Fluctuations of the Northern Hemisphere Mean Surface Air Temperature during Recent 100Years, Estimated by Optimum Interpolation

Abstract

Analyses of the hemispherical or global network data of the surface air temperature during recent 100years have been performed by several authors. Some quantitative disagreements are noticed among their results. Most of the previous works indicate no reliability of the results which is indispensable to confirm any time changes. In the present paper, the optimum interpolation is applied to the northern hemisphere network of the seasonal mean surface air temperature anomaly, and the value and its error for each season from 1876 to 1975 are determined at the grid points on 10° latitude and 30° longitude (45° longitude at 80°N only). These grid point values and their errors make possible to compute easily the northern hemisphere mean temperature anomaly, together with the errors. General tendencies of the warming from the 1880s and the cooling from the 1940s are noticed in the time series of the northern hemisphere mean, similarly to those by Mitchell (1963) and Budyko (1969). However, comparing with their results, the magnitude of range of the temperature change in the present work is much small. On this disagreement, some discussions are given.