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    Observed Southern Hemisphere Eddy Statistics at 500 mb: Frequency and Spatial Dependence

    Source: Journal of the Atmospheric Sciences:;1981:;Volume( 038 ):;issue: 012::page 2585
    Author:
    Trenberth, Kevin E.
    DOI: 10.1175/1520-0469(1981)038<2585:OSHESA>2.0.CO;2
    Publisher: American Meteorological Society
    Abstract: Nearly eight years of daily Southern Hemisphere analyses at 500 mb have been used to define the spatial dependence of the variance fields of geopotential height and the two geostrophic wind components, the corresponding covariance fields, and the transient kinetic energy. The fields are further examined in the frequency domain by using Lorenz' (1979) ?poor man's spectral analysis? technique. In view of the small variation in eddy statistics as a function of the time of the year in the SH, this study removes the first four harmonies of the annual cycle and then considers all data together, so that contributions from all time scales from 2 to 4096 days (?11 years) can be resolved. The main results are based on analyses from May 1972?January 1978 but are verified with analyses from the relatively data-rich FGGE period. Results for the zonal mean statistics are compared with those from previous studies. The zonal means of the geopotential height and westerly wind component have spectra which roughly follow that of red noise with an autocorrelation of about 0.5, whereas the northward wind component spectra closely resembles red noise with autocorretation of 0.2, resulting in considerable anisotropy in the wind fields. The northward component of transient kinetic energy is larger than the eastward component at high frequencies in middle latitudes but the reverse is true for periods of greater than two months. The westerly momentum flux by the transient eddies has a broad spectral peak at 8?32 days and is dominated by contributions from fluctuations of less than about two weeks period. The geographical dependence of the eddy statistics is mapped for four broad frequency bands covering periods of roughly less than one week, one week to two months, two months to two years, and greater than two years, thereby separating out contributions from transient baroclinic eddies, episodes of blocking, and intermonthly and interannual variability. The spatial patterns of the statistics are interpreted in the light of synoptic behavior of systems and storm tracks as defined by synoptic studies and satellite observations in the Southern Hemisphere. For periods less than a week, variances are largest in the southern Indian Ocean and relationships between the storm tracks and eddy statistics are similar to those found in the Northern Hemisphere by Blackmon, Lau, Wallace and others. However, there also are differences associated with the differences in the mean flow in each hemisphere and these are discussed in the context of baroclinic theory. At periods longer than a week geopotential height variances are largest near southern New Zealand and, to a lesser extent, southeast of South America and appear to be related to the incidence of blocking in the Southern Hemisphere. The corresponding transient kinetic energy has a maximum further north in association with cutoff cold-centered lows. In general, the high-frequency transient eddies play a much larger role in the circulation of the Southern Hemisphere than is true for the winter circulation of the Northern Hemisphere, and the eddy statistics are more zonally symmetric.
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      Observed Southern Hemisphere Eddy Statistics at 500 mb: Frequency and Spatial Dependence

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    http://yetl.yabesh.ir/yetl1/handle/yetl/4154232
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    contributor authorTrenberth, Kevin E.
    date accessioned2017-06-09T14:22:41Z
    date available2017-06-09T14:22:41Z
    date copyright1981/12/01
    date issued1981
    identifier issn0022-4928
    identifier otherams-18248.pdf
    identifier urihttp://onlinelibrary.yabesh.ir/handle/yetl/4154232
    description abstractNearly eight years of daily Southern Hemisphere analyses at 500 mb have been used to define the spatial dependence of the variance fields of geopotential height and the two geostrophic wind components, the corresponding covariance fields, and the transient kinetic energy. The fields are further examined in the frequency domain by using Lorenz' (1979) ?poor man's spectral analysis? technique. In view of the small variation in eddy statistics as a function of the time of the year in the SH, this study removes the first four harmonies of the annual cycle and then considers all data together, so that contributions from all time scales from 2 to 4096 days (?11 years) can be resolved. The main results are based on analyses from May 1972?January 1978 but are verified with analyses from the relatively data-rich FGGE period. Results for the zonal mean statistics are compared with those from previous studies. The zonal means of the geopotential height and westerly wind component have spectra which roughly follow that of red noise with an autocorrelation of about 0.5, whereas the northward wind component spectra closely resembles red noise with autocorretation of 0.2, resulting in considerable anisotropy in the wind fields. The northward component of transient kinetic energy is larger than the eastward component at high frequencies in middle latitudes but the reverse is true for periods of greater than two months. The westerly momentum flux by the transient eddies has a broad spectral peak at 8?32 days and is dominated by contributions from fluctuations of less than about two weeks period. The geographical dependence of the eddy statistics is mapped for four broad frequency bands covering periods of roughly less than one week, one week to two months, two months to two years, and greater than two years, thereby separating out contributions from transient baroclinic eddies, episodes of blocking, and intermonthly and interannual variability. The spatial patterns of the statistics are interpreted in the light of synoptic behavior of systems and storm tracks as defined by synoptic studies and satellite observations in the Southern Hemisphere. For periods less than a week, variances are largest in the southern Indian Ocean and relationships between the storm tracks and eddy statistics are similar to those found in the Northern Hemisphere by Blackmon, Lau, Wallace and others. However, there also are differences associated with the differences in the mean flow in each hemisphere and these are discussed in the context of baroclinic theory. At periods longer than a week geopotential height variances are largest near southern New Zealand and, to a lesser extent, southeast of South America and appear to be related to the incidence of blocking in the Southern Hemisphere. The corresponding transient kinetic energy has a maximum further north in association with cutoff cold-centered lows. In general, the high-frequency transient eddies play a much larger role in the circulation of the Southern Hemisphere than is true for the winter circulation of the Northern Hemisphere, and the eddy statistics are more zonally symmetric.
    publisherAmerican Meteorological Society
    titleObserved Southern Hemisphere Eddy Statistics at 500 mb: Frequency and Spatial Dependence
    typeJournal Paper
    journal volume38
    journal issue12
    journal titleJournal of the Atmospheric Sciences
    identifier doi10.1175/1520-0469(1981)038<2585:OSHESA>2.0.CO;2
    journal fristpage2585
    journal lastpage2605
    treeJournal of the Atmospheric Sciences:;1981:;Volume( 038 ):;issue: 012
    contenttypeFulltext
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    DSpace software copyright © 2002-2015  DuraSpace
    نرم افزار کتابخانه دیجیتال "دی اسپیس" فارسی شده توسط یابش برای کتابخانه های ایرانی | تماس با یابش
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