Stratified Troposphere Research Articles

Statistical Characteristics of Mesoscale Fluctuations of Wind Velocity, Temperature, and Gas Concentrations Obtained from Aircraft Measurements in the Troposphere of the Arctic Region

Abstract The results of airborne measurements and statistical characteristics of mesoscale fluctuations of wind velocity, temperature, and concentrations of gas constituents at different heights of a stably stratified troposphere are presented. The measurements were carried out in September 2022 in the Arctic region of Russia with the aircraft laboratory Tu-134 “Optik.” The obtained spectra and structure functions of the fluctuations are interpreted with the theoretical model of formation of the spectrum of mesoscale wind velocity and temperature fluctuations described in the paper. The presence at high wavenumbers of a steep section in the obtained horizontal wavenumber spectra of the fluctuations of wind velocity and greenhouse gas concentration with a slope close to −3 is discussed. The fluctuation spectra along different slanted tracks of the aircraft crossing the tropospheric layer between altitudes of 1 and 9 km are also obtained and analyzed with the theoretical model.

Studying characteristics of a fine layered structure of the lower troposphere on the basis of acoustic pulse sounding

Results of acoustic sounding of the lower troposphere with the aid of detonation generators of acoustic pulses are given. This sounding method is based on a partial reflection of acoustic pulses with shock fronts from vertical wind-velocity and temperature gradients continuously varying with height in the troposphere and on the penetration of reflected signals into the region of acoustic shadow. Experiments on tropospheric sounding were carried out on the ground of the Barva Innovation Scientific and Technical Center (Talin, Armenia) in September 2015. In these experiments, an antihail acoustic system was first used as a generator of acoustic pulses. Experimental results have been compared with data obtained earlier in similar experiments carried out in the vicinity of Zvenigorod with the use of a special detonation generator of acoustic pulses. Due to the high resolution (in height) of the sounding method, which reaches 1 m in the stably stratified lower troposphere within a height range of 250–600 m, the vertical profiles of layered effective sound speed inhomogeneities with vertical scales from a few to a few tens of meters have been retrieved. The influence of these fluctuations on the form and amplitude of acoustic signals at a long distance from their pulsed source has been studied.

Turbulent Entrainment in the Atmospheric Boundary Layer

AbstractTurbulent entrainment – the process by which turbulence inside of the atmospheric boundary layer entrains air from the free troposphere above it – has been investigated using direct numerical simulations in two configurations, one without a cloud and one with a cloud. With the first configuration, we have learned that the entrainment zone in a convective boundary layer growing into a linearly stratified troposphere is better described in terms of a two‐layer structure, with different characteristic scales associated with each of the two sub‐layers. With the second configuration, we have explained how wind shear across the entrainment zone capping a stratocumulus cloud can render evaporative cooling as important as radiative cooling in driving convective motions. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Slope deformation prior to Zhouqu, China landslide from InSAR time series analysis

A major landslide in Zhouqu, China occurred on August 8, 2010 and caused widespread damage and over 1700 casualties. We study the deformation of the slopes over a time period of about three years prior to the landslide by an enhanced StaMPS-SB technique with 16 ascending ALOS/PALSAR images. In particular, the orbit error and stratified troposphere that were not well dealt with in the original StaMPS-SB method have been satisfactorily corrected by a novel phase ramp correction method. The deformation in four regions of the study area has been retrieved with a maximum of up to 70mm/yr. In the Luojiayu–Sanyanyu valley, the slopes where the 2010 giant landslide occurred have been found to be quite unstable before the event. Deformation exceeding 30mm/yr has been detected in the Suoertou slope, which is a well-known place for an ancient fault zone landslide. Fast movement larger than 40mm/yr is observed in the Xieliupo slope, which poses threats of landslide dam and dammed lake to the Pai-lung River together with another slope deformation detected in the opposite slope. In the Nanshanqiaotou slope, the detected ~30mm/yr deformation can be viewed as the prelude of the large landslide occurred in October 2010. More important, it is found that the slope deformation time series has strong correlation with the precipitation in the area as well as with the devastating Wenchuan earthquake that occurred in May 2008 whose epicenter is about 300km away from Zhouqu.

Correction of Refracted Propagation Effects for Airborne Radar Tracking

This paper concerns the correction of refracted propagation effects for airborne radar tracking. An algorithm based on the Kalman filter (KF) is developed that compensates for range and elevation refraction errors, which were analytically derived using a simplified tropospheric model. In particular, the refraction error model applies to a spherically stratified troposphere and does not include the effects of azimuthal refraction errors, small-scale fluctuations, or ducting. The effectiveness of the proposed tracking algorithm is assessed in the presence of tropospheric parameter mismatch and measurement noise. Both theoretical and numerical results are described for a medium range scenario, and a quasi-ellipsoidal racetrack is chosen for the air platform that carries the radar.

