Effects of Solar Heating by Aerosols and Trace Gases on the Temperature Structure Constant

Abstract. Turbulence parameters in the tropo-stratosphere are analyzed using high-resolution balloon temperature measurements collected during the MUTSI (MU radar, Temperature sheets and Interferometry) campaign which took place near the Middle and Upper atmosphere (MU) radar (Japan, 35° N, 136° E) in May 2000. Vertical profiles of the specific dissipation rate of turbulent kinetic energy, ε, and turbulent diffusivity, K, are estimated from the Thorpe lengthscale, LT. The last is obtained by using two methods. The first one consists of measuring directly LT by reordering the potential temperature profiles. The second method is based on estimates of the temperature structure constant, CT2. A relationship between LT and CT2 can be found by assuming either adiabatic vertical displacements or a model based on turbulent energy balance consideration. Analysis shows that the adiabatic assumption gives indirect estimates of LT more consistent with direct measurements. We also found that vertical profiles of analyzed turbulence characteristics show substantial intermittency, leading to substantial scatter of the local, median and average values. General trends correspond to a decrease in ε and K from the boundary layer up to altitudes 20–25 km. Layers of increased turbulence are systematically observed in the tropo-stratosphere, which may be produced by instabilities of temperature and wind profiles. These maxima may substantially increase local values of turbulence diffusivity. Keywords. Meteorology and atmospheric dynamics (Turbulence)

Download Full-text

Cliff–Ramp Patterns and Kelvin–Helmholtz Billows in Stably Stratified Shear Flow in the Upper Troposphere: Analysis of Aircraft Measurements

Journal of the Atmospheric Sciences ◽

10.1175/jas3956.1 ◽

2007 ◽

Vol 64 (7) ◽

pp. 2521-2539 ◽

Cited By ~ 17

Author(s):

Donald E. Wroblewski ◽

Owen R. Coté ◽

Jorg M. Hacker ◽

Ron J. Dobosy

Keyword(s):

Potential Temperature ◽

Structure Constant ◽

Small Scale ◽

Temperature Structure ◽

Aircraft Measurements ◽

Electromagnetic Propagation ◽

Upper Troposphere ◽

Aspect Ratios ◽

Scale Turbulence ◽

Hemisphere Winter

Abstract Cliff–ramp patterns (CR) are a common feature of scalar turbulence, characterized by a sharp temperature increase (cliff) followed by a more gradual temperature decrease (ramp). Aircraft measurements obtained from NOAA best aircraft turbulence probes (BAT) were used to characterize and compare CR patterns observed under stably stratified conditions in the upper troposphere, a region for which there are few such studies. Experimental data were analyzed for three locations, one over Wales and two over southern Australia, the latter in correspondence with the Southern Hemisphere winter subtropical jet stream. Comparison of observed CR patterns with published direct numerical simulations (DNS) revealed that they were likely signatures of Kelvin–Helmholtz (KH) billows, with the ramps associated with the well-mixed billows and the cliffs marking the highly stretched braids. Strong correlation between potential temperature and horizontal velocity supported the KH link, though expected correlations with vertical velocity were not observed. The temperature fronts associated with the cliffs were oriented in a direction approximately normal to the mean wind direction. Locally high values of temperature structure constant near these fronts were associated with steep temperature gradients across the fronts; this may be misleading in the context of electromagnetic propagation, suggesting a false positive indication of high levels of small-scale turbulence that would not correspond to scintillation effects. Billow aspect ratios, braid angles, and length scales were estimated from the data and comparisons with published DNS provided a means for assessing the stage of evolution of the KH billows and the initial Richardson number of the layer.

