海表温度日变化振幅对季节内震荡的相反响应

闫运伟、凌征、陈长霖   2017-08-30

      海表温度日变化振幅(DSST)主要由太阳辐射和海表风速决定:太阳辐射越大(小)、海表风速越小(大),DSST越大(小)。前人工作表明季节内震荡(MJO)对DSST有重要影响:在MJO的活跃期(抑制期),当对流中心位于印度洋/西太平洋时,太阳辐射减小(增大),海表风速增大(减小),DSST减小(增大)【Bernie et al. 2005; Kawai and Kawamura 2005; Bellenger and Duvel 2009; Mujumdar et al. 2011; Li et al. 2013】。而在中太平洋,其背景海表纬向风与印度洋/西太平洋的刚好相反,导致了MJO对海表风速的影响在中太平洋和印度洋/西太平洋相反【Hendon and Glick 1997; Woolnough et al. 2000; Jin et al. 2013】。那么,中太平洋相反的海表风速异常会不会引起相反的DSST异常呢?这是本文要解决的核心问题。

      通过分析TAO/TRITON锚系浮标数据和经验模型结果,我们发现:中太平洋相反的海表风速异常会引起相反的DSST异常,导致DSST对MJO的响应在中太平洋和印度洋/西太平洋是相反的(Figures 1 and 2)。除DSST外,潜热通量(Figure 2)、蒸发速率和海表粗糙度(Figure 3)对MJO的响应在中太平洋和印度洋/西太平洋也是相反的。这表明这一相反的响应特征很可能适应于任一和海表风速密切相关的物理量。 

引用:Yan, Y., Z. Ling and C. Chen. Opposite responses of the diurnal amplitude of sea surface temperature to the Madden-Julian Oscillation. Deep Sea Research Part I: Oceanographic Research Papers, 2017, https://doi.org/10.1016/j.dsr.2017.08.010.


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图一、冬(ab)夏(cd)季海温日变化振幅(DSST)和风速对季节内震荡(MJO)的响应(TAO/TRITON锚系观测数据)。

Fig. 1 The maximum amplitude of lagged regression of DSST (blue bars) and wind speed (red bars) on the MJO index RMM2 (large RMM2 appears in phases 6-7), and its corresponding time lag along 5°S during the boreal winter of 2002 (a, b), and along 5°N during the boreal summer of 2002 (c, d). To obtain scaled values, these regression coefficients are multiplied by one standard deviation of RMM2. Time lag is added by 36 (the MJO propagates from phase 1 to phases 6-7). DSST and wind speed are derived from the TAO/TRITON buoy data. Wind speeds at (170°W, 5°S) in the boreal winter of 2002 and at (165°E, 5°N) and (140°W, 5°N) in the boreal summer of 2002 are missing.

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图二、冬(左栏)夏(右栏)季DSST、太阳辐射、风速和潜热通量对MJO的响应(模型结果)。

Fig. 2 Hovmüller diagrams for anomalies of (a, e) DSST (K), (b, f) solar insolation (W/m2), (c, g) wind speed (m/s), and (d, h) latent heat flux (W/m2) during boreal winter (8°S-2°S; left panels) and boreal summer (3°N-13°N; right panels). Contours are westerly/easterly anomalies in (a, e), and are DSST anomalies in the rest. Contour intervals are 0.6 m/s in (a, e) and 0.05K in the rest. White contour denotes zero, and solid (dashed) black contours denote positive (negative) values. Vertical black line is at 180° in the left panels, and is at 150°E in the right panels. Westerly/easterly (easterly) anomalies in (a, e) show the eastward propagation of the MJO.

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图三、冬(ac)夏(bd)季蒸发速率和海表粗糙度对MJO的响应(ERA-Interim数据)。

Fig. 3 Same as Figure 2, except for (a, c) evaporation rate anomalies (positive downward, m/s) and (b, d) surface roughness anomalies (m) derived from the ERA-Interim global atmospheric reanalysis.