The equivalent slab thickness of Mars' ionosphere: Implications for thermospheric temperature. Issue 9 (5th May 2015)

• Record Type: Journal Article
• Authors: Mendillo, M.; Narvaez, C.; Lawler, G.; Kofman, W.; Mouginot, J.; Morgan, D.; Gurnett, D.
• Is Part Of: Geophysical research letters. Volume 42:Issue 9(2015:May)
• Page Start: 3560
• Page End: 3568
• Publication Date: 2015-05-05
• Subjects: Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1002/2015GL063096
• Languages: English
• ISSNs: 0094-8276

Abstract

<abstract abstract-type="main"> <title>Abstract</title> <p>The total electron content (TEC) of a planetary ionosphere is dominated by plasma near and above the height of maximum electron density (<italic>N</italic>_max). The ratio TEC/<italic>N</italic>_max represents the thickness (<italic>τ</italic>) of a TEC slab of uniform density (<italic>N</italic>_max). For a photochemical ionosphere, <italic>τ</italic> relates to the scale height (<italic>H</italic> = kT/mg) of the ionized neutral gas as <italic>τ</italic> ~ 4 × <italic>H</italic>. Derived temperatures refer to ~160 km in thermosphere height—below the asymptotic temperature of the exosphere. The MARSIS instrument on Mars Express has produced data sets of TEC and <italic>N</italic>_max. We used them to form <italic>τ</italic> patterns versus solar zenith angle and solar cycle phase. For daytime (SZA &lt; 90°) conditions, &lt;<italic>τ</italic> &gt; _day ~ 50 km, decreasing rapidly for solar zenith angle (SZA) &gt; 90° to &lt; <italic>τ</italic> &gt; _night ~ 25 km. These correspond to <italic>T</italic>_n values of 250°K and 125°K. Using Mars Global Surveyor data, <italic>τ</italic> patterns show a mild dependence upon the solar EUV flux proxy <italic>F</italic>_10.7, with Δ<italic>T</italic>_n(°K) ~ 0.3° per unit change in <italic>F</italic>_10.7 at Mars.</p> </abstract>