Modulation of Low‐Altitude Ionospheric Upflow by Linear and Nonlinear Atmospheric Gravity Waves

Abstract

This study examines how thermospheric motions due to gravity waves (GWs) drive ion upflow in the F region, modulating the topside ionosphere in a way that can contribute to ion outflow. We present incoherent scatter radar data from Sondrestrom, from 31 May 2003 which showed upflow/downflow motions, having a downward phase progression, in the field‐aligned velocity, indicating forcing by a thermospheric GW. The GW‐upflow coupling dynamics are investigated through the use of a coupled atmosphere‐ionosphere model to examine potential impacts on topside ionospheric upflow. Specifically, a sequence of simulations with varying wave amplitude is conducted to determine responses to a range of transient forcing reminiscent of the incoherent scatter radar data. Nonlinear wave effects, resulting from increases in amplitude of the modeled GW, are shown to critically impact the ionospheric response. GW breaking deposits energy into smaller scale wave modes, drives periods of large field‐aligned ion velocities, while also modulating ion densities. Complementary momentum transfer increases the mean flow and, through ion‐neutral drag, can increase ion densities above 300 km. Ionospheric collision frequency (cooling) and photoionization effects (heating), both dependent on ionospheric density, modify the electron temperature; these changes conduct quickly up geomagnetic field lines driving ion upflow at altitudes well above initial disturbances. This flow alters ion populations available for high‐altitude acceleration processes that may lead to outflow into the magnetosphere. We have included a representative source of transverse wave heating which, when supplemented by our GWs, illustrates strengthened upward fluxes in the topside ionosphere.

Explaining Solar Flare‐Induced Ionospheric Ion Upflow at Millstone Hill (42.6°N)

“…Burleigh et al. (2018) showed that TID changed the collision frequency of the ionosphere by modulating the electron density, thus leading to the increase or decrease in the electron temperature, and finally driving ion upflow or downflow through the ambipolar electric field. Additionally, solar flares can influence the characteristics of traveling atmospheric disturbances or existing TID (Helmboldt et al., 2015; Qian et al., 2012).…”

“…Traveling ionospheric disturbances (TIDs) are common features of the ionospheric F-region, which are fluctuations of the electron density caused by the excitation of atmospheric gravity waves (Francis, 1974;Hines, 1960). Burleigh et al (2018) showed that TID changed the collision frequency of the ionosphere by modulating the electron density, thus leading to the increase or decrease in the electron temperature, and finally driving ion upflow or downflow through the ambipolar electric field. Additionally, solar flares can influence the characteristics of traveling atmospheric disturbances or existing TID (Helmboldt et al, 2015;Qian et al, 2012).…”

Spatiotemporal Limitations of Data‐Driven Modeling: An ISINGLASS Case Study

“…This multi‐fluid description is coupled to a quasi‐static description of auroral and neutral dynamo electric currents. Well suited to modeling sounding rocket campaigns, data inputs used to drive and constrain GEMINI‐TIA can include perpendicular electric fields, characteristic energy and total energy flux from electron precipitation (Burleigh et al., 2019), neutral winds (Burleigh et al., 2018), and wave heating from broadband extremely low frequency (BBELF) waves (Burleigh & Zettergren, 2017).…”

Transient Ionospheric Upflow Driven by Poleward Moving Auroral forms Observed During the Rocket Experiment for Neutral Upwelling 2 (RENU2) Campaign

“…Inputs for GEMINI‐TIA include topside ionospheric potential, electron precipitation, power spectral density from BBELF waves, and neutral winds (Burleigh et al, ). For this study, GEMINI‐TIA is initialized only with data‐inspired precipitation and DC electric field values to mimic the effects of the observed PMAFs.…”