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[1] Spatial spectra and characteristic scales of stratospheric density fluctuations obtained from the space station Mir observations of stellar scintillations are analyzed in this paper. The remote sensing method described is based on a well-known stellar scintillation phenomenon that arises when observing the stars through the Earth's atmosphere. To interpret scintillation spectra, a model of the three-dimensional (3-D) spectrum of atmospheric density fluctuations consisting of both turbulent and internal wave-associated spectral components is presented here. With the model chosen, we explain scintillation spectra at low frequencies by suggesting the atmospheric density fluctuations to be caused by a random ensemble of internal waves with the −5 power law decay for their 3-D energy spectrum. For the wave-associated anisotropic part of the spectrum, so-called outer and internal vertical scales are introduced to explain behavior of the observed scintillation spectra in their low-frequency range. These scales being earlier proposed only theoretically have been simultaneously revealed in the scintillation spectra presented here. The estimates of the outer scale for the different orbits of the space station are obtained and compared with those found from lidar and rocket soundings of the stratosphere. A possible cause of the observed variation in the wave number bandwidth of the wave-associated part of the spectrum of air density fluctuations is discussed.

S-band phase path measured between two earth satellites—one in an occultation orbit relative to the other—determines the integrated radio refractivity of the neutral earth atmosphere. Atmospheric density is recoverable from such determinations provided an independent estimate of the contribution of water vapor to integrated refractivity is obtained. Transmission measurements in the vicinity of the 22.235-GHz resonant water vapor absorption line provide this estimate. Such data relate to the atmospheric water vapor content integrated precisely over the satellite-to-satellite phase path. The optimum frequency for the transmission measurement is that at which the dependence on line width of the water vapor absorption coefficient is a minimum. The accuracy of the measurement is inversely proportional to the actual atmospheric water vapor content ; but a resultant, nearly tenfold increase in the accuracy of the air density data ultimately recovered from the phase path data can be expected for midtropospheric regions. Phase path could be measured at the optimum frequency for the transmission measurement. A single-frequency system could thus provide all the information necessary for the enhanced density data from the occultation experiment.

The atmospheric pressure waves set off by the explosion of October 30, 1961, were traced over a large portion of the world, including the antipodes in the Antarctic, by means of analyses of available ordinary microbarograph records. The observed geographic variations in propagation speed and maximum amplitude are examined with the aid of air density and wind analyses. Comparison is made with the waves resulting from the great Siberian meteor of 1908 and the Krakatoa eruption of 1883.

The results of a statistical analysis of mesosphere data, together with four other soundings are given. The lowest densities are found in winter in arctic latitudes. At 65 km, the mean winter density is 60% of the mean summer density. The seasonal variation in mid-latitudes is relatively small, amounting to less than 5% below 50 km, with a maximum of 13% at 66 km. The latitudinal gradient is greatest in winter, and greatest at around 65 km. The gradient is directed northward from mid-latitudes, in the AMOUNT OF 2% per degree of latitude (at 65 km), and there is a smaller gradient directed equatorward from mid-latitudes. At mid-latitudes, the standard deviation of density varies from 4% (of the mean density) at 30 km to about 20% near 60 km, remaining nearly constant up to the top of the mesosphere. In arctic latitudes, the standard deviation varies from 11% at 30 km to a maximum of about 40% near 60 km, decreasing to about 30% at 80 km.

For isothermal, steady, two-dimensional flow with constant permeability, an expression has been derived for the quantity of air flowing into a partially cased rectangular snow trench. The formula, which is readily evaluated for any flow geometry, is Q = (K′;/2K) (k/μ) 〈ρ〉 (ps - pw), where Q is the mass flow rate, K′/2K is a configuration factor, 〈ρ〉 is the average air density calculated at mean pressure, and ps and pw are the air pressures at the snow surface and the uncased trench walls, respectively. For field conditions for which permeability is a known function of depth, the above expression, in which k/μ is replaced by 〈k/μ〉 = dt−1∫0dt(k/μ) dy, where dt is the depth of the trench, predicts a flow within 3 per cent of the value obtained from a more exact solution in which numerical techniques are used to account for variable permeability.

