107 research outputs found
The clustering of polarity reversals of the geomagnetic field
Often in nature the temporal distribution of inhomogeneous stochastic point
processes can be modeled as a realization of renewal Poisson processes with a
variable rate. Here we investigate one of the classical examples, namely the
temporal distribution of polarity reversals of the geomagnetic field. In spite
of the commonly used underlying hypothesis, we show that this process strongly
departs from a Poisson statistics, the origin of this failure stemming from the
presence of temporal clustering. We find that a Levy statistics is able to
reproduce paleomagnetic data, thus suggesting the presence of long-range
correlations in the underlying dynamo process.Comment: 4 pages, in press on PRL (31 march 2006?
One Solar Cycle of Heliosphere Observations with the Interstellar Boundary Explorer: Energetic Neutral Hydrogen Atoms Observed with IBEX-Lo from 10 eV to 2 keV
The Interstellar Boundary Explorer (IBEX) is a NASA satellite in Earth orbit, dedicated to observing both
interstellar neutral atoms entering the heliosphere and energetic neutral atoms (ENAs) from the interstellar
boundaries from roughly 10 eV to 6 keV. This work presents the averaged maps, energy spectra, and temporal
variability of heliospheric ENA intensities measured with the IBEX-Lo instrument at 1 au at energies between
10 eV and 2 keV, covering one entire solar cycle from 2009 through 2019. These results expand the range in time
and energy for studying the globally distributed ENA flux and the IBEX Ribbon. The observed ENA intensities
exceed model predictions, in particular below 500 eV. Moreover, the ENA intensities between 50–200 eV energy
show an unexpected rise and fall around the year 2015 in most sky regions
A Study of ^3He Spectra and Abundances in Impulsive Solar Energetic Particle Events - Results from Measurements with ACE/SEPICA, ACE/SIS and SOHO/HSTOF
Energy spectra of the He isotopes and the energy dependence of the ^3He/^4He ratio during a number of impulsive solar energetic particle events (SEP) observed between September 1997 and December 1998 are analyzed. Data covering the energy range from 0.1 to 10 MeV/amu were supplied by three instruments with complementary energy ranges: the Solar Energetic Particle Ionic Charge Analyzer (SEPICA) and the Solar Isotope Spectrometer (SIS) on ACE, and the time-of-flight mass spectrometer HSTOF on SOHO. We confirm the trend of a monotonic increase of the 3He abundance with energy up to a maximum in the region of a few MeV/amu found in previous ISEE studies and extend the analysis to events of intermediate 3He enrichment. We briefly discuss the observational data and their relation to existing theoretical work on selection and acceleration mechanisms in impulsive flares
Future Radiation Damage in Space Due to South Atlantic Anomaly
The geographic limits of the South Atlantic Anomaly, as defined by radiation damage, are compared to contours of geomagnetic total field intensity, as defined by the 1995 IGRF, for the present and recent past. The most likely secular variation of the geomagnetic field is estimated and used to extrapolate the geomagnetic field to the year 2100. This indicates that radiation damage to spacecraft and humans in space will likely increase and to cover a much larger geographic area
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