A Theoretical Model Study of F-Region Response to High Latitude Neutral Wind Upwelling Events
Journal of Atmospheric and Solar-Terrestrial Physics
Neutral wind upwelling events are well documented in both the northern and southern high latitude ionosphere. The vertical winds in the F-region frequently exceed 100 m/s, and winds in excess of 200 m/s have been observed. These upwelling events occur in a latitudinal band of 4°–6° width that extends in local time in the midnight-morning sector; this band always lies poleward of the auroral precipitation. Using the time dependent ionospheric model (TDIM), a series of sensitivity simulations are carried out, based on observational constraints provided by the spectacular upwelling event seen at both the Mawson and Davis stations in the Antarctic on 08 June 1997 (Innis et al., 1999). The model simulations indicate that the F-layer density at any given point may either increase or decrease during an upwelling event, depending upon the past history of the plasma flux tube. Because this past history of the F-layer convection is unknown for the specific upwelling events a detailed case study cannot be undertaken. Instead a series of sensitivity simulations based upon a range of possible convection histories will be studied to determine the relative effect of the upwelling. The absolute density is not dependent upon solar EUV production because of winter conditions, but is sensitive to the auroral electron precipitation. The best F-layer indicator of the upwelling is the height of the layer, hmF2. For upwelling events with vertical drifts of 100 m/s hmF2 can be increased by 100 km in 10 min. Upon leaving an upwelling region, the hmF2 almost as rapidly decreases to its normal height. Resulting from this lifting of the O+ layer is the reduction in O+ recombination and 630-nm emission; this latter consequence is observed as a standard feature of the upwelling events. In the topside ionosphere the electron density is responsive to the upwelling. The total electron content (TEC) is not, in general, sensitive to the uplifting events, however, low elevation slant path GPS TEC measurements might well detect the rapid uplifting of the F-layer. The upwelling event observations are insufficient to constrain our understanding of their impact upon the ionosphere. This model study does imply that upwelling events can modify the F-layer height severely. Such layer height modification can have measurable effects on radio frequency ray paths through the ionosphere. To quantify such effects a fuller description of the upwelling events as well as the past history of ionospheric plasma is needed. Experiments with higher time resolution of both the neutral parameters and F-region at multiple locations are necessary to unravel these complex events.
Sojka, J. J., R. W. Schunk, M. David, J. L. Innis, P. A. Greet, and P. L. Dyson, A theoretical model study of F-region response to high latitude neutral wind upwelling events, J. Atmos. Solar-Terr. Phys., 63, 1571-1584, 2001.