An investigation of transient magnetospheric current sheets as generators of magnetohydrodynamic waves and geomagnetic micropulsations

Abstract

Spectral analysis of micropulsation data from the Dallas Geomagnetic Center and other sites indicates that on geomagnetically quiet days Pc3 and Pc4 micropulsations exhibit an occurrence maximum near local noon an a shift toward longer periods with an increase in the latitude of the observer. Similar analysis of Pi2 pulsations shows an occurrence maximum near local midnight and no latitudinal dependence of oscillation period. Observed Pc3, Pc4, and Pi2 oscillation periods are such, that for quiet geomagnetic conditions, a mid-latitude observer should note a day to night shift toward significantly longer periods. It is shown that analysis based on the transmission of white spectrum MHD waves through a layered ionosphere model does not seem to yield a period shift in the direction actually observed. A new mechanism for the generation and transmission of MHD waves which would produce Pc3, Pc4, and Pi2 micropulsations is proposed. This model explicitly considers a number of recently observed magnetospheric features. An analysis of the model, including the spatial, spectral, and temporal characteristics of expected micropulsations is presented, and measurable such as power spectra, diurnal trends, and latitude dependence are compared with actual data.