Scale dependence and frontal formation of nighttime medium-scale traveling ionospheric disturbances

Abstract

Scale dependence of nighttime medium-scale traveling ionospheric disturbances (MSTIDs) is studied with the midlatitude ionosphere electrodynamics coupling model by changing initial perturbation scales. It is shown that both sporadic E (Es) layer and Perkins instabilities have the scale dependence that a shorter wavelength mode tends to stop growing within a shorter period, whereas a very long wavelength mode grows so slowly in the E region that it does not effectively seed the Perkins instability in the F region. As a result, the typical wavelength of MSTIDs (100-200 km) can be spontaneously generated without scale-dependent forcing. It is also shown that long frontal structures of MSTIDs can be formed by the Pedersen polarization process along the wavefront of MSTIDs by which the wavefront is forced to be uniformly distributed. Key Points Scale dependence and frontal formation of MSTIDs are reproduced A mechanism of the formation of frontal structure of MSTIDs is proposed Scale dependence and frontal formation are consistent with observations ©2013. American Geophysical Union. All Rights Reserved.