Role of unstable sporadic‐E layers in the generation of midlatitude spread F

Abstract

[1] There is growing experimental evidence to suggest that mesoscale spread F is linked to the occurrence of midlatitude coherent backscatter from patchy sporadic-E layers, which are unstable to the gradient-drift and Farley-Buneman plasma instabilities. To validate this suggestion, we have compared E-region backscatter and spread-F ionosonde recordings from about 100 days of joint operation during summer and found a one-to-one relation in the occurrence of both phenomena. Also, midlatitude backscatter studies over the last few years have shown the existence of enhanced electric fields inside patchy sporadic E. These are believed to be polarization fields set up locally by neutral winds that transport the plasma patches horizontally, and by the relatively large Hall-to-Pedersen conductivity ratios at E-region altitudes. Moreover, midlatitude echoes were found to be associated with mostly westward drifting sporadic-E patches with typical scale lengths from 10 to more than 100 km and perturbed eastward electric fields from a few to maybe more than 10 to 15 mV/m. We propose that the enhanced polarization fields set up inside unstable sporadic-E patches can easily map up the magnetic field lines to the F region and thus contribute to the formation of midlatitude spread F. This new mechanism for spread-F generation is basically an image process that can account for key observational properties of the phenomenon. These include the rapid plasma upwelling and the abrupt changes in height (uplifts) of the F layer, as well as the scale sizes involved and morphological characteristics.

Long-term study of medium-scale traveling ionospheric disturbances using O I 630 nm all-sky imaging and ionosonde over Brazilian low latitudes

“…The electrodynamical coupling between the nighttime midlatitude ionospheric E s and F region have been invoked as an explanation for the large polarization electric fields observed in the F region and the consequent uplifts of the F layer which causes spread F [Tsunoda and Cosgrove, 2001]. Haldoupis et al [2003] proposed a mechanism for spread F development in the midlatitude ionosphere driven by northward-upward electric fields, which are generated from a meridional polarization field inside an unstable E s layer and maps to the F region via field lines. Cosgrove and Tsunoda [2004] derived a dispersion relation that describes the coupling behavior between E s layer and Perkins instability.…”

A comparative study of GPS ionospheric scintillations and ionogram spread F over Sanya

“…Tsunoda and Cosgrove (2001) suggested that there is a large feedback polarization electric field mapped from the E layer and contributing to the F region irregularities. To validate the linkage between spread F and Es, Haldoupis et al (2003) investi- gated recordings of ionosonde in summer and found a precise corresponding relation between spread F and the patchy, sporadic E layer. They concluded that the enhanced electric field set up in unstable Es could easily map up to F region and trigger gradient drift instability to form mid-latitude irregularities.…”

On the origin of mesoscale TIDs at midlatitudes

“…Each image has been standardized so that north is at the top and east is to the right (after Kelley et al, 2002, reproduced with permission of Elsevier). Haldoupis et al (2003) and Kelley et al (2003) showed experimentally that the E-and F-regions are closely coupled in this process. Theoretical work has lagged far behind experiments.…”