**3. Model validation**

maximum depths are 5 m and 5000 m, respectively (**Figure 1**). There are 80 layers in the vertical direction using the *s*‐coordinate formulation. The western boundary is closed and the other

The initial temperature and salinity conditions are taken from the 1/4° grid climatological temperature and salinity analyses of October from WOA01 to represent the pre‐typhoon conditions in the South China Sea, which was discussed by Carton and Giese [31]. The climatological monthly data have 24 standard levels with depths varying from 0 to 1500 m and the seasonal data have 33 standard levels with depths from 0 to 5500 m. As the maximum depth in the model is 5000 m, the climatological monthly data are applied in the upper 1500 m and the climatological seasonal data (autumn) are applied from 1500 to 5000 m. The initial current

The lateral boundary conditions for temperature, salinity, sea level and current velocities are obtained from the 5‐day averages from the global simulations of the Simple Ocean Data Assimilation (SODA) dataset with horizontal resolution of 0.5° × 0.5° and 40 vertical layers [31]. The Kuroshio Current transport can be identified on the eastern boundary. The tidal ampli‐ tudes and phases used in this model are obtained from the TPXO Global Inverse solution database [32] with eight primary tide constituents (M2, S2, N2, K2, K1, O1, P1, and Q1) and

three open boundaries are defined by the radiation boundary condition.

70 Recent Developments in Tropical Cyclone Dynamics, Prediction, and Detection

**Figure 1.** Model domain and grids, as well as bathymetry.

velocity is set to zero in this study.

two long‐period constituents (Mf and Mm).

Two Optimally Interpolated (OI) SST daily products (including microwave plus infrared (MWIR) OI SSTs and microwave only TMI AMSRE SSTs) are used in comparisons with the simulated SSTs to validate the model accuracy. MWIR OI SST product is at 9 km resolution, while TMI AMSRE SST product is at 25 km resolution. The validation statistical parameters contain mean error (ME), mean absolute error (MAE), root‐mean‐square (RMS), and correla‐ tion coefficient (R). The formulas to calculate these statistical parameters are presented in [39].

The simulated SSTs (**Figure 2**) are compared with the satellite observations from October 30 to November 6. The validation region is set from 99°E to 120°E and from 0°N to 26°N. For validation of the simulation, the statistical parameters are displayed in **Table 1** for MWIR OI and **Table 2** for TMI AMSRE. The MEs of the simulated SSTs are less than 0.12°C, compared with the MWIR SSTs; for TMI AMSRE SSTs, the MEs are within 0.14–0.24°C. Negative signs indicate that the modelled SSTs are less than the observed SSTs. The MAEs are within the range from 0.4°C to 0.6°C, and the RMS errors are less than 0.9°C. The correlation coefficients between the MWIR OI SST and simulated SST are over 87% from October 30 to November 6, while the correlation coefficients validated with TMI AMSRE SSTs are over 84%. The high values of the correlation coefficients indicate that the simulated SSTs are within a reasonable range. Therefore, we have demonstrated that ROMS can generally reproduce the processes of Typhoon Cimaron in the South China Sea.

**Figure 2.** The simulated SSTs (unit: °C) from October 31 to November 5, 2006.


**Table 1.** Statistics of the simulated SSTs versus MWIR OI SSTs from October 30 to November 6, 2006.


**Table 2.** Statistics of the simulated SSTs versus TMI AMSRE SSTs from October 30 to November 6, 2006.

#### **4. Results**

from 0.4°C to 0.6°C, and the RMS errors are less than 0.9°C. The correlation coefficients between the MWIR OI SST and simulated SST are over 87% from October 30 to November 6, while the correlation coefficients validated with TMI AMSRE SSTs are over 84%. The high values of the correlation coefficients indicate that the simulated SSTs are within a reasonable range. Therefore, we have demonstrated that ROMS can generally reproduce the processes of

Typhoon Cimaron in the South China Sea.

