Atmospheric Temperature Structure Research Articles

Calibration of infrared instruments for the remote sounding of atmospheric temperature

For ir radiometers making remote observations of atmospheric temperature structure, an absolute accuracy of ~(1/2)% in radiance measurement is required and a relative accuracy between measurements of ~0.1%. Such accuracies can be achieved. The present theoretical models of the 15-microm carbon-dioxide band are inadequate for interpretation of remote sounding observations and careful measurements of atmospheric transmission in this region are required.

A quantitative comparison between acoustic sounder returns and the direct measurement of atmospheric temperature fluctuations

Results are presented which show that reasonably accurate estimates of the atmospheric temperature structure paparmeter C T 2 can be derived from the returns of a monostatic acoustic sounder in both stable and convective atmospheric conditions.

Infrasound from convective storms. III. Propagation to the ionosphere

We model mathematically the spectral features of infrasound observed in the ionosphere and believed to be radiated by severe thunderstorms. We explain the dominant 2–5-min wave period as an effect of atmospheric filtering; shorter periods are excessively attenuated by absorption in transit to the ionosphere, and longer periods are attenuated in portions of the atmosphere where the waves are evanescent because their frequencies are below the acoustic cutoff. An observed spectral ’’fine structure’’ within the 2–5-min band is explained in terms of resonant interactions between the waves and the atmospheric temperature structure. Accurate quantitative modeling of all these details of the storm-to-ionosphere transmission coefficient requires numerical integration of the acoustic-gravity wave equation, including the effects of ground reflection, absorption, and partial reflections in the atmosphere. Subject Classification: [43]28.30.

Propagation of severe-storm infrasound to ionospheric heights: a narrow-band atmospheric filter

We set out to model theoretically the spectral features of infrasound observed in the ionosphere and believed to be radiated by severe thunderstorms. We explain the dominant 2–5-min wave period as the effect of atmospheric filtering; shorter periods are excessively attenuated by absorption in transit to the ionosphere, and longer periods are attenuated in portions of the atmosphere where the waves are evanescent because their frequencies are below the acoustic cutoff. An observed spectral “fine structure” within the 2–5-min band is explained in terms of resonant interactions between the waves and the atmospheric temperature structure. Accurate quantitative modeling of all these details of the storm-to-ionosphere transmission coefficient requires numerical integration of the acoustic-gravity wave equation, including the effects of ground reflection and partial reflections in atmosphere.

Atmospheric infrasound radiated by bridges

Constant-frequency infrasound (about 5 to 10 Hz for different sources) has been detected at a number of locations from different directions. In an intensive study of 8.5-Hz infrasound detected regularly at Lamont-Doherty Geological Observatory of Columbia University in Palisades, N. Y., positive sound fixes have been obtained at the Tappan Zee Bridge. Geophones placed at several locations on the bridge recorded vibrations of the same frequency. We conclude that the vibrational motions of bridges radiate infrasound into the atmosphere and that the infrasound is most readily detected during times when atmospheric wind and temperature structure favor acoustic channeling near the ground. The acoustic signal occurs in pulses having a duration which, although fairly constant on a given occurrence, may vary from a fraction of a minute to several minutes.

Mariner 9 ultraviolet spectrometer experiment: Pressure-altitude measurements on Mars

Ultraviolet spectrometer measurements of the reflectance at 3050 Å are modeled to give pressure-altitudes for Mars assuming a quiescent atmosphere. Ultraviolet light that is Rayleigh-scattered by the Mars molecular atmosphere, with allowance for uniform turbidity, is proportional to surface pressure independent of atmospheric temperature structure. All model constants except the over-all scaling factors are found by requiring ultraviolet spectrometer pressures of 47 locations on the planet to be the same when measured at different geometries. The overall scaling factor is found by intercomparison with Mariner 9 occultation pressures. Comparison with other Mars pressure-altitude measurements show deviations from the assumption of uniform turbidity to occur over the Hesperia plateau for ultraviolet measurements obtained during the 13–26 February 1972 time period.

A Comparison of the Low-Level Radiosonde and the Acoustic Echo Sounder for Monitoring Atmospheric Stability

Temperature profiles measured with a radiosonde are compared with returns from an acoustic echo sounder throughout the height range 50–700 m. In general, the sounder records indicate the temperature inversion to be somewhat lower than do the radiosonde records. Reasons for this apparent discrepancy and the advantage of the sounder, in being able to monitor continuously the inversion structure and undulations produced by wind shear, are discussed. It was proved feasible to operate the acoustic sounder in a noisy commercial district with little detrimental effect on the ability to detect atmospheric temperature structure. It is concluded from this preliminary investigation that the combination of the radiosonde and the acoustic echo sounder provides a much more valuable tool for monitoring structure in the stable planetary boundary layer than either device used alone.

Mariner 9 ultraviolet spectrometer experiment: Photometry and topography of Mars

Reflectance properties of Mars are measures in a 100-Å band centered at 3050 Å by the ultraviolet spectrometer. The instrument has an angular resolution which is equivalent to an area of 10 × 30 km on the surface of Mars. The transition from dusty conditions, which prevailed at the time of arrival of Mariner 9 on 14 November 1971, began on 1 January 1972, and relatively clear conditions existed after 23 January 1972. As the atmosphere became clearer, the scattering properties began to show a morning enhancement in both terminator and illuminated disk reflectance. A topographic map of Mars based on the scattering of ultraviolet light from the Mars atmosphere is shown. This map is based upon 3050-Å data obtained after the Mars atmosphere had cleared in the ultraviolet. Ultraviolet light which is Rayleigh-scattered by the Mars molecular atmosphere, with allowance for uniform turbidity, is proportional to surface pressure independent of atmospheric temperature structure. Comparison with Mariner 9 radio occultation measurements determines the fraction of total reflectance that is due to atmospheric scattering.

