The trend of the annual mean SST of the World Ocean in 5°longitude-latitude bins was earlier analyzed by Casey and Cornillon (2001) for the period 1942 - 1993. In comparison with (Casey and Cornillon, 2001) we revealed regional details of high seasonality in SST tendency in the Northwest (NW) Pacific for the second half of 20^th century (1945-2000), estimating linear trend in grid 2°x2°for each month of a year. The SST trends, for two months of both winter and summer seasons, are shown in Figure 4, demonstrating high seasonality.

　

　

Seasonality of SST trend is similar to that of surface air temperature trend over the Northeast Asia (Fig.1). Semi-centennial warming in SST dominates in November - January (Fig.4a), and cooling dominates in July (Fig.4c) - September. It is important that warming tendency in November-December takes place, at first, in western tropic and subtropic area including west Philippine Sea, East-China Sea, Kuroshio region, at second, it occurs in the northwestern subarctic Pacific. Warming in cores of both pools are most significant (99%) and highest (0.8-1.3℃ per 55 years) in December. In this month subarctic pool of warming occupies offshore Oyashio region off the Kuril Islands, as well as areas adjacent to western Aleutian Islands and Kamchatka Peninsula. Most significant positive trend in the Northwest Pacific SST occupies indeed largest area in December. In January subtropical warming pool expands northeastward to Kuroshio Extension and transition zone south of subarctic front (Fig.4a). In January - February the subarctic pool of warming also shifts northeastward to the southwest Bering Sea and ocean area adjacent to the north Kamchatka (Figs. 4a, b). At the same time, in January significant trend of cooling occurs in the latitude band 39°- 45°N east of Tsugaru Strait and Hokkaido Island, extending eastward. This area of long-term cooling is associated with Oyashio, its intrusion and subarctic frontal zone. In February the pool of cooling occupies most of the western subarctic gyre, dominating in the Oyashio Intrusion and western core of the subarctic gyre. In March-May it expands substantially southward, occupying northeast area of the subtropic gyre. Pool of cooling also expands in subarctic gyre in spring, becomes deepest in July, and occupies NW Pacific north of 30°N in August with maximum negative SST trend in the Japan and Okhotsk seas, being weak and insignificant in subtropical area and transitional zone.

　

Features of both SST trends and dynamics of the Japan Sea are very close to that in the Northwest Pacific. Warming in winter SST occurs in south subtropic region adjacent to Korean Strait and north subarctic area adjacent to Tatarskii Strait, but cooling pool occupies central sea area associated with the subarctic gyre and subarctic frontal zone where intermediate low salinity water forms through the subduction mechanism in late fall and winter. Subtropic gyre in the Japan Sea spins up in late 20^th century, which follows from observation data analyses and modeling results presented in (Trusenkova, Ponomarev and Ishida, this volume). Anomalous increased heat transport from the western subtropic Pacific and East-China Sea to the Japan Sea accumulates in its intermediate and deep waters (Ponomarev and Salyuk, 1997; Ponomarev et al., 2000, 2001), but semi-centennial trend in SST of subarctic gyre is negative. Physical mechanism of the SST cooling in the Northwest Pacific subarctic gyre, accompanying warming in Kuroshio region seems to be similar to physics of circulation and climate change in the Japan Sea.

　

　

Climatic tendencies in Northeast Asia in the 20^th century are characterized by significant warming in winter and cooling in summer over offshore continental area west of 120-110°E in mid and moderate latitudes. Difference between summer and winter surface air temperature significantly decreases in this continental area during 20^th century and its second half. Warming tendency being characteristic throughout a year for the area east of 100°120°E accompanies precipitation increase in this area of moderate latitudes. Thus, continental climate in moderate latitudes of the Northeast Asia becomes closer to marine climate. Positive air temperature trend occupies marginal land area adjacent to the Northwest Pacific practically all the year round, with the exception of subtropic continental area adjacent to the East China Sea. Warming tendency in fall and winter accompanies precipitation decrease in Japan and Russian Primorye Region adjacent to the Northwest Japan Sea. Significant precipitation reduce in Japan takes place in October, December and January, with the exception of subarctic area (Hokkaido Island) where precipitation slightly increases in December-March and in August, but decreases in May-July.

　

Statistically significant positive SST trend in Kuroshio region and in the northwest area of the Pacific subarctic gyre dominates from November - February, accompanying warming in the continental and marginal areas of the Northeast Asia. At the same time, semi-centennial negative SST trend occurs in the Oyashio region and occupies southwestern area of subarctic Pacific gyre. On the whole, temperature contrast in subtropic Western Pacific increases, while air temperature contrast over East Asia decreases during second half of the 20th century. Climatic patterns typical for subtropics shift northward in the East Asia, and duration of cold period of a year decreases in marginal subarctic zone and continental area of moderate latitudes.

　

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