arXiv subjects

Sumanta Sarkhel

Publications and source records attributed to Sumanta Sarkhel.

8 recordsLinked to original sources

arXiv2026

Impact of May 2024 ICME Event on Martian UV Dayglow Emissions using MAVEN/IUVS and EMM/EMUS Observations

We present first near-simultaneous observations of large-scale spatial response of the Martian H Lyman-{\alpha} and atomic oxygen dayglow emissions (O(3S) 130.4 nm and O(5S) 135.6 nm) during May 2024 interplanetary coronal mass ejection (ICME). Using coordinated near-simultaneous observations from MAVEN/Imaging Ultraviolet Spectrograph (IUVS) and the EMM/Emirates Mars Ultraviolet Spectrometer (EMUS), we have identified pronounced enhancements in all three emissions relative to quiet-time conditions. Interestingly, coordinated IUVS limb and EMUS disk observations reveal that ICME-driven response extends vertically through the thermosphere and horizontally across broad ranges of latitude, longitude, local-time, and solar zenith angle. Concurrent enhancement of hydrogen and oxygen emissions indicates the simultaneous contribution of proton and electron-driven excitation mechanisms during ICME. These findings reveal a novel planetary-scale response of the Martian dayglow. By highlighting the critical role of energetic-particle precipitation in amplifying this global response, our work carries crucial implications for understanding Martian thermospheric response during intense solar transients.

physics.space-ph↗

arXiv2026

Automatic Characterization of Mid-latitude Multiple Ionospheric Plasma Structures from All-sky Airglow Images using Deep Learning Technique

The F-region ionospheric plasma structures are propagating high and or low electron density regions in the Earth ionosphere. These plasma structures can be observed using ground based all-sky airglow imagers which can capture faint airglow emissions originating from the F-region of ionosphere. This study introduces a novel automatic method for determining the propagation parameters (horizontal velocity and orientation) of these multiple ionospheric plasma structures observed in O(1D) 630.0 nm all-sky airglow images from Hanle, India located in the mid-latitude region. We have used a deep learning-based segmentation model called YOLOv8 (You Only Look Once) to localize and BoT-SORT tracker to track individual mid-latitude ionospheric plasma structures. Three different automatic algorithms are used to characterize the observed plasma structures utilizing the segmented outputs from the YOLO model. Finally, an additional quality control step is introduced that filters the results from the three automatic algorithms and generates a flag to retain the most reliable estimate. The results of the proposed fully automated pipeline are systematically compared with a previously developed semi-automatic approach to assess the estimation efficacy. The automatic technique developed in this study is particularly valuable for all-sky airglow imaging systems having large datasets, where manual intervention or semi-automatic analysis is impractical.

physics.space-ph↗

arXiv2025

Climatology of Mars Topside Ionosphere during Solar Cycles 24 and 25 using MAVEN Dataset of 2015-2024

The Mars ambient space environment evolves with the varying solar activity. Understanding the Martian space environment, particularly the topside ionosphere across different phases of Solar Cycles (SC) 24 \& 25 remains a key research gap in planetary ionospheric science. In this study, we utilized the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) mission data (150-500 km) from Martian years 32-38 (2015-2024) during solar quiet-time. This study investigated the behavior of topside ionosphere (e-, CO2+, O2+, NO+, OH+, O+, N+ \& C+) across different phases of SC over the northern hemisphere. A significant variation in ionosphere is observed over low-latitude (0-30{\deg}N) with higher densities compared to mid-latitude (31-60{\deg}N) across SC. Additionally, we found that the Martian northern ionospheric densities were highest during solar maximum phase on both dayside and nightside compared to low active phases. The dayside densities were approximately 1-2 orders higher compared to those on the nightside. The electron and molecular ions densities increased by factors of 1-5 and 1-13, respectively. While O+ ion density was enhanced by nearly 2-2.5 times, along with an upliftment of 40-50 km in the peak height. The enhanced dayside densities are attributed to the elevated solar irradiance (1.4-2 times) and varying solar wind flux. Furthermore, the enhanced day-to-night plasma transport and elevated solar electron flux during maxima, higher by 33-66\% than during low-activity, can contribute to the increased nightside ionization. This work, for the first time, uses long-term MAVEN datasets across the descending-to-maxima phases of SC to reveal climatology of Martian topside ionosphere.

physics.space-ph↗

arXiv2025

Investigation of Martian UV Dayglow Emissions in the Southern Hemisphere during Solar Quiet-time Conditions: Insights from Multi-year MAVEN/IUVS Observations

