TY - JOUR

T1 - Hodograph method to estimate the latitudinal profile of the field-line resonance frequency using the data from two ground magnetometers

AU - Pilipenko, V. A.

AU - Kawano, H.

AU - Mann, I. R.

N1 - Funding Information:
Acknowledgments. The authors would like to thank the SVEKALAPKO BEAR Working Group, Toivo Korja from the University of Oulu, Finland, and David Milling from the University of Alberta, Canada for the availability of the BEAR data. The research of V.A.P. is partly supported by the Program 22 of Russian Academy of Sciences. This research was also made possible in part by the fellowship to V.A.P. from Nagoya University. The research of H.K. is partly supported by a research program of the International Center for Space Weather Science and Education, Kyushu University. Calculations of the geomagnetic coordinates were made at http://nssdc.gsfc.nasa.gov/space/cgm/cgm.html. A matlab function to realize the Taubin method, CircleFitBy-Taubin.m (written by N. Chernov) was obtained through the “mat-lab central” website http://www.mathworks.co.jp/matlabcentral.

PY - 2013

Y1 - 2013

N2 - 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.

AB - 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.

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U2 - 10.5047/eps.2013.02.007

DO - 10.5047/eps.2013.02.007

M3 - Article

AN - SCOPUS:84881306979

VL - 65

SP - 435

EP - 446

JO - Earth, Planets and Space

JF - Earth, Planets and Space

SN - 1343-8832

IS - 5

ER -