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Abstract:
Global geomagnetic models such as the International Geomagnetic Reference Field (IGRF) and the World Magnetic Model (WMM) describe the large spatial scale features of the core field and its time variation. A key requirement for the use of a geomagnetic model for navigation is the determination of its uncertainty - which primarily arises from the sources that are not considered while modeling. Considerable work has been done to determine various models’ errors at ground level by comparing model outputs with independent point and survey observations of the geomagnetic field. However, the error as a function of altitude has not been studied in detail, chiefly because of the sparse observations of magnetic fields available in near-Earth space. In this presentation, we describe a preliminary study of the errors associated with WMM from ground level up to 10,000 Km above sea level. We compare crustal, ionospheric and magnetospheric models as a function of altitudes at low, middle and high geomagnetic latitudes with the WMM predictions. We find that the model errors at the ground are comparable to that obtained from our previous study. The WMM error steadily decreases with altitude until about 370 Km above the Earth’s surface, except for a small increase centered at 100 Km, in the ionospheric E-region. The error is smallest at 370 Km altitude where the sum of the crustal field, magnetospheric field and ionospheric field is lowest. Above 2000 Km, the WMM error exponentially increases until the magnetospheric field strength becomes comparable to the WMM predictions.