A method is described by which upper-air density and wind velocity might be determined by measuring the drag acceleration of a falling sphere by means of accelerometers mounted on an inertial platform carried within the sphere. An investigation was made to determine the size, weight, and accuracy of available inertial platforms. An analysis based on this information shows that air density and wind velocity can be measured by this method up to altitudes of at least 150 km and 120 km, respectively. The error in air-density measurement would be 20 per cent or less, and the wind-velocity error would be 10 m/sec or less.

Mass densities derived from drag data are compared with densities determined by mass spectrometers, EUV extinction measurements, and observations of the growth of chemiluminescent clouds for an altitude of 150 km. Drag densities fall very close to the Cira 1965 mean atmosphere and are 10 to 20% higher than the average for all rocket measurements discussed. Mass spectrometric and EUV extinction measurements agree quite well for n(N2) and n(O2) but differ significantly for n(O). In order to derive an improved set of parameters of thermospheric density and composition, it is proposed that the Cira 1965 mean density be lowered by 10%, that the measured n(N2) and n(O2) number densities be maintained, and that n(O) be chosen such that the number densities become consistent with the mass density p. This results in the following reference set for 150-km altitude: ρ = 1.96 × 10−12 g cm−3; n(N2) = 2.6 × 1010 cm−3; n(O) = 2.3 × 1010 cm−3; n(O2) = 2.5 × 109 cm−3; n(Ar) = 5 × 107 cm−3; mean molecular weight M = 22.9 g mole−1.

Consideration of the molecular refractivity has led to a value of the radio refractive index referred to zero altitude or sea level that effectively removes the systematic altitude dependence of air density. The advantages of this new parameter are illustrated by two applications. The first application, the preparation of climatic charts of the radio refractive index, illustrates that this new parameter brings climatic differences into sharp relief. The second application deals with the vertical variation of air mass properties across a classic warm front and clearly delineates air mass differences, thus indicating the utility of this new parameter for synoptic studies.

Calculations that will enable an experimenter to estimate the volume of material viewed by an air-borne gamma-ray spectrometer are presented. The effects of altitude, air density, source density, and gamma-ray attenuation coefficient were investigated. It is shown that the altitude is the most important parameter in the determination of the volume of material that produces a given percentage of the total observed signal.

Rigid spheres re-entering the atmosphere at hypersonic speeds are used to determine air density and temperature at strato-mesospheric altitudes. In this system, uncertainities in density due to the drag coefficient are eliminated. Trajectory parameters of the spheres are accurately measured by a coherent tracking sensor, the Tradex radar. Resulting density profiles for 6 nighttime sphere re-entries at Kwajalein, Marshall Islands (9°24′N, 167°39′E) are in satisfactory agreement with tropical monthly models and with the 15°N model (U. S. standard atmosphere supplements, 1966). Difference between maximum and minimum densities representing January and July soundings increases from 7% at 40 km to 15% at 70 km. Derived temperatures near 50 km are 10°K higher than the models, and the difference between extreme observations is 8°K at the stratopause.

The dipole radio signal from a low-altitude atmospheric nuclear explosion of low yield is computed by numerically integrating Maxwell's equations. The source is described by a simple model. The function describing the time history of the rate of gamma output is taken to be an isosceles triangle with a base equal to a fraction of a microsecond. The asymmetry necessary for radiation comes entirely from the variation of air density with altitude. The dipole fields are shown as functions of position for various times after the explosion. These curves form, in effect, a motion picture of the development of the signal.

The index of refraction above 20,000 feet is considered, based on measurements by Essen and Froome, and Barrett, for a wide range of radio frequencies. To an accuracy of one part in a hundred thousand, the density of air alone is of importance, and to an altitude of only 26 km. Effects from water vapor, and electron concentrations in the ionosphere for frequencies of 5,000 Mc/sec, were found negligible to the accuracy indicated.

Measurements of upper-air densities and temperatures from 12 flights of the rocket-borne falling sphere are presented. They show little seasonal variation at 32° and 38° N, but large variations in a few winter days at 59°N. A low arctic density at 60 km results in a linear latitude density gradient of about 2 per cent per degree of latitude. Such a gradient was measured in a latitude survey. An abrupt warming at 45 km was detected at Fort Churchill in January 1958 and related to a warming of larger scope detected by balloons. The average air temperatures above Fort Churchill from January to March are warmer at 75 km and cooler from 50 to 30 km than at 32° to 38°N.