Horizontal and oblique spectra of temperature fluctuations in a stably stratified troposphere

The first experimental studies of the spatial oblique and vertical spectra of temperature fluctuations in a stably stratified troposphere at heights of 2 to 8 km were conducted. The measurements were taken over northern European Russia. The spectra cover the wave number range from 5 10−4 to 3 10−2 rad/m. The estimates obtained for the spectral density are analyzed on the basis of a model developed previously for the three-dimensional (3D) spectrum of temperature fluctuations generated by a statistical ensemble of internal waves. This model made it possible to consider both oblique and horizontal spectra from a unified point of view and to use a unified set of parameters on the basis of the 3D spectrum concept. The quantitative estimates obtained for the parameters of the 3D spectrum have shown that large-scale temperature inhomogeneities with a vertical size of more than a hundred meters are strongly extended along the land surface. They have approximately the same form; their horizontal sizes are at least 20 times greater than their vertical sizes. The anisotropy of temperature inhomogeneities decreases with a decrease in their vertical sizes and reaches 1.5–2 for vertical sizes of 10–20 m or smaller.

Refractivity structure constant and length scales from mm-wave propagation in the stably stratified troposphere

The refractivity structure constant C n 2 and length scales of turbulence are measured at mm-wavelengths with line-of-sight propagation experiments at an average height of 200 m above ground at Bern (Switzerland) and El Leoncito (Argentina) in the stably stratified troposphere. C n 2 at mm-wavelengths is of raised importance for scientific and commercial applications, as this frequency band has become easier accessible in recent years. At Bern, C n 2 varied predominantly between 10 - 14 and 10 - 13 m - 2 / 3 , whereas at the astronomical site of El Leoncito, with its desert-like conditions, it was approximately ten times less. Simultaneously measured potential refractivity gradients M and outer scale lengths of turbulence (proportional to integral scale) L 0 v and L 0 h , in vertical and horizontal directions respectively, has offered opportunities for the determination of the Ozmidov scale L R (proportional to Tatarskii's L 0 ) as well as the overturning turbulent length scale L t . This has been hardly done in the past, and probably never so far with spatially averaged length scales using remote measurement techniques. For weak stratification we found that L R is approximately one order of magnitude larger than L t and the latter is again one order of magnitude larger than L 0 v . During strongly stratified situations L R ≈ L t ≳ L 0 v which is in good agreement with other results from in situ and laboratory measurements. Finally, we empirically found that the turbulence anisotropy L 0 h / L 0 v is roughly proportional to the Richardson number with a proportionality factor of 30.

Inclined acoustic sounding of the atmospheric boundary layer

The method of inclined acoustic sounding of the atmospheric boundary layer has been proposed and realized experimentally. The method is based on the phenomena of the waveducted sound propagation along ground surface under the presence of the positive wind shear. In the experiment the wind velocity profiles and their large-scale time fluctuations were continuously controlled with the SODAR up to the height of 300 m and with the anemometers placed at the mast of 56 m height. The fluctuations of the acoustic pulse travel time with the periods in the range of 3–30 min were measured between the special pulse generator and the three receivers placed on the ground surface 2.5 km apart from each other, forming a horizontal triangle antenna. The obtained cross coherence and phase spectra between the pulse travel time and the wind velocity fluctuations show a peak of coherence with the maximum of about 0.8 to 0.9 for the period of 8 min. Such low-frequency wind velocity fluctuations near the ground surface are thought to be caused by the gravity wave modes propagating in the stable stratified troposphere with the periods close to the Brunt–Vaisalla period. The inclined acoustic sounding is proposed to be used for the acoustic tomographic monitoring of the three-dimensional wind field in the atmospheric boundary layer.

Dynamical and radiative response to the massive injection of aerosol from Kuwait oil burning fires

The effects of the injection of large amount of soot comparable to that produced in the burning of oil wells in Kuwait were studied using a 2‐D mesoscale model. During the three day numerical simulation the ground‐atmosphere system appears to be strongly perturbed. A surface cooling is produced in the first two days above and downwind of the sources. The cooling, between −10 C over the desert and −0.5 C over the sea is dependent on the surface characteristics. The temperature decrease at the ground results in a stratified troposphere which inhibits convection and perturbs the normal diurnal variability of the boundary layer while the upper levels are driven by the radiative warming of the aerosol layer. In this region after few hours the simulation produces a warming of 0.8 C reaching a maximum of 6 C is after 60 hours. During the last 2 days of simulation the long wave radiation emitted by the low altitude atmospheric layers contribute to mitigate the surface cooling. A detailed discussion of the radiative and the dynamical interactions is given and it is shown that beside the specific interest in the short term effects these results may be useful to parameterize the smoke source for a GCM simulation.

