Ionogram-based range-time displays for observing relationships between ionosonde satellite traces, spread F and drifting optical plasma depletions

• A new type of range-time display for ionosondes is demonstrated.
• A specific type of range time-event is identified with drifting optical plasma depletions.
• A relation between satellite traces, equatorial spread F and electron density bubbles is shown.
• Ionosonde range time events are used to measure equatorial bubble drift and occurrence.

A form of range-time plots derived from ionograms taken from a standard digital ionosondes, situated at the low latitude sites of Vanimo, Port Moresby and Darwin, exhibit bursts of spread F at the center of descending and ascending off-angle reflectors. This particular type of event has since been identified with the passage of optically imaged ionospheric plasma depletions (bubbles) over a Darwin ionosonde. This paper describes the process for producing this form of range-time display and its relationship to ionospheric height, satellite traces and range spread F as seen on individual ionograms. First hop satellite traces are proposed to be via direct reflection from the steep electron density gradients at the base of bubbles while second hop satellite traces then involve a single additional ground reflection. Measurements of night equatorial drift velocity were made from the range-time displays and found to be in the range 20–220 m/s peaking at approximately 90–100 m/s in good agreement with values derived from drift measurements made by a variety of other types of equipment.