Physics
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm..sa52a01h&link_type=abstract
American Geophysical Union, Spring Meeting 2001, abstract #SA52A-01
Physics
2443 Midlatitude Ionosphere, 6934 Ionospheric Propagation (2487)
Scientific paper
The E-F valley, presenting almost constantly and varying significantly, can be described by valley depth D (the minimum density in the valley over the E layer peak density) and valley width Hv (the distance between the E-peak height and the height above the peak but with the E-peak density). It is measurable with incoherent scatter radar power experiments. With ionosondes, however, proper inversion procedures need to be developed to extract reliable valley information from good quality ionograms. This presentation proposes such a new procedure that uses the O- and X-mode virtual heights for plasma frequency slightly higher than foE. We construct a single mathematical model of the electron density profile for both regions: E-F valley and the region slightly above the valley, with the unknown D parameter inherent as a variable. The ratio of the O-wave group height over the X-wave one can be calculated for the frequency slightly higher than foE. This ratio, as a function of D, is found to be less sensitive to the valley model selected. Therefore a unique D parameter can be determined from the lower F region traces of both waves. With this known D, Hv, together with the F-region profile, can be finally obtained by best fitting the F-region echo traces. Hv values are so derived that errors due to deviations of our valley model to the actual ionospheric profile can be largely reduced. Using the above technique, we analyzed digisonde ionograms taken at Wuchang (30.5oN, 114.4oE) for high solar activity years (1990-1991) and low solar activity years (1995-1996), 250 days in total, and we compare our results with IRI95 model. It is found that our valley is relatively deep and wide. D varies steadily by day between 0.92 and 0.99; while Hv shows large scatter over their average which are 5-33km by day and 32-130km by night. Not only seasonal but also solar activity dependences of the both parameters can be clearly seen, and are equally evident in terms of the variation amplitude.
Huang Xing
Zhang Sheng
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