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The equivalent slab thickness of Mars' ionosphere: Implications for thermospheric temperature
Author(s) -
Mendillo M.,
Narvaez C.,
Lawler G.,
Kofman W.,
Mouginot J.,
Morgan D.,
Gurnett D.
Publication year - 2015
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2015gl063096
Subject(s) - tec , ionosphere , mars exploration program , solar zenith angle , scale height , atmospheric sciences , total electron content , radio occultation , daytime , electron density , zenith , thermosphere , solar minimum , ionospheric sounding , international reference ionosphere , martian , solar cycle , physics , geology , solar wind , geophysics , plasma , geodesy , astrophysics , astrobiology , quantum mechanics
The total electron content (TEC) of a planetary ionosphere is dominated by plasma near and above the height of maximum electron density ( N max ). The ratio TEC/ N max represents the thickness ( τ ) of a TEC slab of uniform density ( N max ). For a photochemical ionosphere, τ relates to the scale height ( H = kT/mg) of the ionized neutral gas as τ ~ 4 × H . 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 N max . 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 (SZA) > 90° to < τ > night ~ 25 km. These correspond to T n values of 250°K and 125°K. Using Mars Global Surveyor data, τ patterns show a mild dependence upon the solar EUV flux proxy F 10.7 , with Δ T n (°K) ~ 0.3° per unit change in F 10.7 at Mars.