A new simulation model of upper atmospheric dynamics is presented that includes self-consistent electrodynamic interactions between the thermosphere and ionosphere. This model calculates the dynamo effects of thermospheric winds, and uses the resultant electric fields and currents in calculating the neutral and plasma dynamics. A realistic geomagnetic field geometry is used. Sample simulations for solar maximum equinox conditions illustrate two previously predicted effects of the feedback. Near the magnetic equator, the afternoon uplift of the ionosphere by an eastward electric field reduces ion drag on the neutral wind, so that relatively strong eastward winds can occur in the evening. In addition, a vertical electric field is generated by the low-latitude wind, which produces east-west plasma drifts in the same direction as the wind, further reducing the ion drag and resulting in stronger zonal winds.

A thermosphere/ionosphere general circulation model with coupled electrodynamics

This empirical analysis of the terrestrial ring current, as measured by Dst, uses conditional probability density in Dst phase space to determine the evolution of the ring current. This analysis method does not assume a dynamic equation, but merely requires that the evolution of Dst depends on Dst and the solar wind. Our simple model, with seven nontrivial parameters, describes the dynamics of 30 years of hourly Dst with solar wind data provided by the OMNI database. The solar wind coupling is assumed to be determined by VBs. We arrive at a dynamic equation nearly identical to the Burton equation (Burton et al., 1975) with a slight correction. The method is restricted to Dst > −150 nT owing to the rarity of larger excursions. We show that the ring current decay lifetime varies with VBs but not with Dst, and we relate this variation to the position of convection boundaries in the magnetosphere. Convection boundaries closer to the Earth result in shorter charge exchange decay times owing to the higher neutral density near the Earth. The decay time in hours varies as τ = 2.40 exp [9.74/(4.69+VBs)] with VBs in millivolts per meter. We also show that the energy injection function as derived by Burton et al. is essentially correct. The injection Q is zero for VBs Ec. We derive the correction for magnetopause contamination: Dst* = Dst −7.26P1/2 + 11 nT, where P is solar wind dynamic pressure in nanopascals. Finally, we apply the model to a moderate storm and to an intense storm. We demonstrate that, in spite of the fact that spacecraft observe compositional changes in the ring current at intense Dst, the dynamics of the two storms are not obviously different in the context of our model. We demonstrate that the generally observed dependence of the decay parameter on Dst is actually an alias of the coincidence of intense Dst and intense VBs.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/1998JA000437

An empirical phase space analysis of ring current dynamics: Solar wind control of injection and decay

In this paper we review the theory of acoustic-gravity waves, the interaction of such waves with the ionosphere, the experimental support for the existence of such waves in the upper atmosphere, and the role played by acoustic-gravity waves in thermospheric dynamics. After a thorough discussion on the properties of acoustic-gravity waves in an ideal isothermal atmosphere, the effects produced by horizontal winds, sharp boundary discontinuities, and dissipative processes are discussed. The generation of these waves by stationary or moving sources is then treated. It is shown that the atmospheric response to a stationary impulse source can be described by the emission of three waves: acoustic, buoyancy, and gravity. These discussions are then followed by reviewing propagation effects in a realistic atmosphere for both free waves and guided waves. Recent numerical results are given. When acoustic-gravity waves propagate through the ionosphere, interaction between the wave and the ionosphere will take place. The physical processes involved in such an interaction are examined.

Acoustic‐gravity waves in the upper atmosphere

Dayside and nightside merging rates usually differ; first one dominates and then the other to maintain long-term flux balance. The polar cap, defined as the area in the ionosphere penetrated by open field lines, expands when closed field lines open during dayside merging and contracts when open field lines close during tail merging. The patterns of convection, electric field and current for polar cap inflation and deflation differ from those of steady state convection. This report models the flow and electrical parameters of polar cap inflation and deflation. We treat the idealized case of uniform conductivity, a planar ionosphere, and “pure Bz” merging (i.e., no By effect, although we note how the approach used here is readily modified to account for the By effect). For this idealized case, the potential associated with polar cap inflation and deflation is seen to be described by the same equations that govern the two-dimensional hydrodynamic flow into and out of an expanding and contracting cylinder with a gap in its side. The gap corresponds to the breach in the polar cap boundary through which magnetic flux passes as a result of merging. The calculated potential pattern displays the usual two cell convection configuration, but the foci of the two cells are the edges of the flux gaps. Thus the cells are displaced sunward during dayside merging and tailward during tail merging.

