Press Releases

Press Releases

Figure 1 Map of the Northern Hemisphere mid- and high-latitudes
The Greenland Sea is located east of Greenland and is connected to the Arctic Ocean by the Fram Strait. The Gulf Stream, indicated by the orange curve, is the source of warm and high salinity seawater that flows northeastward to the vicinity of the Greenland Sea. In the Greenland Sea, strong temperature gradients are formed as the Gulf Stream flow collides with cold seawater from the Arctic Ocean.

Figure 2 Composited differences in the sea surface temperature (color scale, °C) and atmosphere-ocean surface heat flux (white lines, Wm-2, positive value for upward heat transport) based on the February Empirical Orthogonal Function Mode 1 for the east-west baroclinicity in the vicinity of the Greenland Sea; calculated for the 1958 to 2002 period. Composited differences were calculated by subtracting the average of negative cases from the average of positive cases.
Above the Greenland Sea area, where the water temperature difference is large, there is a similar air temperature difference. Thus, the east-west baroclinicity difference on the west side of the area is large. In the vicinity of the Greenland Sea, large amounts of heat have been released into the atmosphere from areas of warm water and the atmosphere has been warmed. Here, for the 1957 to 2002 period, the patterns shown are the average of extreme positive conditions minus the average of extreme negative conditions. Only the signals associated with the strongest variation patterns for the east-west baroclinicity in the vicinity of Greenland are shown.

Figure 3 Composited differences of the near-surface air temperature (color scale, °C) and winds at around 5000 m altitude (arrows, ms-1) corresponding to the composited differences shown in Figure 2. The southern boundary is 30°N. The thick white line is the zero line between positive and negative.
When there are extreme differences in seawater temperature as seen in Figure 2, there are large differences in winds, flowing northward on the east side of Greenland and flowing southward on the west side of Greenland. Northward heat transport is increased east of Greenland and decreased west of Greenland. Differences in the near-surface air temperature accompanying this are as follows: east of Greenland including most of the Eurasian continent is warmer while Greenland and the region immediately to the west and south are colder. The average of the composited temperature differences for the whole region north of 30° N is about +0.8°C.

Figure 4 Top: Monthly values for the Greenland Sea Surface Temperature Index or GSSTI (thin black dotted lines and open circles), 5 year moving average values for GSSTI (thick black line), Atlantic Multidecadal Oscillation index (red line, values are 5 times actual values to adjust scales). Data are shown for 1957 to 2002. Bottom: 10 year period around 1979, monthly GSSTI anomaly for 1974 to 1983. (Shown here are deviations from the monthly climatological values computed from the entire period, 1957–2002, for each calendar month.)
The Atlantic Multidecadal Oscillation Index is essentially the average surface water temperature for the North Atlantic Ocean from 0°N to 70°N, filtered by the 10 year moving average to remove extreme monthly and annual values. The monthly GSSTI values show an increase in their reference values around 1980. The long term cyclic oscillation of the 5 year moving average of the GSSTI shows a similar transition 10 to 15 years in advance of change in the Atlantic Multidecadal Oscillation. The GSTTI suddenly increased by about 2°C during the period between February and March 1979 and has fluctuated at a high range since then. This sudden rise is prominent, as there are almost no other months from 1957 to 2002 with a sudden change in the monthly anomaly greater than 1°C between two consecutive months.

Figure 5 Values calculated by subtracting the climatological values for February 1958 to 1978 from the climatological values for February 1979 to 2002.
The near-surface air temperature (color scale, °C) and winds at approximately 5000 m altitude (arrows, ms–1). Color scale is half that used in Figure 3. The thick white contours show the boundary zero line between positive and negative. Unlike Figure 2, all cases are included; this includes cases when the Greenland Sea surface temperature was extremely high as well as cases when it was not. Although a difference as large as seen in Figure 3 is not observed, a difference pattern similar to Figure 3 can be seen even when the averages for the two periods are compared. The difference in average February air temperature between the two periods averaged over the whole region north of 30°N is about +0.5°C.

Figure 6 The standard deviation for February land and near sea surface air temperatures for 1979 to 2002 minus the standard deviation for 1957 to 1978 (°C, zero values are shown by the thick white contours). The standard deviation for each period was calculated separately based on the anomalies from the February climatological values for each period. The standard deviation for temperature is a measure of the representative variance from the average monthly value. If the standard deviation is large, it suggests that the amplitude of the standard variance both above and below the annual average value is large. For example, if the average year air temperature for February is 5°C and the standard deviation is 0.5°C, the average temperature for February from 4.5°C to 5.5°C can be considered to be in the range for a typical February. Generally, the larger the amplitude of the standard deviation of the air temperature, the more difficult it is for organisms to adapt to the temperature variations, and the more likely for human socioeconomic activity to suffer from the variations.

Figure 7 Standard deviation for and the near-surface air temperature for August around Japan. Top Left: Standard deviation for 1958 to 1978. Top Right: Standard deviation for 1979 to 2002. Bottom Left: Difference calculated by subtracting the standard deviation for 1958 to 1978 from the standard deviation for 1979 to 2002. Standard deviations were calculated separately for each period based on the anomalies from the August climatological values.
The standard deviation of the August average surface air temperature in the vicinity of Japan has become larger since 1979 by 0.3°C to 0.5°C over a wide area. This indicates that the frequency of cold and hot summers has risen while the severity of cold and hot summers has increased. An increase of 0.5°C in the standard deviation for the monthly average surface air temperature is not negligible. For example, August 2010 was the hottest month in recorded history and the average air temperature in August for Tokyo was just 2.2°C higher than for an average year. Thus, if the amplitude of the standard deviation were to increase from 1.0 to 1.5°C, high temperatures near that of 2010, and conversely, abnormally cold summers, would become more frequent.