Peculiarities of the geomagnetic field, revealed by gradient magnetic measurements at stratospheric altitudes

The results of balloon gradient magnetic surveys in the stratosphere using a long (6 km) vertical oriented measuring base for studying the magnetic field, which is generated by deep-seated sources, are considered. The errors in the current analytical model of the geomagnetic field were analyzed. The device designed to measure the geomagnetic field vertical gradients on a drifting balloon is described. The data of the balloon gradient magnetic surveys, performed at altitudes about 30 km, are analyzed. A new method for separating magnetic anomalies from the data of surveys along extensive profiles is considered. It was shown that the gradients of the magnetic sources located near the bottom of the Earth’s crust are reliably measured by a measuring base with a length of 6 km. An independent new method for determining the errors of global analytical models of the main Earth’s magnetic field (EMF), which are used to separate magnetic anomalies from data of surveys along extensive routes, was justified. The cause of unsatisfactory results of previous magnetic field convertions from the Earth’s surface upward, which is explained by defects of used ground data, was studied. It was shown that the EMF EMM/720 model unsatisfactorily represents an anomalous EMF at an altitude of 30 km. It has been concluded that balloon gradient magnetic surveys is of prime importance in studying and modeling the anomalous magnetic field structure in near-Earth space. A model of EMF, developed up to 720 spherical harmonics, should be constructed based on satellite and balloon gradient magnetic data.