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S. TEWELES and F. G. FINGER

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S. TEWELES, L. ROTHENBERG, and F. G. FINGER

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A recently published set of 10-mb. charts analyzed three times monthly, July 1957 through June 1958, is used as a basis for discussion of the high stratospheric circulation during those first 12 months of the International Geophysical Year, There is a slow, steady transition from summer easterlies to winter westerlies which appear first in high latitudes and then strengthen and expand southward. In January and February 1958, the circulation breaks down rapidly and in a highly complex manner. By May, polar easterlies become established and spread southward to merge with the intensifying subtropical easterlies.

Several related topics on the nature of medium- and large-scale developments are discussed.

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F. G. Finger, M. F. Harris, and S. Teweles

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MILES F. HARRIS, FREDERICK G. FINGER, and SIDNEY TEWELES

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The frictional and thermal contributions to S 2 2,2 (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 temperature variation is apparently caused by eddy transfer of heat from the earth's surface.

The results of the study must be considered in the light of the probable errors arising from data sampling, from the diurnal bias in the radiosonde observations, and from the restrictive assumptions of the theory. Considered in this light, the results suggest that the semidiurnal oscillation may be explained by three processes, of approximately equal importance: (1) eddy transfer of heat from the earth's surface; (2) direct absorption of solar radiation by water vapor and ozone, as computed by Siebert; and (3) surface friction, or eddy transfer of momentum. Surface friction apparently delays the surface pressure oscillation by about one hour.

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F. G. FINGER, R. B. MASON, and S. TEWELES

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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.

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A. J. Miller, H. M. Woolf, and F. G. Finger

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Results of comparisons of wind and temperature data obtained by closely spaced launchings of Japanese MT-135 and American ARCAS meteorological rocket systems are presented. In general, smoothed temperature profiles show a certain disagreement that is unexplained at this time. Perturbation profiles of wind and temperature indicate a degree of correlation that tends to substantiate the existence of small-scale features.

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F. G. FINGER, H. M. WOOLF, and C. E. ANDERSON

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A method of numerical objective analysis has been developed for application to stratospheric constant-pressure data at the 100-, 50-, 30-, and 10-mb. levels (approximately 16, 20, 24, and 31 km., respectively). This system evolved from successive modifications of the programs employed for operational objective analysis of lower-level charts at the National Meteorological Center. For use with stratospheric data, the Automatic Data Processing portion of these programs was expanded to correct for the errors in high-level rawinsonde temperatures and heights caused by short and long-wave radiational effects on the temperature sensor. In addition, procedures for vertical extrapolation of rawinsonde reports and merging of off-time data were incorporated to compensate for the scarcity of reports at a given observation time.

General degradation of stratospheric data with increasing height necessitated more stringent data rejection criteria within the entire system. It was also essential that increased emphasis be placed on wind observations as an analysis parameter. The resulting charts have shown that the objective system employed produces analyses of acceptable quality. Improvements are continually being developed and incorporated to increase the efficacy and objectivity of the procedures and the quality and usefulness of the product.

The main purposes of the computerized system are to provide good quality stratospheric analyses for anticipated operational requirements and to satisfy the needs of research. Daily analysis of Northern Hemisphere charts is being performed during the IQSY and is expected to continue after the end of the period. These maps are recorded for distribution on microfilm and also on punched-card decks containing grid-point data.

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Miles F. Harris, Frederick G. Finger, and Sidney Teweles

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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 the true pressure oscillations in the stratosphere, causing the phase of the latter to be moved toward noon. These results are supported by a similar analysis of rawinsonde data for Ft. Worth, Texas. The diurnal and semidiurnal temperature variations implied by the wind-derived height changes in the stratosphere are in general agreement with the results of determinations based on radiation theory. The diurnal error of the radiosonde temperature observations (observed minus computed temperature change) shows a maximum near noon at levels between 12 and 27 km, the diurnal range increasing from about 1C at the lower to about 2.5C at the upper level.

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F. G. Finger, M. E. Gelman, J. D. Wild, M. L. Chanin, A. Hauchecorne, and A. J. Miller

Daily NMC analyses, constructed from operational TOVS data since 1978, are used to monitor behavior of middle atmospheric temperature. Capability of the upper-stratospheric analyses (5,2,1, and 0.4 mb) to provide temporally consistent temperature fields depends on adjustments derived from ground-truth observations. These adjustments compensate for biases in the analyses caused by behavioral differences in data derived from successive operational satellite instruments and by changes in data and analysis procedures. This paper supports previous studies showing that observations from the datasonde rocket system provide ground-truth adjustments with a precision of 1°–3°C. The number of datasonde observations has diminished substantially in recent years, putting this adjustment system at risk. Falling-sphere rocket temperature data are shown to have variability in excess of that judged to be acceptable for use in the adjustment system.

The capability for Rayleigh lidar to provide high-quality temperature data needed for ground truth is examined by comparing NMC analysis temperatures, adjusted by datasonde measurements, with observational values from regularly operating lidar systems in France since 1978. Agreement between the two databases is found to be good in recent years. This is further verified by comparisons between the datasonde-computed adjustments and independent analysis adjustments derived from the lidar database. It is concluded that high-quality lidar measurements, if made available from low, medium, and high latitudes, could provide the essential data for use in the analysis adjustment system.

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