Characteristics of neutral calcium and Ca+ near the mesopause, and their relationship with sporadic ion/electron layers at Arecibo

Abstract

We present the first simultaneous observations of mesospheric neutral calcium, its ion, and electron density over Arecibo obtained on adjacent nights in December 2009. A good correlation is seen between Sporadic-E and ion layers while the neutrals have different characteristics. The measurements reveal that average abundances in electron densities and ions to be at a maximum on 9 December with values ∼4.8 × 109 electrons cm-2 and 3.4 × 107 ions cm-2, while those of the neutrals to be low, of the order of 9.7 × 106 atoms cm-2. The neutral abundance maximizes with values of 1.8 × 107 atoms cm-2 on 10 December, when both ions and electrons display weak layers with abundances almost 3 times lower than on the previous night. A significant correlation between the ions and neutrals indicates that sudden enhancements are caused by advection while a poor correlation is related to chemistry. This study reveals that the ion-neutral coupling is most efficient between 92 and 95 km. Also, the ion-to-neutral ratio is dependent on the strength of the ions or Sporadic-E and can exceed 3.0 during such events. We present evidence of neutralization of the ionized layers occurring on scales of a few tens of minutes for the first time. This agrees fairly well with the lifetimes of Ca+ against neutralization as predicted by recent ion-neutral reactions. Copyright © 2011 by the American Geophysical Union.