Journal of Tropical Oceanography >
The influence of a new drag coefficient scheme considering sea spay on numerical simulation of upper-ocean temperature response to tropical cyclone
Received date: 2016-10-20
Request revised date: 2017-04-13
Online published: 2017-09-22
Supported by
National Program on Key Basic Research Project (973) Program (2013CB430305)
Copyright
To improve model forecast of upper ocean and offer a more proper momentum exchange scheme for an air-sea coupling model, a new drag coefficient scheme of CD considering sea spay layer on the surface is established and is used in the three-dimensional oceanic circulation model of the Princeton Ocean Model (POM). A case of tropical cyclone Kalmaegi in 2014 is selected, which passed through the center of a buoys array set up by our field experiment in the northern South China Sea. Observation data were collected for both atmosphere and ocean in the process, and are used to verify the model simulation. It is found that the drag coefficient CD under low wind condition is consistent with the traditional CD scheme. However, they are different from each other under high wind condition with CD increasing slowly, even decreasing slightly, if sea spay process is considered by the new CD scheme. Furthermore, numerical experiments are conducted using the POM. The results show that the responses of upper ocean on temperature are more reasonable with a weaker cooling rate of ocean temperature and thermocline strength, and smaller deepening of mixed layer depth in the upper ocean if the new drag coefficient scheme is used.
LIU Xiaoyan , LI Yongping , DUAN Ziqiang . The influence of a new drag coefficient scheme considering sea spay on numerical simulation of upper-ocean temperature response to tropical cyclone[J]. Journal of Tropical Oceanography, 2017 , 36(5) : 24 -32 . DOI: 10.11978/2016103
Fig. 1 Buoy array in the South China Sea and track of Typhoon Kalmaegi. represents the center of typhoon, and●represents the locations of the buoys图1 南海浮标观测阵列及2014年“海鸥”台风路径 |
Fig. 2 Averaged ocean temperature standard deviation between simulation in EXP2 and Argo observations图2 EXP2模式模拟海温与西北太平洋Argo观测海温的标准差 |
Fig. 3 Ocean temperature profiles with depth before Typhoon Kalmaegi passing the locations of B2 (a), B4 (b) and B5 (c). Short dashed line: buoy observations; and solid line: simulated ocean temperature by EXP1图3 9月10日18时(台风影响前)浮标B2(a)、浮标B4(b)和浮标B5(c)海温随深度的变化廓线 |
Fig. 4 Sea surface wind field used by the model at 06:00 on Sep. 15 in 2014. represents the center of typhoon, and●represents locations of buoys图4 2014年9月15日06时的模式强迫海面风场 |
Fig. 5 The observed wind speed (dotted line) and model wind speed (solid line) at B2, B4 and B5 buoy sites, from Sep. 10 to Sep. 19图5 B2(a)、B4(b)和B5(c)浮标所在位置上的2min平均风速的观测(虚线)和模式强迫风速(实线)时间序列 |
Fig. 6 Variation of drag coefficient CD with wind speed and sea spray concentration in EXP1 and EXP2 at the locations of B2 (a) and B5 (b)图6 EXP1和EXP2中浮标B2(a)和B5(b)位置上拖曳系数CD随风速和海洋飞沫体积浓度的变化 |
Fig. 7 Difference of sea surface temperature before and after Typhoon Kalmaegi: a) satellite observations; b) EXP1; and c) EXP2图7 “海鸥”台风经过浮标观测列阵前后的SST变化 |
Fig. 8 Time series of SST for EXP1, EXP2 and observations, respectively, at B2 (a) and B5 (b)图8 海表面温度SST随时间变化 |
Tab. 1 SST decreases in EXP1, EXP2 and observed by buoys (Units: ℃)表1 EXP1、EXP2和观测的SST降温幅度(单位: ℃) |
浮标 | EXP1 | EXP2 | OBS(观测) |
---|---|---|---|
B1 | 2.17 | 1.88 | 1.87 |
B2 | 2.02 | 1.90 | 1.44 |
B3 | 1.61 | 1.31 | 1.24 |
B4 | 1.96 | 1.67 | 1.80 |
B5 | 1.05 | 0.97 | 0.62 |
Fig. 9 Ocean temperature profiles with depth before and after Typhoon Kalmaegi: i) OBS; ii) EXP1; and iii) EXP2. a) Buoy 2; and b) Buoy 4. Solid line: before typhoon passage; and dashed line: after typhoon passage图9 台风影响前后观测(i)、EXP1(ii)和EXP2(iii)海温随深度的变化廓线 |
The authors have declared that no competing interests exist.
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