Latitude Survey Investigation of Galactic Cosmic Ray Solar Modulation during 1994-2007

Monday, 15 December 2014
Waraporn Nuntiyakul1,2, Paul Arthur Evenson3, David J Ruffolo1,4, Alejandro Saiz1,4, John W Bieber3, John Clem3, Roger Pyle3, Marcus Duldig5 and John E Humble5, (1)Mahidol University, Bangkok, Thailand, (2)Chandrakasem Rajabhat University, Physics, Bangkok, Thailand, (3)University of Delaware, Newark, DE, United States, (4)Thailand Center of Excellence in Physics, CHE, Ministry of Education, Bangkok, Thailand, (5)University of Tasmania, School of Physical Sciences, Hobart, Australia
The Galactic cosmic ray spectrum exhibits subtle variations over the 22-year solar magnetic cycle in addition to the more dramatic variations over the 11-year sunspot cycle. Neutron monitors are large ground-based detectors that provide accurate measurements of variations in the cosmic ray flux at the top of the atmosphere above the detector. Furthermore, the Earth serves as a magnetic spectrometer, so a neutron monitor in a given location is sensitive to cosmic rays above a geomagnetic cutoff rigidity, which mainly depends on magnetic latitude. A latitude survey with a ship-borne neutron monitor is a useful technique to improve knowledge of the neutron monitor response function and directly determine solar cycle variations in the Galactic cosmic ray spectrum. In this work, we analyze data from the 1994 through 2007 series of latitude surveys conducted by the Bartol Research Institute, the University of Tasmania, and the Australian Antarctic Division. We report on data correction and calibration, show the differential response function, and summarize the results. Supported in part by the Thailand Research Fund via Royal Golden Jubilee fellowship PHD/0136/2552.