72 Recent Developments in Tropical Cyclone Dynamics, Prediction, and Detection

**Figure 2.** The simulated SSTs (unit: °C) from October 31 to November 5, 2006.

**Oct 30 Oct 31 Nov 1 Nov 2 Nov 3 Nov 4 Nov 5 Nov 6**

ME (°C) −0.12 −0.12 −0.09 −0.04 −0.01 −0.00 −0.09 −0.10 MAE (°C) 0.42 0.45 0.50 0.54 0.58 0.56 0.55 0.58 RMS (°C) 0.56 0.61 0.69 0.76 0.88 0.81 0.78 0.80 R 0.89 0.88 0.88 0.89 0.87 0.88 0.88 0.88

**Table 1.** Statistics of the simulated SSTs versus MWIR OI SSTs from October 30 to November 6, 2006.

#### **4.1. Ocean temperatures**

The ocean surface temperature distributions from October 31 to November 5, 2006 are shown in **Figure 2**. Cimaron entered the South China Sea on October 30, and the simulation of the typhoon‐induced wake suggests that the apparent temperature depression started on October 31. The wake of the typhoon occurred within the region from 15°N to 20°N and from 114°E to 119°E. **Figure 3** shows the time series (daily) of the maximum SST decreasing in the typhoon‐ induced wake, located at 18.51°N and 116.45°E, relative to the pre‐typhoon conditions on October 28. Although bias exists between these two satellite SST observations, both satellite SSTs display the same trend in their variations in the SST cooling amplitude in the wake. The

**Figure 3.** Maximum SST decrease in the typhoon wake from October 31 to November 5, 2006 (the red solid line with squares denotes the model results; the dash line denotes TMI AMSRE satellite observations; the solid line represents MWIR OI satellite observations).

observed SST decreased to an extremely low value on November 3, by which time the ocean was in the forcing stage. Starting from November 3, SSTs had begun to increase, which defines the beginning of the relaxation stage towards a new equilibrium state, with the injection of potential vorticity into the wake by the typhoon winds [1]. Comparing model results to these two satellite SSTs which show that the maximum amplitude of the SST cooling appeared on November 3, with values of 5.1°C for TMI AMSRE and 6.3°C for MWIR OI, the simulated maximum SST cooling was 4.8°C on November 4 (**Figure 3**). Thus, the relaxation of surface temperature in the wake after the typhoon's passage is clearly underestimated in our simula‐ tions.

**Figure 4.** Isotherms of SST in the typhoon wake (unit: °C) from October 31 to November 5, 2006 (with the black lines showing the MWIR OI SSTs and blue lines showing the simulated SSTs).

**Figure 4** shows the comparison of the daily surface isotherms between MWIR OI observations and the model simulations from October 31 to November 5. The isothermal lines ranged from 22°C to 26°C with 1°C intervals. The distributions of the simulated surface isotherms in the wake area are quite consistent with the MWIR OI SSTs, which further demonstrate that the temperature simulations related to Typhoon Cimaron are well reproduced. The southward shift of the location of the maximum SST cooling in the simulation results compared to the satellite observations indicates another common issue during the forecasting of extreme weather conditions, which is the lack of high‐accuracy wind forcing observations. The simulated maximum mixed layer depth was about 53.2 m, located at (18.51°N, 116.44°E) on November 3, 2006 which is an underestimate compared with the maximum deepening of 104.5 m at (19.50°N, 116.26°E) estimated in work [30]. Underestimation of the mixed layer depth and SST cooling is a common problem in the numerical ocean model simulations because of insufficient mixing. To solve this problem, a parameterization of wave‐induced mixing is added to the model to improve the mixing estimates in this chapter (see details in Section 5).

