Abstract
Recent trends for changes of the temperature field in the northern hemisphere are described by using the annual-mean data for 25 years (1950-1974) in the lower layer (1, 000-500mb) and for 20 years (1956-1975) in the upper layer (500-100mb). We expressed a given time series in terms of Tchevychef's orthogonal polynomial, and it was decided by using a statistical test for goodness of fit how many terms should be chosen in the polynomial. The usual type transformed from the above polynomial was used as a trend or a measure for the change of a given time series.
As for long-term-mean temperature fields at first, a characteristic aspect in the upper layer is shown in comparison with that in the lower layer. The zonal-mean temperature in 80°N was a linearly upward change in the lower layer but a linearly downward change in the upper layer. In the lower layer, it has become warmer in the west-hemispherical side of 8°N, where a cold-air source was located, and colder in the east-hemispherical side of 80°N where it was a warmer region. It was assumed that the area between 80°N and 30°N could be classified into three latitudinal zones on trend types and those correspondence between the lower and upper layers. The first is 80°N, the second 70°N and 60°N and the third south of 50°N, and features in each of the zones are mentioned. The trend of areal-mean temperature was expressed by a quadratic formula in the lower layer and by the third-order formula in the upper layer. The changes of the meridional and zonal gradients of temperature both have generally a descending trend in the lower layer and an ascending trend in the upper layer. Namely, the temperature field has changed as becoming flatter in the lower layer and steeper in the upper layer, and it is suggested energetically that the lower layer has lost zonal and eddy available potential energies both and the upper layer has acquired those.
