The quadrupole ionosphere

The principal features that might exist in the terrestrial paleoionosphere, if the geomagnetic field were to assume a quadrupole form during a polarity reversal are discussed. Complicated phenomena would be expected to occur at magnetic equators and magnetospherically-driven plasma convection might occur at latitudes where the magnetic field is steeply inclined. The influence of magnetic field strength on ionospheric structure is considered in general terms

Long-term changes in thermospheric composition inferred from a spectral analysis of ionospheric F-region data

A study of ionospheric data recorded at Slough/Chilton, UK, from 1935 to 2012, has revealed longterm changes in the relative strength of the annual and semiannual variability in the ionospheric F2 layer critical frequencies. Comparing these results with data from the southern hemisphere station at Stanley in the Falkland Islands between 1945 and 2012 reveals a trend that appears to be anti-correlated with that at Chilton. The behaviour of foF2 is a function of thermospheric composition and so we argue that the observed long-term changes are driven by composition change. The ionospheric trends share some of their larger features with the trend in the variability of the aa geomagnetic index. Changes to the semi-annual/annual ratio in the Slough/Chilton and Stanley data may therefore be attributable to the variability in geomagnetic activity which controls the average latitudinal extent of the auroral ovals and subsequent thermospheric circulation patterns. Changes in ionospheric composition or thermospheric wind patterns are known to influence the height of the F2 layer at a given location. Long-term changes to the height of the F2 layer have been used to infer an ionospheric response to greenhouse warming. We suggest that our observations may influence such measurements and since the results appear to be dependent on geomagnetic longitude, this could explain why the long-term drifts observed in F2 layer height differ between locations

EISCAT velocity patterns for theoretical plasma convection models

Theoretical line-of-sight velocities, as would be observed by the EISCAT radar, are computed for idealized models of plasma convection in the polar ionosphere. The calculations give the velocity as a function of range and Universal Time. For several variants of the Volland and Heelis convection models, how the maxima, minima and reversals of velocity depend on beam azimuth is examined. The analysis is designed to be applied to data from the UK-POLAR experiment, an example of which is shown

Variations of thermospheric composition according to AE-C data and CTIP modelling

Data from the Atmospheric Explorer C satellite, taken at middle and low latitudes in 1975-1978, are used to study latitudinal and month-by-month variations of thermospheric composition. The parameter used is the "compositional <i>Ρ</i>-parameter", related to the neutral atomic oxygen/molecular nitrogen concentration ratio. The midlatitude data show strong winter maxima of the atomic/molecular ratio, which account for the "seasonal anomaly" of the ionospheric F2-layer. When the AE-C data are compared with the empirical MSIS model and the computational CTIP ionosphere-thermosphere model, broadly similar features are found, but the AE-C data give a more molecular thermosphere than do the models, especially CTIP. In particular, CTIP badly overestimates the winter/summer change of composition, more so in the south than in the north. The semiannual variations at the equator and in southern latitudes, shown by CTIP and MSIS, appear more weakly in the AE-C data. Magnetic activity produces a more molecular thermosphere at high latitudes, and at mid-latitudes in summer.<br><br> <b>Key words.</b> Atmospheric composition and structure (thermosphere – composition and chemistry

The whole-atmosphere response to changes in the Earth’s magnetic field from 1900 to 2000: an example of “top-down” vertical coupling

We study the effects of changes in the Earth's magnetic field between 1900 and 2000 on the whole atmosphere (0–500 km altitude), based on simulations with the Whole Atmosphere Community Climate Model eXtension. Magnetic field changes directly affect the temperature and wind in the upper atmosphere (> ~110 km) via Joule heating and the ion drag force. However, we also find significant responses in zonal mean temperature and zonal wind in the Southern Hemisphere (SH) middle- to high-latitude troposphere, stratosphere, and mesosphere of up to ±2 K and ±2 m/s, as well as regionally significant changes in Northern Hemisphere (NH) polar surface temperatures of up to ±1.3 K, in December-January-February. In the SH, changes in gravity wave filtering in the thermosphere induce a change in the residual circulation that extends down into the upper mesosphere, where further changes in the mean wind climatology are generated, together with changes in local planetary wave generation and/or amplification and gravity wave filtering. This induces further changes to a residual circulation cell extending down into the troposphere. However, inaccuracies in the simulated SH upper mesospheric wind climatology probably mean that the simulated temperature and wind responses in the SH lower and middle atmosphere are also inaccurate. The NH middle atmosphere response is zonally asymmetric, consisting of a significant change in the positioning and shape of the upper stratospheric polar vortex, which is dynamically consistent with the surface temperature response. However, the downward coupling mechanism in the NH is generally less clea

Directional currents in nocturnal E-region layers

In the mid-latitude E-region, the wind-shear mechanism produces thin ionized layers at levels where the vertical ion velocity is zero. We show that such layers conduct electric current only towards the magnetic equator, and not in the zonal direction. We surmise that this property may influence the electric field distribution in the nocturnal ionosphere, and possibly also the coupling between ion drifts and neutral air winds in the F-region. Detailed case studies of nocturnal layers located near the peak of ion Pedersen conductivity (around 130km) are needed to test this idea.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24070/1/0000322.pd

A Multi-Ion, Flux-Corrected Transport Based Hydrodynamic Model for the Plasmasphere Refilling Problem

The objective of this paper is the application of a newly-developed Flux-Corrected Transport (FCT) based hydrodynamic solution methodology to the plasmasphere refilling problem following a geomagnetic storm. The FCT method is extremely well-suited to the solution of nonlinear partial differential equations with shocks and discontinuities. In this solution methodology, every ion species is modeled as two separate fluids originating from the northern and southern hemispheres. We present refilling results that includes three ion (H+, He+ and O+) species and two neutrals (H and O). We believe that with additional modifications, the model can be adapted to the solution of other ionosphere-magnetosphere coupling problems