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The formation and dynamics of cold- dome northeast of Taiwan Mao-Lin Shen 1 Yu-Heng Tseng 1 Sen Jan 2 1 Atmospheric Sciences,

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Presentation on theme: "The formation and dynamics of cold- dome northeast of Taiwan Mao-Lin Shen 1 Yu-Heng Tseng 1 Sen Jan 2 1 Atmospheric Sciences,"— Presentation transcript:

1 The formation and dynamics of cold- dome northeast of Taiwan Mao-Lin Shen 1 Yu-Heng Tseng 1 Sen Jan 2 1 Atmospheric Sciences, Nation Taiwan University, Taiwan (R.O.C.) 2 Institute of Oceanography, Nation Taiwan University, Taiwan (R.O.C.) October 26, 2010

2 Mao-Lin Shen, Yu-Heng Tseng and Sen Jan Page /5/9 Outline Overview of the documented cold-dome and suggested formation mechanisms Temporal SST variation during and Argo data northeast of Taiwan Numerical model and the associated results Analysis of formation mechanisms Conclusion

3 Mao-Lin Shen, Yu-Heng Tseng and Sen Jan Page 3 Introduction (1/5) Sea Surface Temperature (SST) November

4 Mao-Lin Shen, Yu-Heng Tseng and Sen Jan Page /5/9 Introduction (2/5) An active upwelling and nutrient-rich area The exchange of Kuroshio Water and Continental Water of East China Sea (Isobe, 2008; Matsuno et al., 2009) Fundamental characteristics have been well- documented by Gong et al. (1992), Lin et al. (1992), Tang and Tang (1994), Chen et al. (1995) and Tang et al. (1999), etc.

5 Mao-Lin Shen, Yu-Heng Tseng and Sen Jan Page /5/9 Introduction (3/5) Cheng, Ho et al., 2009, Sensors Chen, 1995 Kuroshio Tropical Water Kuroshio Surface Water

6 Mao-Lin Shen, Yu-Heng Tseng and Sen Jan Page 6 Introduction (4/5) Liu et al., 1992 Suggested the year round upwelling should be 5 m/day. Chen et al., 1995 Contribution of Kuroshio Water Kuroshio Tropical Water Hsueh, Wang, Chern, 1992, JGR. Stated how the baroclinic transport work in this region.

7 Mao-Lin Shen, Yu-Heng Tseng and Sen Jan Page 7 Introduction (5/5) What contribute to the formation mechanisms of cold- dome ? Which one dominates the formation process? What kind of connections between cold-dome and the surrounding currents, e.g. Kuroshio and Taiwan Strait flow?

8 Mao-Lin Shen, Yu-Heng Tseng and Sen Jan Page /5/9 Observation (1/3) ─ MW and IR merged SST May May Jul Typhoon Fung- Wong passed on Jul 28. Nov Area for meridional averaging Hovmoller plot

9 Mao-Lin Shen, Yu-Heng Tseng and Sen Jan Page /5/9 Time-longitude plot of filtered SST north of Taiwan. the dashed lines denote typhoons from left to right is Kalmaegi, Fung-Wong, Sinlaku and Jangmi, respectively. Of 2009 the dashed line denotes typhoon Morakot.

10 Mao-Lin Shen, Yu-Heng Tseng and Sen Jan Page /5/9 Observation (3/3) ─ cold-dome in winter Argo float, WMOID , for (a) the trajectory; (b) MW_IR SST and a marker denotes the Argo data on December 16, The rests are subsurface comparisons of (c) temperature and (d) salinity.

11 Mao-Lin Shen, Yu-Heng Tseng and Sen Jan Page 11 DUPOM (North Pacific adaptation of TIMCOM)

12 Mao-Lin Shen, Yu-Heng Tseng and Sen Jan Page /5/9 Numerical model (1/2) Surface sources of heat and fresh water Levitus94 seasonal climatology Bathymetry unfiltered ETOPO-2 depth data supplemented with the Taiwan’s NCOR 1-minute high accuracy depth archive in the Asian Seas Winds stress monthly Hellerman and Rosenstein winds stress Vertical mixing Modified Richardson number dependent formula based on Pacanowski and Philander (1981)

13 Mao-Lin Shen, Yu-Heng Tseng and Sen Jan Page /5/9 Numerical model (2/2) ─ Domain

14 Mao-Lin Shen, Yu-Heng Tseng and Sen Jan Page /5/9 Numerical results (1/4) On day 157, Year 37 Model results Z = 6 mZ = 54 m Z = 75 m Z = 98 m

15 Mao-Lin Shen, Yu-Heng Tseng and Sen Jan Page /5/9 Numerical results (2/4) ─ Trajectories Kuroshio Tropical Water (KTW), m.

16 Mao-Lin Shen, Yu-Heng Tseng and Sen Jan Page /5/9 Numerical results (3/4) ─ Trajectory North Mien-Hua Canyon Mien-Hua Canyon A trajectory shows the route of Kuroshio Tropical Water. The background flow field are model results at z = 159 m.

