Acta Geophysica DOI: 10.2478/s11600-008-0038-6 ________________________________________________ © 2008 Institute of Geophysics, Polish Academy of Sciences Techniques for Characterizing Weak Transients in Cosmic Ray Records, as Measured by Neutron Monitor Networks Thierry DUDOK de WIT 1 , Ashot A. CHILINGARIAN 2 , and Grigori G. KARAPETYAN 2 1 LPCE, CNRS and University of Orléans, Orléans, France e-mail: ddwit@cnrs-orleans.fr (corresponding author) 2 Yerevan Physics Institute, Cosmic Ray Division, Yerevan, Armenia e-mails: chili@crdlx5.yerphi.am, gkarap@crdlx5.yerphi.am Abstract The analysis of weak variations in the energetic particle flux, as de- tected by neutron or muon monitors, can often be considerably improved by analysing data from monitor networks and thereby exploiting the spa- tial coherence of the flux. We present a statistical framework for carrying out such an analysis and discuss its physical interpretation. Two other applications are also presented: filling data gaps and removing trends. This study focuses on the method and its various uses. Key words: galactic cosmic rays, neutron monitor networks, multiva- riate analysis. 1. INTRODUCTION Many studies have investigated the possibility for monitoring and forecast- ing geomagnetic storms and solar energetic particle events from the variabil- ity of the energetic particle flux on ground (Bieber et al. 2000, Kudela et al. 2000, Chilingarian et al. 2003, Mavromichalaki et al. 2006, Chilingarian and Reymers 2007). The diagnostic of such solar and heliospheric events, how- ever, requires the investigation of weak variations in the cosmic ray flux. Turning precursory anisotropies into a proxy for space weather has turned