Abstract. The morphology of middle latitude ionospheric disturbances in response to geomagnetic storms has been investigated to determine the phenomenological differences between positive and negative ionospheric storm effects, using foF2 observations from azimuthal chain of stations. To better organize the disturbance signatures, two ionospheric indices were introduced to describe the maximum positive (Dfuindex) and negative (Dr-index) deviation observed during an ionospheric storm. A systematic appearance of nighttime positive effects was determined with a 24-hour recurrence.The thermospheric-ionospheric view associated with positive and negative storm effects proposed by Prolss (1993) was extended to encompass our observations. This test clearly demonstrates that such a model can capture most of the basic aspects of ionospheric storms, nevertheless the prominent feature of large nighttime enhancements in the ionization density have yet to be explained.

No abstract

Recently, substoichiometric titanium nitrides (x = 0.45 and 0.61) and carbonitrides (x = y = 0.35) have been synthesized by multiple-energy ion implantation at the surface of pure titanium. Changes in the binary and ternary alloy electronic properties versus defect impurity and vacancy concentrations have been studied by means of core Ti 2p and valence x-ray photoemission spectra (XPS). Moreover, self-consistent tight-binding linear-muffin-tin-orbital calculations with empty spheres in place of the missing nitrogen and/or carbon atoms give, among other information, the total density of occupied states, for comparison with the observed valence XPS value.