17 Mao-Lin Shen, Yu-Heng Tseng and Sen Jan Page /5/9

18 Mao-Lin Shen, Yu-Heng Tseng and Sen Jan Page /5/9 Mechanism Analysis (1/10) Possible mechanisms Wind-driven Ekman upwelling Boundary layer effect Current-driven Ekman upwelling Ekman boundary mixing Dynamic uplift due to geostrophic adjustment mesoscale eddy Kuroshio Topographically controlled upwelling Vertical mixing

19 Mao-Lin Shen, Yu-Heng Tseng and Sen Jan Page /5/9 Mechanism Analysis (2/10) Wind-driven Ekman upwelling Boundary layer effect Current-driven Ekman upwelling Ekman boundary mixing Dynamic uplift: mesoscale eddy Kuroshio Topographical upwelling Vertical mixing Garrett et al. (1993), ARF. Boundary mixing

20 Mao-Lin Shen, Yu-Heng Tseng and Sen Jan Page /5/9 Mechanism Analysis (3/10) Wind-driven Ekman upwelling Boundary layer effect Current-driven Ekman upwelling Ekman boundary mixing Dynamic uplift: cyclonic eddy Kuroshio Topographical upwelling Vertical mixing

21 Mao-Lin Shen, Yu-Heng Tseng and Sen Jan Page /5/9 Mechanism Analysis ─ Wind-driven upwelling Wind-driven Ekman upwelling, : the thickness of Ekman layer Chang, Wu and Oey, 2009 Mean: -0.3 m/day Max: 0.7 m/day Wind-driven Ekman upwelling Needs 4~5 months to uplift 100 m with maximum upwelling velocities (7)

22 Mao-Lin Shen, Yu-Heng Tseng and Sen Jan Page /5/9 Mechanism Analysis ─ Boundary layer effects Boundary layer effect Current-driven Ekman upwelling Max: only about m/day Ekman boundary mixing Meridional current velocity distribution (Tang et al., 2000). Garrett et al. (1993), ARF. Boundary mixing W (m/day) Garrett et al. (1993), ARF. Boundary mixing Inverse currents introduced little dowelling transport.

23 Mao-Lin Shen, Yu-Heng Tseng and Sen Jan Page /5/9 Mechanism Analysis (6/10) Wind-driven Ekman upwelling: -0.3 m/day Boundary layer effect Current-driven Ekman upwelling: m/day Ekman boundary mixing: inverse flow Dynamic uplift mesoscale eddy Kuroshio Topographically controlled upwelling Vertical mixing Isotherm redistribution due to upwelling. Zonal temperature profile at 25.6°N Buoyancy instabilityDiffusion, little H. Advection Temperature increasing UpwellingMixing

24 Mao-Lin Shen, Yu-Heng Tseng and Sen Jan Page /5/9 Mechanism Analysis (7/10) Isothermal plain have lower depth east of Kuroshio and higher depth on CDFR. The isothermal plain on CDFR can be shallower than 50 m deep. Isothermal plain at 21 ℃ calculated by model output.

25 Mao-Lin Shen, Yu-Heng Tseng and Sen Jan Page /5/9 Mechanism Analysis (8/10) ─ Isotherm uplift Comparison of uplift height introduced by different mechanism. Topographical upwelling, eddy-introduced dynamic uplift and other minor effects.

26 Mao-Lin Shen, Yu-Heng Tseng and Sen Jan Page /5/9 Mechanism Analysis (9/10) ─ Topographic effects Only the realistic bathymetry can constrain sufficient cold water source for surface cold-dome formation. Flow field and temperature at 50 m numerical experiments. (a) Realistic bathymetry (b) Deepened Case(c) Shallowed Case

27 Mao-Lin Shen, Yu-Heng Tseng and Sen Jan Page /5/9 Mechanism Analysis (10/10) ─ vertical mixing Instantaneous zonal profiles of temperature and eddy diffusivities at 25.6°N. The vertical temperature gradient near surface coupled with the high surface eddy diffusivities suggested energetic vertical heat transfer in surface cold-dome. (a) Zonal Temperature ( ℃ ) profile (b) Vertical eddy diffusivities (cm 2 /s)

28 Mao-Lin Shen, Yu-Heng Tseng and Sen Jan Page /5/9 Conclusion (1/2) Different cold-dome patterns from the observations. Evident cold-domes can be found due to the typhoons. Dynamic uplift introduced by Kuroshio dominates the fundamental pattern of cold-dome. Bathymetry not only suggests topographically controlled upwelling, but also constrains cold water in deep sea northeast of Taiwan.

29 Mao-Lin Shen, Yu-Heng Tseng and Sen Jan Page /5/9 Conclusion (2/2) Mesoscale eddy contributes few dynamic uplift but can reduces horizontal advection for cold-dome. Dynamic due to the surface and bottom boundary layers is too weak for the observed cold-dome formation. Vertical mixing plays an important role for surface cold-dome formation.

30 Mao-Lin Shen, Yu-Heng Tseng and Sen Jan Page /5/9 Thank you for your attention. Questions?

31 Mao-Lin Shen, Yu-Heng Tseng and Sen Jan Page /5/9 Observation ─ Argo floats Fig. 5. The Argo data, marked as red solid circles, since 3 August 2001 to 6 September 2009 in the study region, only 2047 data are available. Argo data gathered on Kuroshio main stream totally 21 profiles in from May to October, stand for summer pattern (b), and 12 profiles in from November to April, stand for winter pattern (c). (a) (b) (c)

32 Mao-Lin Shen, Yu-Heng Tseng and Sen Jan Page /5/9 Mechanism Analysis ─ Uplift height Take the depth of isotherm 21 ℃ at 122.8°E and 24.4°N as reference. Large uplifted height in summer. Fig. 15. Contour of Uplift height.

33 Mao-Lin Shen, Yu-Heng Tseng and Sen Jan Page /5/9

34 Mao-Lin Shen, Yu-Heng Tseng and Sen Jan Page /5/9 Observation ─ cold-dome in summer Fig. 7. Argo float, WMOID , for (a) trajectory of the float; (b) MW_IR SST and the a marker denotes the Argo data on 17 July The rest figures are subsurface comparisons of (c) temperature, (d) salinity, and (e) T-S profiles of the four measures. Typhoon Kalmaegi passed this region on July The path of Typhoon Kalmaegi are marked as hollow circles in (a).

35 Mao-Lin Shen, Yu-Heng Tseng and Sen Jan Page 35


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