scholarly journals Sodium Layer Heights Over Antarctica

1964 ◽  
Vol 17 (2) ◽  
pp. 257
Author(s):  
GR Cresswell
Keyword(s):  
Experimental Data ◽  
Resonance Scattering ◽  
Scale Height ◽  
Layer Height ◽  
Sodium Layer ◽  
Sodium Atoms

Measurements of the twilight sky luminosity variations in Na D at Saskatoon, Canada, were found by Hunten and Shepherd (1954) to be consistent with a distribution of sodium atoms centred at a height of 85 km with a scale height of 7�5 km above and below the peak, the luminosity being due to resonance scattering of sunlight. By fitting Hunten's (1954) luminosity curve to experimental data obtained in Australia and Antarctica, O'Brien (1960) found a sodium layer height of90�5 km

The bistatic LGS scheme for sodium layer height characterization (based on the Teide Observatory experimental setup)

2008 ◽  
Author(s):  
Julio A. Castro-Almazán ◽  
Jesús J. Fuensalida ◽  
Ángel Alonso ◽  
Sergio Chueca
Keyword(s):  
Experimental Setup ◽  
Layer Height ◽  
Sodium Layer

Experimental Study of Acoustic Wave Propagation through Resonating Devices

1998 ◽  
Vol 5 (1) ◽  
pp. 39-55
Author(s):  
Y.K. Lai ◽  
C.F. Ng
Keyword(s):  
Experimental Data ◽  
Experimental Study ◽  
Function Method ◽  
Transmission Loss ◽  
Stop Band ◽  
Resonance Scattering ◽  
Acoustic Wave Propagation ◽  
Transfer Function Method ◽  
Bandwidth Control ◽  
Filter Effects

The acoustic filter effects of periodic obstructions in a square section of duct are studied experimentally. The two-microphone transfer function method is employed to measure the transmission loss across the periodic elements of different profiles. The experiments aim to measure the Bragg Stop Band and the Resonance Scattering Stop Band and their interaction. The experimental data show that the Bragg effect is spatial dependent. The Resonance Scattering Stop Band is strongly affected by obstacles and demonstrates a possibly useful interaction between the Bragg Stop Band and the Resonance Scattering Stop Band. Results also indicate that for specific situations, the overall Resonance Scattering Stop Band contribution can be dominant and effective, both in terms of magnitude and bandwidth control. The asymmetric placement of the obstructing elements is shown to be nonreversible.

scholarly journals A case study on generation mechanisms of a sporadic sodium layer above Tromsø (69.6° N) during a night of high auroral activity

2015 ◽  
Vol 33 (8) ◽  
pp. 941-953 ◽  
Author(s):  
T. Takahashi ◽  
S. Nozawa ◽  
T. T. Tsuda ◽  
Y. Ogawa ◽  
N. Saito ◽  
...  
Keyword(s):  
Electric Field ◽  
Electron Density ◽  
Sodium Ion ◽  
High Electron ◽  
Sodium Ions ◽  
Sodium Layer ◽  
Sodium Atoms ◽  
Sporadic E ◽  
Lower Temperature ◽  
Generation Mechanisms

Abstract. We have quantitatively evaluated generation mechanisms of a sporadic sodium layer (SSL) based on observational data obtained by multiple instruments at a high-latitude station: Ramfjordmoen, Tromsø, Norway (69.6° N, 19.2° E). The sodium lidar observed an SSL at 21:18 UT on 22 January 2012. The SSL was observed for 18 min, with a maximum sodium density of about 1.9 × 1010 m−3 at 93 km with a 1.1 km thickness. The European Incoherent Scatter (EISCAT) UHF radar observed a sporadic E layer (Es layer) above 90 km from 20:00 to 23:00 UT. After 20:00 UT, the Es layer gradually descended and reached 94 km at 21:18 UT when the SSL appeared at the same altitude. In this event, considering the abundance of sodium ions (10 % or less), the Es layer could provide only about 37 % or less of the sodium atoms to the SSL. We have investigated a temporal development of the normal sodium ion layer with a consideration of chemical reactions and the effect of the (southwestward) electric field using observational values of the neutral temperature, electron density, horizontal neutral wind, and electric field. This calculation has shown that those processes, including contributions of the Es layer, would provide about 88 % of sodium atoms of the SSL. The effects of meteor absorption and auroral particle sputtering appear to be less important. Therefore, we have concluded that the major source of the SSL was sodium ions in a normal sodium ion layer. Two processes – namely the downward transportation of sodium ions from a normal sodium ion layer due to the electric field and the additional supply of sodium ions from the Es layer under relatively high electron density conditions (i.e., in the Es layer) – played a major role in generating the SSL in this event. Furthermore, we have found that the SSL was located in a lower-temperature region and that the temperature inside the SSL did not show any remarkable temperature enhancements.

