Short wavelength stabilization of the gradient drift instability due to velocity shear

Huba, J. D.; Lee, L. C.

doi:10.1029/gl010i004p00357

Cited by 28 publications

(30 citation statements)

References 13 publications

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“…Boundary value analyses by Guzdar et al (1983), Huba and Lee (1983), and Satyanarayana et al (1984) indicated that shear flow generally stabilizes ionospheric interchange instabilities. However, Fu et al (1986), Ronchi et al (1989), andFlaherty et al (1999) challenged this idea by pointing out the limitations of boundary value analysis, which is incomplete when applied to non-normal models like those describing sheared flows.…”

Section: Discussionmentioning

confidence: 99%

Possible ionospheric preconditioning by shear flow leading to equatorial spread <i>F</i>

2005

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Abstract. Vertical shear in the zonal plasma drift speed is apparent in incoherent and coherent scatter radar observations of the bottomside F region ionosphere made at Jicamarca from about 1600-2200 LT. The relative importance of the factors controlling the shear, which include competition between the E and F region dynamos as well as vertical currents driven in the E and F regions at the dip equator, is presently unknown. Bottom-type scattering layers arise in strata where the neutral and plasma drifts differ widely, and periodic structuring of irregularities within the layers is telltale of intermediate-scale waves in the bottomside. These precursor waves appear to be able to seed ionospheric interchange instabilities and initiate full-blown equatorial spread F . The seed or precursor waves may be generated by a collisional shear instability. However, assessing the viability of shear instability requires measurements of the same parameters needed to understand shear flow quantitatively -thermospheric neutral wind and off-equatorial conductivity profiles.

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Section: Discussionmentioning

confidence: 99%

Possible ionospheric preconditioning by shear flow leading to equatorial spread <i>F</i>

2005

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“…This is done by retaining the spatial dependence in both the parameters and the amplitude of the perturbations and thus establishing a differential eigenvalue problem. The boundary conditions imposed on the solution determine then the allowed values for the complex eigenfrequency co. Doles, 1975;Huba and Lee, 1983;Fu et al, 1986]. They have shown that velocity shear can stabilize the short-wavelength modes of the instability and preferentially excite a longer-wavelength mode than would be expected solely on the basis of local theory.…”

Section: Introductionmentioning

confidence: 99%

A nonlocal linear theory of the gradient drift instability in the equatorial electrojet

Ronchi¹,

Similon²,

Sudan³

1989

J. Geophys. Res.

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The linear global eigenmodes of the gradient drift instability in the daytime equatorial electrojet are investigated. A main feature of the analysis is the inclusion of ion‐neutral and electron‐neutral collision frequencies dependent on altitude. It is found that the basic characteristics and localization of the unstable modes are determined mainly by the profiles of the Pedersen and Hall mobilities, which are derived from the Cowling conductivity model and experimental data. The equilibrium density profile is parabolic, which is fairly representative of the actual measurements. The unstable modes are sensitive not to the details of this profile, but only to the average value of the gradient. The results are obtained from a direct numerical integration of the nonlocal linearized equations. They are further analyzed through an eikonal analysis, which provides both an interpretation of the transient modes observed by Fu et al. (1986) and some additional physical insight into the linear evolution of the global unstable modes. Finally, it is shown that the previously reported short‐wavelength stabilization effect due to velocity shear may be overshadowed by the presence of regions in which the transient modes can develop into absolute instabilities.

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“…However, Huba and Lee (1983) showed that the growth rate predicted by the linear, local dispersion relation actually peaks in the vicinity of kL ≈ 100. Thus, local theory favors the existence of intermediate-scale waves, whereas largescale waves are observed to predominate.…”

Section: Theoretical Backgroundmentioning

confidence: 99%

Imaging radar observations and nonlocal theory of large-scale plasma waves in the equatorial electrojet

Hysell

Chau

2002

Ann. Geophys.

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Abstract. Large-scale (λ ∼ 1 km) waves in the daytime and nighttime equatorial electrojet are studied using coherent scatter radar data from Jicamarca. Images of plasma irregularities within the main beam of the radar are formed using interferometry with multiple baselines. These images are analyzed according to nonlocal gradient drift instability theory and are also compared to nonlinear computer simulations carried out recently by Ronchi et al. (1991) and Hu and Bhattacharjee (1999). In the daytime, the large-scale waves assume a non-steady dynamical equilibrium state characterized by the straining and destruction of the waves by shear and diffusion followed by spontaneous regeneration as predicted by Ronchi et al. (1991). At night, when steep plasma density gradients emerge, slowly propagating large-scale vertically extended waves predominate. Eikonal analysis suggests that these waves are trapped (absolutely unstable) or are nearly trapped (convectively unstable) and are able to tunnel between altitude regions which are locally unstable. Intermediate-scale waves are mainly transient (convectively stable) but can become absolutely unstable in narrow altitude bands determined by the background density profile. These characteristics are mainly consistent with the simulations presented by Hu and Bhattacharjee (1999). A new class of large-scale primary waves is found to occur along bands that sweep westward and downward from high altitudes through the E-region at twilight.

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Short wavelength stabilization of the gradient drift instability due to velocity shear

Cited by 28 publications

References 13 publications

Possible ionospheric preconditioning by shear flow leading to equatorial spread <i>F</i>

Possible ionospheric preconditioning by shear flow leading to equatorial spread <i>F</i>

A nonlocal linear theory of the gradient drift instability in the equatorial electrojet

Imaging radar observations and nonlocal theory of large-scale plasma waves in the equatorial electrojet

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Short wavelength stabilization of the gradient drift instability due to velocity shear

Cited by 28 publications

References 13 publications

Possible ionospheric preconditioning by shear flow leading to equatorial spread &lt;i&gt;F&lt;/i&gt;

Possible ionospheric preconditioning by shear flow leading to equatorial spread &lt;i&gt;F&lt;/i&gt;

A nonlocal linear theory of the gradient drift instability in the equatorial electrojet

Imaging radar observations and nonlocal theory of large-scale plasma waves in the equatorial electrojet

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Possible ionospheric preconditioning by shear flow leading to equatorial spread <i>F</i>

Possible ionospheric preconditioning by shear flow leading to equatorial spread <i>F</i>