The Ionosphere and Thermosphere GEM 2013 Student Tutorial Ian Cohen UNH Space Science Center

Structure of Ionosphere & Neutral Atmosphere separated by mass uniform composition 2013 GEM Student Tutorial: The Ionosphere & Thermosphere 9/10/2018

Atmospheric Composition F region NOTE: ~108 less ions than neutrals From Kelley [2009] 2013 GEM Student Tutorial: The Ionosphere & Thermosphere 9/10/2018

2013 GEM Student Tutorial: The Ionosphere & Thermosphere Thermospheric Basics Differentiated by height due to gravity (mass) Overall neutral density varies based on temperature Two-cell wind pattern (significant seasonal variation) 2013 GEM Student Tutorial: The Ionosphere & Thermosphere 9/10/2018

Thermospheric Dynamics Dynamics controlled by: UV/EUV heating wave & tidal phenomena propagating upward from mesosphere ion drag interactions with ionosphere magnetospheric convection auroral precipitation 2013 GEM Student Tutorial: The Ionosphere & Thermosphere 9/10/2018

2013 GEM Student Tutorial: The Ionosphere & Thermosphere Ionospheric Basics “region of an atmosphere where significant numbers of free thermal (< 1eV) electrons and ions are present” [Shunck and Nagy, 2009] Predicted in 1902 by Kennelly & Heaviside Discovered by Appleton in 1924 [1947 Nobel Prize] E-region named by Appleton after electric field in radio wave reflected by ionosphere, D & F regions are named off of that, allowing definition of more regions alphabetically… 9/10/2018 2013 GEM Student Tutorial: The Ionosphere & Thermosphere

Ionospheric Structure Separated into regions based on density “topside ionosphere” [> 500 km] F region [~150-500 km] density peaks here (“F peak”) often separated into F1 & F2 regions (molecular ions) E region [~90-150 km] D region [< 90 km] disappears at night because solar radiation isn’t present 2013 GEM Student Tutorial: The Ionosphere & Thermosphere 9/10/2018

2013 GEM Student Tutorial: The Ionosphere & Thermosphere 9/10/2018

Significance of Ionosphere to GEM Overlap region between GEM and CEDAR communities Inclusion of Magnetosphere-Ionosphere (MI) coupling is integral to magnetospheric models Ion outflow (from ionosphere) provides mass-loading in magnetosphere Plays important role in current closure with magnetotail More in tutorial on High Latitude Electrodynamics by Zou 2013 GEM Student Tutorial: The Ionosphere & Thermosphere 9/10/2018

Ionospheric Feedback Instability (IFI) First proposed by Atkinson [1970] Local variation Increased conductivity Decreased EI Maps to EM δE/δx Polarization currents Field-aligned currents (FACs)  aurora = local variation Aurora from Atkinson [1970] 2013 GEM Student Tutorial: The Ionosphere & Thermosphere 9/10/2018

2013 GEM Student Tutorial: The Ionosphere & Thermosphere Small-scale EM waves First in situ measurements of both observational characteristics of IFI in IAR [Cohen et al., 2013] Motivated by MI-coupling model by Streltsov and Lotko [2008] – to be presented at GEM/CEDAR workshop Density enhancement 2013 GEM Student Tutorial: The Ionosphere & Thermosphere 9/10/2018

2013 GEM Student Tutorial: The Ionosphere & Thermosphere Neutral Upwelling Thermal upwelling of neutrals (from thermosphere) can cause satellite drag Observations from CHAMP showed “bumps” in acceleration near cusp region Luhr et al. [2004] 2013 GEM Student Tutorial: The Ionosphere & Thermosphere 9/10/2018

Theories for Neutral Upwelling Combination of ion outflow and electron precipitation cause neutral upwelling (model by Otto et al. [2003]) Direct collisional excitation of neutrals by electron precipitation directly (Clemmons et al. [2008]) Small-scale Joule heating at higher altitudes (model by Zhang et al. [2012]) 2013 GEM Student Tutorial: The Ionosphere & Thermosphere 9/10/2018

2013 GEM Student Tutorial: The Ionosphere & Thermosphere Ion Outflow Loss of ionospheric ions to magnetosphere Electrons in ionosphere are heated and move upwards Movement of electrons drags ions upwards Complex (debated) mechanisms cause high-velocity ions to escape into magnetosphere from Yau et al. [2006] 2013 GEM Student Tutorial: The Ionosphere & Thermosphere 9/10/2018

Useful Reference Texts Kelley, M.C., The Earth’s Ionosphere, 2nd ed., 2009. Schunk, R. and Nagy, A., Ionospheres: Physics, Plasma Physics, and Chemistry, 2nd ed., 2009. Tascione, T., Introduction to the Space Environment, 1988. Jursa, A. S. (ed.), Handbook of Geophysics and the Space Environment, 1985. 2013 GEM Student Tutorial: The Ionosphere & Thermosphere 9/10/2018

Incoherent Scatter Radar 2013 GEM Student Tutorial: The Ionosphere & Thermosphere 9/10/2018