On wind-driven electrojets at magnetic cusps in the nightside ionosphere of Mars

Mars has a complex magnetic topology where crustal magnetic fields can interact with the solar wind magnetic field to form magnetic cusps. On the nightside, solar wind electron precipitation can produce enhanced ionization at cusps while closed field regions adjacent to cusps can be devoid of significant ionization. Using an electron transport model, we calculate the spatial structure of the nightside ionosphere of Mars using Mars Global Surveyor electron measurements as input. We find that localized regions of enhanced ionospheric density can occur at magnetic cusps adjacent to low density regions. Under this configuration, thermospheric winds can drive ionospheric electrojets. Collisional ions move in the direction of the neutral winds while magnetized electrons move perpendicular to the wind direction. This difference in motion drives currents and can lead to charge accumulation at the edges of regions of enhanced ionization. Polarization fields drive secondary currents which can reinforce the primary currents leading to electrojet formation. We estimate the magnitude of these electrojets and show that their magnetic perturbations can be detectable from both orbiting spacecraft and the surface. The magnitude of the electrojets can vary on diurnal and annual time scales as the strength and direction of the winds vary. These electrojets may lead to localized Joule heating, and closure of these currents may require field-aligned currents which may play a role in high altitude acceleration processes

On the origin of aurorae on Mars

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95268/1/grl20829.pd

Model calculations of electron precipitation induced ionization patches on the nightside of Mars

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94812/1/grl23162.pd

Statistical mechanical analysis of Raman spectroscopic order parameter changes in pressure-induced lipid bilayer phase transitions.

The statistical mechanical cluster theory of Fisher as applied by Kanehisa and Tsong to phospholipid bilayers is modified to describe the effects of hydrostatic pressure on the state of an aqueous dispersion of the phospholipid dipalmitoyl phosphatidylcholine. A high pressure Raman scattering cell has been built to obtain the Raman spectra of aqueous dispersions of phospholipids as a function of the applied hydrostatic pressure from 0 to 100 atmospheres. Predicted thermal and pressure-induced phase transitions are compared with an experimentally obtained Raman order parameter derived from the ratio of two bands in the C-H stretching region of the Raman spectrum of the sample. The parameters of the theory are adjusted to obtain a satisfactory fit of the Raman order parameter versus temperature. The theory is then found to give an excellent prediction of the observed pressure dependence of the Raman order parameter with no changes in the adjustable parameters. The implications of the success of the theoretical fit is discussed. Particularly of interest is the rather high value of the critical temperature, Tc, for lipid bilayers which is predicted by the model