Sidney Teweles

Verification of Prognostic Charts

Desirable characteristics of a system for scoring prognostic charts are discussed. A successful system now in use at the WBAN Analysis Center is described in detail. The preliminary score produced is a function of the pressure difference between pairs of stations over the area of the chart. A secondary score, the deviation from a running mean of daily scores adjusted by handicaps assigned to the individual forecasters, is a measure of forecasting skill relatively independent of many spurious effects. The slowly varying handicap is a useful means of ranking the ability of the forecasters.

ANOMALOUS WARMING OF THE STRATOSPHERE OVER NORTH AMERICA IN EARLY 1957

Abstract The anomalous stratospheric warming of January and February 1957 is studied in detail by means of constant pressure charts, time sections, and cross sections. The warming occurred as the meandering Arctic stratospheric jet stream of wave number two developed into a pair of vortices extending to above the 10-mb. surface. It is concluded that development of stratospheric waves in the Northern Hemisphere is facilitated by autumnal growth of a forced perturbation locked in place by a warm ridge over the Aleutian area. The baroclinicity and rate of development were in agreement with Fleagles criteria for the growth of disturbances. Interaction between the tropospheric jet stream and Arctic stratospheric jet stream during the period of development is believed responsible for the great intensity of the 1957 warming.

Diurnal Variation of Wind, Pressure, and Temperature in the Troposphere and Stratosphere over the Azores

Abstract The diurnal and semidiurnal variations of wind, pressure, and temperature at Lajes Field, Terceira, Azores, were computed for each month of the year for 30 levels between the surface and 10 mb. The semidiurnal variations were found to agree fairly closely with those at Washington, D.C., where data for the troposphere during the summer months are available for comparison. However, the diurnal variations of pressure and wind at the two stations are quite dissimilar. In order to check the consistency of the wind and pressure variations at Lajes Field, the diurnal and semidiurnal height variations were computed from the wind variation at each isobaric surface by the use of a model based on a linearized form of the equations of motion, frictionless flow, and the assumption that the oscillations are simple progressive waves. Results of the analysis indicate that the radiosonde observations contain diurnal, and smaller semidiurnal, temperature errors which superimpose fictitious pressure variations on t...

REDUCTION OF DIURNAL VARIATION IN THE REPORTED TEMPERATURES AND HEIGHTS OF STRATOSPHERIC CONSTANT-PRESSURE SURFACES

Abstract Because temperature and height data reported by different types of radiosondes at constant-pressure surfaces high in the synoptic stratosphere are often incompatible, an empirical study has been made of diurnal changes computed from successive radiosonde observations taken in daylight and darkness and the variation of these changes with solar elevation angle. An attempt has been made to evaluate the spurious portion of these changes for principal types of instruments used by weather agencies of the United States during the International Geophysical Year. Graphs are presented giving temperature and height corrections that may be applied to the reported data to improve compatibility between stations, even across the line separating daylight from darkness. The method by which data were examined should prove useful in arriving at a similar system of corrections for any particular type of radiosonde.

A Spurious Diurnal Variation in Radiosonde Humidity Records

Abstract In dealing with differences in upper-air relative humidity over short distances and during small time intervals, investigators have noted a tendency for low values to be reported by U.S. radiosondes, particularly those sent aloft in daytime. This paper summarizes the proceedings of a colloquium of experts who described the nature of the spurious diurnal variation and recommended the manner in which the radiosonde should he modified and in which archived data might he corrected. The billiard sharp whom anyone catches, His dooms extremely hard– Hes made to dwell in a dungeon cell On a spot thats always barred. And there he plays extravagant matches In fitless finger stalls On a cloth untrue, with a twisted cue And elliptical billiard balls! The Mikado, Act II.

