The Manifestation of the Madden–Julian Oscillation in Global Deep Convection and in the Schumann Resonance Intensity

Abstract

This study determines the relationship between intraseasonal oscillations observed in two independent measures of global lightning activity: a global mean convective index (a proxy for deep convection) derived from the Goddard Television Infrared Observational Satellite (TIROS) Operational Vertical Sounder (TOVS) Pathfinder infrared cloud observations, and Schumann resonance magnetic intensity recorded at Arrival Heights, Antarctica. The study was initiated when previous results indicated a possible link between intraseasonal variations in Schumann resonances and variability of sunspot numbers on the timescale of the solar rotation period. The authors used seven years (1989?95) of daily records, though the Schumann resonance record had a number of gaps. Results of cross-spectrum and composite analysis show that intraseasonal oscillations in deep convection modulate the global variations in the Schumann resonance intensity. In the Tropics, the intraseasonal wave in deep convection has a wavenumber-1 structure with the region from 120°W to 60°E having one phase, while the other hemisphere has the opposite phase. The Schumann resonances are enhanced when a maximum in deep convection lies in the former hemisphere that comprises the main lightning-producing regions of South America and Africa. Conversely, Schumann resonances are suppressed when the convection propagates eastward to the Indian Ocean and the western Pacific Ocean. This relationship between the deep convection and Schumann resonances was best defined during the Northern Hemisphere springs of 1990 and 1992 but was less evident in 1993 and 1994.