Polar cap inflation and deflation

Vertical drift measurements have been made at Jicamarca for more than half a solar cycle. The data from periods of high and low activity are appreciably different. Daytime drift velocities during sunspot minimum are usually larger than during the maximum, while the opposite is true for nighttime periods. The evening reversal occurs earlier during sunspot minimum than during the maximum, but the morning reversal is not altered. The period of eastward electric field (upward drift) is thus shortest during sunspot minimum and local winter. By integrating the drift velocity data with respect to time, one can obtain a measure of the total potential drop between reversal points (near the terminators). This drop is largest at solar maximum. There is also a pronounced seasonal variation, with a minimum in mid-December during both solar minimum and maximum. The general features of the data cannot be explained solely on the basis of tidal winds driving an E region dynamo; polarization fields related to the F region dynamo are of major importance, particularly in helping to explain the enhancement of the daytime upward drift which often occurs shortly before the drift reverses to downward in the evening. In order to account quantitatively for the observed variations, however, numerical models considerably more sophisticated than those presently available are needed.

https://works.bepress.com/bela_fejer/133/download/

Dependence of equatorial F region vertical drifts on season and solar cycle

Magnetospheric electric fields and currents and their influence on large scale thermospheric circulation and composition

In the following five chapters, we deal with electric fields and currents generated in thunderstorms Thunderstorms behave like batteries which are connected with the highly conducting ionosphere and earth via the barely conducting lower and middle atmosphere (Fig 31) The passive electric quasicontinuous current flowing outside the thunderstorm regions down to the earth is part of the global electric circuit In this chapter, we outline some characteristics of the global electric circuit In the following chapters, we discuss the thunderstorm as area of charge separation, lightning events as breakdown electric currents, and sferics as the electromagnetic radiation of the lightning currents

Global Electric Circuit

A three-dimensional model of thermosphere dynamics—I. Heat input and eigenfunctions

The physical behavior of the upper atmosphere deduced from satellite drag data

The radio science investigations planned for Galileo’s 6-year flight to and 2-year orbit of Jupiter use as their instrument the dual-frequency radio system on the spacecraft operating in conjunction with various US and German tracking stations on Earth. The planned radio propagation experiments are based on measurements of absolute and differential propagation time delay, differential phase delay, Doppler shift, signal strength, and polarization. These measurements will be used to study: the atmospheric and ionospheric structure, constituents, and dynamics of Jupiter; the magnetic field of Jupiter; the diameter of Io, its ionospheric structure, and the distribution of plasma in the Io torus; the diameters of the other Galilean satellites, certain properties of their surfaces, and possibly their atmospheres and ionospheres; and the plasma dynamics and magnetic field of the solar corona. The spacecraft system used for these investigations is based on Voyager heritage but with several important additions and modifications that provide linear rather than circular polarization on the S-band downlink signal, the capability to receive X-band uplink signals, and a differential downlink ranging mode. Collaboration between the investigators and the spacecraft communications engineers has resulted in the first highly-stable, dual-frequency, spacecraft radio system suitable for simultaneous measurements of all the parameters normally attributed to radio waves.

Hans Volland

Papers

Magnetospheric electric fields and currents and their influence on large scale thermospheric circulation and composition

Global Electric Circuit

A three-dimensional model of thermosphere dynamics—I. Heat input and eigenfunctions

The physical behavior of the upper atmosphere deduced from satellite drag data

Galileo Radio Science Investigations