1987, 7(2): 146-153.
doi: 10.11728/cjss1987.02.146
Abstract:
The propagation of whistler-mode waves in the ionosphere is assumed to be the ducted propagation. In other words, the waves will be presumed as travelling along magnetic field lines. An analytic solution of the whistler dispersion equation is obtained in terms of the electron density models of the ionosphere the transverse gradient of the electron density required for guiding of whistler-mode waves along a magnetic field line, and an empirical formula for the magnetic field lines of 1980's IGRF (n = 8). In this paper, the electron density enhancement factor is defined as Nc/Ng-l (the Nc is the electron density at the centre of duct; the Ng is the background electron density at the latitude that is what the centre of duct lies). Thus, the integral mean value of the enhancement factor required and the path latitude (i.e. the exit point latitude of whistlers) can be analytically determined by a set of observed values: NmF2 and hmF2 of the ionosphere, and D (whistler dispersion). Using the data of D, NmF2 and hmF2 in Hainan Island of China, The above evaluation and come to the following conclusions are made. (1) The integral mean value of the enhancement factor required for ducting of low-latitude whistlers ranges from 7% to 31%. (2) The whistler dispersion Dhas a positive correlation with NmF2; and a negative correlation with hmF2 when the parth latitude φ90≤10.5° (IGRF, n = 8). Conversely, if (φ90>12° (IGRF, n=8) Dhas a positive correlation with hmF2. It is found that 94.5% of the whistlers observed at Sanya (18.24°N, 109.5°E; geomag. lat. 7.04°N; IGRF, n = 8, lat. 9.64°N) of Hainan Island have their path latitudes φ90<10.5°. Therefore, Dshould have a negative correlation with hmF2, which is agreeable to observations.
