A Possible Link Between the Occurrence of Metallic Calcium Ions Within the Intermediate Descending Layers at Arecibo and Equatorial Electrodynamics

Abstract:

Metallic calcium ion (Ca⁺) is the only ion that can be observed using ground based resonance lidars. Arecibo offers unique opportunity to make observations of these ions along with Incoherent Scatter Radar (ISR), which gives electron concentrations or total ion density. Such simultaneous observations provide new insights into mesospheric/thermospheric chemistry, E and F-region dynamics, and latitudinal coupling.

The motivation for this study originates from a recent work that reported intriguing observations of metal calcium ions (Ca⁺) above the meteoric ablation zone (> 120 km) over Arecibo obtained on three nights in November 2016. These were coordinated with the Incoherent Scatter Radar (ISR) measurements, which were part of “World Day” experiments. These observations resulted in the first detection of metallic Ca⁺ ions at themospheric altitudes that occurred only during pre-dawn hours, and were associated with strong downward ion drifts. However, this first report does not discuss in details the reasons for the detection of Ca⁺ within the intermediate descending layers that occurred during geomagnetically quiet conditions. A preliminary examination of DMSP satellite and TEC data sets reveal plasma depletions in the equatorial sector on the nights when these events were observed over Arecibo. Jicamarca ISR data showed northward drifts when Ca⁺ was detected in the F-region valley over Arecibo. Strong uplift of the F-region over Jicamarca was also observed on these nights, indicating the presence of large electric fields that are considered as a pre-cursor to Equatorial spread-F and could result in strong equatorial fountain effect or Appleton anomaly. These observations strongly suggest a coupling between equatorial and low latitudes (it is worth mentioning that Arecibo is geographically a low latitude site (~18.35° N) but geomagnetically a mid latitude location (mag. latitude ~ 28° N).

Additionally, evidence of strong coupling between E and F-region over Arecibo is also observed in the lidar/ISR observations on 30^th Nov 2016. In this paper, we plan to discuss the factors responsible for such coupling and will explore the influence of ionospheric conductance, and electric fields/winds in both altitudinal and latitudinal coupling processes.