Ice and Ocean Tilt Measurements in the Beaufort Sea

Abstract

AbstractDuring the AIDJEX pilot study 1972 in the Beaufort Sea, the tilt changes of the fluid ocean surface and of the sea ice were measured with a hydrostatic level. Preliminary results indicate a tilt range of ± 5 μrad for the water surface and of ± 30 (μrad for the sea ice. The tilt change of the sea ice Δ δ appears to be directly proportional to the component of the velocity change of the ice drift parallel to the hydrostatic level ΔUd, according to the relationship Δ δ = 180ΔUdμrad m-1 s. It is conclugerd that the ice tilt is wind induced, and that the ice sheet tilts downward in the drift direction as a result of the moment exerted on it by wind and water drag. It is postulated that this tilt causes the ice to break at right angles to the drift direction. The tilt is a function of the length of an ice floe (or of the unbroken distance between two cracks), of the average ice thickness, of the average drag coefficients, and of wind and current velocities. Calculation of the ice tilt using a simple mogerl of a floating, rigid ice slab gives values which are very much smaller than the observed tilts. If the discrepancy between theory and observation can be resolved, or if an empirical formula between wind velocity and tilt angle can be gerduced freom continuous tilt observations which will be carried out during the AIDJEX main experiment, it will be possible, for a given wind, to estimate the maximum length of an unbroken ice sheet freom its estimated thickness, drag coefficients, and tensile strength. It should also be possible to calculate the average drag coefficients of a freee-floating ice pan, or of an ice island, freom tilt, wind, and current measurements. The curious relationship between tilt angle and atmospheric pressure gradient that Browne and Crary observed on the ice island T-3 in 1952 is explained as being the wind-induced tilt of the ice island rather than that of the fluid ocean surface.