Viscosity in the<i>F</i>region

Dungey, J. W.; Willson, A. J.

doi:10.1029/jz060i004p00521

Cited by 3 publications

(4 citation statements)

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“…If the ionization is rotating at this level, then it must similarly rotate at all higher levels that are linked to it magnetically (cf. Dungey 1955) in accordance with the arguments of the preceding section. Geomagnetic field lines that rise at a latitude of 65", for example, rise to a height of 5-6 earth radii over the equator, and enclose a vast torus of ionization that is believed to corotate with the earth.…”

Section: (B) Rotationsupporting

confidence: 83%

“…Finally, wind shear in the presence of the geomagnetic field can lead to a stratification of ionization, because of the anistropic response of the ions to the collisional forces exerted on them. This was first pointed out by Dungey (1956), and illustrated by him for the case of a vertical shear in the north-south wind (see Fig. 8).…”

mentioning

confidence: 65%

“…This was first pointed out by Dungey (1956), and illustrated by him for the case of a vertical shear in the north-south wind (see Fig. 8).…”

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confidence: 93%

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The upper atmosphere in motion

Hines¹

1963

Quart J Royal Meteoro Soc

256

118

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SUMMARYThe atmosphere above 8 0 h exhibits a wide range of dynamical phenomena. These are largely hydrodynamic in nature, and their sources of energy are likely to lie principally at lower levels. The regions are ionized, however, and hydromagnetically controlled motions also exist. They are generated from above as well as below.The observational evidence is reviewed broadly here, in groupings determined by the physical processes that are thought to be operative, and the corresponding theories are measured against it. Many shortcomings are disclosed and assessed, and profitable avenues for future research are tentatively explored. Several areas are indicated in which the dynamical processes modify other features of the upper atmosphere, but these are not analysed in detail.

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Section: (B) Rotationsupporting

confidence: 83%

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confidence: 65%

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The upper atmosphere in motion

Hines¹

1963

Quart J Royal Meteoro Soc

256

118

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“…Below this curve, the cut-off in the spectrum of turbulence at the small eddy end is controlled by viscosity in the usual way and occurs at the scale L2. Above this curve, the cut-off in the spectrum of turbulence is given by the molecular mean free path l• , as contemplated by I)ungey and Willson [41]. It is seen that, over the majority of the permitted are•, and over practically all of the area in which we are likely to be interested, the cut-off in the spectrum of turbulence is likely to be determined by viscosity in the usual way.…”

Section: The Right-hand Boundary Of the Permitted Area Inmentioning

confidence: 92%

Turbulence in the ionosphere with applications to meteor-trails, radio-star scintillation, auroral radar echoes, and other phenomena

Booker¹

1956

J. Geophys. Res.

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The irregularities in electron‐density responsible for incoherent scattering of radio waves in the ionosphere are discussed on the assumption of isotropic turbulence in the neutral molecules, with allowance made for the effect of the earth's magnetic field on the associated irregularities in the density of the charges particles. The atmospheric model used is based on rocket observations, extrapolated upwards in height where necessary. Tentative formulas are deduced for the large eddies based on a non‐standard application of the Richardson number. For the small eddies, the standard formulas of turbulence‐theory are used. These formulas all depend on a quantity w, which is the rate of supply of turbulence‐energy to the large eddies and also the rate of removal of turbulence‐energy from the small eddies, measured per unit mass of atmosphere. The value of w at the meteoric level (90 km) is found to be around 25 watts/kg by comparison between the theory and meteoric observations (both visual and radio). By the same technique, a more tentative value of 1,000 watts/kg is deduced for the level responsible for scintillation of radio stars, although a lower value is probably appropriate when scintillation is weak. These values of w in the ionosphere are high compared with Brunt's value of 5×10−4 watt/kg for the troposphere. It is shown, however, that these high values of w in the ionosphere are quite possible and even reasonable. It is deduced that the time of onset of irregular fading of meteoric echoes in the VHF band is more likely to be due to roughness of the trail caused by the small eddies than to gross distortion of the trail caused by the large eddies. It follows that, after about a second, VHF radar echoes from a meteor‐trail must be calculated using a theory based on incoherent scattering, thereby questioning the theory of Kaiser and Closs [37] as an explanation of long‐duration meteor‐echoes. It is also shown that radio‐star scintillation cannot be explained in terms of turbulence at a level of 400 km, but that reasonable results can be obtained if the level is reduced to 200–300 km. Among other applications considered is the possibility of radio communication via incoherent scattering in the F region of the atmosphere. The conditions under which such communication should be sought are described in section 11.

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Scott¹

1956

J. Geophys. Res.

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Viscosity in theFregion

Cited by 3 publications

References 3 publications

The upper atmosphere in motion

The upper atmosphere in motion

Turbulence in the ionosphere with applications to meteor-trails, radio-star scintillation, auroral radar echoes, and other phenomena

List of recent publications

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