THE SIMULATION OF VIBRATIONAL POPULATIONS OF ELECTRONICALLY EXCITED N2 IN TITAN’S UPPER ATMOSPHERE DURING PRECIPITATIONS OF HIGH-ENERGETIC PARTICLES

2021 ◽  
Vol 44 ◽  
pp. 122-125
Author(s):  
A.S. Kirillov ◽  
◽  
R. Werner ◽  
V. Guineva ◽  
◽  
...  
Keyword(s):  
Molecular Nitrogen ◽  
Excitation Energy Transfer ◽  
Electron Excitation ◽  
Energetic Particles ◽  
Upper Atmosphere ◽  
Radiative Processes ◽  
Calculated Volume ◽  
Ion Production ◽  
Electronically Excited ◽  
Volume Emission

We study the electronic kinetics of singlet molecular nitrogen in Titan’s upper atmosphere during precipitations of high-energetic particles. Both radiative processes and processes of electron excitation energy transfer during inelastic collisions with N2 and CH4 molecules were considered in the calculation of vibrational populations of electronically excited singlet states a'1Σu–, a1Πg, w1Δu of molecular nitrogen in the upper atmosphere of Titan. It is shown that the calculated volume emission intensities of the Lyman-Birge-Hopfield bands correlate with the profiles of the ion production rate in the atmosphere of Titan during the considered cases of electron precipitation for considered interval of the energies 30-1000 eV of magnetospheric electrons. This fact is explained by the negligible contribution of collisional processes to the vibrational populations a1Πg(v'=0-6) in the considered range of heights above 900 km.

scholarly journals Electronically excited molecular nitrogen and molecular oxygen in the high-latitude upper atmosphere

2008 ◽  
Vol 26 (5) ◽  
pp. 1159-1169 ◽  
Author(s):  
A. S. Kirillov
Keyword(s):  
High Latitude ◽  
Molecular Nitrogen ◽  
Upper Atmosphere ◽  
Wavelength Shift ◽  
Auroral Ionosphere ◽  
Not Given ◽  
Auroral Electron ◽  
Vibrational Levels ◽  
Electronically Excited ◽  
Vibrational Population

Abstract. Relative vibrational populations of triplet B3Πg, W3Δ,sub>u, B'3Σu− states of N2 and the b1Σg+ state of O2 are calculated for different altitudes of the high-latitude upper atmosphere during auroral electron precipitation. It is shown that collisional processes cause a wavelength shift in the distribution of relative intensities for 1PG Δv=3 sequence of N2. The calculation of relative populations for vibrational levels v=1–5 of the b1Σg+ state in the auroral ionosphere has not given an agreement with experimental results. Preliminary estimation of the contribution of the reaction O2++NO to the production of O2(b1Σg+) on the basis of a quantum-chemical approximation does not allow for an explanation of the observable vibrational population of the b1Σg+ state in the aurora.

scholarly journals Inferring thermospheric composition from ionogram profiles: a calibration with the TIMED spacecraft

2021 ◽  
Vol 39 (2) ◽  
pp. 309-319
Author(s):  
Christopher J. Scott ◽  
Shannon Jones ◽  
Luke A. Barnard
Keyword(s):  
Dissociative Recombination ◽  
Molecular Ions ◽  
Upper Atmosphere ◽  
Global Network ◽  
G Factor ◽  
Important Region ◽  
Term Change ◽  
Ion Production ◽  
Sensitive Function

