Mesoscale Nowcasting of Sea Ice Movement through the Bering Strait with a Description of Major Driving Forces

Abstract

Surface atmospheric pressure data from a triangular station network surrounding the Bering Strait are used to calculate hypothetical geostrophic wind velocities. Net daily Strait sea ice movement is derived from visible and infrared NOAA satellite imagery for November through May, 1974 to 1984. These historical ice-motion data and network wind-velocity data are used to develop an empirical 12-h advance forecast (nowcast) sea ice movement model with all-weather capabilities. A necessary outgrowth of this study has been the identification and classification of three modes of ice movement and two modes of ice immobilization according to their major driving forces. The first ice-movement mode is from the Chukchi to the Bering Sea requiring a minimum northeasterly geostrophic wind of 12 m s?1. The second and third modes represent ice movement from the Bering to the Chukchi Sea. Mode 2 is driven by a preexisting north-flowing ocean current that offsets weak winds from the northeast. Mode three is large movement due to a combination of southwesterly winds and north-flowing ocean current. The first immobilization mode (maximum duration one week) is an apparent balance between northerly wind stress, current stress from the south, and internal ice stresses. The second immobilization mode (least common) is due to double, solid sea ice arches forming across the Strait. These arches remained intact under strong northeasterly geostrophic winds (20?26 m s?1) and can last up to four weeks.