Continued decline of South Pole neutron monitor counting rate

Abstract

[1] The counting rate of a neutron monitor at South Pole, Antarctica, displays a long-term decline over the 49 year span from March 1964 to the present. The counting rate follows an 11 year cycle with maxima at times of low solar activity. However, after adjusting for the unusually high overall cosmic ray fluxes in 2009, we find that the 2009 peak rate (based on 27 day averages) was approximately 10% lower than the 1965 peak rate. This change is much larger than that recorded by any other neutron monitor. We suggest that the South Pole monitor, owing to its unique position at both high latitude and high altitude may have a hitherto unsuspected sensitivity to secular changes in the magnetic field of the Earth.

Updated Neutron‐Monitor Yield Function: Bridging Between In Situ and Ground‐Based Cosmic Ray Measurements

“…Kiel, Germany) data contains a few apparent jumps and a moderate trend (≈ −0.3%/year); • LMSK NM (Lomnicky Štit, Slovakia) exhibits an apparent trend and a few jumps; • MGDN NM (Magadan, Russia) exhibits some moderate jumps and a trend in data; • MRNY NM (Mirny, Antractica, operated by Russia) has a trend, probably caused by a jump in late 2013, and a small seasonal wave; • NANM NM (Nor-Amberd, Armenia) exhibits a strong trend and several big jumps; • NRLK NM (Norilsk, Russia) data are distorted by apparent big jumps; • NVBK NM (Novisibirsk, Russia) exhibits a clear trend of ≈ −0.4%/year; • SOPO NM (South Pole, operated by USA) depicts a weak trend of ≈ −0.2%/year, which is insignificant on the 6-year interval analyzed here, and disagrees with the long-term drift found for the SOPO NM(Bieber et al, 2013); • TXBY NM (Tixie Bay, Russia) data exhibit a strong seasonal wave and a big jump toward the end of the time interval; • YKTK NM (Yakutsk, Russia) exhibits an apparent trend of ≈ −0.5%/year.…”

“…Most NMs were found stable during the period of 2011–2017, but some specific cases are discussed below: BJNG NM (Beijing, China) exhibits a trend of 0.3%/year; BKSN NM (Baksan, Russia) exhibits significant apparent jumps; BRBG NM (Barentsburg, Norway, operated by Russia) has a clear trend of about 0.4%/year; DRBS NM (Dourbes, Belgium) exhibits significant apparent jumps; ESOI NM (Mt. Hermon, Israel) suffers from severe seasonal cycles caused by snow in the winter seasons; IRK2/IRK3 NMs (Irkutsk, Russia) exhibit significant apparent jumps; JUN1 NM (Jungfraujoch, Switzerland) exhibits a strong ( 10%) seasonal cycle and jumps, related to the snow cover; KIEL NM (Kiel, Germany) data contains a few apparent jumps and a moderate trend ( 0.3%/year); LMSK NM (Lomnicky Štit, Slovakia) exhibits an apparent trend and a few jumps; MGDN NM (Magadan, Russia) exhibits some moderate jumps and a trend in data; MRNY NM (Mirny, Antractica, operated by Russia) has a trend, probably caused by a jump in late 2013, and a small seasonal wave; NANM NM (Nor‐Amberd, Armenia) exhibits a strong trend and several big jumps; NRLK NM (Norilsk, Russia) data are distorted by apparent big jumps; NVBK NM (Novisibirsk, Russia) exhibits a clear trend of 0.4%/year; SOPO NM (South Pole, operated by USA) depicts a weak trend of 0.2%/year, which is insignificant on the 6‐year interval analyzed here, and disagrees with the long‐term drift found for the SOPO NM (Bieber et al, ); TXBY NM (Tixie Bay, Russia) data exhibit a strong seasonal wave and a big jump toward the end of the time interval; YKTK NM (Yakutsk, Russia) exhibits an apparent trend of 0.5%/year. …”

Solar Cosmic Rays

“…The process of SCR penetration into the near-Earth space, in particular, at high geomagnetic latitudes and during geomagnetically active time periods, is still not be modeled accurately enough for certain analyses of ground-based cosmic ray measurements (e.g., Bieber et al 2013b). Thus, recent and further progress in the art of mapping the Earth's magnetosphere is highly appreciated by the cosmic ray community (e.g., Flückiger and Kobel 1990;Cramp et al 1997;Lovell et al 1998;Pchelkin et al 2000;Plainaki et al 2010;Papaioannou et al 2014).…”

Assessment of spectral and angular characteristics of sub-GLE events using the global neutron monitor network

“…The DOMC/B and both South Pole NMs (Bieber et al, 2013), in addition to marginal cut-off rigidity possess lower atmospheric cut-offs compared to a sea level station, because of their high elevation (Tab. B1) .…”