Earth Planets Space, Vol. 65 (No. 5), pp. 435-446, 2013
V. A. Pilipenko1,2, H. Kawano3,4, and I. R. Mann5
1Institute of the Earth Physics, Moscow 123995, Russia
2Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya 464-8601, Japan
3Department of Earth and Planetary Sciences, Kyushu University, Fukuoka 812-8581, Japan
4International Center for Space Weather Science and Education, Kyushu University, Fukuoka 812-8581, Japan
5Department of Physics, University of Alberta, Alberta T6G 2E1, Canada
(Received July 4, 2012; Revised January 12, 2013; Accepted February 27, 2013; Online published June 10, 2013)
The hodograph method enables estimating the latitudinal profile of the field-line resonance (FLR) frequency (fR) using the data from two ground magnetometers. This paper provides the full details of this method for the first time, and uses a latitudinal chain of ground magnetometers to examine its validity and usefulness. The hodograph method merges the widely-used amplitude-ratio and cross-phase methods in a sense that the hodograph method uses both the amplitude ratio and the phase difference in a unified manner; further than that, the hodograph method provides fR at any latitude near those of the two ground magnetometers. It is accomplished by (1) making a complex number by using the amplitude ratio (phase difference) as its real (imaginary) part; (2) drawing thus obtained complex numbers (one number for one frequency) in the complex plane to make a hodograph; and (3) fitting to thus obtained hodograph a model satisfying the FLR condition, which is a circle with the assumption that the resonance width is independent of the latitude. To examine the validity and usefulness of the hodograph method, we apply it to a Pc 4 event observed by the Scandinavian BEAR array. We also apply the amplitude-phase gradient method (Pilipenko and Fedorov, 1994; Kawano et al., 2002) to the same event, and compare the results; this is the first article applying the both methods to the same dataset.
Key words: Hodograph method, field-line resonance, ground magnetometers, amplitude-phase gradient method.