Our analysis in Papers I and II (Grechnev et al., 2014, Solar Phys. 289, 289 and 1279) of the 18 November 2003 solar event responsible for the 20 November geomagnetic superstorm has revealed a complex chain of eruptions. In particular, the eruptive f
ilament encountered a topological discontinuity located near the solar disk center at a height of about 100 Mm, bifurcated, and transformed into a large cloud, which did not leave the Sun. Concurrently, an additional CME presumably erupted close to the bifurcation region. The conjectures about the responsibility of this compact CME for the superstorm and its disconnection from the Sun are confirmed in Paper IV (Grechnev et al., Solar Phys., submitted), which concludes about its probable spheromak-like structure. The present paper confirms the presence of a magnetic null point near the bifurcation region and addresses the origin of the magnetic helicity of the interplanetary magnetic clouds and their connection to the Sun. We find that the orientation of a magnetic dipole constituted by dimmed regions with the opposite magnetic polarities away from the parent active region corresponded to the direction of the axial field in the magnetic cloud, while the pre-eruptive filament mismatched it. To combine all of the listed findings, we come to an intrinsically three-dimensional scheme, in which a spheromak-like eruption originates via the interaction of the initially unconnected magnetic fluxes of the eruptive filament and pre-existing ones in the corona. Through a chain of magnetic reconnections their positive mutual helicity was transformed into the self-helicity of the spheromak-like magnetic cloud.
At a horizontally homogeneous isothermal atmosphere approximation, we derive an ordinary six-order differential equation describing linear disturbances with consideration for heat conductivity and viscosity of medium. The wave problem may be solved a
nalytically by representing the solution through generalized hypergeometric functions only at a nonviscous heat-conducting isothermal atmosphere approximation. The analytical solution may be used to qualitatively analyze propagation of acoustic and internal gravity waves (AGWs) in the real atmosphere: a) to classify waves of different frequencies and horizontal scales according to a degree of attenuation and thus according to their ability to appear in observations and in general dynamics of the upper atmosphere; b) to describe variations in amplitude and phase characteristics of disturbances propagating in a height region with dominant dissipation; c) to analyze applicability of quasi-classical wave description to a medium with exponentially growing dissipation. In this paper, we also present wave and quasi-classical methods for deriving waveguide solutions (dissipative ones corresponding to a range of internal gravity waves (IGWs)) with consideration of wave leakage into the upper atmosphere. We propose a qualitative scheme which formally connects the wave leakage solution to the wave solution in the upper dissipative atmosphere. Spatial and frequency characteristics of dissipative disturbances generated by a waveguide leakage effect in the upper atmosphere are demonstrated to agree well with observed characteristics of middle-scale traveling ionospheric disturbances (TIDs).
An algorithm for calculating three gauge-invariant helicities (self-, mutual- and Berger relative helicity) for a magnetic field specified in a rectangular box is described. The algorithm is tested on a well-known force-free model (Low and Lou, 1990) presented in vector-potential form.
Possibilities in principle for satisfactory removal of the 180-azimuthal ambiguity in the transverse field of vector magnetograms and the extrapolation of magnetic fields independently of their position on the solar disk are shown. Revealed here is a
n exact correspondence between the estimated field and the nonpotential loop structure on the limb. The Metropoliss algorithm modified to work in spherical geometry is used to resolve the azimuthal ambiguity. Based on a version of the optimization method from Rudenko and Myshyakov (2009), we use corrected magnetograms as boundary conditions for magnetic field extrapolation in the nonlinear force-free approximation.
