Chemistry and Physics Faculty Proceedings, Presentations, Speeches, Lectures


Equatorial F-region neutral winds and shears near sunset measured with chemical release techniques

Event Name/Location

2015 Coupling, Energetics and Dynamics of Atmospheric Regions conference in Seattle, Washington

Event Name

2015 Coupling, Energetics and Dynamics of Atmospheric Regions conference

Event Location

Seattle, Washington

Document Type


Publication Date


Date Range

21-25 June 2015


The period near sunset is a dynamic and critical time for the daily development of the equatorial nighttime ionosphere and the instabilities that occur there. The pre-conditions necessary for the development of Equatorial Spread F (ESF) plasma instabilities are a result of the rapid transition of the ionosphere during these hours. The neutral dynamics of the sunset ionosphere contribute greatly to the generation of currents and electric fields; however, the behavior of the neutrals is experimentally understood primarily through single-altitude measurements or measurements that provide weighted altitude means of the winds as a function of time. Vertically-resolved neutral wind measurements in the F region at sunset are very limited. We present two sets of sounding rocket chemical release measurements, one from a launch in the Marshall Islands on Kwajalein atoll and one from Alcantara, Brazil. Analysis of the chemical tracer motions has yielded vertically-resolved neutral wind profiles that show strong vertical gradients in the zonal wind that are unexpected by classical assumptions about the behavior of the neutral wind at these altitudes at sunset near the geomagnetic equator. In addition, these observations show that the direction of the neutral wind reverses over a period of approximately 20 minutes, indicating that the neutrals may be responding quickly to the rapidly changing solar conditions during sunset.