This is the lead proposal for project WINDY (waves and instabilities from a neutral dynamo). We propose to study the stability of the postsunset equatorial F region ionosphere and the factors that predispose it to equatorial spread F (ESF), a phenomenon characterized by broadband plasma turbulence which degrades radio and radar signals at low magnetic latitudes. The goal of the investigation is to lay the foundation for a strategy to forecast the disruptive phenomenon. The focus of the investigation will be on the influence of zonal thermospheric winds. It is well established that the neutral wind dynamo in the equatorial F region is imperfectly efficient just after sunset. This implies the existence of significant vertical current. Closure of this current through the lower ionosphere is believed to be the cause of vertical shear in the zonal plasma flow, a feature that is persistently observed in the bottomside. Moreover, recent modeling work suggests that the vertical current contributes significantly to ionospheric instability and also influences the dominant wavelength of the irregularities that emerge. If so, then shear flow should be predictive of ESF occurrence and morphology. Thin scattering layers believed to be driven by zonal neutral winds are also known to emerge in the bottomside where the zonal plasma drifts are retrograde (westward, in opposition to the usual direction of the neutral winds). These layers too should be predictive of ESF if the causality chain implied above holds. We propose to test the chain by evaluating three of its components pertaining to the cause of shear and retrograde flow, the influence of vertical current on ionospheric stability, and the role of the thin scattering layers that often precede ESF. The investigation will be conducted from the Reagan Test Site (RTS) on Kwajalein Atoll in the Marshall Islands in August of 2017. It will involve the launch of one instrumented sounding rocket to measure ionospheric number densities and electric and magnetic fields and another sounding rocket to measure thermospheric winds through the release of chemical trails --- TMA in the MLT region and lithium in the thermosphere. Camera sites would be deployed regionally for trail photography and triangulation. The ALTAIR radar will be used to assess launch conditions and to monitor the evolution of the ESF after the launches. A ground-based Fabry Perot interferometer would also be deployed to monitor the evolution of the winds after the launches and to provide context about day-to-day variability. The investigation will lead to a deeper understanding of a complex common natural phenomenon and should ultimately lead to a means of anticipating ESF and the associated effects on communication, navigation, and imaging systems. The research is relevant to the strategic goals expressed in the NASA Heliophysics 2009-2030 roadmap including RFA F3: Understand the creation and variability of magnetic dynamos and how they drive the dynamics of solar, planetary, and stellar environments RFA H2: Understand changes in the Earth's magnetosphere, ionosphere, and upper atmosphere to enable specification, prediction, and mitigation of their effects Both goals are reflected in the 2013 Decadal Survey for Solar and Space Physics in AIMI goal 4, which asks ''how do neutrals and plasmas interact to produce multiscale structures in the AIM system?'' Both support the Heliophysics Science Objective to ''build the knowledge to forecast space weather throughout the helipsphere.''