#### **4.2. Ocean currents**

observed SST decreased to an extremely low value on November 3, by which time the ocean was in the forcing stage. Starting from November 3, SSTs had begun to increase, which defines the beginning of the relaxation stage towards a new equilibrium state, with the injection of potential vorticity into the wake by the typhoon winds [1]. Comparing model results to these two satellite SSTs which show that the maximum amplitude of the SST cooling appeared on November 3, with values of 5.1°C for TMI AMSRE and 6.3°C for MWIR OI, the simulated maximum SST cooling was 4.8°C on November 4 (**Figure 3**). Thus, the relaxation of surface temperature in the wake after the typhoon's passage is clearly underestimated in our simula‐

74 Recent Developments in Tropical Cyclone Dynamics, Prediction, and Detection

**Figure 4.** Isotherms of SST in the typhoon wake (unit: °C) from October 31 to November 5, 2006 (with the black lines

**Figure 4** shows the comparison of the daily surface isotherms between MWIR OI observations and the model simulations from October 31 to November 5. The isothermal lines ranged from 22°C to 26°C with 1°C intervals. The distributions of the simulated surface isotherms in the

showing the MWIR OI SSTs and blue lines showing the simulated SSTs).

tions.

When Typhoon Cimaron entered the South China Sea on October 30, the upper ocean's response was almost instantaneous. Typhoon‐induced cyclonic currents caused divergence of upper ocean water over the surface areas by tens of kilometres (in scale) with cold water that is upwelled from the deeper ocean, accounting for the formation of a cold‐core eddy. The cyclonic currents flowed in a roughly circular motion around the mesoscale cold eddy, with the maximum velocity reaching 2.5 m s−1 at location (18.44°N, 115.3°E) on October 31. An alongshore current flowing through the Taiwan Strait into the South China Sea, driven by the northeast monsoon winds, was strengthened by the typhoon forcing on October 31 and November 1. The intrusion of Kuroshio Current meandering towards the South China Sea through the Luzon Strait was strengthened too, with the current velocity reaching 1.6 m s−1 north of the Philippines Islands on November 1.

A very large amount of potential and kinetic energy is injected into the ocean surface layer from the strong typhoon winds during the typhoon generation and development process. The power of the injected energy and the vorticity can be calculated using the following formulae:

$$
\mathbf{V} = \overrightarrow{\mathbf{F}} \cdot \overrightarrow{\mathbf{U}} = \mathbf{\tau}\_{\mathbf{x}} \mathbf{u} + \mathbf{\tau}\_{\mathbf{y}} \mathbf{v} \tag{1}
$$

$$\mathbf{J} = \frac{\partial \mathbf{v}}{\partial \mathbf{x}} - \frac{\partial \mathbf{u}}{\partial \mathbf{y}} \tag{2}$$

where W represents the power in the units of W m−2. Here, F represents the wind stress with (τx, τy) the two components corresponding to the (x, y) coordinates, respectively. U(u, v) is the simulated surface current velocity and ζ represents the vorticity.

Strong cyclonic currents caused by Typhoon Cimaron lasted for several days after typhoon's passage. Strengthened by the long‐lasting intense typhoon wind forcing, the cyclonic eddy generated by the cyclonic circulation reached a maximum positive vorticity of 3.56 × 10−5 s−1 at the location (116.8°E, 18.3°N) on October 30, and continued intensifying to 5.36 × 10−5 s−1 on October 31 and 5.07 × 10−5 s−1 on November 1 (**Figure 5**). **Figure 6** shows estimates for the power of the injected oceanic kinetic energy from October 30 to November 4. The power input from the wind forcing was mostly located on the right side of the typhoon's track with maxima of 1.45 W m−2 on October 31, and 1.43 W m−2 on November 1 and 0.54 W m−2 on November 2. The power input was low in the typhoon's eye area where the winds were very weak. The initial oceanic state was changed under the effect of the strong typhoon winds. On October 30, there is a large region with negative kinetic energy injected by the typhoon, appearing on the right side of the typhoon's track; this suggests that the oceanic kinetic energy was decreased by the typhoon. Thus, the intense typhoon winds changed the original pre‐typhoon sea state conditions. The maximum decrease in the oceanic kinetic energy in the wake of the typhoon was 0.83 W m−2. On October 31, the power reached a maximum value of 2.3 W m−2, and on November 1, this value was 2.0 W m−2.

