MAVEN and the total electron content of the Martian ionosphere

Model studies of the ionosphere of Mars under daytime conditions reveal that for solar zenith angles of 0 degrees-40 degrees, the shapes and magnitudes of the electron density profiles N-e(h) change by only small amounts. This suggests that midday observations made by MAVEN instruments along slanted orbit segments can be used to represent vertical profiles. The total electron content (TEC), defined as the height integral of N-e(h), is a measure of the cold plasma reservoir of the Martian ionosphere. During MAVEN's Deep-Dip-#2 campaign of April 2015, observations of total ion density by Neutral Gas and Ion Mass Spectrometer and electron density by Langmuir Probe and Waves from periapse (similar to 130km) to 400 km were used to form <TEC>(topside)-validated by independent diagnostics and models. Orbit-by-orbit changes in topside TEC were then used to assess the magnitudes of plasma escape associated with both large and small changes in the topside slope of N-e(h)-called an "ionopause episode." The TEC changes due to these episodes, generalized to a global change, resulted in an escape flux of similar to 3-6x10(24)ions/s, an escape rate consistent with prior observation by Phobos-2, Mars Express, and MAVEN's own in situ studies.