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- Author or Editor: William Emery x
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Abstract
A study of the heat budget of the upper northeastern Pacific Ocean demonstrates the importance of heat changes due to vertical motion. Bathythermograph observations are used to form time series of monthly average thermal structure at ocean weather station November (30°N, 140°W) and various 5° and 2° quadrangles between California and Hawaii. These time series are first used to explore correlations between heat content in a 250 m thick layer and the depth of the 14°C isotherm. High negative correlations between these quantities suggest that vertical motion at 250 m, indicated by the fluctuations of the 14°C isotherm, must play a significant role in altering the heat content of the upper layer. A heat budget equation is derived that includes the heat changes due to vertical motion. At all test locations, correlations between terms show that a stronger relationship exists between surface heat exchange and heat content change when the heat changes due to vertical motion are included. The mean square difference between surface heat exchange and heat content change is computed with and without heat changes due to vertical motion. The ratio of these differences shows about a 50% improvement when heat changes due to vertical motion are included.
Abstract
A study of the heat budget of the upper northeastern Pacific Ocean demonstrates the importance of heat changes due to vertical motion. Bathythermograph observations are used to form time series of monthly average thermal structure at ocean weather station November (30°N, 140°W) and various 5° and 2° quadrangles between California and Hawaii. These time series are first used to explore correlations between heat content in a 250 m thick layer and the depth of the 14°C isotherm. High negative correlations between these quantities suggest that vertical motion at 250 m, indicated by the fluctuations of the 14°C isotherm, must play a significant role in altering the heat content of the upper layer. A heat budget equation is derived that includes the heat changes due to vertical motion. At all test locations, correlations between terms show that a stronger relationship exists between surface heat exchange and heat content change when the heat changes due to vertical motion are included. The mean square difference between surface heat exchange and heat content change is computed with and without heat changes due to vertical motion. The ratio of these differences shows about a 50% improvement when heat changes due to vertical motion are included.
Abstract
Four empirical equations relating sound velocity, salinity, temperature and pressure are examined to determine the errors in computing salinity from measurements of temperature, pressure and sound velocity. The measurement errors in these variables lead to rms salinity errors of 0.2‰ for a moored instrument. The magnitude of the salinity error appears independent of the equation used. Salinities using Lovett's and Del Grosso's equations agree well and differ from those computed using either of Wilson's equations.
Abstract
Four empirical equations relating sound velocity, salinity, temperature and pressure are examined to determine the errors in computing salinity from measurements of temperature, pressure and sound velocity. The measurement errors in these variables lead to rms salinity errors of 0.2‰ for a moored instrument. The magnitude of the salinity error appears independent of the equation used. Salinities using Lovett's and Del Grosso's equations agree well and differ from those computed using either of Wilson's equations.
Abstract
A method is developed for the computation of dynamic height from temperature data alone by using a mean T-S relationship to provide salinity values. This method is tested at three Pacific weathership locations where a large number of hydrographic stations were available. At weatherships Victor (34N, 164E) and November (30N, 140W), the difference between dynamic height found by this method and dynamic height computed from temperature and salinity observations was smaller (0.2 m2 s−2) than either the theoretical measurement error (0.4 m2 g−2;) or observed variation in dynamic height. At location Pape (50N, 145W), however, the difference was greater than the uncertainties in dynamic height, due to a thermal inversion. The small difference at Victor and November means that when the temperature salinity (T-S) relationship is “tight,” as it is at these locations, dynamic height can be computed from temperature (XBT) data alone.
Abstract
A method is developed for the computation of dynamic height from temperature data alone by using a mean T-S relationship to provide salinity values. This method is tested at three Pacific weathership locations where a large number of hydrographic stations were available. At weatherships Victor (34N, 164E) and November (30N, 140W), the difference between dynamic height found by this method and dynamic height computed from temperature and salinity observations was smaller (0.2 m2 s−2) than either the theoretical measurement error (0.4 m2 g−2;) or observed variation in dynamic height. At location Pape (50N, 145W), however, the difference was greater than the uncertainties in dynamic height, due to a thermal inversion. The small difference at Victor and November means that when the temperature salinity (T-S) relationship is “tight,” as it is at these locations, dynamic height can be computed from temperature (XBT) data alone.
