PUBLICATIONS Geophysical Research Letters RESEARCH LETTER The equivalent slab thickness of Mars’ ionosphere: 10.1002/2015GL063096 Implications for thermospheric temperature Key Points: M. Mendillo1, C. Narvaez1, G. Lawler1, W. Kofman2,3, J. Mouginot4, D. Morgan5, and D. Gurnett5 • The ratio TEC/Nmax of a planetary ionosphere represents the 1Center for Space Physics, Boston University, Boston, Massachusetts, USA, 2Institut de Planetologie et d’Astrophysique, slab thickness 3 4 • Slab thickness relates to the neutral Grenoble, France, Space Research Centre of the Polish Academy of Sciences, Warsaw, Poland, Department of Earth 5 atmosphere’s scale height System Science, University of California, Irvine, California, USA, Department of Physics and Astronomy, University of Iowa, and temperature Iowa City, Iowa, USA • Mars’ ionosphere has a nighttime slab thickness of 25 km that doubles in daytime Abstract The total electron content (TEC) of a planetary ionosphere is dominated by plasma near and above the height of maximum electron density (Nmax). The ratio TEC/Nmax represents the thickness (τ) of a TEC slab of uniform density (Nmax). For a photochemical ionosphere, τ relates to the scale height Correspondence to: (H = kT/mg) of the ionized neutral gas as τ ~4×H. Derived temperatures refer to ~160 km in thermosphere C. Narvaez, height—below the asymptotic temperature of the exosphere. The MARSIS instrument on Mars Express has
[email protected] produced data sets of TEC and Nmax. We used them to form τ patterns versus solar zenith angle and solar cycle phase. For daytime (SZA < 90°) conditions, <τ > day ~ 50 km, decreasing rapidly for solar zenith angle Citation: (SZA) > 90° to < τ > ~ 25 km.