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Eberhard W. Wahl

An investigation of temperature and additional records shows the existence of a pronounced January thaw in New England. This singularity can be connected to the existence of typical changes in the circulation over the United States. Further world-wide relations indicate important consequences valuable for further research on singularities.

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Climatological Studies of the Large-Scale Circulation in the Northern Hemisphere

I. ZONAL AND MERIDIONAL INDICES AT THE 700-MILLIBAR LEVEL

EBERHARD W. WAHL

Abstract

Within the framework of a detailed dynamic climatology of the large-scale circulation over the Northern Hemisphere, data from 15 yr of daily 700-mb maps have been used to investigate the temporal behavior of hemispherically averaged geostrophic zonal and meridional indices. A number of such indices were derived for both fixed and variable latitude bands. Their mean annual pattern, interannual variability, and time history through the 15 yr of record have been established.

The absence of statistically significant correlations between zonal and meridional flow on a short-term time scale (days to weeks) is established, while high correlations are apparent on the annual scale. The 15-yr record also indicates the sensitivity of the meridional indices to changes in the analysis techniques used to derive the hemispheric gridpoint data from the raw radiosonde observations. Finally, the capability of attaining a high resolution in time (about 3 days on the average) because of the daily data record allows a much more detailed description of the annual change in the large-scale circulation character than was previously possible by means of monthly averages. Certain times of the year appear to be fairly quiet while, at other times, distinct breaks in the circulation patterns are evident. This is a first indication that hemispheric wide singularities indeed exist.

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Eberhard W. Wahl

A sudden increase in the probability of snow occurrence during the month of October at Denver, Colorado, had been reported. It is shown that this increase can be associated with the development of a widespread weather singularity occurring at that time of the year. The normal sea-level pressure-pattern changes derived from 40 years of data over the United States show the synoptic development of this singularity. This development leads to peculiarities in various weather elements at that time.

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Eberhard W. Wahl

Abstract

By statistical methods an attempt was made to obtain long-range predictions of large-scale circulation parameters for the Northern Hemisphere. Using lag relationships going back in time up to 50 months and attempting to predict coefficients of monthly sea level pressure eigenvectors, statistically significant results could be obtained in a set of independent data.

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Eberhard W. Wahl

Abstract

The association of local or regional weather “singularities” with the state of the general atmospheric circulation is described. The concept of “primary singularities,” reflecting characteristic features of the general circulation, and their effect on local or “secondary singularities” is discussed, with principal respect to the Boston daily record of temperature and precipitation.

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