This report describes a method for obtaining the so-called “molecular weight” of air at high altitudes of the earth's atmosphere above the transition region for the dissociation of molecular into atomic oxygen. A reasonable working model, based upon the ratio of absolute temperature to molecular weight T/M, which is proportional to the slope of the loge pressure υs altitude curve, is presented. The region considered is from 90 to 600 km, assuming that the composition of the atmosphere is constant up to 90 km. The calculations are based upon experimental data reported by Byram, Chubb, and Friedman from Aerobee 16, 1 December 1953. Since the 1956 Model Atmosphere of the Air Research and Development Command employs a variable scale height gradient with altitude, the diffusive equilibrium and mixing formulas of Nicolet and Mange were modified to obtain the vertical distributions of the various atmospheric constituents. The mass densities are found by multiplying the number densities by the respective molecular mass of the individual components of the atmosphere. The molecular weights at the various altitudes were calculated from the formula Knowing the composition of the atmosphere at any altitude, it is possible to determine the temperature through the relationship of the scale height to temperature, H = RT/Mg.

One of the main limitations, at present, to the accuracy of measurements of long baselines by optical methods is the uncertainty in the average index of refraction over the optical path due to nonuniformity and turbulence of the atmosphere [Thompson et al., 1960]. This uncertainty is due primarily to lack of knowledge of the air density, although a small correction for water vapor is also required. Our purpose in this note is to point out that simultaneous measurements of the optical distance over the same path for blue and red light can be used to provide the required correction for the atmospheric index of refraction. The application of this method to interferometric distance measurements has previously been discussed [Erickson, 1962a].

A recent paper by Jones, Peterson, Schaeffer, and Schulte [1959] reporting large mesospheric air density variations at high latitudes in winter may be of considerable interest regarding the anomalous winter daytime absorption of medium-and high-frequency radio waves. A plot of noon absorption of vertically reflected 2 Mc/s radio waves at Slough from year to year shows that the absorption in winter is usually much greater than would be expected if it were simply related to the zenith angle of the sun [Whitehead, 1957]. Noon absorption has been measured over long periods at low as well as at high latitudes, but the effect has been reported only in the event of the latter. It is not present, for instance, in the absorption measured at Singapore and published in the Slough Bulletin.

The annual cycles of sea level and surface pressures and the atmospheric pressure owing to water vapor have been analyzed in detail. Global sea level pressures undergo an annual cycle of 0.5 mbar range with a maximum in the northern winter. Global surface pressures, which represent the total mass of the atmosphere, also undergo an annual cycle of 0.5 mbar range but with the maximum in the southern winter. The changes in water vapor concentrations are responsible for the latter—water vapor has a maximum in the southern winter. The constancy of the mass of dry air is used as a check on the accuracy of computations. The total mass of the atmosphere is 513.7 × 1016 kg with a standard error of 0.02 × 1016 kg and an annual cycle of amplitude 0.1 × 1016 kg. The corresponding global mean surface pressure of the atmosphere is 984.68 mbar. The mean total mass of water vapor is 1.3 × 1016 kg which corresponds to 2.53 cm of precipitable water or 12906 km3 of water at 0°C. The distribution of pressure and mass as a function of latitude are also presented. A substantial annual exchange of mass occurs between the hemispheres amounting to 0.7 × 1016 kg of dry air (2.7 mbar range in hemispheric averaged pressure). Maximum pressures occur in winter, and the summer loss of mass is partially compensated for by increased water vapor amounts. The maximum net meridional flow occurs across 5°N in the transition seasons. In the northern hemisphere, water vapor undergoes an annual cycle with a range of 1.5 mbar (area averaged) and a summer maximum, and the sea level pressure owing to dry air undergoes an annual cycle of range 5 mbar and a winter maximum. Of this, 54% is due to exchanges with the southern hemisphere and 46% is due to changes in the artificial atmospheric mass used to correct from the surface to sea level.

