The Intriguing Relation Between Earth's Rotation, Geomagnetic Field, and Climate at Multidecadal Time Scales: Insights from NCEP 20th Century Reanalysis

High correlations between length-of-day (LOD) and climate variables (sea-surface temperature, surface air temperature) have been pointed out in numerous studies (e.g., Lambeck and Cazenave 1976, Dickey et al. 2011, Marcus 2016) in the recent years at both decadal and multidecadal time scales. Moreover, the multidecal LOD variations (that reach several milliseconds) have been shown to have their origin in variations in the core angular momentum and are associated with variations of the Earth magnetic field now modeled back to the middle of the 19th century. Though the climate variations unlikely arise from the core, some authors suggested that they could result from modulation of incoming cosmic ray flux by Earth's magnetic field through cloud formation. In this study, we propose to check correlations between LOD, Earth dipolar magnetic field, and climate variables as taken from a century reanalysis (gridded air temperature and cloud coverage from NCEP 20th Century Reanalysis V2 and V3) in order to (i) confirm results of previous studies about a possible causality between geomagnetism, LOD, and climate, and (ii) locate the hot spots where the link between geomagnetism and cloud formation could be significant.