Photoelectrons on closed crustal field lines at Mars

A statistical survey of dayside photoelectrons in the Mars upper ionosphere is presented and discussed. A methodology for isolating photoelectron spectra on strong crustal field lines is developed and used to obtain a database of over 280,000 distributions from the Mars Global Surveyor (MGS) electron reflectometer instrument. The relationship of these electron fluxes to various controlling factors is explored and presented. It is found that much of the flux variation can be explained by a linear fit with the EUV solar radiation proxy, adjusted for the Sun‐Mars distance and local solar zenith angle. The state of the lower atmosphere seems to also play a critical role in the photoelectron flux intensity. An interval with a global dust storm shows an increased flux and steepened slope for the relationship with EUV radiation. This implies that the dust storm is altering the density, composition, and/or temperature of the photoelectron source region within the thermosphere and perhaps even the characteristics of the Mars exosphere above the MGS orbit. Other parameters considered had either no influence or a small perturbation compared to this dominant trend.