**Figure 5.** Surface vorticity from October 30 to November 4, 2006.

From November 2 onwards, the injected energy into the wake region of the typhoon showed the decreasing tendency pattern. However, the vorticity of the current induced by typhoon persisted for a long time after typhoon's passage. The study presented here shows that the energy input induced by the typhoon winds was responsible for the ocean‐enhanced mixing processes.

Upper Ocean Physical and Biological Response to Typhoon Cimaron (2006) in the South China Sea http://dx.doi.org/10.5772/64099 77

**Figure 6.** The power input to the ocean surface by the typhoon winds from October 30 to November 4, 2006.

#### **4.3. Biological results**

of the injected oceanic kinetic energy from October 30 to November 4. The power input from the wind forcing was mostly located on the right side of the typhoon's track with maxima of 1.45 W m−2 on October 31, and 1.43 W m−2 on November 1 and 0.54 W m−2 on November 2. The power input was low in the typhoon's eye area where the winds were very weak. The initial oceanic state was changed under the effect of the strong typhoon winds. On October 30, there is a large region with negative kinetic energy injected by the typhoon, appearing on the right side of the typhoon's track; this suggests that the oceanic kinetic energy was decreased by the typhoon. Thus, the intense typhoon winds changed the original pre‐typhoon sea state conditions. The maximum decrease in the oceanic kinetic energy in the wake of the typhoon was 0.83 W m−2. On October 31, the power reached a maximum value of 2.3 W m−2, and on

November 1, this value was 2.0 W m−2.

76 Recent Developments in Tropical Cyclone Dynamics, Prediction, and Detection

**Figure 5.** Surface vorticity from October 30 to November 4, 2006.

processes.

From November 2 onwards, the injected energy into the wake region of the typhoon showed the decreasing tendency pattern. However, the vorticity of the current induced by typhoon persisted for a long time after typhoon's passage. The study presented here shows that the energy input induced by the typhoon winds was responsible for the ocean‐enhanced mixing The monthly chlorophyll *a* concentration gridded datasets are obtained from the SeaWiFS observations, with a horizontal spatial resolution of 0.0417° × 0.0417°. **Figure 7** shows the monthly distributions of surface chlorophyll *a* concentration on October 16 and November 16, 2006 in the South China Sea. These two satellite images represent the pre‐ and post‐typhoon situations for the primary production; it is evident that a phytoplankton bloom area exists around the location of the typhoon's wake after it had passed. Although the concentration of the chlorophyll *a* achieved high values, in excess of 4 mg cm−3 along the coast, the averaged concentration was about 0.09 mg cm−3 in the area that became the wake (the black box in **Figure 7**) before the appearance of Typhoon Cimaron. However, by November 16, the concentration in this area reached 0.85 mg cm−3, which was much higher than the normal expected conditions, indicating that the maximum increase of chlorophyll *a* concentration was about 0.75 mg cm−3 at the location (17.02°N, 115.57°E) in the wake area. While the monthly dataset may be interpolated in both spatial and temporal dimensions, the detailed processes related to the development of the phytoplankton bloom triggered by Typhoon Cimaron are still not clear. The application of the biological numerical model can provide more details for the study of the subsurface water layers and can complement the limitations of the satellite remote sensing.

**Figure 7.** Chlorophyll *a* concentration (unit: mg cm−3) from SeaWiFS on October 16 (upper panel) and November 16 (lower panel), 2006 (black box represents the areas in the wake of the typhoon; the pentagram marks the location used for calculation in **Figure 9**).

**Figure 8** shows the simulated daily maximum surface concentrations of chlorophyll *a* and nitrate in the typhoon's wake area through October 28 to November 30. In the pre‐typhoon condition, the nitrate concentration maintained a stable value of 0.03 mmol Nm−3. During November 1–3, Cimaron lingered in locations that were quasistationary and caused strong mixing in the wave areas. Thus the nitrate concentration largely increased in the ocean surface layer in the wake, reaching a maximum of 1.24 mmol Nm−3 on November 3. By November 3, Cimaron had passed from this (wake) region. The surface nitrate concentration remained high, in excess of 1.1 mmol Nm−3 for an additional 3 days, from November 3–5, and then decreased to a rather stable level of 0.1 mmol Nm−3 from November 11 onwards.

