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A. S. Thorndike

Abstract

An array of about 20 drifting data buoys was established in the Arctic Ocean during the early months of 1979. The position of each buoy and the surface pressure and temperature are measured several times daily. The program expands our capability for monitoring the polar atmosphere at a time when operational activity at high latitudes is increasing. It provides the first synoptic view of ice motion and atmospheric parameter for the Arctic Basin.

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A. S. Thorndike

Abstract

Many useful statistical properties can be derived for isotropic, stationary, homogeneous, Gaussian random fields. The field of surface pressure in the region north of 70°N is shown to approximately satisfy these conditions. Under these conditions, all properties of the field are related to the autocovariance, which is a function of time and space lag. In particular, the following quantities are derived: the time and space covariance functions for the geostrophic wind; the covariance functions for the vorticity of the geostrophic wind; the average number of highs, lows and saddles per unit area; the average number of highs, lows and saddles at which the vorticity exceeds a specified threshold; and the probability density function for the Gaussian curvature of the pressure surface. The horizontal shear in the geostrophic wind is also investigated, as is the number of umbilic points per unit area. Estimates for all these quantities are constructed using observations of surface pressure from the Arctic Basin during 1979 and 1980. The comparison between theory and observation is favorable. At least when these several quantities are considered, the isotropic, stationary, homogeneous, Gaussian random process is a good model of the actual pressure field.

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R. Colony and A. S. Thorndike

Abstract

Four ice floes in the permanent arctic ice pack were instrumented during the summer of 1975. Spectral and cross-spectral analysis of the complex time series of the ice motion and of the surface winds are given. The results show that the local low-frequency surface motion is linearly related to the local low-frequency winds. The higher frequency surface motion, including the significant inertial motion, cannot be entirely described by a linear model forced by the local winds. Cross-spectral analysis of the motion of floes separated by a hundred kilometers reveals a high coherency of the inertial motions.

Two simple mathematical models are studied to explain observed cross spectra between stations. The spectral properties of these models are determined directly from the spectral properties of the winds. Qualitative agreement between the models and observations suggest that some coupling mechanism is at work in the ice pack even during summer.

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