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.

A case study on occurrence of an unusual structure in the sodium layer over Gadanki, India

“…In any case, with the absence of any ionosonde observations close to the lidar location during these observations, it is difficult to comment further on the occurrence/influence of E S layer over Gadanki region. Sporadic-E layers are related to the neutral enhancements via ion-neutral coupling (Raizada et al 2011(Raizada et al , 2012, any structure-like appearance of billow-like features are usually linked to dynamical instabilities (Sarkhel et al 2012b). In order to address this aspect comprehensively, further investigations involving instrument clusters are needed (Mathews 1996).…”

A new model of meteoric calcium in the mesosphere and lower thermosphere

“…The first run was WACCM-Ca from 1996 to early 2000 (termed the standard run), covering the period when the Ca and Ca + lidar measurements were made at Kühlungsborn, Germany (54.1°N, 11.7°E) (Gerding et al, 2000). The second model run was WACCM-Ca and WACCM-Na from 2004-2014, to obtain a 10-year climatology which also covers the period when lidar measurements were made at Arecibo, Puerto Rico (18°N, 293°E) (Raizada et al, 2011). The third run was a sensitivity experiment, where the rate coefficients k24 and k25 were changed from their experimental 30 values to their ion-molecule capture rate coefficients, calculated using Langevin Theory (Smith, 1980) (see footnote to Table 1).…”

“…The lidar system at the Arecibo Observatory (18 o N) employed for measurements of neutral Ca at 423 nm has been described 15 previously (Raizada et al, 2011;Raizada et al, 2012). Nd:YAG-pumped dye laser output at 701 nm is mixed with the YAG fundamental at 1064 nm to produce 423 nm light by sum frequency.…”

“…the resonance lidar technique, and shown to peak around 90 km (Granier et al, 1985). Since then, a relatively small number of lidar studies of Ca and Ca + (which uniquely among the meteoric metal ions can be observed by ground-based lidar) have been performed (Alpers et al, 1996;Gerding et al, 2000;Granier et al, 1989;Qian and Gardner, 1995;Raizada et al, 2011;Raizada et al, 2012).…”

Role of Tropical Convective Cells in the Observed Middle Atmospheric Gravity Wave Properties from Two Distant Low Latitude Stations

“…The average power at 532 nm is 30 Watts. This instrument is mainly used for resonance measurements of different mesospheric metals (Tepley et al, 2003, Raizada et al, 2004, Raizada et al, 2011. Such observations are obtained by tuning the transmitter wavelength to a specific resonance wavelength of a metal to be studied.…”