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The Influence of the Subtropical Sea Surface Temperature over the Western Pacific on Spring Persistent Rains
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摘要: 利用NCAR提供的第5代全球大气环流模式CAM3.1探讨了春季西太平洋副热带地区海表面温度对我国江南春雨的影响。数值试验结果表明：春季西太平洋副热带地区海表面温度升高可引起同期东亚—西太平洋副热带纬向海陆热力差异减弱，进而引起3—4月青藏高原东南侧的低涡强度减弱，该低涡与西太平洋副热带高压之间的位势梯度减小，中低纬度西太平洋副热带高压强度减弱，其北侧的850 hPa西南风强度相应减弱，因此西南暖湿气流输送也随之减弱，造成江南地区的水汽通量辐合强度明显减弱，这种环流分布状况将不利于出现较强的江南春雨，导致江南春雨强度明显减小。
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关键词:
- 气候学;
- 江南春雨;
- 数值模拟;
- 春季西太平洋副热带地区海表面温度
Abstract: Using the Community Atmospheric Model Version 3.1 (CAM3.1) provided by National Center for Atmospheric Research (NCAR), the influence of the East Asian subtropical zonal land-sea thermal difference on the spring persistent rains is studied. The results show that the monthly sea surface temperature over the western Pacific (15°—35°N, 120°—150°E) are two months ahead of schedule, the seasonal conversion of the East Asia—the western Pacific subtropical zonal land-sea thermal difference is delayed, and the thermal difference between the East Asia and the western Pacific in spring is decreased. Under this condition, the intensity of the southwest winds at 850 hPa over East China in March and April decreases, and the rainfall over the region to south of 30°N decreases during the period from March to April, the remarkable decreasing periods are mid-March and mid-late April. The result shows that the intensity of spring persistent rains decreases due to the little land-sea thermal difference. The important role of the East Asian subtropical zonal land-sea thermal difference on the spring persistent rains over Southeastern China is verified. As far as the mechanisms are concerned, the results are as follows.When the land-sea thermal difference of subtropical zonal is minished, the intensity of vortex over the southeastern Tibetan Plateau weakens and then the geopotential difference between this vortex and the western Pacific subtropical high minishes. The western Pacific subtropical high over the middle and low latitudes weakens, and the intensity of the southeast wind decreases over the region to north of the western Pacific subtropical high. Therefore, the southeast warm moist airflows decrease and the convergence intensity of the moisture flux divergence weakens. Under this general circulation conditions, there are no heavy spring persistent rains. -
图 1 WPSST试验与CTL试验500 hPa温度纬向分布 (单位:℃)
(a) 20°~30°N平均偏差，(b)20°~30°N，80°~120°E与20°~30°N, 120°~150°E两区域温度差异
Fig. 1 Zonal difference of 500 hPa temperature between WPSST and CTL (unit:℃)
(a) departure between WPSST and CTL over 20°—30°N, (b) difference between regions of 20°—30°N, 80°—120°E and 20°—30°N, 120°—150°E
图 2 110°~120°E平均时间-经向剖面图 (a) 降水强度 (单位:mm·d-1)，(b)850 hPa风场 (矢量：风向；阴影：风速)
Fig. 2 Meridian-time cross section of precipitation intensity (unit:mm·d-1) (a) and wind fields at 850 hPa (vectors:wind direction; shaded areas:wind speed) (b) averaged over 110°—120°E
图 3 110°~120°E平均降水强度时间-经向剖面图 (单位:mm·d-1) (a) CTL试验, (b) WPSST试验, (c) WPSST试验与CTL试验偏差
(阴影区表示通过0.1的显著性检验)
Fig. 3 Meridian-time cross section of precipitation intensity averaged over 110°—120°E (unit: mm·d-1) (a) CTL, (b) WPSST, (c) difference between WPSST and CTL
(shaded areas: passing the test of 0.1 level)
图 4 我国东部 (110°~120°E) 气候平均850 hPa风场时间-经向剖面图 (矢量：风向；阴影：风速)
(a) CTL试验, (b) WPSST试验
Fig. 4 Meridian-time cross section of 850 hPa wind fields averaged over 110°—120°E in the east part of China (vectors:wind direction; shaded areas:wind speed) (a) CTL, (b) WPSST
图 5 3—4月平均850 hPa位势高度场 (单位:gpm)(虚线为1500 m地形高度线)
(a) CTL试验, (b) WPSST试验
Fig. 5 850 hPa mean geopotential height fields in March and April (unit: gpm) (dashed line: the topography of 1500 m)(a) CTL, (b) WPSST
图 6 3—4月平均850 hPa风场
(虚线为1500 m地形高度线; 阴影区表示通过0.05的显著性检验) (a) CTL试验, (b) WPSST试验, (c) WPSST试验与CTL试验偏差
Fig. 6 850 hPa mean wind fields in March and April
(dashed line: the topography of 1500 m; shaded areas: passing the test of 0.05 level) (a) CTL, (b) WPSST, (c) difference between WPSST and CTL
图 7 3—4月平均850 hPa水汽通量散度场 (单位: 10-5 g·kg-1·s)(虚线为1500 m地形高度线；阴影区表示通过0.05的显著性检验)
(a) CTL试验, (b) WPSST试验, (c) WPSST试验与CTL试验偏差
Fig. 7 850 hPa mean moisture flux in March and April (unit: 10-5 g·kg-1·s) (dashed line: the topography of 1500 m; shaded areas: passing the test of 0.05 level)
(a) CTL, (b) WPSST, (c) difference between WPSST and CTL
图 8 3—4月平均降水强度分布 (单位: mm·d-1) (虚线为1500 m地形高度线; 阴影区表示通过0.05的显著性检验) (a) CTL试验, (b) WPSST试验, (c) WPSST试验与CTL试验偏差
Fig. 8 Mean precipitation intensity in March and April (unit: mm·d-1) (dashed line: the topography of 1500 m; shaded areas: passing the test of 0.05 level) (a) CTL, (b) WPSST, (c) difference between WPSST and CTL
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