Investigation of the ice-tide interaction in the Arctic Ocean

Z. Kowalik - PI, A. Proshutinsky - Co PI, R. H. Thomas - Manager, NASA Polar Research Program.


Data analysis of recent measurements obtained at various locations in the Arctic Ocean indicates a strong energy peak in the tidal frequency band, both in the water and in ice movement. The tide motion, through periodic divergence and convergence of the pack ice, generates mesoscale ice openings. The resulting residual motion sustains polynyas along the Eurasian Shelf. These periodic openings of the pack ice influence heat exchange and enhance the rate of ice production. The ice-tide interaction is also a primary source of the mixing in both the shallow water and the deep Arctic Ocean, where circulation appears to be sluggish.

In this project, distribution of the main semidiurnal and diurnal tide components in the Arctic Ocean and North Atlantic have been described with a high degree of accuracy. The basic tools used to achieve this goal were computer models and ground station and satellite data on sea level, currents and ice distribution.

The system of tidal equations for the water and ice was solved on a stereographic map projection using a large-scale model, 440x440 grid points and a spatial resolution of about 14 km. The fine-space lattices located over various subdomains in the Arctic Ocean have been connected to the large-scale model.

An interesting and important result concerns the diurnal constituents. In the diurnal band of oscillations enhanced tidal current structures are generated by near-resonant shelf waves of tidal origin which are trapped or partially trapped over the bottom topography. Numerical computations performed in the Arctic Ocean and North Atlantic revealed about 30 regions of enhanced currents (Figure 1). It is important to stress that due to low resolution the near-resonant phenomenon is not reflected in the Schwiderski computation (1980) used for the elimination of tides from the satellite altimetry data.

In Figure 2, the maximum tidal currents in the Arctic Ocean are depicted. These currents are due to M2, S2, O1 and K1 tidal constituents. The largest currents in the Arctic Ocean occur at the entrance to the White Sea and at the Spitsbergenbanken, south from Spitsbergen. Relatively large currents also occur along the continental slope of the Arctic Ocean from Spitsbergen to the New Siberian Islands. Investigation of the enhanced velocity along the continental slope shows that these currents are caused by near-resonant amplification of the diurnal tides by the continental slope topography [Kowalik and Proshutinsky, 1993]. The topographically-amplified diurnal tidal currents are especially strong over the Yermak Plateau, located northeast from Spitsbergen [Kowalik, 1994]. Topographically-amplified semidiurnal tidal currents are found in the vicinity of Bear Island in the Barents Sea [Kowalik and Proshutinsky, 1995].

Tide propagation that generates leads in the ice cover can be of practical significance to navigation. We use maximal shear of ice velocity as a measure of the ice cover deformation.

Distribution of this parameter in the Arctic Ocean is plotted in Figure 3. The most likely areas for the occurrence of leads, where maximal shear exceeds 10E-6/s, are: the entrance of the White Sea, the Spitsbergenbanken area, the northern part of the western Greenland continental slope, the continental slope of the Laptev and East Siberian Seas, and the Wrangel Island region (Figure 3). In this figure, one can identify a number of narrow, elongated areas of increased ice deformation. Results from this numerical model may serve as a data base for correction of satellite observations of ice drift due to tides.

The amplitude, phase, current ellipses and ice motion related to the 8 tidal constituents are computed in a stereographic coordinate system. For data dissemination, the computations from stereographic projection were interpolated into a spherical grid with a space resolution of 10x10 minutes (170x2160 cells). An example of the tidal chart is depicted in Figure 4. Here amplitude (cm) and phase (degree) for the M2 constituent are given.

The tidal data is available via anonymous ftp:

	% ftp ftp.ims.uaf.edu
	username: anonymous or ftp
	password: your email address
	ftp> cd tide
	ftp> binary
	ftp> get or mget ....
	ftp> bye
The files include the diurnal (K1, O1, Q1, P1) and semidiurnal (M2, S2, K2 and N2) sea level amplitudes and phases:
	IMS_UAF_M2_tide-level.Z
	IMS_UAF_S2_tide-level.Z
	IMS_UAF_K2_tide-level.Z
	IMS_UAF_N2_tide-level.Z
	IMS_UAF_K1_tide-level.Z
	IMS_UAF_O1_tide-level.Z 
        IMS_UAF_Q1_tide-level.Z
	IMS_UAF_P1_tide-level.Z
The files containing amplitudes and phases of U (zonal component) or V (meridian component) velocity of tidal waves are:
	IMS_UAF_M2_U_velocity.Z
	IMS_UAF_M2_V_velocity.Z
	IMS_UAF_S2_U_velocity.Z
	IMS_UAF_S2_V_velocity.Z
	IMS_UAF_K2_U_velocity.Z
	IMS_UAF_K2_V_velocity.Z
	IMS_UAF_N2_U_velocity.Z
	IMS_UAF_N2_V_velocity.Z
	IMS_UAF_K1_U_velocity.Z
	IMS_UAF_K1_V_velocity.Z
	IMS_UAF_O1_U_velocity.Z
	IMS_UAF_O1_V_velocity.Z
	IMS_UAF_P1_U_velocity.Z
	IMS_UAF_P1_V_velocity.Z
	IMS_UAF_Q1_U_velocity.Z
	IMS_UAF_Q1_V_velocity.Z}.
Information on amplitudes and phases of tidal ice motion can be prepared on request. At the present time the ice motion extracted from satellite images does not include correction for the tide motion. The tidal model results can be used for this correction.

Some additional files are included in the tidal data base. The file README contains instructions for reading data and a description of file structure. The file DATA_BASE contains results of tidal observations in the Arctic Ocean. The file ARCTIC_DEPTH includes bathymetry of the Arctic Ocean (space resolution of 10x10 minutes in spherical coordinates).


References
  Kowalik, Z. and A.Yu. Proshutinsky. The diurnal tides in 
the Arctic Ocean. J.  Geophys. Res., 98,  16,449-16,468, 
1993.

  Kowalik, Z. Modeling of topographically amplified diurnal
tides in the Nordic Seas. J. Phys. Oceanogr., 24(8), 
1717-1731, 1994.

  Kowalik, Z. and A.Yu. Proshutinsky. The Arctic Ocean tides, 
In: The Polar Oceans and their Role in Shaping the Global 
Environment AGU, 137-158, 1994.

  Kowalik Z. and A. Yu. Proshutinsky. Topographic enhancement 
of tidal motion in the western Barents Sea. J.  Geophys. Res.,
100, 2613-2637, 1995.

  Schwiderski, E. W. On charting global ocean tides. Rev.
Geoph. Space Phys., 18, 243--268, 1980.

Questions concerning this data should be addressed to ffzk@tide.ims.uaf.edu.