Compared to the quick response of nitrate to Typhoon Cimaron, the response of the phyto‐ plankton is a relatively slow process. The chlorophyll *a* concentration remained at the prety‐ phoon level of about 0.06 mg cm−3 for some time beyond November 3. Although the mixed layer depth deepened to its maximum on November 3, the chlorophyll *a* concentration was still increasing at that time, having increased slightly over the previous 2 days, as triggered by the upwelling induced by the approaching storm. Thereafter, the chlorophyll *a* concentration increased rapidly in early November, reaching a rate of 0.5 mg cm−3 d−1, and attaining a maximum concentration of 1.76 mg cm−3 on November 7. The phytoplankton blooms occurred 5 days after Typhoon Cimaron's passage. The chlorophyll *a* concentration began to decrease from November 8 onwards, returning to a quasistable level of 0.3 mg cm−3 by November 18. The maximum concentration of chlorophyll *a* on November 16 was simulated at the value of 0.65 mg cm−3, which was about 0.2 mg cm−3 less than the satellite observations. The surface ocean was restored to an equilibrium state again by about 10–20 days after the interruption that Cimaron introduced. Moreover, the concentrations of both nitrate and chlorophyll *a* in the resulting re‐equilibrium of the ocean state are higher than those of the former pre‐typhoon state.

dataset may be interpolated in both spatial and temporal dimensions, the detailed processes related to the development of the phytoplankton bloom triggered by Typhoon Cimaron are still not clear. The application of the biological numerical model can provide more details for the study of the subsurface water layers and can complement the limitations of the satellite

78 Recent Developments in Tropical Cyclone Dynamics, Prediction, and Detection

**Figure 7.** Chlorophyll *a* concentration (unit: mg cm−3) from SeaWiFS on October 16 (upper panel) and November 16 (lower panel), 2006 (black box represents the areas in the wake of the typhoon; the pentagram marks the location used

**Figure 8** shows the simulated daily maximum surface concentrations of chlorophyll *a* and nitrate in the typhoon's wake area through October 28 to November 30. In the pre‐typhoon condition, the nitrate concentration maintained a stable value of 0.03 mmol Nm−3. During November 1–3, Cimaron lingered in locations that were quasistationary and caused strong mixing in the wave areas. Thus the nitrate concentration largely increased in the ocean surface layer in the wake, reaching a maximum of 1.24 mmol Nm−3 on November 3. By November 3, Cimaron had passed from this (wake) region. The surface nitrate concentration remained high, in excess of 1.1 mmol Nm−3 for an additional 3 days, from November 3–5, and then decreased

Compared to the quick response of nitrate to Typhoon Cimaron, the response of the phyto‐ plankton is a relatively slow process. The chlorophyll *a* concentration remained at the prety‐

to a rather stable level of 0.1 mmol Nm−3 from November 11 onwards.

remote sensing.

for calculation in **Figure 9**).

**Figure 8.** Simulated maximum concentrations of nitrate and chlorophyll *a* in the typhoon wake from October 28 to No‐ vember 30, 2006.