The effect of atmospheric conditions on plume rise

The buoyant rise of chimney plumes is discussed for relatively large distances from the source, where atmospheric turbulence is the dominant cause of mixing (rather than turbulence due to the plume's own upward motion). A simple theory is developed which shows a number of different shapes plumes can have under different atmospheric conditions (particularly in an unstable environment).Experimental data are then presented, which were collected in the field near Toronto, with reasonably detailed supporting information on the atmospheric temperature structure. These (and earlier results) often show quite complex plume behaviour at large distances from the source, which can, however, be readily understood in terms of the simple theory presented.

The Effect of Changing CO2Concentration on Radiative Heating Rates

Carbon dioxide is the largest global pollutant by mass and atmospheric concentrations are increasing at about 0.7 ppM ..nu.. per year. The influence of this change on the atmospheric temperature structure is unknown. One method for investigating this is to compute the radiative heating rate as the local imbalance of radiative fluxes, for each altitude and for different CO/sub 2/ mixing ratios, keeping other factors constant. This manuscript is a discussion of the application of this approach. Data of the local rate of temperature change produced by infrared radiative divergence due to CO/sub 2/, H/sub 2/O, and O/sub 3/ are presented. At lower levels the net cooling rate was slightly diminished while at upper levels it was significantly increased by a change in CO/sub 2/ from 320 to 400 ppM..nu... The physical reasons for the two changes differ and are discussed. To place the CO/sub 2/ contribution to temperature in perspective it was compared with other radiative components (H/sub 2/O and O/sub 3/) at two levels (5 to 10 mb and 850 to 1000 mb). Clear skies were assumed. Carbon dioxide was secondary to water vapor in the troposphere and dominant in the lower stratosphere. When searching for a potentialmore » influence of global pollution on the tropospheric temperature the author suggested it would be wise to pay careful attention to the water cycle and its possible modification, particularly as it enters also through the effect of latent heat.« less

Optical Effects of Thermal Structure in the Lower Atmosphere

Ascending convective plumes of inhomogeneous warm air interspersed with regions of air that are remarkably free from temperature fluctuations are sometimes observed in the lower layers of the atmosphere. A close correlation is demonstrated between intervals of good optical seeing along an upwardslanting path 20 m long and such periods of below average, air-temperature fluctuation. This correlation is sensitive to the azimuthal angle between wind direction and the vertical plane containing the optical path. The occurrence of temperature-quiescent periods at a given height is also shown to require the horizontal wind speed to be less than a critical value, and there is evidence that the thermal structure tends to be elongated in the direction of the wind. The range of amplitudes of image dancing observed in these experiments is comparable with that encountered in solar observations. The atmospheric temperature structure coefficients calculated from these optical experiments compare favorably with independent direct measurements.

Dependence of Image Quality on Horizontal Range in a Turbulent Atmosphere

The dependence of the complex optical transfer function of an image-forming system on range through the atmosphere has been investigated experimentally. The simple case of a horizontal line of sight over flat terrain has been studied and empirical equations have been obtained which relate the transfer function to range and to the atmospheric temperature structure function. These equations agree with a general theory of wave propagation in a turbulent medium and are therefore applicable to a wide range of situations, provided that the distribution of the temperature structure function along the line of sight can be obtained. The experimental results also furnish evidence that the Kolmogorov expression for the temperature structure function (“the two-thirds law”) is applicable to scale sizes of about a centimeter or so.

Optical Image Quality in a Turbulent Atmosphere

Measurements of the time-average modulation transfer function of an optical system comprising an objective and a horizontal air path correlate with a parameter which characterizes the magnitude of temperature fluctuations in the lower layers of the atmosphere. Evidence is produced to support an exponential relationship between the transfer function and the atmospheric temperature structure function. The transfer function fluctuates rapidly about a mean; visual estimates of resolution limit agree more closely with the maxima than with the mean. The significance of these results is discussed in relation to the choice of conditions for good terrestrial and astronomical seeing.

Upper atmosphere wind and temperature structure by Skylark rocket-grenade experiments at Woomera, Australia, 1957—59

An account is presented of the first grenade experiments carried out at the Woomera rocket range during 1957-59. A description is given of the grenades and their rocket installation; and of the optical and acoustical instrumentation required to determine their burst positions and to find the times of travel of the sound waves to the ground. The method and theory of the experiment are outlined, and details of the firings and results obtained are presented. The accuracy of the measurements is discussed and comparisons made with simultaneous measurements by other methods. Determinations of wind speed and temperature (derived from the speed of sound) have been extended from the upper balloon limit to about 85 km, and a comparison between summer and winter conditions has been possible. Wind measurements have been extended to greater heights by means of the glow phenomenon. Pressure and density profiles have been determined and agree very closely with the COSPAR International Reference Atmosphere, 1961.

Some Considerations Concerning the Measurement of the Atmospheric Temperature Field by Electromagnetic Means

A system for determining atmospheric temperature structure by using an electromagnetic radiometer probe is described. The relationship between the electromagnetic sensor reading and atmospheric conditions is developed for both the microwave and infrared sensor utilizing a unified approach for the two cases. It is shown that, with the assumption of horizontal homogeneity, several alternate procedures for inversion of sensor readings to yield the spacial-temperature field are possible. One of these procedures which was used to invert theoretical radiometer readings from an assumed atmospheric structure is described in detail. The results of the inversion which was accomplished with the aid of a UNIVAC 1105 computer are included.