scholarly journals Eddy diffusion coefficients and their upper limits based on application of the similarity theory

2015 ◽  
Vol 33 (7) ◽  
pp. 857-864 ◽  
Author(s):  
M. N. Vlasov ◽  
M. C. Kelley
Keyword(s):  
Experimental Data ◽  
Energy Dissipation ◽  
Heat Transport ◽  
Diffusion Coefficients ◽  
Similarity Theory ◽  
Lower Thermosphere ◽  
Eddy Diffusion ◽  
Scale Height ◽  
Cooling Rates ◽  
Maximum Value

Abstract. The equation for the diffusion velocity in the mesosphere and the lower thermosphere (MLT) includes the terms for molecular and eddy diffusion. These terms are very similar. For the first time, we show that, by using the similarity theory, the same formula can be obtained for the eddy diffusion coefficient as the commonly used formula derived by Weinstock (1981). The latter was obtained by taking, as a basis, the integral function for diffusion derived by Taylor (1921) and the three-dimensional Kolmogorov kinetic energy spectrum. The exact identity of both formulas means that the eddy diffusion and heat transport coefficients used in the equations, both for diffusion and thermal conductivity, must meet a criterion that restricts the outer eddy scale to being much less than the scale height of the atmosphere. This requirement is the same as the requirement that the free path of molecules must be much smaller than the scale height of the atmosphere. A further result of this criterion is that the eddy diffusion coefficients Ked, inferred from measurements of energy dissipation rates, cannot exceed the maximum value of 3.2 × 106 cm2 s−1 for the maximum value of the energy dissipation rate of 2 W kg−1 measured in the mesosphere and the lower thermosphere (MLT). This means that eddy diffusion coefficients larger than the maximum value correspond to eddies with outer scales so large that it is impossible to use these coefficients in eddy diffusion and eddy heat transport equations. The application of this criterion to the different experimental data shows that some reported eddy diffusion coefficients do not meet this criterion. For example, the large values of these coefficients (1 × 107 cm2 s−1) estimated in the Turbulent Oxygen Mixing Experiment (TOMEX) do not correspond to this criterion. The Ked values inferred at high latitudes by Lübken (1997) meet this criterion for summer and winter polar data, but the Ked values for summer at low latitudes are larger than the Ked maximum value corresponding to the criterion. Analysis of the experimental data on meteor train observations shows that energy dissipation with a small rate of about 0.2 W kg−1 sometimes can induce turbulence with eddy scales very close to the scale height of the atmosphere. Our results also explain the discrepancy between the large cooling rates calculated by Vlasov and Kelley (2014) and the temperatures given by the MSIS-E-90 model because, in these cases, the measured eddy diffusion coefficients used in calculating the cooling rates are larger than the maximum value presented above.

Correlation of Prototype and Model-Scale Wave Wake Characteristics of a Catamaran

2009 ◽  
Vol 46 (01) ◽  
pp. 1-15
Author(s):  
Gregor J. Macfarlane
Keyword(s):  
Experimental Data ◽  
Experimental Investigation ◽  
Water Depth ◽  
Correlation Factor ◽  
Scale Height ◽  
Full Scale ◽  
Scale Model ◽  
Model Scale ◽  
Speed Range ◽  
Scale Data

This paper summarizes an experimental investigation into the correlation of model-scale wave wake measurements against full-scale trial results for a 24-meter long catamaran operating over a range of length Froude numbers. Both full-scale and 1/15th-scale model experiments were conducted over the range of length Froude numbers of approximately 0.3 to 1.0 (full-scale speed range of 6 to 28 knots). The water depth during the experiments was approximately 12 meters, with corresponding depth Froude numbers ranging from subcritical (~0.3), through a transcritical range (~0.8 to 1.1) into low supercritical speeds (up to ~1.3). The results of the investigation confirm that a correlation factor of close to unity be applied when using model-scale experimental data to predict the full-scale height and period of the maximum wave generated by similar catamarans operating within such speed ranges. Consequently, it is expected that the energy of the maximum waves can also be accurately predicted from model-scale data. This paper also provides useful guidance notes for the conduct of full-scale wave wake experiments and highlights some issues regarding the identification of the maximum wave(s) generated when vessels operate at trans and/or supercritical depth Froude numbers.

