Variations of the thermospheric nitric oxide mass mixing ratio as a function of Kp, altitude, and magnetic local time

In this letter, data from the Halogen Occultation Experiment (HALOE) and th e Particle Environment Monitor on the Upper Atmospheric Research Satellite are presented. Five years of data from each instrument have been used to cr eate high-latitude maps of Nitric Oxide (NO) mass mixing ratio and electron impact and bremsstrahlung ionization rates as a function of altitude and K p. We show that enhancements in NO at 100 km are coupled to the auroral ova l and to increases in the local ionization rate, with both the peak in the ionization rate and NO mass mixing ratio occuring in the dawn magnetic loca l time sector between 60 degrees and 70 degrees magnetic latitude. Below th is altitude, the NO is shown to be enhanced at lower latitudes and sunward of the dawn-dusk meridian, most likely due to solar illumination. Above 100 km, the NO density enhancement stays in approximately the same MLT sector, while the peak ionization rate expands in MLT towards the night side. This is attributed to a build up of NO created by particle precipitation during the night, which is corotated towards the dawn region.