Similarities and Differences of ISO Activity Characteristics over the Tropical Indian Ocean and Pacific
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摘要: 基于再分析资料，对比分析了热带印度洋和太平洋地区大气季节内振荡（ISO）活动特征的异同。结果表明：印度洋和西太平洋地区ISO活动中心在4月和10月存在季节性跳跃，并且ISO在西太平洋地区活动中心位置南北跳跃的经向距离较印度洋偏大。ISO较强的活动中心也是ISO强度年较差较大的地区，并且各个活动中心ISO强度达到最强的时间存在明显的差异。ISO活动存在显著的年际和年代际变化，在20世纪80年代ISO的活动强度和变化趋势都存在一个明显的转折。夏季印度洋和西太平洋地区ISO都存在较强的北传，赤道地区印度洋ISO强度较强，而赤道以外地区西太平洋ISO强度较强；并且ISO在西太平洋地区北传的速度较印度洋偏慢。无论是冬季还是夏季，当ISO活跃于印度洋和西太平洋时，ISO的空间分布和垂直结构特征都有着明显的差异。Abstract: The characteristics of atmospheric Intraseasonal Oscillation (ISO) activity over the tropical Indian Ocean and the Pacific are compared based on the reanalysis data. The results show seasonal jumps in the ISO activity centers over the Indian Ocean and the western Pacific in April and October. In addition, the meridional jumping distance of the ISO activity center over the western Pacific is larger than that over the Indian Ocean. The activity centers of stronger ISO are also the areas with greater annual amplitude in ISO intensity, and the ISO intensity of each activity center reached the peak at significantly different times. Considerable interannual and interdecadal variation is observed in ISO activity, and the intensity and variation trend of ISO show an obvious turning point in the 1980s. In summer, a strong northward propagation of ISO occurs over the Indian Ocean and the western Pacific. The equatorial ISO over the Indian Ocean is stronger than the ISO beyond the equator, and the ISO beyond the equator over the western Pacific is stronger than the equatorial ISO. Moreover, the northward propagation of ISO is slower over the western Pacific Ocean than over the Indian Ocean. When the ISO is active over the Indian Ocean and Western Pacific in winter and summer, its spatial distribution and vertical structure characteristics are obviously discrepant.
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图 1 1949～2016年（a、c）夏季和（b、d）冬季ISO强度（a、b）年平均和（c、d）年际标准差。图中矩形区域为文中定义ISO强度指数所使用的区域
Figure 1. (a, b) Intensity and (c, d) annual standard deviation of ISO (intraseasonal oscillation) averaged in (a, c) summer and (b, d) winter from 1949 to 2016. The rectangular region in the figure is the area used to define the ISO strength index in this paper
图 2 1949～2016年平均ISO强度（a）年较差（黑色等值线为1.2 m s−1）及其（b）占年平均值的比例（黑色等值线为0.6）
Figure 2. (a) Annual amplitudes of ISO intensity and (b) their proportion to the annual mean value from 1949 to 2016. The black contour line is 1.2 m s−1 in (a) and 0.6 in (b)
图 3 1949～2016年平均（a）印度洋（70°E～90°E）和（b）西太平洋（120°E～140°E）区域平均的ISO强度的纬度—时间演变。黑色等值线为2.1 m s−1，黑色虚线为ISO活动强度中心所在位置
Figure 3. Latitude–time distribution of ISO intensity averaged over (a) the Indian Ocean (65°E–95°E) and (b) the western Pacific (105°E–145°E) from 1949 to 2016. The black contour line is 2.1 m s−1, and the dotted black line is the center of ISO activity intensity
图 4 1949～2016年平均（a）夏季和（b）冬季ISO活动中心逐月的ISO强度（单位：m s−1）
Figure 4. Monthly ISO intensity (m s−1) of ISO activity centers in (a) summer and (b) winter from 1949 to 2016
图 5 1949～2016年夏季（a）A区域（黑色）和B区域（紫色）、（b）C区域（蓝色）和D区域（绿色）、（c）E区域（红色）平均的ISO强度的年际变化及其线性趋势（图中直线）
Figure 5. Interannual variation in ISO intensity averaged over (a) area A (black) and area B (purple), (b) area C (blue) and area D (green), and (c) area E (red) and its linear trend (straight line in the figure) in summer from 1949 to 2016
图 7 夏季（a、c）印度洋和（b、d）西太平洋ISO指数超前滞后回归的ISO OLR纬度—时间剖面：（a、c）70°E～90°E平均ISO OLR；（b、d）120°E～140°E平均ISO OLR。ISO指数平均的区域分别是：（a）（5°S～10°N，70°E～90°E），（b）（5°S～10°N，120°E～140°E），（c）（10°N～20°N，70°E～90°E），（d）（10°N～20°N，120°E～140°E）。黑色实线表示经向传播速度为1°/d。打点表示通过0.1显著性检验
