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- Author or Editor: MILES F. HARRIS x
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Abstract
The usefulness of a number of variables as predictors of the 1000-500 mb thickness is explored. These predictors are utilized, in several combinations, to form multiple regression equations from which four series of 12-hour thickness forecasts are prepared. Verification scores are presented and compared with the scores of 12-hr numerical thickness predictions for the same period.
Abstract
The usefulness of a number of variables as predictors of the 1000-500 mb thickness is explored. These predictors are utilized, in several combinations, to form multiple regression equations from which four series of 12-hour thickness forecasts are prepared. Verification scores are presented and compared with the scores of 12-hr numerical thickness predictions for the same period.
Abstract
It is proposed that both the semi-diurnal and the diurnal components of the daily pressure wave are the result of horizontal divergence associated with the daily temperature variation. A combined theoretical-empirical approach suggests that the divergence can be attributed to the Brunt-Douglas isallobaric wind if certain modifications are introduced into the original Brunt-Douglas equation. These modifications include the retention of the vertical Coriolis term in the equations of motion, and the assumption that accelerations caused by changes in the thermal gradient are continually and automatically balanced by changes in the pressure gradient resulting from the horizontal divergence. The proposed theory offers a quantitative explanation for the observed latitudinal distribution of the daily barometric wave.
Abstract
It is proposed that both the semi-diurnal and the diurnal components of the daily pressure wave are the result of horizontal divergence associated with the daily temperature variation. A combined theoretical-empirical approach suggests that the divergence can be attributed to the Brunt-Douglas isallobaric wind if certain modifications are introduced into the original Brunt-Douglas equation. These modifications include the retention of the vertical Coriolis term in the equations of motion, and the assumption that accelerations caused by changes in the thermal gradient are continually and automatically balanced by changes in the pressure gradient resulting from the horizontal divergence. The proposed theory offers a quantitative explanation for the observed latitudinal distribution of the daily barometric wave.
Abstract
No Abstract Available.
Abstract
No Abstract Available.
Abstract
The observed semidiurnal wind in the troposphere at five mid-latitude stations shows a phase lead over the wind deduced from frictionless theory, and a smaller amplitude, especially near the earth's surface, than the theoretical value. By making use of the observed fact that the tidal pressure-dependent (frictionless) wind changes much less rapidly with height than does the observed wind in the friction layer, it is possible to extend the Ekman theory to explain approximately the observed solar semidiurnal wind distribution. It is concluded that the existence of surface friction causes the time of maximum of the semidiurnal pressure wave to be advanced relative to the time that frictionless theory should predict; or, in agreement with Gold's conclusion that friction produces a phase lag of the tide with increase in elevation. The theoretical argument would appear to be valid for the lunar atmospheric tide also, but direct evidence that similar conclusions apply to the lunar tide is lacking.
Abstract
The observed semidiurnal wind in the troposphere at five mid-latitude stations shows a phase lead over the wind deduced from frictionless theory, and a smaller amplitude, especially near the earth's surface, than the theoretical value. By making use of the observed fact that the tidal pressure-dependent (frictionless) wind changes much less rapidly with height than does the observed wind in the friction layer, it is possible to extend the Ekman theory to explain approximately the observed solar semidiurnal wind distribution. It is concluded that the existence of surface friction causes the time of maximum of the semidiurnal pressure wave to be advanced relative to the time that frictionless theory should predict; or, in agreement with Gold's conclusion that friction produces a phase lag of the tide with increase in elevation. The theoretical argument would appear to be valid for the lunar atmospheric tide also, but direct evidence that similar conclusions apply to the lunar tide is lacking.
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 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.
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 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.
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 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.
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 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.
