Ambiguity in Identification of Polar Cap F-Region Patches: Contrasting Radio and Optical Observation Techniques
Journal of Atmospheric and Solar-Terrestrial Physics
The phenomenon referred to as polar cap F-region patches can be observed by many different techniques, including measurements of the radio wave critical frequency, the 630 nm intensity, the in situ electron density, and radio wave coherent scatter from irregularities on the patches. Consequently, the definition of a patch may be technique-dependent or at least ambiguous. In this study we used a physical model of the ionosphere to study the relationship between ground-based 630 nm intensity and simulated critical frequency measurements of patches. The results show that the 630 nm intensity and NmFm are not well correlated without a knowledge of hmF2, the peak altitude of the F-layer. In the polar cap the variation of hmF2 could well be ±100 km, resulting in variations of a factor of four in 630 nm intensity for a constant NmF2 value. Hence, correlating patches observed in 630 nm with NmF2 requires a detailed knowledge of hmF2. Ionospheric model simulations have been parameterized such that the model predictions of the 630 nm intensity — NmF2 — hmF2 dependencies are available as an aid in interpreting patch measurements. These results also indicate that the search for neutral atmospheric gravity waves via their effect on 630 nm emissions is even more difficult than anticipated previously.
Sojka, J. J., R. W. Schunk, M. D. Bowline, and D. J. Crain, Ambiguity in identification of polar cap F-region patches: Contrasting radio and optical observation techniques, J. Atmos. Sol. Terr. Phys., 59, 249-258, 1997.