Evidence for electrodynamic linkages between spread-F, ion rain, the intermediate layer, and sporadic E: results from observations and simulations

Details Evidence for electrodynamic linkages between spread-F, ion rain, the intermediate layer, and sporadic E: results from observations and simulations Evidence for electrodynamic linkages between spread-F, ion rain, the intermediate layer, and sporadic E: results from observations and simulations

Sep 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001jastp..63.1529m&link_type=abstract

Journal of Atmospheric and Solar-Terrestrial Physics, Volume 63, Issue 14, p. 1529-1543.

Physics

11

Scientific paper

High resolution ISR observations of the evening and nighttime E- and F-regions at Arecibo during both ``normal'' low-activity periods and during an active spread-F event reveal apparent electrodynamic links between the low-lying layers, ion-rain, and the spread-F instability process. In particular, during a 22 November 1994 event, streaks of ionization-ion rain [Mathews et al., Geophys. Res. Lett. 24 (1997) 1411]-appear to descend from the highly structured F-region base onto the /100-110km Tidal Ion Layer (TIL) system. The evening intermediate tidal ion layer, if present, is almost totally disrupted while the spread-F event is characterized by deep, almost vertical folds in electron concentration. The amplitudes of these structures are 100% with fold-structures extending from the nominal F-region base to well above the nominal peak of the F-region. Apparent periods range from less than 10min for small-scale structures to about 40min for the largest-scales. We suggest that the E-region structures are a manifestation of polarization electric fields that ``map'' into the E-region and are well in excess of 1mV/m in contrast to low-activity period small-scale fields of order 1mV/m. These E-fields are hypothesized to be generated in the ``field'' of linear (low-activity) and/or non-linear (high-activity spread-F periods) Perkins-like instabilities that are individually of relatively small horizontal-scales but occur over large horizontal distances in the bottom-side of the nighttime F-region. We present numerical simulations of 3-dimensional ion trajectories in tidal wind and electric field structures similar to those implied by these observations. These simulations extend the results of Machuga and Mathews (J. Atmos. Solar-Terres. Phys., 2001, 63(14), 1519-1528, this issue.) (Paper I) and demonstrate the formation of parallel sheets of ionization that form in the tilted plane oriented transverse to the bulk flow of the F-region that sweeps ~1mV/m amplitude E-fields quasi-periodically through a fixed location in the E-region. A fixed pointing radar sees these ionization sheets as ion-rain-like features.

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