Abstract
An automated neural network cloud classifier that functions over both land and ocean backgrounds is presented. Motivated by the development of a combined visible, infrared, and microwave rain-rate retrieval algorithm for use with data from the 1997 Tropical Rainfall Measuring Mission (TRMM), an automated cloud classification technique is sought to discern different types of clouds and, hence, different types of precipitating systems from Advanced Very High Resolution Radiometer (AVHRR) type imagery. When this technique is applied to TRMM visible–infrared imagery, it will allow the choice of a passive microwave rain-rate algorithm, which performs well for the observed precipitation type, theoretically increasing accuracy at the instantaneous level when compared with the use of any single microwave algorithm. A neural network classifier, selected because of the strengths of neural networks with respect to within-class variability and nonnormal cluster distributions, is developed, trained, and tested on AVHRR data received from three different polar-orbiting satellites and spanning the continental United States and adjacent waters, as well as portions of the Tropics from the Tropical Ocean and Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE). The results are analyzed and suggestions are made for future work on this technique. The network selected the correct class for 96% of the training samples and 82% of the test samples, indicating that this type of approach to automated cloud classification holds considerable promise and is worthy of additional research and refinement.
Abstract
An automated neural network cloud classifier that functions over both land and ocean backgrounds is presented. Motivated by the development of a combined visible, infrared, and microwave rain-rate retrieval algorithm for use with data from the 1997 Tropical Rainfall Measuring Mission (TRMM), an automated cloud classification technique is sought to discern different types of clouds and, hence, different types of precipitating systems from Advanced Very High Resolution Radiometer (AVHRR) type imagery. When this technique is applied to TRMM visible–infrared imagery, it will allow the choice of a passive microwave rain-rate algorithm, which performs well for the observed precipitation type, theoretically increasing accuracy at the instantaneous level when compared with the use of any single microwave algorithm. A neural network classifier, selected because of the strengths of neural networks with respect to within-class variability and nonnormal cluster distributions, is developed, trained, and tested on AVHRR data received from three different polar-orbiting satellites and spanning the continental United States and adjacent waters, as well as portions of the Tropics from the Tropical Ocean and Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE). The results are analyzed and suggestions are made for future work on this technique. The network selected the correct class for 96% of the training samples and 82% of the test samples, indicating that this type of approach to automated cloud classification holds considerable promise and is worthy of additional research and refinement.
Abstract
A satellite-tracked drifting buoy, deployed unintentionally in the Bering Sea in 1982, completed a circuit of that basin in about one year. During its cyclonic passage around the Bering Sea, it experienced many different flow regimes ranging from steady alongshelf motion at the shelf break to highly variable tidal flow on the shelf itself. The buoy trajectory differs from previous descriptions of the deep Bering Sea circulation, because it moved southwestward in the central Bering Sea rather than along the western boundary, as other depictions have suggested. Many of the Bering Sea mesoscale eddies reported earlier were evident, indicating that possibly these eddies are permanent features. The forces which caused the buoy to move between the various flow regimes are unclear, but the data suggest an annual period for the deep Bering Sea circulation.
Abstract
A satellite-tracked drifting buoy, deployed unintentionally in the Bering Sea in 1982, completed a circuit of that basin in about one year. During its cyclonic passage around the Bering Sea, it experienced many different flow regimes ranging from steady alongshelf motion at the shelf break to highly variable tidal flow on the shelf itself. The buoy trajectory differs from previous descriptions of the deep Bering Sea circulation, because it moved southwestward in the central Bering Sea rather than along the western boundary, as other depictions have suggested. Many of the Bering Sea mesoscale eddies reported earlier were evident, indicating that possibly these eddies are permanent features. The forces which caused the buoy to move between the various flow regimes are unclear, but the data suggest an annual period for the deep Bering Sea circulation.
