The dependence of peak electron density in the ionosphere of Mars on solar irradiance

Girazian, Z.; Withers, Paul

doi:10.1002/grl.50344

Cited by 29 publications

(39 citation statements)

References 34 publications

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“…At Mars the dominating neutral species is CO 2 whose ionizing threshold is 90nm, while the dominant species in the atmosphere of Titan is N 2 , whose photoionization threshold is 79.6nm [ Schunk and Nagy , ]. The observational value of the power law exponent k was found to be 0.47±0.02 by Girazian and Withers [], in good agreement with theoretical predictions. We therefore follow their study and use the solar energy flux, in the range 1–80nm, for our proxy of the ionizing flux.…”

Section: Observationssupporting

confidence: 75%

“…The data are obtained from the TIMED‒SEE website at LASP (lasp.colorado.edu/see/l3_data_page.html), and the ready routines (PLOT_SEE.PRO) that we use for extrapolating the data are available through that site. Note that the same data and the same routines have been used in a recent similar study for the Mars ionosphere, where similar results as in this paper were presented [ Girazian and Withers , ].…”

Section: Instruments and Coordinate Systemsmentioning

confidence: 55%

“…The ion (and electron) production rate should, according to Chapman theory, be proportional to the square root of the ionizing flux increase, and we do find a power law exponent k =0.54±0.18, which is in very good agreement with theory. We have followed the procedure of Girazian and Withers [] and used the 1–80nm integrated solar spectral irradiance as a proxy for the ionizing flux and obtained results very similar to theirs for the ionosphere of Mars.…”

Section: Discussionmentioning

confidence: 97%

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Solar cycle modulation of Titan's ionosphere

et al. 2013

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[1] During the six Cassini Titan flybys T83-T88 (May 2012 to November 2012) the electron density in the ionospheric peak region, as measured by the radio and plasma wave science instrument/Langmuir probe, has increased significantly, by 15-30%, compared to previous average. These measurements suggest that a long-term change has occurred in the ionosphere of Titan, likely caused by the rise to the new solar maximum with increased EUV fluxes. We compare measurements from TA, TB, and T5, from the declining phase of solar cycle 23 to the recent T83-T88 measurements during cycle 24, since the solar irradiances from those two intervals are comparable. The peak electron densities normalized to a common solar zenith angle N norm from those two groups of flybys are comparable but increased compared to the solar minimum flybys (T16-T71). The integrated solar irradiance over the wavelengths 1-80 nm, i.e., the solar energy flux, F e , correlates well with the observed ionospheric peak density values. Chapman layer theory predicts that N norm / F k e , with k = 0.5. We find observationally that the exponent k = 0.54˙0.18. Hence, the observations are in good agreement with theory despite the fact that many assumptions in Chapman theory are violated. This is also in good agreement with a similar study by Girazian and Withers (2013) on the ionosphere of Mars. We use this power law to estimate the peak electron density at the subsolar point of Titan during solar maximum conditions and find it to be about 6500 cm -3 , i.e., 85-160% more than has been measured during the entire Cassini mission.

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Section: Observationssupporting

confidence: 75%

Section: Instruments and Coordinate Systemsmentioning

confidence: 55%

Section: Discussionmentioning

confidence: 97%

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Solar cycle modulation of Titan's ionosphere

et al. 2013

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“…At higher altitudes, above ∼170–180 km, the ionosphere is no longer in photochemical equilibrium and the configuration is instead dictated by transport processes, giving rise to complex vertical structuring [ Shinagawa and Cravens , , ; Nagy et al , ; Kopf et al , ; Morgan et al , ; Němec et al , ]. It has been shown that the photochemical ionosphere responds to variations in insolation much as is to be expected from application of simple Chapman theory [ Breus et al , ; Morgan et al , ; Withers et al , ; Lillis et al , ; Němec et al , ; Zou et al , ; Girazian and Withers , ]. In contrast to Venus, Mars does not possess a sustained nightside ionosphere.…”

Section: Introductionmentioning

confidence: 99%

Determination of local plasma densities with the MARSIS radar: Asymmetries in the high‒altitude Martian ionosphere

et al. 2013

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[1] We present a novel method for the automatic retrieval of local plasma density measurements from the Mars advanced radar for subsurface and ionospheric sounding (MARSIS) active ionospheric sounder (AIS) instrument. The resulting large data set is then used to study the configuration of the Martian ionosphere at altitudes above 300 km. An empirical calibration routine is used, which relates the local plasma density to the measured intensity of multiple harmonics of the local plasma frequency oscillation, excited in the plasma surrounding the antenna in response to the transmission of ionospheric sounding pulses. Enhanced accuracy is achieved in higher-density (n e > 150 cm -3 ) plasmas, when MARSIS AIS is able to directly measure the fundamental frequency of the local plasma oscillation. To demonstrate the usefulness of this data set, the derived plasma densities are binned by altitude and solar zenith angle in regions over weak (|B c | < 20 nT) and strong (|B c | > 20 nT) crustal magnetic fields, and we find clear and consistent evidence for a significant asymmetry between these two regions. We show that within the 300-1200 km altitude range sampled, the median plasma density is substantially higher on the dayside in regions of relatively stronger crustal fields than under equivalent illuminations in regions of relatively weaker crustal fields. Conversely, on the nightside, median plasma densities are found to be higher in regions of relatively weaker crustal fields. We suggest that the observed asymmetry arises as a result of the modulation of the efficiency of plasma transport processes by the irregular crustal fields and the generally horizontal draped interplanetary magnetic field.

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“…What is more evident in this dataset is the increase of the peak altitude with solar activity, especially at high solar zenith angle. Girazian and Withers (2013) propose an empirical relationship, with the maximum electron density varying as the square of F10.7. Sanchez-Cano et al (2015) used Mars Express radar data covering almost one solar cycle and analyzed differences in the shape of the topside electron density profiles.…”

Section: Variability Of the Upper Atmospherementioning

confidence: 99%

Mars: a small terrestrial planet

Mangold

Baratoux

Witasse

et al. 2016

Astron Astrophys Rev

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Mars is characterized by geological landforms familiar to terrestrial geologists. It has a tenuous atmosphere that evolved differently from that of Earth and Venus and a differentiated inner structure. Our knowledge of the structure and evolution of Mars has strongly improved thanks to a huge amount of data of various types (visible and infrared imagery, altimetry, radar, chemistry, etc) acquired by a dozen of missions over the last two decades. In situ data have provided ground truth for remote-sensing data and have opened a new era in the study of Mars geology. While large sections of Mars science have made progress and new topics have emerged, a major question in Mars exploration-the possibility of past or present life-is still unsolved. Without entering into the debate around the presence of life traces, our review develops various topics of Mars science to help the search of life on Mars, building on the most recent discoveries, going from the exosphere to the interior structure, from the magmatic evolution to the currently active processes, including the fate of volatiles and especially liquid water.

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The dependence of peak electron density in the ionosphere of Mars on solar irradiance

Cited by 29 publications

References 34 publications

Solar cycle modulation of Titan's ionosphere

Solar cycle modulation of Titan's ionosphere

Determination of local plasma densities with the MARSIS radar: Asymmetries in the high‒altitude Martian ionosphere

Mars: a small terrestrial planet

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