Comparisons of Spectra of Ulysses Electrons, 20-40 Degrees Heliolatitude

Details Comparisons of Spectra of Ulysses Electrons, 20-40 Degrees Heliolatitude Comparisons of Spectra of Ulysses Electrons, 20-40 Degrees Heliolatitude

May 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agusmsh42b..07t&link_type=abstract

American Geophysical Union, Spring Meeting 2002, abstract #SH42B-07

Other

7514 Energetic Particles (2114), 7522 Helioseismology

Scientific paper

We compare estimates of the power spectrum from three sections of Ulysses data: 20-40 deg. S, (Nov. 1992- Sept 1993, Orbit 1), 40-20 deg. N, (March - Dec, 1996, Orbit 1), and 20-40 deg. S, (Jan.- Dec. 1999, Orbit 2). In all cases multitaper spectrum estimates are computed from logarithms of low-energy ( ~50 - 200 keV) electron fluxes from three independent channels of the HISCALE instrument. In addition, three overlapping data sections with 8 Slepian sequences on each section are used, so that the average spectra used in the comparisons have over 100 degrees-of-freedom each. The spectra from solar minimum in 1996 have the lowest power over a wide range of frequencies. The power spectra estimated from the 1993 data during the declining phase of the solar cycle, when co-rotating interaction regions were ubiquitous, is somewhat higher than that from the 1999 data during the increase to solar maximum. (Both are from 20 to 40 deg. South). As solar activity, as measured by sunspot numbers, was lower, 54.6, in 1993 than in 1993, 93.3, this provides yet another example where the falling edge of a solar cycle is more variable than the rising edge. Many of the peaks in the spectra of the three time series appear as common features in all spectra. Further, the spectra contain peaks at the frequencies reported in TML 95. Detailed comparisons of the frequencies of the peaks in the different spectra suggest that the frequencies may be slightly dependent on solar activity.

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