The ionosphere is much more structured and variable than ever predicted. Solar Driven Model Since 2000, we have seen more, very clear evidence that the solar- driven view of the ionosphere does not match reality. Instead, the structure of the ionosphere changes with seasons, and often shows greatest dynamo action over the continents. There must be another driver, and whatever it is, it’s large and controlling. Reality The effects of terrestrial weather are now thought to be the key to understanding this. TIMED-GUVI, England et al. (2009)

Weather and temperature at the lower bound of space show a similar pattern. GSWM Temp Amplitude OTD/LIS-Global Lightning Occurrence 115 km 0-20 km Planetary weather – Powerful tropical weather systems produce large-scale atmospheric waves at the equator that travel upward and into space. 100-300 km Latitude Altitude Planetary wind dynamo – Iono-spheric plasma production is intensified by strong neutral winds, making dense ionospheric bands about the equator. 300 km TIMED-FUV Radiance

ICON’s most important science result It is now clear that we are observing the effects of a planetary weather dynamo in space. Understanding how this “planetary weather dynamo” works and controls our space environment will be ICON’s most important science result 300 km GSWM Temp Amplitude 115 km TIMED-FUV Radiance

ICON fully addresses the fundamental science topic of atmosphere-ionosphere coupling. ICON addresses the coupling of the atmosphere and ionosphere by examining variability on three key temporal scales. These map directly to ICON’s 3 Science Questions. This is why ICON is a low latitude mission. Q1: Orbit to Orbit C/NOFS showed us the critical consequences of ionospheric variability, but what is the source? Q2: Seasonal New data show tropospheric effects up to 1000 km. How does the lower atmosphere modify the ionosphere? Q3: Geomagnetic Events How do electric fields and winds drive extreme changes in the ionosphere during geomagnetic storms?

ICON’s instruments provide the required measurements of both drivers and responses. The Ionospheric Dynamo, driven by the neutral atmosphere, governs the motion of the plasma: We need to measure the drivers: Neutral winds and composition of the atmosphere along with the responses: electric field, plasma motion and plasma density in the ionosphere. All within the context of solar wind and radiative forcing. Drivers and response, cause and effect, must be measured, and these need to be measured at all altitudes in the dynamo region To understand the ionospheric dynamo, the drivers and response must be measured at all relevant altitudes and at the same time.

ICON’s instruments provide the required measurements of both drivers and responses. The Ionospheric Dynamo, driven by the neutral atmosphere, governs the motion of the plasma: We need to measure the drivers: Neutral winds and composition of the neutral thermosphere along with the responses: electric field, plasma motion and plasma density in the ionosphere. The remote sensing instruments each return height profiles of the wind, composition and plasma density throughout the region of the dynamo, while the in-situ instrument makes measurements of the dynamo fields that result. ICON makes the complete set of required measurements of the dynamo drivers and response.

ICON’s elegant observing strategy delivers the required measurements from a single satellite. Time 3 Time 2 We measure the wind VECTOR, not just magnitude. At Time 1 we get one component of the wind. At Time 2 we look along the magnetic field line to get the neutral and ion composition and density. At Time 3 we get another component of the wind and produce a wind vector At all times we have the electric field and plasma motion….a complete set of measurements! The remote measurements are combined in the following manner. At point 2, at the apex of the magnetic field, one characterizes the neutral and ion density profiles with limb views along the magnetic field. Further, one measures the motion of the plasma on the field line that is connected to region in the limb FOV. Wind VECTOR COMPLETE ALTITUDE PROFILES. EQUIPOTENTIAL FIELD LINES. WIND IS A VECTOR! Time 1 To understand the connection of the atmosphere to the ionosphere, ICON makes these observations throughout the entire altitude range of the dynamo.