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A. H. Gordon

Abstract

Global and hemispheric series of surface temperature anomalies are examined in an attempt to isolate any specific features of the structure of the series that might contribute to the global warming of about 0.5°C which has been observed over the past 100 years. It is found that there are no significant differences between the means of the positive and negative values of the changes in temperature from one year to the next; neither do the relative frequencies of the positive and negative values differ from the frequencies that would be expected by chance with a probability near 0.5. If the interannual changes are regarded as changes of unit magnitude and plotted in a Cartesian frame of reference with time measured along the x axis and yearly temperature differences along the y axis, the resulting path closely resembles the kind of random walk that occurs during a coin-tossing game.

We hypothesize that the global and hemispheric temperature series are the result of a Markov process. The climate system is subjected to various forms of random impulses. It is argued that the system fails to return to its former state after reacting to an impulse but tends to adjust to a new state of equilibrium as prescribed by the shock. This happens because a net positive feedback accompanies each shock and slightly alters the environmental state.

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A. H. Gordon

Abstract

The mean upper wind structure over Bahrein and Aden in 1962 is studied. Patterns of the zonal and meridional wind speed components are presented. Eddy and advective fluxes of the momentum are calculated and mean annual height profiles drawn for both stations. The transport of momentum by synoptic scale eddies is more important at Bahrein than at Aden. Transport of momentum by the local mean meridional wind is larger in magnitude and fluctuates in an irregular way from month to month at both stations. The vertical integral of the momentum suggests export of relative momentum from the Bahrein-Aden sector in winter and import in summer. These conclusions are supported by 1963 data from the Ahmadabad-Madras sector. In the belt of latitude considered the winter surface winds have an easterly component and gain momentum from the earth while the summer surface winds have a westerly component and lose momentum to the earth. The results of the short period analysis for the sectors studied suggest broad agreement with the synoptic climatology of the region.

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Alfred H. Woodcock and Gordon A. Riley

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A. H. Gordon and N. C. Wells

Abstract

Anomalies from the respective decadal means of the monthly mean temperatures for central England covering a period of 250 years are ranked to form a quintile distribution. Contingency tables are then prepared which show the percentage frequencies of the changes in the temperature anomalies from one calendar month to the following calendar month for each quintile. Correlation coefficients for a lag of one month are computed for each calendar month-to-month change throughout the years, and for lags 1–12 months inclusive for the whole data series.

It is shown that persistence of extreme anomalies at certain times of the year are double the frequency which would be expected by chance, while the changes from one extreme quintile to the other occur with very low frequency compared with chance.

It is suggested that application of the tables would produce results as good, and perhaps a little better, at forecasting temperature anomalies for a month ahead than the official long-range forecasts supplied by the Meteorological Office for central and southeast England.

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Gordon A. Hammons, J. Paul Dallavalle, and William H. Klein

Abstract

For the last few years the National Weather Service has been producing centralized guidance forecasts of calendar day maximum and minimum temperatures by applying multiple regression equations derived statistically from numerical model output. At fist the equations were developed from a six-month stratification of the numerical forecasts, but later we were able to stratify the dependent data into three-month seasons. At the same time we added a number of new potential predictors. These two changes increased the skill of the automated guidance. Here we discuss the dependent data statistics for the three-month season equations and compare their forecasts with those made by the older six-month equations. Finally, we present verification statistics on the objective guidance for the fall and winter seasons from August 1973 to February 1976.

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William H. Klein, Frank Lewis, and Gordon A. Hammons

Abstract

Recent changes in the National Weather Service's automated system of forecasting maximum and minimum surface temperatures are described and illustrated. Modifications include use of the primitive equation model, later surface reports, computer-analyzed isotherms, and climatologically-determined forecast limits. Verification figures are presented to show the improvement of the new system over the old and to justify the replacement of centralized subjective temperature forecasts by completely objective ones.

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A. L. Gordon, D. T. Georgi, and H. W. Taylor

Abstract

The component of the FDRAKE-75 data obtained by the R/V Conrad in the western Scotia Sea reveals a definite sequence of thermohaline stratification zones encountered on passing from Antarctic to Sub-antarctic waters. A Polar Front Zone, displaying multiple temperature minima, separates the Antarctic Zone, characterized by a single intense T-min above 200 m, from the Subantarctic Zone with its nearly isohaline layer from 100 m to over 400 m. The Antarctic Zones of the Weddell and the Scotia Seas aye separated by a cold, relatively homogeneous zone situated in the southern Scotia Sea called the Weddell-Scotia Confluence.

The boundaries of the Polar Front Zone are highly meandered and isolated eddies of Subantarctic water may occur within the zone. The main axis of the Antarctic Circumpolar Current apparently lies close to the Subantarctic boundary of the, Polar Front Zone, while a secondary axis is associated with the southern limit of the Polar Front Zone. Inspection of the Islas Orcadas and Melville data, the western section of the FDRAKE-75 data set, also shows a meandered Polar Front Zone. It further suggests the possibility of eddies of Polar Front Zone water within the Subantarctic Zone.

The thick, nearly isohaline layer of the Subantarctic Zone possesses a weak negative salinity gradient (at least within a few hundred kilometers of the Polar Front Zone). It is proposed that this structure is a remnant of a winter period homogeneous layer, which is altered from above by summer sea-air interaction and from below by upward mixing of Antarctic water introduced into the Subantarctic Zone by cross-frontal isopycnal exchange. This latter process may cool and freshen the overall characteristics of the Subantarctic water in relation to expected characteristics by local sea-air factors.

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A. H. Gordon, R. A. D. Byron-Scott, and J. A. T. Bye

Abstract

When quasi-triennial periodicities have been found in climatic data, their presence has often been attributed to QBO-SO interaction. Although a mixture of idealized QBO and SO signals can give rise to a quasi-triennial carrier wave modulated at the sunspot-cycle period, neither of the latter periods appears in spectral analysis of the resultant time series. It is therefore concluded that quasi-triennial spectral peaks are more likely to be of physical origin than a result of QBO-SO interaction.

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John A. T. Bye, Roland A. D. Byron-Scott, and Adrian H. Gordon

Abstract

The authors present an analytical climate model, which has the features that (i) the atmosphere is a simple oscillator for all periods ≤1 year, (ii) the ocean stores heat, (iii) the ocean exchanges momentum with the atmosphere, and (iv) random forcing exists due to atmospheric thermodynamics and oceanic dynamics. The piecewise analytical integration of coupled linear equations for sea temperature, air-sea temperature difference, and air-sea velocity difference generates experimental climates. The exchange parameters of the algorithm, except for the exchange coefficient for heat with the deep ocean, am calibrated to the observed climate using the annual cycle, and random forcing is applied over intervals of one year. The atmospheric random forcing leads to bounded random walks, the extent of which increases as the exchange coefficient with the deep ocean decreases, and the oceanic random forcing generates a stationary response. It is found that the observed statistics of the global temperature series can be reproduced by either a relatively large heat exchange coefficient with the deep ocean and little oceanic variability or a smaller exchange coefficient with a larger oceanic variability. Plausible exchange coefficient values imply random walk lengths of at least a century-long timescale.

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