The vertical profiles of the density, both of chlorophyll *a* and nitrate concentrations at the location (18.66°N, 115.89°E), as shown in **Figure 7**, in the typhoon wake are investigated with respect to the underwater impacts of Cimaron, comparing the pre‐ and post‐typhoon profiles through October 28 to November 30 in **Figure 9**. Before the typhoon, the nutrient and phyto‐ plankton in the surface layer are both at low concentrations, as the surface waters received strong light irradiation, which is not conducive to the growth and reproduction of the phytoplankton. Phytoplankton populations grow and reproduce mostly in the euphotic zone. The depth of the euphotic zone can be estimated from the chlorophyll *a* concentration of the surface layer, based on the assumption of Case‐I waters; the equation is shown in [40]. After

the typhoon's passage, cyclonic eddies caused by Typhoon Cimaron exhibited the upward doming of isopycnals from October 31 and the isopycnals were uplifted with high nutrient concentrations into the euphotic zone, which furthermore, had a positive influence on the photosynthetic performance. The chlorophyll *a* concentration in the surface layer increased and reached about 0.237 mg cm−3 on November 7 in **Figure 9**. Both the profiles of nitrate and chlorophyll *a* are significantly elevated after the typhoon's passage. The euphotic zone depth was estimated as 87.0 m before typhoon and 36.2 m after typhoon in the wake, with respect to the chlorophyll *a* concentrations obtained from the satellite for pre‐ and post‐typhoon Cimar‐ on. The euphotic zone was uplifted by 50.0 m in the wake of Typhoon Cimaron.

**Figure 9.** Profiles of chlorophyll *a* and nitrate concentration at the location (18.66°N, 115.89°E), shown in **Figure 7** in the typhoon wake from October 28 to November 30, 2006.

#### **5. Discussion: effect of the wave‐induced mixing**

The mixed layer deepening induced by Typhoon Cimaron is underestimated in the three‐ dimensional ocean model simulations, which is a common situation in ocean model simula‐ tions. To strengthen the insufficient mixing, in our chapter, we incorporated the wave‐induced mixing term, BV into ROMS to investigate the effect of BV on the mixed layer deepening and ocean surface temperature cooling caused by Typhoon Cimaron.

The wave‐induced mixing term BV, is added into ROMS, as part of the vertical kinematic viscosity, as expressed by Qiao et al. [29]

$$\mathbf{B}\_{\text{V}} = \boldsymbol{\alpha} \left[ \int\_{\bar{\mathbf{k}}} \mathbf{E} \left( \bar{\mathbf{k}} \right) \exp \left( 2 \mathbf{k} \mathbf{z} \right) d\bar{\mathbf{k}} \frac{\partial}{\partial \mathbf{z}} \right] \left[ \int\_{\bar{\mathbf{k}}} \boldsymbol{\alpha}^{2} \mathbf{E} \left( \bar{\mathbf{k}} \right) \exp \left( 2 \mathbf{k} \mathbf{z} \right) d\bar{\mathbf{k}} \right]^{1/2} \tag{3}$$

where ω is the wave angular frequency, z is the vertical coordinate axis downward positive with z = 0 at the surface,k is the wave number, and E k represents the wave number spectrum including both wind wave and swell waves. BV can be calculated by the wave model. In this study, the wave‐induced mixing term is directly derived from the Key Laboratory of Marine Science and Numerical Modeling (MASNUM) wave model [28] and is added into the vertical viscosity and diffusivity term of the K‐profile parameterization (KPP) mixing scheme which is applied in ROMS. Because the wave mixing is dominant in the upper ocean layer, the BV term is confined to the range from 1000 m depth up to the surface. The weighting coefficient was set to 0.1 in our study, as suggested by Wang et al. [41]. In the wake of the typhoon, the vertical mixing was strengthened with the vertical viscosity coefficient of 0.1 m2  s−1 from

October 31 to November 2.

the typhoon's passage, cyclonic eddies caused by Typhoon Cimaron exhibited the upward doming of isopycnals from October 31 and the isopycnals were uplifted with high nutrient concentrations into the euphotic zone, which furthermore, had a positive influence on the photosynthetic performance. The chlorophyll *a* concentration in the surface layer increased and reached about 0.237 mg cm−3 on November 7 in **Figure 9**. Both the profiles of nitrate and chlorophyll *a* are significantly elevated after the typhoon's passage. The euphotic zone depth was estimated as 87.0 m before typhoon and 36.2 m after typhoon in the wake, with respect to the chlorophyll *a* concentrations obtained from the satellite for pre‐ and post‐typhoon Cimar‐

**Figure 9.** Profiles of chlorophyll *a* and nitrate concentration at the location (18.66°N, 115.89°E), shown in **Figure 7** in the

The mixed layer deepening induced by Typhoon Cimaron is underestimated in the three‐ dimensional ocean model simulations, which is a common situation in ocean model simula‐ tions. To strengthen the insufficient mixing, in our chapter, we incorporated the wave‐induced

typhoon wake from October 28 to November 30, 2006.