Use of atmospheric emission to estimate refractive errors in a non‐horizontally stratified troposphere

Tropospheric refraction introduces errors into radar and radio communication systems by causing radio waves to travel along a curved path and at a speed which changes with position. Common error correction techniques, such as making estimates of refractive effects from surface refractivity, rely implicitly on the assumption that the troposphere is horizontally stratified. This study demonstrates that such an assumption may be unwarranted especially at elevation angles below 10°, and that such reliance can lead to substantial errors. The end product of this research is a system which employs atmospheric emission measurements in addition to surface refractivity to estimate refractive bending and range error. This approach relies on the similar dependence of refraction and emission on atmospheric parameters to account for nonhorizontal stratification. Performance results establish that such a system need employ no more than one radiometer channel to provide potential error reduction of more than 40% over conventional approaches, along with a potentially automated, real‐time operational capability.

Propagation in a Superrefractive Troposphere with a Trapping Surface Layer

The problem of UHF propagation is examined for the case of a spherically stratified troposphere having a profile of refractive modulus with a minimum near the surface of the earth. The methods of R. E. Langer are used to develop an asymptotic solution in terms of Whittaker functions, and eigenvalues are determined numerically with a fast computer. The results, which agree with those obtained earlier by other methods, are used to show how the distant field strength varies as the profile changes from a ‘normal’ case to a highly superrefractive case.

The distortion of electromagnetic pulses undergoing total internal reflection in a stratified troposphere

The treatment of total internal reflection of electromagnetic pulses at the sharp boundary of two homogeneous half-spaces is extended to cover the case of total internal reflection in a stratified nonionized half-space. It is indicated that any inhomogeneity of the reflecting medium perturbs each harmonic spectral component of the reflected pulse in phase and amplitude as both the real and the imaginary parts of the reflection coefficient actually become functions of the frequency.

Diffraction of Radio Waves in a Stratified Troposphere

The problem of diffraction around a smooth, finitely conducting earth is reexamined with the objective of obtaining an exact solution for the case of an exponential profile of refractivity. The methods employed are largely conventional. However, care is taken to avoid approximations of doubtful accuracy, and the solution is illustrated by numerical computations. It is shown that the method of using an effective earth radius and assuming a homogeneous medium is generally sound.

An approach to tropospheric duct propagation

A modal solution for the em propagation in a spherical stratified troposphere is derived, via the Marcuvitz-Schwinger formalism. The approximations due to the small curvature of the earth are illustrated. The representation of the sources via the complete set of modal solutions is presented, as well as the excitation factors, computed for the vertical electric or magnetic dipole. The possible use of digital and analog computers is highlighted. Future plans for the work are the computations of a great deal of digital and analog solutions, and also the study of the influence of the random variability of the tropospheric refraction index. In the Appendix, a preliminary case [f(z)=az] is presented.

On the theory of wave propagation through a concentrically stratified troposphere with a smooth profile. Part II. Expansions of the rigorous solution

On the theory of wave propagation through a concentrically stratified troposphere with a smooth profile. Part II. Expansions of the rigorous solution

On the theory of wave propagation through a concentrically stratified troposphere with a smooth profile

On the theory of wave propagation through a concentrically stratified troposphere with a smooth profile

Propagation of Short Radio Waves in a Normally Stratified Troposphere

Experiments of the past decade give stronger fields well beyond the horizon than are calculated by the 4/3 airless earth approximation. Post-war work on the theory of the WKB approximation for wave propagation in slowly varying inhomogeneous media, and the peculiar results for eigenvalues of the bilinear refractive index proffle offer valuable clues in the search for an oversight in conventional propagation theory. If the absolute value as well as the gradient of the refractive index at the earth's surface be specified, with a refractive index profile which tapers to vacuum at some arbitrarily large height, then allowed modes of the wave equation permit the field to be calculated within, just beyond, and well beyond the horizon, in agreement with many vhf and microwave experiments. Modes thus calculated are supported by ordinary coherent molecular scattering in normal air dielectric layer. At times, superrefraction and macroscopic turbulence are additional mechanisms for propagation deep into the shadow of the earth bulge.