Mediterranean. In summer, the first pair of canonical variates reveals a covariability between T-850hPa and SST in the western Mediterranean, and the second one shows a covariability in the eastern Mediterranean, without the existence of any strong spatial teleconnection. The analysis is repeated, using time lags of 1 month, or longer, in order to detect any possible non-synchronous relation. Statistically significant results are found only when T-850hPa leads SST with a time lag of 1 month. In particular, the results are statistically significant for winter only, and the findings are similar to those of the first analysis. Therefore, the existence of a 1 month time scale SST persistence is detected for winter months.