海洋锋海表风速最小值及其成因

周琰; 刘宣飞; 李智

doi:10.16032/j.issn.1004-4965.2017.02.003

海洋锋海表风速最小值及其成因

doi: 10.16032/j.issn.1004-4965.2017.02.003

南京信息工程大学气象灾害预报预警与评估协同创新中心和气象灾害教育部重点实验室，江苏南京 210044

基金项目:

江苏高校优势学科建设工程资助项目 PAPD

详细信息

通讯作者:
刘宣飞，男，江西省人，博士，教授，研究方向：季风与海气相互作用。E-mail：liuxf@nuist.edu.cn

中图分类号: P425.4.1
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出版历程
- 收稿日期: 2015-08-30
- 修回日期: 2016-12-28
- 刊出日期: 2017-04-01

SURFACE WIND MINIMUM ALONG THE SST FRONTS AND ITS CAUS

Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters and Key Laboratory of Meteorological Disaster of Ministry of Education, NUIST, Nanjing 210044, China

摘要

摘要: 利用2000—2008年AVHRR、QuickSCAT等高分辨率卫星观测资料和CFSR再分析资料，分析了墨西哥湾流区、东海黑潮锋区、巴西-马尔维纳斯合流区和厄加勒斯回流区等全球主要海洋锋区的大气响应特征，发现在上述海洋锋区普遍存在海表矢量风速的最小值分布，并对这一现象的产生原因进行探讨。研究指出：夏季（6—8月）墨西哥湾流区、6月东海黑潮锋区附近有明显的矢量风速最小值分布，而巴西-马尔维纳斯合流区及厄加勒斯回流区海洋锋附近则终年存在矢量风速最小值。产生这一现象的条件是大尺度气压背景场梯度方向与海洋锋附近海表温度梯度方向接近一致，其物理过程为：海洋锋暖（冷）水区一侧上空对应有低（高）气压，由此产生的局地气压梯度与大尺度背景气压梯度方向接近相反，导致锋区附近叠加后的气压梯度最小，海表风速因此也最小。同时，摩擦作用使海表风偏向低压一侧，于是沿锋区走向（跨锋区走向）的风速分量差在暖水区一侧产生气旋性切变涡度（风速辐合），进而造成上升运动和强降水，而该分量差在冷水区一侧则产生相反的大气响应特征。
- 海洋锋 /
- 气压调整机制 /
- 海表矢量风速 /
- 最小值
Abstract: By using QuickSCAT and AVHRR high resolution satellite data and CFSR reanalysis data during 2000—2008, the atmospheric response to the SST fronts in the Gulf Stream (GS), the East China Sea Kuroshio (ESK), the Brazil-Malvinas Confluence (BMC) and the Agulhas Return Current (ARC) is investigated. The minimum surface wind is found to be universal along the above fronts, which occurs in JJA for the GS, June for ESK, year-round both for the BMC and ARC. The pre-condition for generating the minimum surface wind is that the large-scale sea level pressure (SLP) gradient (SLPG) is basically in the same direction with the local sea surface temperature gradient near the fronts. This can be explained as follows according to the SLP adjustment mechanism: the warmer (colder) side of the fronts will produce lower (higher) SLP, and such a local SLPG will counteract with the large-scale SLPG, thus leading to the minimum resultant SLPG as well as the minimum surface wind along the fronts. Furthermore, the surface wind will turn to the lower SLP side due to the friction. The difference between components of surface wind along (across) the fronts will produce cyclonic shear vorticity (convergence in wind speed) over the warmer side of the fronts, thereby forming ascending motion and enhanced precipitation there. The atmospheric response is opposite to that over the colder side of the fronts.
- oceanic front /
- pressure adjustment mechanism /
- sea surface vector wind /
- minimum

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图 1 2000—2008年AVHRR的SST（黑色等值线，间隔1 ℃）及其梯度（填色区，℃/(100 km)）

a. 6—8月GS；b. 6月ESK；c.年平均BMC；d.年平均ARC。虚线A1-B1、A2-B2、A3-B3、A4-B4表示跨锋区的直线。

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图 2 2000—2008年CFSR（上）和同期QuickSCAT（下）的海表面10 m风矢量（箭头）及高通滤波后的矢量风速（填色区，单位：m/s）以及同期AVHRR的SST（红色等值线）和梯度（蓝色等值线，间隔0.5 ℃/(100 km)）

a、e为6—8月GS；b、f为6月ESK；c、g为年平均BMC；d、h为年平均ARC。

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图 3 同图 2，但为海表面10 m散度（彩色阴影，单位：10^-5 s^-1）

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图 4 同图 2a~2d，但为高通滤波后的降水（填色区，单位：mm/d）

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图 5 同图 2，但为高通滤波后的海表面10 m涡度 (填色区，单位：10^-5 s^-1)

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图 6 高通滤波后的2000—2008年CFSR垂直速度（填色区，单位：10^-2 Pa/s）沿直线A1-B1（a）、A2-B2（b）、A3-B3（c）、A4-B4（d）的垂直剖面

图下方的黑曲线为AVHRR海温梯度，单位：℃/(100 km)。

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图 7 2000—2008年CFSR海平面气压（黑色等值线，单位：hPa) 及其高通滤波后的气压梯度（填色区，单位：hPa/（100 km））以及同期AVHRR的SST（红色等值线）和梯度（蓝色等值线，0.5 ℃/(100 km))

a. 6—8月GS；b. 6月ESK；c.年平均BMC；d.年平均ARC。a、b中海平面气压的间隔是1 hPa，c、d中海平面气压的间隔是2 hPa。

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图 8 海温负拉普拉斯（上图填色区，单位：10^-10 km^-2）和1 000~850 hPa厚度负拉普拉斯（下图填色区，单位：10^-10 m^-1）以及同期AVHRR的SST（红色等值线）及其梯度（蓝色等值线，单位：0.5 ℃/(100 km)）

a、e为6—8月GS；b、f为6月ESK；c、g为年平均BMC；d、h为年平均ARC。

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图 9 北半球（左）和南半球（右）的海洋锋海表面风速最小值成因示意图

蓝色粗实线SSTF代表海洋锋，黑色空心箭头-▽P为大尺度气压背景场梯度，紫色空心箭头-▽P '为附加气压梯度，黑色箭头$\overrightarrow V $为海洋锋冷、暖两侧的海表风，其沿锋区走向（跨锋区走向）的分量为u (v)，红色箭头$\overrightarrow {{V_0}} $为海洋锋区的海表风，其沿锋区走向（跨锋区走向）的分量为u₀（v₀），橙（蓝）色填色框有气旋性（反气旋性）切变涡度、风速辐合（辐散）、上升（下沉）运动和强（弱）降水。

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图 10 逐日样本合成的QuickSCAT海表面10 m风矢量（箭头）和高通滤波后的矢量风速（填色区，单位：m/s）以及同期AVHRR的SST（红色等值线）及其梯度（蓝色等值线，间隔0.5 ℃/(100 km)）

a. GS；b. ESK；c. BMC；d. ARC。

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