On the relation between sea surface and lower temperature over the northern hemisphere

In this work the covariability of sea surface and lower troposphere temperatures (SST-AT) is investigated for
winter (DJFM) and summer (JJAS), over the whole northern hemisphere, by utilizing monthly anomalies in
grid boxes for a 22-year period. Air temperature variations in the lower troposphere are examined in terms
of 1000-500 hPa thickness. At first, factor analysis (FA) is applied on both sets of data in order to reduce their
dimensionality and to group objectively grid points with a similar long term temperature variability. Also, FA
revealed numerous teleconnections in both fields, most important being those governed by PNA in the
Pacific Ocean and NAO in the Atlantic Ocean. Then, by using the FA results as a guide, correlation coefficients
between the mean temperature time series of the subareas defined by FA in the two fields are estimated.
The highest values, up to r=0.70, were found for subareas located one over/under the other. Finally,
by introducing time lags, an attempt of forecasting either SST form AT or AT from SST is made. Although
in some cases the coefficients appear increasing, test showed that the increase is not statistically significant.
In any case, it appears that, on monthly time scale, it is the AT that controls SST and not the vice versa.