Spatial structure of ULF waves: Comparison of magnetometer and Super Dual Auroral Radar Network data

The spatial structure of ultralow frequency (ULF) waves is usually, though not exclusively, estimated from ground-based magnetometer measurements. This paper compares ULF wave spatial structure obtained from coincident ground magnetometer and HF radar measurements and addresses the interpretation of Pc5 azimuthal wave numbers. ULF spatial structures estimated from magnetometer and radar data were quite different for the October 23, 1994, event presented by Ziesolleck et al. [1998]. Azimuthal wave numbers (m) were 3–5 and 12 for the ground and ionosphere, respectively. We reexamine this event and attempt to explain why the spatial structure of the ULF wave in the ionosphere, seen by the Saskatoon Super Dual Auroral Radar Network (SuperDARN) radar, may differ from that deduced from the magnetometer data. The radar data are used to develop a two-dimensional (2-D) model of the spatial distribution of ULF amplitude and phase in the ionosphere. Our modeling shows that the differences between ground and ionosphere measurements may be explained by spatial integration. In general, m numbers deduced from ground measurements should be smaller than the ionospheric values, and they are strongly dependent on the ionospheric ULF amplitude and phase distribution in both latitude and longitude.

[1]  J. Samson,et al.  Pc5 field line resonance frequencies and structure observed by SuperDARN and CANOPUS , 1998 .

[2]  R. A. Greenwald,et al.  ULF high- and low-m field line resonances observed with the Super Dual Auroral Radar Network , 1995 .

[3]  D. D. Wallis,et al.  Magnetometer and radar observations of magnetohydrodynamic cavity modes in the Earth's magnetosphere , 1991 .

[4]  W. Allan,et al.  Transient ULF pulsation decay rates observed by ground based magnetometers: the contribution of spatial integration , 1985 .

[5]  R. A. Greenwald,et al.  Energetics of long period resonant hydromagnetic waves , 1980 .

[6]  W. F. Stuart,et al.  Stare auroral radar observations of Pc 5 geomagnetic pulsations , 1979 .

[7]  J. Olson,et al.  Longitudinal phase variations of Pc 4‐5 micropulsations , 1978 .

[8]  W. Hughes,et al.  The screening of micropulsation signals by the atmosphere and ionosphere , 1976 .

[9]  D. Southwood.  Interpretation of apparent phase motion in micropulsation signals , 1975 .

[10]  W. Hughes.  The effect of the atmosphere and ionosphere on long period magnetospheric micropulsations , 1974 .

[11]  G. Rostoker,et al.  Latitude‐dependent characteristics of long‐period geomagnetic micropulsations , 1971 .

[12]  T. Kitamura,et al.  DETERMINATION OF THE MAGNETOSPHERIC PLASMA DENSITY BY THE USE OF LONG- PERIOD GEOMAGNETIC MICROPULSATIONS. , 1968 .

[13]  Masahisa Sugiura,et al.  OSCILLATION OF THE GEOMAGNETIC FIELD LINES AND ASSOCIATED MAGNETIC PERTURBATIONS AT CONJUGATE POINTS , 1964 .

[14]  T. Obayashi,et al.  Geomagnetic Pulsations and the Earth's Outer Atmosphere , 1958 .

[15]  Ian R. Mann,et al.  Excitation of magnetospheric waveguide modes by magnetosheath flows , 1999 .

[16]  R. Greenwald,et al.  An HF phased‐array radar for studying small‐scale structure in the high‐latitude ionosphere , 1985 .

[17]  K. Glassmeier.  On the influence of ionospheres with non-uniform conductivity distribution on hydromagnetic waves , 1984 .

[18]  A. V. Gul'el'mi.  THEORY OF HYDROMAGNETIC SOUNDING OF PLASMA CONCENTRATION IN THE EXOSPHERE. , 1967 .