Some new aspects of the transient ionization layer of comet Siding Spring origin in the Martian upper atmosphere

Rao, N. V. S.; Mohanamanasa, P.; Jayaraman, A.; Rao, Sandhya

doi:10.1002/2015ja022189

Cited by 9 publications

(15 citation statements)

References 31 publications

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“…The highest frequency that reflects from the ionosphere is from its main peak (denoted by a “cusp” in Figure b). Exceptions to this, however, were noted during the CSS event when strong ionization due to metallic ions was observed with a peak at ~115 km (Gurnett et al, ; Schneider et al, ; Venkateswara Rao et al, ). In this case, the peak density of the metallic ion layer was much greater than that of the ionospheric main peak, and hence, the highest frequency reflected from ionized targets was from the metallic ion layer.…”

Section: Marsis and Oblique Echoesmentioning

confidence: 97%

“…In fact, the echoes appear merged on several consecutive ionograms. The characteristics of these ionization bulges, their occurrence at multiple altitudes and their formation mechanisms are well studied by several authors (Andrews et al, ; Diéval et al, ; Duru et al, ; Gurnett et al, ; Mohanamanasa et al, ; Nielsen et al, ; Venkateswara Rao et al, ; Venkateswara Rao et al, ). One important aspect that can be clearly noted from Figure is that the peak frequencies of the vertical and oblique echoes in an ionogram are nearly the same or differ slightly.…”

Section: Marsis and Oblique Echoesmentioning

confidence: 98%

“…In addition to layers in its vertical structure, the Martian ionosphere also displays spatial inhomogeneities in its horizontal structure. The Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) instrument aboard the Mars Express spacecraft regularly detects bulges of ionization in the Martian ionosphere (Andrews et al, ; Diéval et al, ; Duru et al, ; Gurnett et al, ; Mohanamanasa et al, ; Nielsen et al, ; Venkateswara Rao et al, ; Venkateswara Rao et al, ). These bulges are predominantly observed in regions of strong vertical magnetic fields.…”

Section: Introductionmentioning

confidence: 99%

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Enhanced Ionization in Magnetic Anomaly Regions of the Martian Lower Ionosphere Associated With Dust Storms

et al. 2019

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The Mars Advanced Radar for Subsurface and Ionospheric Sounding instrument aboard the Mars Express spacecraft observes vertical echoes from the normal ionosphere and oblique echoes from ionization bulges. The peak frequencies of these two kinds of echoes are, in general, nearly equal. In the present study, we report the detection of oblique echoes whose peak frequencies are much larger than those of the vertical echoes. These echoes were observed on 15 June, 21 June, 28 June, and 10 July 2007, respectively. All these oblique echoes were observed from a region of strong crustal magnetic fields. After correcting for dispersion effects, the maximum electron density in the first case is found to be 3.75 × 10 5 cm −3 and is observed at an altitude of~88 km. In subsequent cases, a gradual decrease in peak electron density and an increase in altitude are observed. The causative mechanism of these oblique echoes is examined by considering various forces from top and bottom. During the times of the observations, there were no solar flares or meteor in fall. The presence of solar energetic particles also could not be firmly established. We found that these strong oblique echoes were observed at the initial phase and during the progression of a planet-encircling dust storm in Martian Year 28. A similar, but weaker features were observed in other dust storm seasons as well. Mechanisms causing such oblique echoes in regions of strong magnetic fields are discussed.