Figure 7. ISO OLR (W m−2) averaged over the (a, c) 70°E–90°E and (b, d) 120°E–140°E lag regressed onto (a, c) the Indian Ocean and (b, d) western Pacific ISO index in summer, respectively. The average regions of ISO index (a to d) are as follows: (5°S–10°N, 70°E–90°E), (5°S–10°N, 120°E–140°E), (10°N–20°N, 70°E–90°E), (10°N–20°N, 120°E–140°E). The solid black line indicates a meridional velocity of 1°/d. The stipplings indicate the results pass the 0.1 significance test
图 8 夏季印度洋（左列）（5°N～15°N，70°E～90°E）和西太平洋（右列）（5°N～15°N，120°E～140°E）ISO指数回归的各物理量分别在70°E～90°E和120°E～140°E平均的垂直剖面：（a、b）经向风（单位：m s−1）；（c、d）位势高度（单位：gpm）；（e、f）温度（单位：K）；（g、h）垂直速度（单位：10−2 Pa s−1）；（i、j）比湿（单位：10−1 g kg−1）；（k、l）OLR（单位：W m−2）。打点表示通过0.1显著性检验
Figure 8. Vertical profile of each physical variable averaged over 70°–90°E and 120°–140°E regressed onto the Indian Ocean (left column) ( 5°N–15°N, 70°E–90°E) and western Pacific (right column) (5°N–15°N, 120°E–140°E) ISO index in summer, respectively: (a, b) Meridional wind (m s−1); (c, d) geopotential height (gpm); (e, f) temperature (K); (g, h) vertical velocity (10−2 Pa s−1); (i, j) specific humidity (10−1 g kg−1); (k, l) OLR (W m−2). The stipplings indicate that the results pass the 0.1 significance test
图 9 夏季（a）印度洋（5°N～15°N，70°E～90°E）和（b）西太平洋（5°N～15°N, 120°E～140°E）ISO指数回归的850 hPa水平风场（矢量，单位：m s−1）和OLR（阴影，单位：W m−2）。黑色箭头和打点表示通过0.1显著性检验的风场和OLR
Figure 9. Horizontal wind (vector, units: m s−1) at 850 hPa and OLR (shadow, units: W m−2) regressed onto the ISO index of (a) the Indian Ocean (5°N–15°N, 70°E–90°E) and (b) western Pacific (5°N–15°N, 120°E–140°E) in summer. The black arrows and stipplings indicate the wind field and OLR that pass the 0.1 significance test, respectively
图 10 冬季（a）印度洋（10°S～10°N，70°～90°E）和（b）西太平洋（10°S～10°N，120°E～140°E）ISO指数超前滞后回归的10°S～10°N平均的ISO OLR。打点表示通过0.1显著性检验
Figure 10. ISO OLR averaged over the 10°S–10°N lag regressed onto the ISO index of (a) the Indian Ocean (10°S–10°N, 70°E–90°E) and (b) western Pacific (10°S–10°N, 120°E–140°E) in winter. The stipplings indicate that the results pass the 0.1 significance test
图 11 冬季印度洋（左侧）（10°S～10°N，70°E～90°E）和西太平洋（右侧）（10°S～10°N，120°E～140°E）ISO指数回归的10°S～10°N平均的各物理量的垂直剖面：（a、b）纬向风（单位：m s−1）；（c、d）位势高度（单位：gpm）；（e、f）温度（单位：K）；（g、h）垂直速度（单位：10−2 Pa s−1）；（i、j）比湿（单位：10−1 g kg−1）；（k、l）OLR（单位：W m−2）。打点表示通过0.1显著性检验
Figure 11. Vertical profile of each physical variable averaged over 10°S–10°N regressed onto the Indian Ocean (left column) (10°S–10°N, 70°–90°E) and western Pacific (right column) (10°S–10°N, 120°–140°E) ISO index in winter, respectively: (a, b) zonal wind (m s−1); (c, d) geopotential height (gpm); (e, f) temperature (K); (g, h) vertical velocity (10−2 Pa s−1); (i, j) specific humidity (10−1 g kg−1); (k, l) OLR (W m−2). The stipplings indicate that the results pass the 0.1 significance test
图 12 冬季（a）印度洋（10°S～10°N，70°E～90°E）和（b）西太平洋（10°S～10°N，120°E～140°E）ISO指数回归的850 hPa风场（矢量，单位：m s−1）和OLR（阴影，单位：W m−2）。黑色箭头和打点表示通过0.1显著性检验的风场和OLR
Figure 12. Horizontal wind (vector, units: m s−1) at 850 hPa and OLR (shadow, units: W m−2) regressed onto the ISO index of (a) the Indian Ocean (10°S–10°N, 70°E–90°E) and (b)western Pacific (10°S–10°N, 120°E–140°E) in winter. The black arrows and stipplings indicate the wind field and OLR that pass the 0.1 significance test, respectively
表 1 夏季和冬季的ISO活动中心的区域
Table 1. Areas of ISO activity centers in summer and winter
区域 夏季ISO活动中心 冬季ISO活动中心 A 10°N～20°N，65°E～95°E 7.5°S～17.5°S，45°E～65°E B 5°S～5°N，75°E～95°E 2.5°S～12.5°S，75°E～100°E C 5°N～20°N，102.5°E～122.5°E 5°S～15°S，110°E～150°E D 5°N～20°N，122.5°E～150°E 2.5°S～10°N，120°E～150°E E 5°N～15°N，95°W～125°W 0°～10°S，160°E～160°W 
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表 2 夏季和冬季不同区域ISO活动中心强度的线性趋势
Table 2. Linear trend of ISO activity center intensity in summer and winter at different periods
m s−1 （10 a）−1 区域 1949～1979年ISO
强度线性趋势1986～2016年ISO
强度线性趋势夏季 冬季 夏季 冬季 A 0.169 0.157 0.032 −0.088 B 0.199** −0.107 −0.142* −0.107 C 0.198 0.156* 0.136 0.110 D 0.160* −0.053 0.020 −0.060 E 0.219** 0.240* −0.157* −0.061 *和**分别表示通过0.1和0.05显著性检验。
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