Dependence of the charge exchange lifetimes on mirror latitude

Abstract

The dependence of the charge exchange lifetimes on the mirror latitude for ions mirroring off the geomagnetic equator has been re‐computed using the improved hydrogen distribution models which have become available since the earlier calculation by Liemohn. The Chamberlain model, with the input parameters determined by recent satellite observations, has been used to define the spatial distribution of the neutral hydrogen environment through which the ring current ions traverse. The resultant dependence of the charge exchange lifetime, τ, on mirror latitude, λm, is best fit by the approximation τm = τe cos3.5λm, where τe is the charge exchange lifetime for the equatorial particles. This is a significant change from the cos6λm approximation of the previous results.

Inference of the ring current ion composition by means of charge exchange decay

“…By analyzing the measured decay rates of the ions after geomagnetic storms and assuming two or more ions were present and that the decays were exponential in nature we were able to establish three separate lifetimes for the ions. By using the recently revised charge exchange decay lifetimes [Smith and Bewtra, 1978] and the dependence of these lifetimes on the mirror lati-tudes of these particles we determined for three geomagnetic storms the expected charge exchange lifetimes for H +, O +, and He + in the 6nefgy and L value range of the data. In this paper we showed the close agreement of the fitted decay lifetimes from the measurements to the charge exchange decay lifetimes to these three ions and inferred that H +, O +, and He + existed in the storm time ring currents we considered.…”

“…Their results showed that the off-90 ø pitch angle ion fluxes would not charge exchange decay as rapidly as was previously thought. In the review of the recent work associated with the determination of the charge exchange lifetimes for various ions in the• magnetosphere, Smith and Bewtra [1978] provide the updated and corrected lifetime values especially through the ring current region. While this area of space research has been experiencing some recent controversy over the various mechanisms, there is no question but that our understanding of the ring current source and loss mechanisms is progressing in a significant manner.…”

“…In this paper we examine the consequences of making the assumption that, besides protons, ions such as helium and oxygen can represent a major fraction of the storm time ring current particle flux. All of the improvements and new mea-• •,, ß suremerits in determining the charge exchange lifetimes [Smith and Bewtra, 1978] are used. The charge exchange decay mechanism then is used to infer the ion composition in the ring current during the recovery phase of geomagnetic storms.…”

“…Based on the work by Smith and Bewtra (1976) regarding the predicted pitch angle dependence for the charge exchange decay mechanism and on the revised charge exchange lifetime values reviewed by Smith and Bewtra (1977), the Explorer 45 measurements have been re-analyzed. The following rew procedures were employed:…”

“…a better determination of the neutral hydrogen density and charge exchange cross sections. Additional oro g ress was made by J...ith and Bewtra (1976) and independently by Cowl ey (1977) in recomputing the relationship between the lifetimes of equatorially mirroring particles and those particles mirroring off the geomagnetic equator. Their results showed that the otf-90° pitch angle ion fluxes would not charge exchange decay as rapidly as was previously thought.…”