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Section: Marsis and Oblique Echoesmentioning

confidence: 97%

Section: Marsis and Oblique Echoesmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

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Enhanced Ionization in Magnetic Anomaly Regions of the Martian Lower Ionosphere Associated With Dust Storms

et al. 2019

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“…This suggests that these structures are longitudinally extended so that over a global plot, they appear as zonally elongated half cylindrical structures (Duru et al, 2006). During the passage of comet siding spring, the oblique echoes associated with magnetic anomalies were observed at altitudes of~100 km, though a complete hyperbola could not be observed (Venkateswara Rao et al, 2016). Recently, the oblique echoes associated with MCDS were also observed from the topside layer of the Martian ionosphere (Venkateswara Rao et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

Magnetically Controlled Density Structures in the Martian Ionosphere: Are they Stably Recurring?

et al. 2018

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MARSIS instrument aboard the Mars Express spacecraft regularly detects the magnetically controlled density structures (MCDSs) in the Martian ionosphere. In this paper, we studied the recurrence characteristics of these MCDSs using long‐term (more than a decade) MARSIS observations over a selected region of 35° to 40° longitude and −10° to 10° latitude, where a strong magnetic anomaly is present. Instead of a conventional echogram analysis, we used the peak density echogram analysis as the latter is able to consider all the vertical and oblique echoes even if their peak densities are varying. The results of the present study show that MCDSs are in fact formed persistently on all dayside periapsis passes. More importantly, there are discontinuities in the hyperbola shape in a peak density echogram display that appear at different locations on different orbital passes. In addition, the apices of the hyperbolas associated with an MCDS are observed at different latitudes on different orbital passes. From these results, we infer that the locations and shapes of MCDSs are disturbed by some time‐varying external factors so that some parts of the MCDS cannot give specular reflections. These hypotheses were demonstrated with some simple ray propagation simulations. Nearly similar features are observed with the nightside MCDS, but they occur only 60% of the passes. We surmise that wave dynamics associated with tides and gravity waves and so forth might be responsible for altering the shape and location of MCDS, both on the dayside and nightside.

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“…The bulges of ionization are probably formed by the interaction of Mars ionosphere with shocked solar wind through open magnetic fields [ Ness et al , ; Gurnett et al , ; Duru et al , ] or by the redistribution of the ionospheric plasma along vertical magnetic fields [ Matta et al , ]. These oblique echoes, which are usually observed in the main layer of the ionosphere, are also observed at meteor ion layer altitudes during the passage of comet Siding Spring and are found in regions of vertical magnetic fields [ Venkateswara Rao et al , ].…”

Section: Introductionmentioning

confidence: 99%

Magnetically controlled density structures in the topside layer of the Martian ionosphere

2017

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Magnetically controlled density structures in the main layer of the Martian ionosphere are regularly detected by the Mars Advance Radar for Subsurface and Ionospheric Sounder (MARSIS) on board the Mars Express spacecraft when it passes over the regions of strong crustal magnetic fields. These structures appear as oblique echoes in an ionogram and as hyperbola‐shaped feature in a radargram. For the first time, we observed such oblique echoes from the topside layer of the Martian ionosphere. Comparison with a crustal magnetic field model suggests that these echoes mostly occur in regions close to magnetic field anomalies. The MARSIS ionograms that show these oblique echoes are limited in number. One reason for such limited occurrence is the fact that these echoes occur at the low‐frequency end of an ionogram where local plasma frequency lines and electron‐cyclotron lines make it difficult to discern these echoes. In one case, however, we observed the topside layer with oblique echoes on several continuous ionograms and a hyperbola‐shaped feature on a radargram. The apex of the hyperbola falls in the region of vertical magnetic fields. Unlike the main layer, the recurrent occurrence of the topside layer at the same location is not common. More importantly, the oblique echoes from the topside layer are always associated with those from the main layer of the ionosphere, but not vice versa. The simultaneous observation of oblique echoes from the main and topside layers is explained by considering the formation of ionization bulges at the respective layer altitudes.

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Some new aspects of the transient ionization layer of comet Siding Spring origin in the Martian upper atmosphere

Cited by 9 publications

References 31 publications

Enhanced Ionization in Magnetic Anomaly Regions of the Martian Lower Ionosphere Associated With Dust Storms

Enhanced Ionization in Magnetic Anomaly Regions of the Martian Lower Ionosphere Associated With Dust Storms

Magnetically Controlled Density Structures in the Martian Ionosphere: Are they Stably Recurring?

Magnetically controlled density structures in the topside layer of the Martian ionosphere

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