Abstract

Local Intermittency Measure (LIM) is a development of wavelet analysis particularly suited to the diagnosis of isolated, intermittent events in time series. We construct LIM scalograms of Neutron Monitor (NM) data for an example each of a large GLE and a Forbush decrease. Both kinds of event show distinctive LIM signatures. In the case of the Forbush decrease the method also identifies a second, much smaller event that took place in the same time period. LIM may thus be a useful tool for automated or semi-automated detection of such events in NM data.

Highlights

  • The data provided by the global neutron monitor (NM) network offer a detailed look at many aspects of solar high-energy phenomena and solar-terrestrial interactions

  • We give more details of Local Intermittency Measure (LIM) formalism and what it says about a time series before applying it to Neutron Monitor (NM) data to show that it can be effective at identifying ground level enhancements (GLE) and Forbush decreases (FD)

  • The LIM2 signature of the GLE is seen in a scalogram calculated using data from the Terre Adelie NM

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Summary

Introduction

The data provided by the global neutron monitor (NM) network offer a detailed look at many aspects of solar high-energy phenomena and solar-terrestrial interactions. Semi-regular changes in count rates reflect known periodicities in solar phenomena: the solar rotation rate, the activity cycle. Fourier and wavelet decompositions of the NM count rate time series have been used to extract information about such quasi-periodic behaviour (e.g. Kudela et al 2010). Time series analysis methods focusing on quasi-periodic behaviour may not be the best tools for studying them. We suggest that Local Intermittency Measure (LIM) may be a useful tool for identifying and characterising such events in NM data. We give more details of LIM formalism and what it says about a time series before applying it to NM data to show that it can be effective at identifying GLEs and FDs. Section 4 offers some concluding comments

LIM introduced and applied to NM data
GLE of 6 November 1997
Forbush decreases
Discussion and conclusions

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