**5. Discussion: effect of the wave‐induced mixing**

on. The euphotic zone was uplifted by 50.0 m in the wake of Typhoon Cimaron.

80 Recent Developments in Tropical Cyclone Dynamics, Prediction, and Detection

**Figure 10.** Maximum SST decrease in the wake from October 31 to November 5, 2006 (red solid line with asterisks de‐ notes the model results; the dash line denotes TMI AMSRE satellite observations; the solid line represents MWIR satel‐ lite observations).

**Figure 10** shows the maximum SST decrease in the wake of the typhoon, comparing the simulations by adding BV with the two sets of satellite observations. Under the effect of the strengthened mixing estimates, SST in the wake reached the lowest temperature on November 3 with a value that is consistent with both sets of satellite observations. The maximum SST decreases on November 2 and November 3, respectively, relative to the pre‐typhoon conditions on October 28, which were 5.9°C and 6.2°C, which are close to the MWIR observations of 5.8°C and 6.3°C. Compared to the maximum temperature decreases without the BV term of 4.1°C on

November 2 and 4.8°C on November 3 in the typhoon's wake, the wave‐induced mixing can improve the SST cooling by 1.7°C on November 2 and 1.4°C on November 3. This is with a weighting coefficient of 0.1. The associated mixed layer deepening was increased by 30 m on November 3.

### **6. Conclusions**

A three‐dimensional simulation of the upper ocean in response to Typhoon Cimaron is investigated in this study, including both the physical and biological processes. The validation of SST was compared with two satellite observations, TMI AMSRE and MWIR OI SSTs, from October 30 to November 6. High correlation (over 84%) and low bias (between 0.4°C and 0.6°C) show that ROMS can reproduce the process of upper ocean response to Typhoon Cimaron quite well. Detailed analysis indicates that the surface cooling is underestimated due to the insufficient mixing in the ROMS model. To solve this problem, the wave‐induced mixing with a certain weighting coefficient was introduced into the KPP mixing scheme to improve the simulation of SST cooling. Values up to 6.2°C are obtained, which is close to the observed MWIR cooling estimate of 6.3°C on November 3, whereas the ROMS simulation without the wave‐induced mixing gives an underestimated cooling of 4.8°C. The simulation accuracy is enhanced by adding the wave‐induced mixing, which increases the SST cooling by 1.4°C and deepens the mixed layer by 30 m in the wake of typhoon.

A strong mesoscale ocean eddy, as characterized by the cyclonic currents, was caused by Typhoon Cimaron in the South China Sea. The water within the eddy diverged over surface areas on a scale of tens of kilometres. Under the divergent condition, cold nutrient‐rich water upwelled from deeper waters. The positive vorticity kept a high value over 5.0 × 10−5 s−1 on October 31 and November 1. Moreover, the concentration of nitrate in the surface wake area increased to a maximum during these 2 days, which indicates that upwelling played a key role on the phytoplankton blooming after typhoon's passage. The simulated maximum concentra‐ tion of chlorophyll *a* in the wake increased from a pre‐typhoon value of 0.1 mg cm−3 to a post‐ typhoon value of 0.65 mg cm−3 on November 16, which is close to the satellite observation of 0.85 mg cm−3 on November 16. The euphotic zone was uplifted by 50.0 m after Typhoon Cimaron's passage. Thereafter, the ocean restored to a new equilibrium state with higher concentrations of chlorophyll *a* and nitrate than those existing in the pre‐equilibrium state in the wake area.