Abstract. We present a method for augmenting spacecraft measurements of thermospheric composition with quantitative estimates of daytime thermospheric composition below 200 km, inferred from ionospheric data, for which there is a global network of ground-based stations. Measurements of thermospheric composition via ground-based instrumentation are challenging to make, and so details about this important region of the upper atmosphere are currently sparse. The visibility of the F1 peak in ionospheric soundings from ground-based instrumentation is a sensitive function of thermospheric composition. The ionospheric profile in the transition region between F1 and F2 peaks can be expressed by the “G” factor, a function of ion production rate and loss rates via ion–atom interchange reactions and dissociative recombination of molecular ions. This in turn can be expressed as the square of the ratio of ions lost via these processes. We compare estimates of the G factor obtained from ionograms recorded at Kwajalein (9∘ N, 167.2∘ E) for 25 times during which the Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics (TIMED) spacecraft recorded approximately co-located measurements of the neutral thermosphere. We find a linear relationship between G and the molecular-to-atomic composition ratio, with a gradient of 2.55±0.40. Alternatively, using hmF1 values obtained by ionogram inversion, this gradient was found to be 4.75±0.4. Further, accounting for equal ionisation in molecular and atomic species yielded a gradient of 4.20±0.8. This relationship has potential for using ground-based ionospheric measurements to infer quantitative variations in the composition of the neutral thermosphere via a relatively simple model. This has applications in understanding long-term change and the efficacy of the upper atmosphere on satellite drag.

scholarly journals The emission of the negative system of nitrogen from the upper atmosphere and the significance of the twilight flash in the theory of the ionosphere

1949 ◽  
Vol 196 (1047) ◽  
pp. 562-591 ◽  
Keyword(s):  
Transition Probability ◽  
Molecular Nitrogen ◽  
Charged Particles ◽  
High Energy ◽  
Upper Atmosphere ◽  
Ionization Mechanisms ◽  
Direct Excitation ◽  
Negative Band ◽  
Resonance Emission ◽  
Excitation Mechanisms

The cause of the emission of the negative band system of nitrogen from the upper atmosphere during twilight is investigated. A study is made of the two possible excitation mechanisms, N 2 ( X 1 Ʃ g + ) + hv →N 2 + ( B 2 Ʃ u + ) + e and N 2 + ( X 2 Ʃ g + ) + hv →N 2 + ( B 2 Ʃ u + ). It is shown that the latter is far more effective than the former, irrespective of the assumptions adopted regarding the solar flux in the unobservable spectral region. From the transition probability associated with it (which is evaluated in the appendix) combined with various intensity estimates, an upper limit is obtained for the number of N 2 + ions normally present in the E and F layers during twilight. It appears that N 2 + ions form but a minute fraction of the total ion content. The significance of this in the theory of the formation of the ionized layers is discussed. The simplest interpretation is that ionization of molecular nitrogen is unimportant; and a reasonable scheme that invokes only the ionization of oxygen atoms and molecules is available. However, by introducing certain arbitrary assumptions a more elaborate interpretation is conceivable so that the view that the E layer arises from the action of high-energy coronal photons, which ionize all atmospheric constituents, cannot be finally rejected. Various aspects of the layers are discussed, and observational and experimental work, which might yield evidence on the ionization mechanisms operative, is suggested. It is pointed out that the remarkable rarity of N 2 + ions proves conclusively that recombination between the charged particles present in the ionosphere cannot be the origin of the nocturnal radiation of the nitrogen band systems. On some occasions the resonance emission at twilight is of unusually high intensity. It is presumed that this is due to incident charged particles increasing the concentration of N 2 + ions. The possible contribution that these charged particles may make to the night-sky light by direct excitation collisions is briefly examined. Sunlit aurorae (which are essentially similar to the twilight flash) are also discussed.

scholarly journals Plasma environment of Titan: a 3-D hybrid simulation study

2006 ◽  
Vol 24 (3) ◽  
pp. 1113-1135 ◽  
Author(s):  
S. Simon ◽  
A. Bößwetter ◽  
T. Bagdonat ◽  
U. Motschmann ◽  
K.-H. Glassmeier
Keyword(s):  
Plasma Flow ◽  
Molecular Nitrogen ◽  
Hybrid Simulation ◽  
Spherical Geometry ◽  
Magnetospheric Plasma ◽  
Simulation Code ◽  
Plasma Environment ◽  
Ion Production ◽  
Solar Uv ◽  
Magnetohydrodynamic Models

