ABSTRACT
The naturally produced geomagnetic eld variations recorded at the earth’s surface or at satellite altitudes is of dual origin: external and internal. The external part originates from the current systems generated in the ionosphere and the distant magnetosphere by the interaction of the solar wind with them. As a result, different types of geomagnetic variations based on the solar intensity having different periodicities are generated. A small portion of the internal part arises due to the eddy currents induced in the conductive layers of the earth by the time-varying external eld diffusing within the earth. In addition to induction by external sources, the major contribution for the internal part, known as the earth’s permanent magnetic eld or dipole eld, originates from the earth’s liquid outer core. This is a slowly varying eld with time. More than 95% of the earth’s magnetic eld is believed to
CONTENTS
Introduction ......................................................................................................... 195 Role of Wavelets and Complex Wavelets in Geomagnetism ........................ 199 Data Processing of Global Magnetic Observatory Data ................................ 199 Wavelet Analysis ................................................................................................. 201
Estimation of Ridge Functions Using Real Wavelets ................................ 202 Complex Wavelet Analysis of GJs ................................................................ 204
Region-Wise Study of GJs .................................................................................. 204 Polar Region .................................................................................................... 204 High-Latitude to Mid-Latitude Region ....................................................... 207 Mid-Latitude to Equatorial Region .............................................................. 209 Southern Hemisphere Region ...................................................................... 209
Discussion ............................................................................................................ 209 Acknowledgments .............................................................................................. 216 References ............................................................................................................. 216
be due to the electric currents generated within the uid outer core. An additional contribution of approximately 2% comes from the earth’s lithosphere and crust. Thus, the science of geomagnetism opens up a plethora of research topics related to terrestrial and extraterrestrial phenomena, and facilitates the studies of external source current systems, secular variations, and electrical conductivity variations within the earth. Figure 7.1 depicts a schematic of the broad classication of geomagnetic eld variations. Figure 7.2 describes the vector representation of the earth’s magnetic eld at any point in the northern hemisphere of the earth.
