Welcome to the Mars Initial Reference Ionosphere Home Page

About MIRI | Access MIRI

Background (2013)

It is time to begin the discussion on how best to formulate a Reference Ionosphere for Mars. Preliminary sponsorship for such an effort is being sought from COSPAR, and hopefully an international group can meet on this topic during the next COSPAR meeting in Moscow in 2014. At the time, a true Mars International Reference Ionosphere (MIRI) effort can commence. As part of the COSPAR meeting in Paris in 2004, a small group met to discuss reference atmospheres and ionospheres in the Solar System. At that time, the consensus was that insufficient data existed for Mars and thus theoretical models of the martian upper atmosphere and ionosphere offered the only practical solution at that time [1]. In the decade since that meeting, a remarkable amount of new observations became available from the Mars Global Surveyor (MGS) and Mars Express (MEX) satellites. The first attempt to create a reference ionosphere model for Mars ---- one called the Mars Initial Reference Ionosphere (MIRI) model---led to a semi-empirical formulation for the maximum electron density (Nmax). The model[2] was based upon the photo-chemical-equilibrium equation that related Nmax to solar irradiance (using the proxy F10.7 radio flux) and solar zenith angle (SZA). It was calibrated using over 100,000 values of Nmax obtained by the MARSIS instrument on the MEX satellite from 2005 to 2012.

Update (2017): MIRI-Mark-2

This website summarizes the first attempt to created an initial version of a reference ionosphere-one we call the Mars Initial Reference Ionosphere (MIRI Mark-1). It is a semi-empirical model that links the photo-chemical-equilibrium equation to observations of maximum electron density (Nmax) obtained from the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) onboard the MEX spacecraft. Over 100,000 values of peak electron density from the years 2005-2019 were used to create parameterizations for a semi-empirical MIRI Mark-1. A full description of the approach taken is available [2]. The model gives a single output parameter: the maximum electron density (Nmax) of the martian ionosphere versus solar zenith angle (SZA).

The new version extends MIRI to the full electron density profile, Ne(h), and its integral, called the total electron content (TEC). An expanded data set from MARSIS was used (July 2005 - May 2015) for better coverage of a full solar cycle. A new analysis method relates Nmax to solar flux* and solar zenith angle, resulting in coverage that extends past SZA = 90o for a single post-sunset estimate of nighttime values. The resultant Nmax value is used to calibrate Ne(h) profiles for every 10-degrees of SZA, with the topside ionosphere coming from MARSIS [3] and the bottomside ionosphere from a theoretical model [4].

Use of MIRI

To obtain a run of MIRI, the user selects a date from an interactive calendar. If a specific solar zenith angle (SZA) is desired, the user inputs that value. If not, MIRI uses its archive of Mars' distances from the Sun and solar radio fluxes (F10.7) spanning the years 1965-2019 to compute Nmax vs. SZAs (between 0o and 90o and a single profile for SZA > 90o) at Mars for that date. Uncertainty levels are given for the model values based on the variability patterns in the data used in its formulation. A graphical output shows the date requested, the distance of Mars from the Sun, its orbital longitude, the "rotated Sun date", and solar radio flux measured at 1 AU that is applied at Mars (together with its contextual 3-month mean). The model can be used for dates in the past (back to 1965) and well as for the future (to 2019). Forecasts involve use of predicted solar flux conditions. Tabulated values are provided.

Give it a try! We welcome comments and suggestions.

*Prior to the MAVEN mission, solar fluxes were only measured from 1 AU. To apply a solar flux measured at Earth to Mars, one has to take into account both radial distance effects (1/d2), as well as the difference in their orbital longitudes. Thus, the hemisphere of the Sun facing Mars on a given day faced Earth on a different day (except for the dates when Mars was in opposition phase). Correcting for this effect is accomplished by determination of the “rotated Sun date”—a correction that can be ±14 days from the date of interest at Mars. MIRI-Mark-2 determines the rotated-Sun-date and specifies it as an output parameter. A daily value of solar radio flux (F10.7) can show a significant difference from it prior day or subsequent day value. There is a sluggishness to the response of the martian ionosphere to such effects, and thus an “effective flux” parameter (Feff) is used in MIRI. This blends the daily value with its three-solar rotation average:

Feff = 1/2 [F10.7(day) + <F10.7>(81-day)]

[1] Approaches to a Mars International Reference Ionosphere, M. Mendillo, P. Withers and the MIRI Team, Paper presented at the 35th COSPAR Meeting, Paris, 22 July 2004.

[2] A New Semi-empirical Model of the Peak Electron Density of the Martian Ionosphere, M. Mendillo, A. Marusiak, P. Withers, D. Morgan and D. Gurnett, Geophysical Research Letters, 40, 1-5, doi:10.1002/2013GL057631, 2013.

[3] The equivalent slab thickness of Mars' ionosphere: Implications for thermospheric temperature, M. Mendillo, C. Narvaez, G. Lawler, W. Kofman, J. Mouginot, D. Morgan, and D. Gurnett, Geophys. Res. Lett., 42, 3560–3568. doi: 10.1002/2015GL063096, 2015.

[4] MAVEN and the total electron content of the Martian ionosphere, M. Mendillo,et al., J. Geophys. Res. Space Physics, 122, 3526–3537, doi:10.1002/2016JA023474, 2017.

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Last Updated 22 August 2017