The effects of atmospheric parameters (pressure, temperature, relative humidity, and wind) on the induced corona current through a corona probe are evaluated through a laboratory investigation. The corona probe has a high series resistance, which tends to linearize the relationship between the induced corona current and the electric field. From a best fit of the data, the slope of the linear relationship for corona currents greater than 1.5 μA varies with air density D as (DO/D)0.15. For lower currents the slope varies as (DO/D)0.33. The onset electric field required to initiate corona varies slightly with air density; this relationship is (D/DO)0.15. The high series resistance significantly reduces the effects of variations in the relative humidity and in low wind velocities across the corona point. When balloon borne, the probe can reliably measure thunderstorm electric fields.

Variations in the hydrological cycle and the water vapor content of the atmosphere form a vital part of the “greenhouse” feedback mechanism that can substantially enhance perturbations in the atmosphere arising from changes in forcing, such as those associated with increases in the carbon dioxide content of the atmosphere. An analysis is therefore made of the mean annual cycle, interannual variability and trends in global-scale water vapor content of the atmosphere for December 1978 through December 1985, using global analyses from the European Centre for Medium Range Weather Forecasts. Since the variations in total atmospheric mass are almost entirely due to water vapor, two entirely independent global measures of the water vapor content can be compared. These are the total surface pressure due to water vapor from humidity analyses and the total surface pressure itself. For the mean annual cycle these show excellent agreement, and the analyses are therefore compatible with the constraint that the total mass of dry air is conserved. However, it appears that both the interannual variability and trends in water vapor are sufficiently small that they are lost in the noise level of the data. A new estimate of the total mass of the atmosphere is 5.1361×1018 kg for the annual mean, corresponding to a mean surface pressure of 984.43 mbar. It ranges from 5.1352×1018 kg in January to 5.1371×1018 kg in July, owing to the annual cycle in global water vapor which has an amplitude of 1.0×1015 kg (0.2 mbar). The total mass of dry air is estimated to be 5.123×1018 kg (or 981.9 mbar). Also presented is the partitioning of the mass for both the total and the water vapor into the contributions from each hemisphere and as a function of latitude. Mean annual surface pressures in the northern and southern hemispheres are found to be 981.92 and 986.93 mbar, respectively. Monthly mean hemispheric fluctuations in surface pressures of ±1 mbar are not uncommon and tend to be reflected by opposite anomalies in the other hemisphere (consistent with conservation of mass), but the residual in the global monthly mean is of the order of 0.1 mbar. Since this is greater than the magnitude of the possible signal in water vapor surface pressure, the available evidence indicates that the analyzed global monthly anomalies are mostly noise.

The density calculations of the following paragraphs are based on the assumptions of diffusion as indicated by Table 3 and temperature-distribution as shown in Figure 7. The calculations for the atmospheric conditions of summer nights are given in detail since it was considered these figures would be the most useful. The change in atmospheric pressure per centimeter can be calculated for any height Z by the equation or in words PZ+1, the pressure at altitude (Z+1), is equal to the pressure at Z minus the weight of one cubic centimeter of gas at Z. Equation (13) may be written then log PZ = log P0-Σ0Z log [1 + (WZ/PZ)] but here W0, PC, T0, g0, and M0 represent the weight per cubic centimeter, pressure per square centimeter, temperature, acceleration due to gravity, and molecular weight of any given gas at the initial point, Z = 0, and WZ, PZ, TZ, gZ, and MZ represent the same quantities for the gas at altitude Z. In table 11, calculated values of WZ/PZ are given in column 1 and values of log (1 + WZ/PZ) in column 2 for altitudes from 0 to 100 km. The value of MZ/M0 was considered to be unity below the diffusion-levels given in Table 4, column 4, for all gases; at these levels an abrupt change is considered to take place and for greater altitudes (MZ/M0) for a given gas is taken as the molecular weight of the given gas divided by 28.95, the molecular weight of air. The change in density is calculated separately for each gas for altitudes greater than 100 km. Table 12 gives values of W/P and log (1 + W/P) for altitudes 100, 500, and 1000 km for the condition of summer night based on the assumption of gravity-equilibrium for each gas For these calculations (W0/P0), (T0/TZ), and (MZ/M0) are considered constants ; the only variable term in the value of (WZ/PZ).is therefore (gZ/g0), which maybe replaced by (r02/rZ2) where r0 and rZ are distances from the center of the Earth at sea-level and at the height Z, respectively. The change in (WZ/PZ) is then very nearly linear for these altitudes.