FRICTIONAL AND THERMAL INFLUENCES IN THE SOLAR SEMIDIURNAL TIDE

Abstract The frictional and thermal contributions to S22,2 (p), the dominant wave type in the progressive solar semidiurnal pressure wave, are evaluated from upper air observations at nine rawinsonde stations. The theoretical basis for the investigation follows from the approximation of friction as a potential force in the tidal equations. The model parameters and boundary conditions are those adopted by Siebert. Surface friction is evaluated semi-empirically, by the use of a friction model which is essentially an adaptation, to the semidiurnal motions, of the Ekman theory of the boundary layer. The assumption of a constant coefficient of the vertical transfer of momentum leads to uncertainties in the magnitude of the frictional contribution to the wave. Further uncertainties arise from a systematic error in the observed temperatures, caused by radiation effects on the radiosonde instrument. The latter error, however, is believed to be negligible in the lower troposphere, where an unexpectedly large tempe...

A SPECTRAL STUDY OF THE WARMING EPOCH OF JANUARY–FEBRUARY 1958*

Abstract Contour and isotherm patterns of 100-, 50-, and 30-mb. charts have been subjected to harmonic analysis after the manner of Saltzman and Fleisher. The resulting wave-number statistics permit a detailed examination of the sudden warming and circulation breakdown that occurred in the Northern Hemisphere stratosphere in January–February 1958. The stratospheric warming epoch of January 1958 was preceded by a marked expansion in the ring of tropospheric westerlies. Thereafter in the stratosphere the kinetic energy of wave number 1 increased by nearly the same amount transferred to it by the zonal flow and the other waves. However a subsequent great increase in the kinetic energy of wave number 2 occurred simultaneously with a large transfer of kinetic energy from that wave to both the zonal flow and the other waves. This development of wave number 2 thus appears to have been baroclinic in nature. Correlation of daily spectral statistics for the stratosphere and troposphere show a number of significant ...

TIME SECTION AND HODOGRAPH ANALYSIS OF CHURCHILL ROCKET AND RADIOSONDE WINDS AND TEMPERATURES

Abstract Winds and temperatures to above 80 km. measured during the International Geophysical Year by grenade, sphere accelerometer, and Pitot-static tube experiments at Churchill, Manitoba are combined with radiosonde data in time sections. The resulting analyses are discussed in reference to 10-mb. constant pressure charts showing the horizontal circulation near the 30-km. level. Periods in July, August, and December 1957 and January–February 1958 are covered. The nature of the circulation in successive layers of the stratosphere and mesosphere is suggested by this investigation. In summer, irregular wind flow that is predominantly from the east appears in the middle and upper stratosphere. Strong easterlies in the lower and middle mesosphere are bounded in the upper mesosphere above 75 km. by a sharp vertical wind shear layer with highly variable west winds above, suggesting the existence of rapidly moving, intense cellular circulations near the mesopause. In winter when the boundary of the polar night...

Quasi-Biennial Cycles in Angular Momentum Transports at 500 mb

Abstract Geostrophic angular momentum transport at 500 mb has been computed as a function of latitude and zonal wave number for a 10-yr period. The record has been inspected for evidence of periodic variations at latitudes 17.5N, 27.5N, 42.5N, and 57.5N. A quasi-biennial cycle is most prominent in the case of the planetary waves, with wave numbers 1 and 3 out of phase with wave number 2. The cyclone waves display a phase shift with time that implies a varying scheme of interaction with the long waves. Monthly average values of the 500-mb mean zonal wind, based on the same 10-yr record, do not indicate any strong periodicity.

DIURNAL VARIATION IN STRATOSPHERIC TEMPERATURES AND HEIGHTS REPORTED BY THE U.S. WEATHER BUREAU OUTRIGGER RADIOSONDE

Abstract The diurnal change in temperature and height measured by the new U.S. Weather Bureau outrigger radiosonde at and above 100 mb. has been determined from pairs of successive radiosonde observations taking place in daylight and darkness. Analyzed graphs of the change as a function of solar elevation angle are presented. For a given solar angle, the observed diurnal variations are found to be larger with afternoon daylight than with morning daylight. Furthermore, values computed for Plateau stations with afternoon daylight are particularly large. Use of the white 50-mil rod thermistor with outrigger mounting has radically improved the compatibility of reported temperatures and heights at adjacent stations, primarily because the radiational temperature error has been reduced by a factor of about two to four. The observed diurnal variations measured by this new instrument are comparable with those of the military outrigger radiosonde, allowing for the slightly smaller thermistor of the latter.