Abstract
Two series of very high resolution thermal infrared satellite images, off Vancouver Island, are examined for evidence of baroclinic waves. A 1979 winter sequence of three images exhibits cold tongues, extending seaward from Vancouver Island, which have separations (wavelengths), northwest phase speeds and growth rates consistent with a model of baroclinically unstable waves. An earlier summer series of eight images displays no such propagation behavior, which may be due to upper layer thermal changes from solar insulation.
Abstract
Two series of very high resolution thermal infrared satellite images, off Vancouver Island, are examined for evidence of baroclinic waves. A 1979 winter sequence of three images exhibits cold tongues, extending seaward from Vancouver Island, which have separations (wavelengths), northwest phase speeds and growth rates consistent with a model of baroclinically unstable waves. An earlier summer series of eight images displays no such propagation behavior, which may be due to upper layer thermal changes from solar insulation.
Abstract
Mean temperature-salinity (TS) curves are computed from all available hydrographic data for 10° quadrangles in the Pacific between 20°S and 40°N. These curves together with temperature profiles from hydrographic stations are used to compute a quantity called TS dynamic height. The rms differences between dynamic and TS dynamic height indicate where mean TS curves may be reliably used to compute dynamic height from temperature profiles.
Abstract
Mean temperature-salinity (TS) curves are computed from all available hydrographic data for 10° quadrangles in the Pacific between 20°S and 40°N. These curves together with temperature profiles from hydrographic stations are used to compute a quantity called TS dynamic height. The rms differences between dynamic and TS dynamic height indicate where mean TS curves may be reliably used to compute dynamic height from temperature profiles.
Abstract
Frequency-wavenumber spectra of sea surface temperature and wind-stress curl are computed from 11 years of surface marine observations taken in the eastern North Pacific. These data were averaged by month and 2° quadrangles to yield spectra with periods from 2 to 48 months and zonal wavelengths from 400 to 4000 km. Spectra were computed for all 2° zonal bands between 16 and 40°N using data from the area between 120 and 160°W. Missing monthly values led to the computation of these spectra using a least-squares Fourier expansion which eliminated the need for temporal interpolation. Frequency spectra computed with this technique compare well with spectra using standard Fourier methods.
The resulting spectra were found to separate naturally into two regions; one between 29 and 40°N and the second between 15 and 29°N. Even within these zonal bands there were some important north–south changes. The annual signal was found to dominate the spectra of sea surface temperature at almost all wavelengths. The semiannual and 2-year periods were often also significant in sea surface temperature spectra. The annual peak dominated many of the wind-stress curl spectra at the longest wavelengths (∼2000–4000 km). Most of the energetic peaks in all spectra were symmetric with respect to east–west wavenumber. There were, however, some asymmetries suggesting both east and westward phase propagation. Generally, wind-stress curl spectra were white in frequency and red in wavenumber while sea surface temperature spectra were red in wavenumber but dominated by the 2-year, annual and semiannual periods in frequency.
Abstract
Frequency-wavenumber spectra of sea surface temperature and wind-stress curl are computed from 11 years of surface marine observations taken in the eastern North Pacific. These data were averaged by month and 2° quadrangles to yield spectra with periods from 2 to 48 months and zonal wavelengths from 400 to 4000 km. Spectra were computed for all 2° zonal bands between 16 and 40°N using data from the area between 120 and 160°W. Missing monthly values led to the computation of these spectra using a least-squares Fourier expansion which eliminated the need for temporal interpolation. Frequency spectra computed with this technique compare well with spectra using standard Fourier methods.
The resulting spectra were found to separate naturally into two regions; one between 29 and 40°N and the second between 15 and 29°N. Even within these zonal bands there were some important north–south changes. The annual signal was found to dominate the spectra of sea surface temperature at almost all wavelengths. The semiannual and 2-year periods were often also significant in sea surface temperature spectra. The annual peak dominated many of the wind-stress curl spectra at the longest wavelengths (∼2000–4000 km). Most of the energetic peaks in all spectra were symmetric with respect to east–west wavenumber. There were, however, some asymmetries suggesting both east and westward phase propagation. Generally, wind-stress curl spectra were white in frequency and red in wavenumber while sea surface temperature spectra were red in wavenumber but dominated by the 2-year, annual and semiannual periods in frequency.