Mise au point d'une méthode de détermination de la température moyenne de la mésosphère à partir de la mesure de la vitesse de phase des ondes longues sur un trajet grande distance

1993 ◽  
Vol 71 (3-4) ◽  
pp. 106-114
Author(s):  
M. Ayachi
Keyword(s):  
Nitric Oxide ◽  
Experimental Data ◽  
Mean Value ◽  
Scale Height ◽  
Height Distribution ◽  
Long Distance ◽  
Phase Measurements ◽  
Mesospheric Temperature ◽  
D Region ◽  
Solar Angle

The.mechanism of the Lyman α ionization of nitric oxide, which is mainly responsible for the formation of the D region, the lowest part of the ionosphere, is first briefly reviewed. From equations of the photochemical equilibrium, a model of the height distribution of the electron density is proposed as a function of the solar angle Θ and the scale height H, which is a function of the mesospheric temperature T. A method named Geoscanner based upon a set of curves that illustrate the theoretical relations between the phase of a continuous VLF radio wave for a long-distance transmission and the different parameters of the daytime atmosphere is described. This method is applied to analyse experimental data obtained by phase measurements for the 10.2 kHz transmission Trelew (Argentina) – Caen (France), nearly 12 000 km distant. It provides a mean value of the mesospheric temperature that is a characteristic of the studied path and day. The significance of such an integrated temperature, ranging between 190 and 200 K, is discussed.

Microdiffraction Patterns of Small Metallic Particles II; Theoretical Analysis

1982 ◽  
Vol 40 ◽  
pp. 668-669
Author(s):  
A. Gómez ◽  
P. Schabes-Retchkiman ◽  
M. José-Yacamán ◽  
T. Ocaña
Keyword(s):  
Experimental Data ◽  
Electron Diffraction ◽  
Theoretical Analysis ◽  
Size Range ◽  
Dynamical Theory ◽  
Metallic Particles ◽  
Splitting Effect

The splitting effect that is observed in microdiffraction pat-terns of small metallic particles in the size range 50-500 Å can be understood using the dynamical theory of electron diffraction for the case of a crystal containing a finite wedge. For the experimental data we refer to part I of this work in these proceedings.

Evidence for ordered Fe3Ni

1987 ◽  
Vol 45 ◽  
pp. 216-217
Author(s):  
K.B. Reuter ◽  
D.B. Williams ◽  
J.I. Goldstein
Keyword(s):  
Experimental Data ◽  
Martensitic Transformation ◽  
Electron Diffraction ◽  
Room Temperature ◽  
Direct Evidence ◽  
Transformation Product ◽  
Iron Meteorites ◽  
X Ray ◽  
Ni Content ◽  
Temperature Transformation

In the Fe-Ni system, although ordered FeNi and ordered Ni3Fe are experimentally well established, direct evidence for ordered Fe3Ni is unconvincing. Little experimental data for Fe3Ni exists because diffusion is sluggish at temperatures below 400°C and because alloys containing less than 29 wt% Ni undergo a martensitic transformation at room temperature. Fe-Ni phases in iron meteorites were examined in this study because iron meteorites have cooled at slow rates of about 10°C/106 years, allowing phase transformations below 400°C to occur. One low temperature transformation product, called clear taenite 2 (CT2), was of particular interest because it contains less than 30 wtZ Ni and is not martensitic. Because CT2 is only a few microns in size, the structure and Ni content were determined through electron diffraction and x-ray microanalysis. A Philips EM400T operated at 120 kV, equipped with a Tracor Northern 2000 multichannel analyzer, was used.

EELS white line intensities calculated for the 3d and 4d metals

1989 ◽  
Vol 47 ◽  
pp. 388-389
Author(s):  
C. C. Ahn ◽  
D. H. Pearson ◽  
P. Rez ◽  
B. Fultz
Keyword(s):  
Experimental Data ◽  
Line Intensity ◽  
Transition Probabilities ◽  
Initial Increase ◽  
White Line ◽  
Hartree Fock ◽  
Line Intensities ◽  
Integrated Intensity ◽  
X Ray Absorption ◽  
The Continuum

Previous experimental measurements of the total white line intensities from L2,3 energy loss spectra of 3d transition metals reported a linear dependence of the white line intensity on 3d occupancy. These results are inconsistent, however, with behavior inferred from relativistic one electron Dirac-Fock calculations, which show an initial increase followed by a decrease of total white line intensity across the 3d series. This inconsistency with experimental data is especially puzzling in light of work by Thole, et al., which successfully calculates x-ray absorption spectra of the lanthanide M4,5 white lines by employing a less rigorous Hartree-Fock calculation with relativistic corrections based on the work of Cowan. When restricted to transitions allowed by dipole selection rules, the calculated spectra of the lanthanide M4,5 white lines show a decreasing intensity as a function of Z that was consistent with the available experimental data.Here we report the results of Dirac-Fock calculations of the L2,3 white lines of the 3d and 4d elements, and compare the results to the experimental work of Pearson et al. In a previous study, similar calculations helped to account for the non-statistical behavior of L3/L2 ratios of the 3d metals. We assumed that all metals had a single 4s electron. Because these calculations provide absolute transition probabilities, to compare the calculated white line intensities to the experimental data, we normalized the calculated intensities to the intensity of the continuum above the L3 edges. The continuum intensity was obtained by Hartree-Slater calculations, and the normalization factor for the white line intensities was the integrated intensity in an energy window of fixed width and position above the L3 edge of each element.

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