| Based on ERA5 monthly averaged data of combined wind waves and swell,significant wave height of wind waves and total swell and monthly sea surface temperature,the temporal and spatial variation characteristics of sea surface temperature and wind speed and significant wave height were analyzed in the Southern oceans.The Mann-Kendall test method is used to analyze the inter-annual variation of wind speed and significant wave height and the Empirical Orthogonal Function(EOF)method is used to study the spatial distribution characteristics of wind speed and significant wave height and the inter-annual variation of the South Atlantic subtropical dipole.The results show:(1)The South Atlantic wind direction rotates counterclockwise with 30°S and10°W as the center.The areas with high wind speed are mainly under the southeast trade wind belt and the west wind belt,and the low value areas are mainly under subtropical high pressure and subpolar low-pressure belt.The distributions of wind speeds and wind directions throughout the year are related to the seasonal changes of the subtropical high,the westerly belt and the southeast trade wind belt.The overall significant wave height is the largest in winter,and the distribution characteristics of the four seasons are mainly related to wind speed,sea ice cover and swell.The results of M-K test show that both the wind speed and the significant wave height show an inter-annual upward trend.The wind speed has abrupt changes around 2006 and 2009,and the significant wave significant has abrupt changes around 1994.The correlation coefficient between the wind speed and the significant wave height in most sea areas passed the 95% significance test.The first mode of EOF of wind speed shows that the trade wind belt-westerly belt and the subtropical high-low pressure belt control areas are in reverse distribution.Combined with the time coefficient,the wind speed of the former shows an upward trend,while the wind speed of the latter shows a downward trend.The first mode of EOF of the anomaly field shows that the positive value area is located in the sea area of 35°S-50°S,and the negative value area is located in the sea area south of 50°S.When the time coefficient is positive,the wind speed anomaly of the former is higher and the latter is low.When the time coefficient is negative,the trend is opposite.The first modal display of the significant wave height EOF: the positive value area is located in the sea north of 60°S,and the negative value area is located in the south of 60°S,combined with the time coefficient,the positive value area is an increasing trend,and the negative value area is a decreasing trend.The sea area from the equator to 30°S of SST presents a distribution characteristic of "high in the west and low in the east".According to the subtropical sea temperature anomaly distribution index of the South Atlantic Ocean,it can be calculated that there are 8 years of positive events and 8 years of negative events.(2)The overall wind direction of the South Indian Ocean rotates counterclockwise,and the average wind speed is about 3 m/s.The sea area south of 60°S is mainly controlled by a low pressure zone.The sea area near the equator is at a small value throughout the year,and there is a northwest monsoon blowing from the equator in summer.The four seasons in the trade wind control area have obvious changes.The spring and winter are significantly higher than those in summer and autumn.The southeast monsoon is strong in winter,and the area with high trade winds in summer retreats eastward to the coastal areas of western Australia.The range of the subtropical high control area has a phenomenon of "swelling southward and retreating westward" with seasonal changes.The four seasons in the west wind zone do not change significantly,but in winter,the wind direction in the sea east of 100°E is mostly NW,and the average wind speed is about 2.5m/s.Mann-Kendall test results show that the sudden change of wind speed is around 1993.The EOF analysis results show that the equator to 7°S,the subtropical high control zone and the waters south of 60°S are negative values,and the trade wind and westerly zone control zones are positive values.Combined with the time coefficient,the wind speed of the former is in a downward trend.The first mode of the anomaly field shows that the positive value area is located in the sea area of 30°S-45°S,and the negative value area is located in the sea area of 45°S-60°S.When the time coefficient is positive,the area of 30°S-45°S wind speed anomaly is relatively high,and the sea area of 45°S-60°S is relatively low.When the time coefficient is negative,the trend is opposite.In summer,the sea area from the equator to 30°S of significant wave height is relatively small,and the area with a large significant wave height in winter covers the widest range throughout the year.In the seas south of 60°S,there are areas without wave heights in all four seasons,and the sea ice coverage in spring and winter is wider than that in summer and autumn.Mann-Kendall test results show that the change period is around 1989.The EOF results show that the negative value area is located in the seas south of the equator to 7°S and 60°S,and the positive value area is located in the trade wind and westerly zone control areas.Combined with the time coefficient,the former has a downward trend and the latter has an upward trend.The seasonal variation of SST is mainly distributed in low equatorial seas and subtropical seas.The range of high value areas and average SST in summer and autumn are higher than those in spring and winter,and the highest average SST can reach 28.75?.The SST contour is basically parallel to the latitude,and as the latitude increases,the SST decreases.(3)In the waters west of 150°W in the South Pacific in summer,the tropical convergence zone crosses the equator and "lifts southward" to near the equator in the southern hemisphere.The position of the subtropical high in spring and autumn is basically the same,while in summer and winter,there are characteristics of "southern elevation" and "north elevation" respectively.The trade winds in spring and winter are stronger than those in summer and autumn,and the location of the large value area is related to the seasonal movement of the subtropical high.In summer,the wind speed of the westerly belt is greater in the eastern seas than in the western seas.Mann-Kendall test results showed that the wind speed has abrupt changes between 1997 and 2005.Wind speed EOF analysis results show that the sea area west of 180°W near the equator,the subtropical high control area and the sea area south of 60°S are negative value areas,the trade wind control area and the west wind belt control area are positive value areas,combined with the time coefficient,the former shows a downward trend,while the latter shows an upward trend.The first mode of the anomaly field shows that the positive value area is located in the sea area west of 180°W at low latitudes,the sea area west of 30°S-45°,and the sea area south of 60°S.The negative value area is mainly distributed in the eastern sea area of 45°S-60°S.If the time coefficient is positive,the anomaly of the positive value area is higher,and the anomaly of the negative value area is lower.If the time coefficient is negative,the opposite is true.The significant wave height in the sea area from the equator to 30°S does not change significantly during the four seasons,and it is relatively small in summer,and is below 2.75 m throughout the year.The distribution range of the large-value area in the sea area of 30°S-60°S in autumn is wider than that in spring and winter,and the large-value area can reach 4.25 m.Mann-Kendall test results showed that the mutation period was around 1988.The EOF analysis results show that the sea area from the equator to 28°S and the sea area south of 67°S are positive,and most other sea areas are negative.Combined with the time coefficient,the former shows a downward trend and the latter shows an upward trend.The high SST seasons are summer and autumn.The seasonal changes in the seas south of 30°S are not obvious,and the SST generally decreases with increasing latitude. |
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