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Roderick S. Quiroz

Abstract

Knowledge of the air density at altitudes above 30 km is needed for such applications as the calculation of space shuttle reentry heating. A method is described for deriving hemispheric (or global) horizontal density fields at 40–60 km directly from radiance maps based on infrared measurements by such instruments as the Nimbus 4 Satellite Infrared Spectrometer and the Selective Chopper Radiometer. Direct regression of air density with the radiance measured in individual channels of these instruments is investigated. From hydrostatic considerations, maximum density-radiance correlation is expected to occur at about 2.5 scale-heights above the level of maximum temperature-radiance correlation; the latter is found near the peak of the transmittance weighting function for each channel. This expectation is substantially verified with the aid of a statistical sample of rocketsonde temperature and density profiles and radiances computed with the appropriate transmittance data. Regression equations are developed for specifying the density with a standard error within 5–7% of the observed density. For the period of a major stratospheric warming in January–February 1973, sample density maps at 50 km are shown, derived from radiance measurements of the NOAA-2 Vertical Temperature Profile Radiometer. These indicate a density increase by more than 50% near the North Pole, from late January to early February.

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Roderick S. Quiroz
and
Alvin J. Miller

Abstract

Unexpectedly large increases in the density of the stratosphere and mesosphere have been noted previously in association with atmospheric changes at remote altitudes. Modified forms of the hydrostatic equation and the equation of state suggest a positive correlation between the density at some altitude and the pressure and temperature at neighboring lower altitudes, under the controlling influence of vertical motion. In this paper, correlation coefficients are determined as a function of altitude separation, by season and latitude, on the basis of data at 20–60 km from four years of rocket soundings. Consistent patterns of correlation are found. These are characterized, in particular, by distinct maxima in the vertical arrays of correlation between pressure and density and between temperature and density, with the density at a fixed upper altitude. The highest pressure-density correlations are approximately +0.88 to +0.99, depending on latitude, season and height domain, and occur with a typical lag of 8 km. The corresponding range and height lag for maximum temperature-density correlations are +0.73 to +0.94, and 20 km. A physical-mathematical explanation for the occurrence of these maxima is suggested in terms of the pressure-scale height. Finally, the manner in which the correlation results may be used to predict the density at rocket altitudes is briefly indicated.

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Roderick S. Quiroz
and
Robert M. Henry

Abstract

Eight ARCAS meteorological rockets were fired from Wallops Island (38N, 75W) before, during and after the total solar eclipse of 7 March 1970. Detailed temperature and wind data were acquired to an altitude of about 65 km. Pressures and densities were derived by hydrostatic integration of the corrected temperature profiles. A time-height cross section of the temperature data (smoothed to suppress small-scale detail) shows significant cooling mainly in the layer 40–60 km. Maximum amplitude of the temperature perturbation is about 9K, near 50 km. Maximum pressure variation, amounting to a decrease of at least 7%, occurred about one scale height higher, near 58 km. The ARCAS wind observations are independent of the thermodynamic measurements; a time-height analysis of the winds shows a large amplification of the meridional flow, which is found to be consistent with the observed pressure changes. Derivatives in the perturbation equation of motion are evaluated with the aid of a space-time transformation based on the speed of the eclipse shadow. Consistency between the wind and thermodynamic data is indicated by approximately a three-fold increase, with altitude, of both the observed perturbation wind and the geostrophic wind specified by the perturbation model. Evidence supporting the observed temperature variation includes not only the ARCAS wind data, but also Pitot-probe and balloon measurements at Wallops Island and falling-sphere eclipse measurements in Florida. The cooling rate observed in the eclipse exceeds computed cooling rates at 50 km.

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RODERICK S. QUIROZ
and
ALVIN J. MILLER

Abstract

Rocket wind soundings for several stations within 10° latitude of the equator are used to analyze details of the structure of the recently discovered semi-annual wind variation in the equatorial upper stratosphere. The cycle is characterized by winter and summer easterlies and equinoctial westerlies and in 1966 appeared to have maximum amplitude at 45–50 km. Its global extent is confirmed with the aid of rocket data from widely separated longitudes. The semi-annual variation is discussed in relation to the quasi-biennial oscillation, which has maximum amplitude in the lower stratosphere. A possible explanation of the origin of the semi-annual variation is mentioned and attention is called to semi-annual variations in other parameters in the upper atmosphere.

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RODERICK S. QUIROZ
and
MELVYN E. GELMAN

Abstract

The direct use of measured radiances for determining the thickness of stratospheric layers is investigated. We hypothesize that the equivalent blackbody temperature, weighted according to the transmittance weighting functions for the stratospheric channels of the satellite infrared spectrometers and the selective chopper radiometer, gives a good approximation of the geometric mean temperature of some layer within the transmittance (τ v ) domain 0<τ v <1. A priori, it is shown that under certain conditions this is not a good assumption. However, it is of interest to determine for what atmospheric layers acceptably small error in the mean temperature, and therefore in the thickness, would be incurred. Layers based at 100-10 mb, with upper boundaries at 10-0.5 mb, are investigated using a carefully selected family of stratospheric temperature profiles and computed radiances. On the basis of physical reasoning, a high correlation of thickness with radiance is anticipated for deep layers, such as the 100- to 2-mb layer (from about 15 to 43 km), that emit a substantial part of the infrared energy reaching a satellite radiometer in a particular channel. Empirical regression curves relating thickness and radiance are developed and are compared with “blackbody” curves obtained by substituting the blackbody temperature in the hydrostatic equation. Maximum thickness-radiance correlation is found, for each infrared channel, for the layer having the best agreement of empirical and blackbody curves. For these layers, the data from a single radiation channel accounts for a reduction of variance by up to 97 percent. The utility of thickness data based on actual radiances is demonstrated through independent testing and with a sample 2-mb map constructed by adding thicknesses based on measured radiances to the observed 100-mb height field.

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