Satellite altimetry reveals small-scale variations of diurnal tides near the North Kuril Islands

1. 1Sakhalin Research Institute of Fisheries and Oceanography, Yuzhno-Sakhalinsk 2Russian Institute of Satellite Instruments, Moscow Satellite altimetry reveals small-scale variations of diurnal tides near the North Kuril Islands (ALTIMETRY OBSERVATIONS OF DIURNAL SHELF WAVES NEAR SAKHALIN AND THE NORTH KURIL ISLANDS) George Shevchenko1 and Alexander Romanov2

2. Small-scale variations of tidal wave’s amplitudes and phases are focus of interest because they are a cause of strong tidal currents and tidal energy dissipations. Usually we found these variations in the narrow bays, estuaries, narrow straits etc. The special case are diurnal shelf waves – they are the cause of strong tidal current in the areas with relatively simple and homogenous topography. Satellite altimeters give us information about tidal sea level oscillations in the areas were we have no direct sea levels and currents measurements. The question: can we use satellite altimetry data to investigate diurnal shelf waves?

3. Areas where diurnal shelf waves are found: Northeastern Sakhalin shelf [Rabinovich and Zhukov, 1984; Putov and Shevchenko, 1998; Ohshima et al., 2002; Shevchenko et al., 2004; Thomson et al., 2007] Northern Hokkaido shelf [Odamaki, 1994] Southern Kuril shelf [Efimov and Rabinovich, 1980; Kovalev and Rabinovich, 1980] Central Kuril shelf (baroclinic CTW) [Nakamura et al., 2000; Rabinovich and Thomson, 2001] Northern Kuril shelf (present study)

4. Tidal energy flux for K1 wave from numerical simulations [Kowalik and Polyakov, 1998] Areas of strong tidal currents and significant tidal energy dissipation

5. We used obtained K1 and O1amplitudes and phases to analyze their variability on the northeastern Sakhalin shelf and North Kuril shelf Spots on the Topex\Poseidon sub-satellite tracks in which altimetry data were analysed using high-resolution modification of least squares method for tidal wave’s amplitudes and phases determination [Shevchenko, Romanov, 2006]. Root-mean-square amplitude of residual sea level variations is shown.

6. Cape Elizabeth Spatial variations of K1 amplitude and phase of north-directed velocity component on the northeastern Sakhalin shelf obtained from current (30 moorings) and ice-drift measurements (3 coastal radar stations) [Shevchenko et al, 2005] Strong diurnal currents in the narrow nearshore zone between Elizabeth Cape and Lunsky Bay 180º Lunsky Bay

7. Computed K1 tidal ellipses [from Kowalik and Polyakov, 1998] Spatial salinity distribution during ebb tides. Predicted tidal currents. Shelf waves are responsible for the current divergence and convergence zones

8. Ascending TP tracks (51, 127 and 203) crossing northeastern shelf of Sakhalin Island. Area of shelf waves There are no diurnal shelf waves southerly from Lunsky Bay (shelf is too narrow) 180º

9. K1 and O1 amplitude variability on the northeastern Sakhalin shelf 51 t.51 t.127 t.203 127 t.51 t.127 203 t.203

10. K1 and O1 phase variability on the northeastern Sakhalin shelf 51 t.127 t.203 t.51 127 t.127 203 t.203 t.51

11. K1 sea level amplitude and phase distribution on the base of coastal and mooring observations [Putov, Shevchenko, 1998] Negative contribution of shelf wave ≈ 25 deg Positive contribution of shelf wave Amplitude, cm Phase, deg

12. First Kuril Strait Kamchatka Descending T/P tracks (160, 84, 8 and 186) Assumed area of diurnal shelf waves Shelf is too narrow and deep Paramushir I. Onekotan I. Shiashkotan I. Matua I.

13. K1 and O1 amplitude variability on the North Kuril shelf t.160 160 t.84 t.8 t.160 84 t.84 8 t.8

14. K1 and O1 phases variability on the North Kuril shelf 160 t.8 t.84 t.160 84 t.8 8 t.84 t.160

15. We found decreasing K1 and O1 amplitudes along TP track 84 and increasing along track 8. Also we can see significant phase shifts between these tracks. Similar amplitudes and phases variations we found on the shelf of Sakhalin Islands (TP tracks 51 and 127). We consider this result as evidence of diurnal shelf waves existence on the North Kuril shelf. We did not found similar variations on the track 160. It means that there are no diurnal shelf waves near southeastern coast of Kamchatka Peninsula. Shelf in this area is almost the same as near Paramushir Island. As we see, extended shallow shelf is not enough for diurnal shelf wave existence. Their generation is result of lager-scale tidal waves diffraction. Probably, diurnal shelf waves generation is result of diffraction by First Kuril Strait which separates Kuril Ridge and Kamchatka Peninsula.

16. Dispersion curves We used results of (Kulikov, Shevchenko, 1991) relating shelf waves generation in the area of North Kuril Islands by traveling cyclone Generation coefficients h0 = 60 m, L=120 km, α=0.02 km-1 Minimal period equals 23.7 h Cross-shore distance, km

17. K1 wave structure as combination of Kelvin and shelf waves Shelf wave parameters: Wavelength: 274 km Phase speed: 11.4 km/h Level amplitude: 10 cm Current speed: 31 cm/s Kelvin wave parameters: Wavelength: 21000 km Phase velocity: 880 km/h Level amplitude: 30 cmCurrent speed: 2 cm/s First Kuril Strait Shiashkotan I. Phase, deg Track 8 Amplitude, cm Track 84 Longshore distance, km

18. The distance between First Kuril Strait and Shiahkotan Island is close to diurnal shelf waves wavelength. Southwesterly from Shiashkotan Island there are no conditions of diurnal shelf waves existence (shelf is too narrow and deep). These result is connected with zero group velocity of diurnal shelf waves: no wave energy propagation from the area of North Kuril Islands, seeming phase propagation caused by positive-negative sea level elevations in the different parts of study area.

19. ESTIMATION OF DIRNAL SHELF WAVE DISSIPATION (in the area λ L over tidal period T) Were ρ – water density, r – bottom friction coefficient (0.003), T – tidal period, v0 – neashore velocity amplitude, λ– wavelength and λ λ Potential energy of shelf waves is small, kinetic energywe can estimate as

20. Tidal energy dissipation as function of cross-shore distance Diurnal shelf wave dissipation (in the area λ L over tidal period T) K1 W=ΔЕ/T= 3.6 108 Wt (ΔЕisabout 37% of Ek) O1 W= 2.1 108 Wt (ΔЕ isabout 32% of Ek) About 75% dissipates in the nearshore zone λ 30 km Dimensionless long-shore and cross-shore velocities Dimensionless integral J1 Cross-shore distance, km.

21. Conclusion We found increasing and decreasing K1 and O1 amplitude along TP tracks 51 and 127 and significant phase shift between neashore sports of these tracks on the northeastern Sakhalin shelf. Similar amplitudes and phases variations we found on the shelf of North Kuril Islands (TP tracks 84 and 8). These result we consider as evidence of diurnal shelf waves existence in this area. Estimation of diurnal shelf waves level and velocity amplitudes are not enough exact. We consider obtained results as preliminary finding. For more exact estimations we need mooring current measurements in this area.