Busan, South Korea 12-20 July 2017 On possible revision of the defjnition of GLE and a new class of "sub-GLE" events S. Poluianov 1,2 , A. Mishev 2 , I. Usoskin 1,2 , D. Smart 3 , M. Shea 3 1-Sodankylä Gephysical Observatory, University of Oulu, Finland 2-Space Climate Research Unit, University of Oulu, Finland 3-SSSRC, Nashua, NH, USA
Neutron monitor network 53 neutron monitor stations
High-elevation polar sites A high-elevation polar site has: Thin atmosphere above → Low atmospheric cutofg, ● Proximity to the geomagnetic pole → Negligible geomagnetic cutofg. ● Very favorable for detection of SEP . There are only two such sites at the Earth: The top of the glacier in Greenland (3205 m a.s.l.) ● The Antarctic plateau (average elevation about 3000 m a.s.l.) ●
High-elevation polar NMs Unfortunately, there is no high- elevation CR station in Geenland, but there are two such stations in Antarctica: South Pole NM (SOPO/B, 2835 m asl, ● since 1964), Dome C NM (DOMC/B, 3233 m asl, ● since 2015). Both setups have “standard” and “bare” (lead-free) NMs.
Ground-level enhancements GLE #67 on 02 Nov 2003 GLE – Ground-Level ● Enhancement (of the NM count rate over the GCR background) is an event sporadically caused by solar energetic particles (SEP). At the moment, 71 GLE have ● been registered since 1942. (gle.oulu.fj)
The defjnition of GLE The defjnition is very important for SEP studies, and crucial for ones based on the GLE occurrence rate. It has been formulated approximately as this: A GLE event is registred when there are simultaneous statistically signifjcant enhancements of the count rates of at least two difgerently located NMs and a corresponding enhancement in the proton fmux measured by a space-borne instrument(s).
SEP event registered by NMs on 29 October 2015 (gle.oulu.fj) This event formally matches the defjnition of GLE.
Rigidity spectrum of SEP event on 29 October 2015 GLE71 (17 May 2012, approx. plot) subGLE (29 Oct 2015) GCR for 2015 More details in the talk given by A. Mishev [SH024]
Proposal 1. New defjnition of GLE. A GLE event is registred when there are simultaneous statistically signifjcant enhancements of the count rates of at least two difgerently located NMs including at least one NM near the sea level and a corresponding enhancement in the proton fmux measured by a space- borne instrument(s). “Near the sea level” means not higher than one interaction length of the nucleonic component of the CR cascade above the sea level (approx. 900 g/cm 2 or 1000 m). The proposal does not afgect the present list of GLEs, because all 71 “offjcial” events have been registered by at least one of near sea level NMs.
Proposal 2. New class “sub-GLE”. A sub-GLE event is registred when there are simultaneous statistically signifjcant enhancements of the count rates of at least two difgerently located high-elevation NMs and a corresponding enhancement in the proton fmux measured by a space-borne instrument(s), but no statistically signifjcant enhancement in the count rates of NMs near the sea level. On the term: it is already in use (e.g., Atwell et al., ICES2015), although is not clearly defjned.
The proposals briefmy THE PRESENT DEFINITION THE PROPOSING DEFINITIONS (from the 1970s) GLE – registered by at least two GLE – registered by at least two differently located NMs including NMs in different locations at least one near the sea level subGLE – registered by at least two differently located high- elevation NMs, but not by sea-level NMs. The proposal does not afgect the present list of GLEs, because all 71 “offjcial” events have been registered by at least one of near sea level NMs.
Thank you!
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