Abstract. Titan possesses a dense atmosphere, consisting mainly of molecular nitrogen. Titan's orbit is located within the Saturnian magnetosphere most of the time, where the corotating plasma flow is super-Alfvénic, yet subsonic and submagnetosonic. Since Titan does not possess a significant intrinsic magnetic field, the incident plasma interacts directly with the atmosphere and ionosphere. Due to the characteristic length scales of the interaction region being comparable to the ion gyroradii in the vicinity of Titan, magnetohydrodynamic models can only offer a rough description of Titan's interaction with the corotating magnetospheric plasma flow. For this reason, Titan's plasma environment has been studied by using a 3-D hybrid simulation code, treating the electrons as a massless, charge-neutralizing fluid, whereas a completely kinetic approach is used to cover ion dynamics. The calculations are performed on a curvilinear simulation grid which is adapted to the spherical geometry of the obstacle. In the model, Titan's dayside ionosphere is mainly generated by solar UV radiation; hence, the local ion production rate depends on the solar zenith angle. Because the Titan interaction features the possibility of having the densest ionosphere located on a face not aligned with the ram flow of the magnetospheric plasma, a variety of different scenarios can be studied. The simulations show the formation of a strong magnetic draping pattern and an extended pick-up region, being highly asymmetric with respect to the direction of the convective electric field. In general, the mechanism giving rise to these structures exhibits similarities to the interaction of the ionospheres of Mars and Venus with the supersonic solar wind. The simulation results are in agreement with data from recent Cassini flybys.

scholarly journals Inferring thermospheric composition from ionogram profiles: A calibration with the TIMED spacecraft

2019 ◽  
Author(s):  
Christopher J. Scott ◽  
Shannon Jones ◽  
Luke A. Barnard
Keyword(s):  
Dissociative Recombination ◽  
Temporal Variations ◽  
Molecular Ions ◽  
Upper Atmosphere ◽  
Global Network ◽  
G Factor ◽  
Satellite Drag ◽  
Important Region ◽  
Ion Production ◽  
Sensitive Function

Abstract. Measurements of thermospheric composition via ground-based instrumentation are challenging to make and so details about this important region of the upper atmosphere are currently sparse. We present a technique that deduces quantitative estimates of thermospheric composition from ionospheric data, for which there is a global network of stations. The visibility of the F1 peak in ionospheric soundings from ground-based instrumentation is a sensitive function of thermospheric composition. The ionospheric profile in the transition region between F1 and F2 peaks can be expressed by the G factor, a function of ion production rate and loss rates via ion-atom interchange reactions and dissociative recombination of molecular ions. This in turn can be expressed as the square of the ratio of ions lost via these processes. We compare estimates of the G factor obtained from ionograms recorded at Kwajalein (9° N, 167.2° E) for 25 times during which the TIMED spacecraft recorded approximately co-located measurements of the neutral thermosphere. We find a linear relationship between √G and the molecular: atomic composition ratio, with a gradient of 2.23 ± 0.17 and an offset of 1.66 ± 0.19. This relationship reveals the potential for using ground-based ionospheric measurements to infer quantitative variations in the composition of the neutral thermosphere. Such information can be used to investigate spatial and temporal variations in thermospheric composition which in turn has applications such as understanding the response of thermospheric composition to climate change and the efficacy of the upper atmosphere on satellite drag.

Calculation of auroral Bahner volume emission height profiles in the upper atmosphere

1994 ◽  
Vol 56 (4) ◽  
pp. 503-508 ◽  
Author(s):  
F. Sigernes ◽  
D.A. Lorentzen ◽  
C.S. Beehr ◽  
K. Henriksen
Keyword(s):  
Upper Atmosphere ◽  
Volume Emission ◽  
Emission Height
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