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  • Author or Editor: Robert R. Dickson x
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Robert R. Dickson

Abstract

Power spectra of daily mean surface air temperature at eight locations in the United States were computed for each season of a 21-year period (March 1943–February 1969). After partitioning the spectra into what appear to be physically meaningful frequency bands, time series of power in spectral segments were related statistically to time series of seasonal mean 700-mb heights at each point of a grid extending from mid-Atlantic to mid-Pacific.

Gross aspects of resultant fields of simple linear correlation coefficients were found amenable to reasonable physical interpretation. In an overall sense, power is concentrated in progressively longer period temperature oscillations as the seasonal mean circulation proceeds from fast westerlies in the vicinity of the station to highly amplified wave patterns. Certain previously established persistent circulation regimes are shown by the present study to be associated with a concentration of power in the long-period portion of the power spectrum of daily temperature.

Multiple linear regression equations were derived relating the seasonal mean 700-mb height field to the apportionment of power in the variance spectra of daily mean temperatures. Validation of these equations awaits the accumulation of an adequate independent data sample.

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Robert R. Dickson

Abstract

Monthly values of the anomaly of percent possible sunshine at 21 locations in the United States were related to the field of monthly mean 700 mb height anomaly by correlation and regression analysis. Data were generally for the 1950–69 period, grouped by seasons. Reduction in variance afforded by the derived multiple linear regression equations, averaged over all locations and seasons, was 0.47 for the development data sample. In general, results were best over the western half of the nation and poorest along the eastern seaboard. Correlation fields and multiple linear regression equations relating percent possible sunshine at Memphis, Tenn., to the field of monthly mean 700 mb height anomaly are discussed in detail.

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Robert R. Dickson

Abstract

The apparent inverse relationship between Eurasian mean winter snow cover extent and the following warm season Indian monsoon rainfall, described by Hahn and Shukla for the 1967–75 period, is substantiated by the addition of five subsequent years of data if known deficiencies in satellite snow observations are accommodated. In this respect, elimination of a bias due to under-observation of snow cover in the Himalayan region during 1967–74 was crucial for the attainment of statistically significant correlations.

Nonsignificant correlations for a shorter period (1971–80) suggest that Eurasian and Himalayan region winter snow cover extent, as well as that of Eurasia less the Himalayan region, are all about equally well related to the subsequent Indian monsoon rainfall. Furthermore, Eurasian and Himalayan snow cover extent derived from satellite observations are found to be highly correlated.

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Robert R. Dickson

Abstract

Where significant, the relationship between mean temperatures of successive months in the United States, based on 60–80 years of data, was found to be generally of a persistent nature. Maximum persistence occurs in mid-nation in summer with secondary maxima found in the West from April to May and in the East from December to January.

The geographical distribution of persistence allows tentative identification of large-scale components of the atmospheric circulation associated with persistence throughout the year. Persistence distribution, further-more, is found to be generally compatible with current theories suggesting that persistence is of local origin arising from the anomalous thermal state of the earth's surface.

It is found that month-to-month temperature persistence is essentially independent of long-term temperature trends and of relationships between the temperatures of a given month in adjacent years. However, regions of month-to-month persistence are found to correspond broadly to areas of maximum secular temperature fluctuation. Furthermore, in central portions of winter, spring, and summer persistence regions, instances of warm and cold month-to-month persistence were to a large extent confined to warm and cold epochs, respectively. It is therefore postulated that the basic mechanisms responsible for secular temperature fluctuations and month-to-month temperature persistence are essentially the same.

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Robert R. Dickson
and
Robert E. Livezey

Abstract

It is known that the Southern Oscillation Index (SOI) and the mean sea surface temperature off the Peru Coast are highly coherent and that variations of the latter are dominated by infrequent warming episodes. The present study examines the relative contribution of these warming episodes to the covariance of statistically significant correlations between the fall SOI and winter mean 700 mb heights in the Northern Hemisphere. The degree of dominance of the warming episode years in this context is evaluated by Monte Carlo methods.

It was found that, for the 30-year period studied, data pairs following tropical east Pacific warming events contributed disproportionately to major correlation maxima in much of the Northern Hemisphere. Such covariance concentrations, however, were found to be fairly likely outcomes (probability > 9%) if groups of years are chosen at random from the appropriate covariance arrays. Thus, we conclude that the influence of the fall SOI upon the subsequent winter mean 700 mb height distribution is a rather pervasive one, not limited to tropical east Pacific warming situations.

In contrast to other areas, correlation maxima in the North American sector received disproportionately small covariance contributions from the warming episode years. In northwest Canada, the contribution of those years was small and opposite in sign to the total covariance.

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