Showing papers by "Sarah T. Gille published in 2005"

Global observations of the land breeze

Abstract: [1] Four-times daily satellite wind observations from the QuikSCAT and ADEOS-II tandem scatterometer mission are used to study the land/sea breeze circulation. These observations provide a global view of diurnal wind variations over the ocean. Results agree with frictional linear theory: winds follow an elliptical hodograph through the course of the day, but indicate that diurnal wind variations propagate offshore progressively like nonlinear gravity waves and are detectable several hundred kilometers from the coast.

Global Observations of the Land Breeze

Abstract: [1] Four-times daily satellite wind observations from the QuikSCAT and ADEOS-II tandem scatterometer mission are used to study the land/sea breeze circulation. These observations provide a global view of diurnal wind variations over the ocean. Results agree with frictional linear theory: winds follow an elliptical hodograph through the course of the day, but indicate that diurnal wind variations propagate offshore progressively like nonlinear gravity waves and are detectable several hundred kilometers from the coast.

Statistical Characterization of Zonal and Meridional Ocean Wind Stress

Abstract: Four years of ocean vector wind data are used to evaluate statistics of wind stress over the ocean. Raw swath wind stresses derived from the Quick Scatterometer (QuikSCAT) are compared with five different global gridded wind products, including products based on scatterometer observations, meteorological analysis winds from the European Centre for Medium-Range Weather Forecasts, and reanalysis winds from the National Centers for Environmental Prediction. Buoy winds from a limited number of sites in the Pacific Ocean are also considered. Probability density functions (PDFs) computed for latitudinal bands show that mean wind stresses for the six global products are largely in agreement, while variances differ substantially, by a factor of 2 or more, with swath wind stresses indicating highest variances for meridional winds and for zonal winds outside the Tropics. Higher moments of the PDFs also differ. Kurtoses are large for all wind products, implying that PDFs are not Gaussian. None of the available gridded products fully captures the range of extreme wind events seen in the raw swath data. Frequency spectra for the five gridded products agree with frequency spectra from swath data at low frequencies, but spectral slopes differ at higher frequencies, particularly for frequencies greater than 100 cycles per year (cpy), which are poorly resolved by a single scatterometer. In the frequency range between 10 and 90 cpy that is resolved by the scatterometer, spectra derived from swath data are flatter than spectra from gridded products and are judged to be flatter than 2/3 at all latitudes.

Adjustment of the Southern Ocean to Wind Forcing on Synoptic Time Scales

Abstract: This study addresses the response of the Southern Ocean to high-frequency wind forcing, focusing on the impact of several barotropic modes on the circumpolar transport. A suite of experiments is performed with an unstratified model of the Southern Ocean, forced with a stochastic wind stress that contains a large range of frequencies with synoptic time scales. The Southern Ocean adjustment displays a different character for frequencies below and above 0.2 cpd. The low-frequency range is dominated by an “almost-free-mode” response in the region where contours of f /H are obstructed by only a few bathymetric features; the truly free mode only plays a minor role. Topographic form stress, rather than friction, is the dominant decay mechanism of the Southern Mode. It leads to a spindown time scale on the order of 3 days. For the high-frequency range, the circumpolar transport is dominated by the resonant excitation of oscillatory modes. The “active” response of the ocean leads to strong changes and eve...

An Introduction to Ocean Remote Sensing

Abstract: For more than three decades, satellites have been observing the ocean from several hundred kilometers above the surface of the Earth From the vantage of space, they have given us a global view of the ocean surface and its variability Satellite instruments that are in orbit today detect a broad range of ocean variables that touch on all aspects of oceanography These include sea surface temperature, surface wind velocity, chlorophyll, sea surface elevation, and ice cover, among others The unifying element of satellite remote sensing is not just that measurements are made from space, but more specifically that satellite instruments detect electromagnetic radiation that is either emitted from or reflected off the surface of the ocean

Energetics of wind-driven barotropic variability in the Southern Ocean

Abstract: This study addresses the energetics of the Southern Ocean, in response to high-frequency wind forcing. A constant-density, multi-layer model is forced with a band of stochastically varying wind stress. The focus is on the interplay between the surface layer and the interior circulation. In line with previous examinations, it is concluded that the interior ocean is not directly energized by the wind work, but rather through the work done by the pressure field. The spatial and temporal characteristics of these terms differ substantially. Although the wind work may be negative in extensive regions of the World Ocean, the pressure work energizes the interior circulation almost everywhere. For low-frequency variability, the total work done by the wind and pressure on the barotropic flow is comparable, but discrepancies may arise for high-frequency variability. A mechanism is identified through which kinetic energy can leak from the wind-driven surface layer to the barotropic flow.