南海东北部混合层深度对热带气旋海鸥和凤凰的响应

doi:10.11978/2016045

摘要/Abstract

摘要：

利用Argo浮标和多源卫星遥感获取的温度、盐度剖面数据和海表面温度(sea surface temperature, SST)、海表面风场等数据, 结合美国国家环境预报中心(National Centers for Environmental Prediction Ⅱ, NCEP Ⅱ)再分析资料, 研究了南海东北部混合层深度(mixed layer depth, MLD)对2014年9月中下旬相继过境的热带气旋“海鸥”(台风)和“凤凰”(热带风暴)的响应。结果表明, 受“海鸥”和“凤凰”过境时的“风泵”作用, 海-气界面向上进入大气的最大净热通量由170W·m^-2升高至400W·m^-2, 引起SST最大降温达到3.02℃。在时间尺度上, 后续的“凤凰”使“海鸥”引发的“冷迹”持续超过10天, 出现SST降温的“叠加效应”。“海鸥”过境1天后, 其“冷迹”MLD从23m加深至50m; 而“凤凰”过境8h后, 风应力驱动的离岸埃克曼输送引发了沿岸上升流, 导致台湾西南部近岸海域MLD从31m加深至91m。热带气旋过境后, 在混合层内, 剖面盐度迟于剖面温度达到充分均匀, 且盐度恢复快于温度, 揭示混合层响应的“时滞效应”。在空间分布上, MLD与SST在两个热带气旋路径右侧(沿其移动方向)的变化幅度均大于左侧, 而“冷迹”内MLD的不均匀加深, 甚至变浅, 可能揭示了下层冷水因埃克曼抽吸在上升流与下降流之间转换而被抬升到不同高度。

关键词: 混合层, 热带气旋, SST, 风应力, 海洋遥感

Abstract:

Utilizing the vertical profiles of temperature and salinity data obtained by Argo floats and multi-source satellite remote sensing data, including sea surface temperature (SST) and sea surface wind fields, combined with the National Centers for Environmental Prediction (NCEP) Ⅱ reanalysis data, we analyzed changes of mixed layer depth (MLD) in the northeastern South China Sea (SCS) in responses to tropical cyclones Kalmaegi (typhoon) and Fung-Wong (tropical storm), which passed the SCS in succession in mid and late September 2014. The results indicate that the maximum net heat flux (upward into the air) increased from 170 to 400 W·m^-2 at the air-sea interface, caused the maximum SST cooling of 3℃ by the “wind pump” effect after Kalmaegi and Fung-Wong passed through. The “cold wake” induced by Kalmaegi lasted for more than 10 days thanks to the following tropical storm Fung-Wong, indicating the effect of superposition in SST cooling. MLD was deepened from 23 to 50 m in the “cold wake” one day after Kalmaegi passed by. MLD was deepened from 31 to 91 m eight hours after Fung-Wong passed by, due to the coastal upwelling induced by offshore Ekman transport driven by wind stress at the southwestern of Taiwan Island. After the tropical cyclones passed by, salinity profile in the mixed layer showed uniformity later than temperature profile, and recovered earlier than temperature profile, revealing the time lag in mixed layer responses. For the spatial variation response to the two tropical cyclones, the changes of SST and MLD were larger on the right-hand side of the tropical cyclones (along the moving directions of tropical cyclones) than on the left-hand side. The uneven deepening even shallowing in MLD in the cold wake may reveal that different depths of deep cold water uplifted by the vertical current switch between upwelling and downwelling in the Ekman layer due to the change of Ekman pumping velocity.

Key words: mixed layer, tropical cyclone, SST, wind stress, marine remote sensing

宋勇军, 唐丹玲. 南海东北部混合层深度对热带气旋海鸥和凤凰的响应[J]. 热带海洋学报, 2017, 36(1): 15-24.

Yongjun SONG, Danling TANG. Mixed layer depth responses to tropical cyclones Kalmaegi and Fung-Wong in the northeastern South China Sea[J]. Journal of Tropical Oceanography, 2017, 36(1): 15-24.

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浮标	海鸥(9月14~16日^*)						凤凰(9月19~21日^*)
	与路径的关系		SST降低/℃		MLD/m		与路径的关系		SST降低/℃		MLD/m
	位置	距离/km	遥感数据	Argo 数据	过境前	最大深度	位置	距离/km	遥感数据	Argo 数据	最大深度	恢复深度
Argo 1	右	125	0.48	0.41	31	35	左	260	0.88	0.60	43	46
Argo 2	左	160	2.15	2.35	23	50	左	400	2.68	×	37	31
Argo 3	中	10	0.70	0.96	40	41	左	100	1.45	×	45	36
Argo 4	右	180	0.45	0.54	31	×	中	0	1.40	1.42	42	36
Argo 5	右	480	0.36	×	31	×	左	25	0.75	0.51	91	49