Download Full-text

Re-Visiting Acoustic Sounding to Advance the Measurement of Optical Turbulence

Applied Sciences ◽

10.3390/app11167658 ◽

2021 ◽

Vol 11 (16) ◽

pp. 7658

Author(s):

Steven Fiorino ◽

Santasri Bose-Pillai ◽

Kevin Keefer

Keyword(s):

Large Scale ◽

Velocity Structure ◽

Sonic Anemometer ◽

Structure Constant ◽

Vertical Wind Shear ◽

Index Of Refraction ◽

Image Motion ◽

Index Structure ◽

Temperature Structure ◽

Optical Turbulence

Optical turbulence, as determined by the widely accepted practice of profiling the temperature structure constant, CT2, via the measurement of ambient atmospheric temperature gradients, can be found to differ quite significantly when characterizing such gradients via thermal-couple differential temperature sensors as compared to doing so with acoustic probes such as those commonly used in sonic anemometry. Similar inconsistencies are observed when comparing optical turbulence strength derived via CT2 as compared to those through direct optical or imaging measurements of small fluctuations of the index of refraction of air (i.e., scintillation). These irregularities are especially apparent in stable atmospheric layers and during diurnal quiescent periods. Our research demonstrates that when care is taken to properly remove large-scale index of refraction gradients, the sonic anemometer-derived velocity structure constant, Cv2, coupled with the similarly derived turbulence-driven index of refraction and vertical wind shear gradients, provides a refractive index structure constant, Cn2, that can more closely match the optical turbulence strengths inferred by more direct means such as scintillometers or differential image motion techniques. The research also illustrates the utility and robustness of quantifying Cn2 from CT2 at a point using a single sonic anemometer and establishes a clear set of equations to calculate volumetric Cn2 data using instrumentation that measures wind velocities with more spatial/temporal fidelity than temperature.

Download Full-text

Generation of 4H and 6H Structures During the Hexagonal-Rhombohedral Transformation in Dy2Co17

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100113810 ◽

1975 ◽

Vol 33 ◽

pp. 38-39

Author(s):

C. W. Allen ◽

D. L. Kuruzar

Keyword(s):

Elevated Temperatures ◽

Layer Structure ◽

Transition Element ◽

Temperature Structure ◽

Allotropic Transformation ◽

Layer Plane ◽

Planar Defects ◽

Topologically Close Packed ◽

Transformation Mechanisms ◽

Shear Transformation

The rare earth/transition element intermetallics R2T17 are essentially topologically close packed phases for which layer structure models have already been presented. Many of these compounds are known to undergo allotropic transformation of the type at elevated temperatures. It is not unexpected that shear transformation mechanisms are involved in view of the layering character of the structures. The transformations are evidently quite sluggish, illustrated in furnace cooled Dy2Co17 by the fact that only rarely has the low temperature rhombohedral form been seen. The more usual structures observed so far in furnace cooled alloys include 4H and 6H in Dy2Co17 (Figs. 1 and 2) . In any event it is quite clear that the general microstructure is very complicated as a consequence of the allotropy, illustrated in Fig. 3. Numerous planar defects in the layer plane orientation are evident as are non-layer plane defects inherited from a high temperature structure.

Download Full-text

Direct phase determination in electron crystallography: small organic molecules

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100130468 ◽

1992 ◽

Vol 50 (2) ◽

pp. 1166-1167

Author(s):

Douglas L. Dorset

Keyword(s):

Organic Molecules ◽

Data Sets ◽

Temperature Structure ◽

3D Analysis ◽

Intensity Data ◽

Electron Crystallography ◽

Phase Determination ◽

Measured Intensity ◽

3D Data

The quantitative use of electron diffraction intensity data for the determination of crystal structures represents the pioneering achievement in the electron crystallography of organic molecules, an effort largely begun by B. K. Vainshtein and his co-workers. However, despite numerous representative structure analyses yielding results consistent with X-ray determination, this entire effort was viewed with considerable mistrust by many crystallographers. This was no doubt due to the rather high crystallographic R-factors reported for some structures and, more importantly, the failure to convince many skeptics that the measured intensity data were adequate for ab initio structure determinations.We have recently demonstrated the utility of these data sets for structure analyses by direct phase determination based on the probabilistic estimate of three- and four-phase structure invariant sums. Examples include the structure of diketopiperazine using Vainshtein's 3D data, a similar 3D analysis of the room temperature structure of thiourea, and a zonal determination of the urea structure, the latter also based on data collected by the Moscow group.

Download Full-text