The southern hemisphere of Mars possesses concentrated region of strong crustal magnetic fields (CMF), which generate localized magnetic anomalies that can influence atmospheric dynamics and energy deposition in the Martian thermospheric-ionospheric system. Although their effects on the atmosphere (>200 km) in the southern hemisphere are well documented, however their role in modulating the behavior of atmospheric plasma and neutrals below 200 km are poorly understood. The atmosphere at these altitudes can be comprehended by studying the variation of dayglow emissions. We have investigated few dayglow emissions over the CMF and non-CMF regions using the MAVEN remote-sensing measurements from Martian Years 33-37. Particularly, the CO Cameron bands, CO2+ ultraviolet doublet, and atomic oxygen emissions at 297.2 nm, 130.4 nm, and 135.6 nm have been studied below 200 km during solar quiet-time conditions. The results show strong seasonal variations in all the emissions peak altitudes and intensities in the dayside and near-terminator regions. The variation in the peak altitude of molecular and atomic emissions are nearly 20 km and 30 km, respectively. On the dayside, the emissions show minimal variation across CMF and non-CMF regions, indicating a minimal effect of the CMF at these altitudes, suggesting a key role of plasma demagnetization and photochemical processes. In addition, an insignificant variation in the dayglow emissions is likely masked by compensating mechanisms such as energy-dependent electron shielding and thermospheric expansion. This work presents the first focused investigation on the dayglow emissions over CMF and non-CMF regions across different seasons and solar zenith angles.

physics.space-ph↗

arXiv2024

Evidence of potential thermospheric overcooling during the May 2024 geomagnetic superstorm

During intense geomagnetic storms, the rapid and significant production of NO followed by its associated infrared radiative emission in lower thermosphere contributes crucially to the energetics of the upper atmosphere. This makes NO infrared radiative cooling a very important phenomenon which needs to be considered for accurate density forecasting in thermosphere. This study reports the investigation of variations in thermospheric density, and NO radiative cooling during the recent geomagnetic superstorm of May 2024. A very rare post-storm thermospheric density depletion of about -23% on May 12 was observed by Swarm-C in northern hemisphere in comparison to the prestorm condition on May 9. This overcooling was observed despite the continuous enhancement in solar EUV (24-36 nm) flux throughout the event. The thermospheric NO infrared radiative emission in the recovery phase of the storm seems to be the plausible cause for this observed post-storm density depletion. The TIMED/SABER observed thermospheric density between 105 and 110 km altitude shows an enhancement during this thermospheric overcooling. Our analysis also suggests an all time high thermospheric NO radiative cooling flux up to 11.84 ergs/cm2/sec during May 2024 geomagnetic superstorm, which has also been compared with famous Halloween storms of October 2003.

physics.space-ph↗

arXiv2024

A case study on the impact of interplanetary coronal mass ejection on the Martian O(1S) 557.7 nm dayglow emission using ExoMars TGO/NOMAD-UVIS observations: First Results

We report, for the first time, the impact of an interplanetary coronal mass ejection (ICME) on the recently discovered O($^1$S) 557.7 nm dayglow emission in the Martian atmosphere. Although there are only a few studies on the seasonal variation are available in the literature, the impact of ICME on 557.7 nm dayglow emission has not been investigated so far. Using the instruments aboard ExoMars-TGO and MAVEN spacecrafts, we show that the primary emission peak (75-80 km) remains unaffected during the ICME event compared to quiet-times. However, a noticeable enhancement has been observed in the brightness of secondary emission peak (110-120 km) and the upper altitude region (140-180 km). The enhancement is attributed to the increased solar electrons and X-ray fluxes, augmenting the electron-impact process and causing the enhancement in the brightness. These analyses have an implication to comprehend the role of intense solar transients like ICME on the Martian dayglow emissions.

physics.space-ph↗

arXiv2024

Seasonal variation in nighttime NO radiative cooling as observed by TIMED/SABER in lower thermosphere during solar maximum and solar minimum

Both composition and temperature play a crucial role in determining the NO radiative cooling in lower thermosphere as observed by TIMED/SABER. In this work, we present a detailed investigation of seasonal variation in thermospheric NO radiative cooling. We have carried forward the investigation of \cite{li2018} regarding the variations in local nighttime peak NO radiative cooling and its altitude during solar maximum and solar minimum conditions. By analyzing latitudinal changes over quiet times for each month in year 2018, it is evident that both the investigative parameters exhibit summer-winter variability. The qualitative contribution of different species (i.e., NO, and O), and temperatures in determining the vertical profile of NO radiative cooling for different latitudes is investigated by utilizing the NRLMSISE-00 estimated parameters, and SNOE observed NO density. The temperature, NO density, meridional wind, and associated compositional variations due to asymmetrical solar heating in both the hemispheres during solar minimum conditions seem to be the dominating factor in controlling the NO radiative cooling during different seasons. The altitudes at which maximum cooling by NO occurs exhibits an inverse correlation with the amount of radiative cooling. The region of enhanced NO densities (polar and summer hemispheric low-mid latitude regions) have larger NO radiative cooling with lower peak altitudes in comparison to other regions (equatorial to winter hemispheric low-mid latitude regions), where NO radiative cooling is low with higher peak altitude values.

physics.space-ph↗

arXiv2023

A comparison of the impacts of CMEs and CIRs on the Martian dayside and nightside ionospheric species

Measurements from the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft, orbiting Mars are used for investigating the impact of coronal mass ejections (CMEs) and corotating interaction regions (CIRs) on Martian ionospheric species. We have chosen 15 CME and 15 CIR events (2015-2020) at Mars from the existing catalogs. We have extensively analyzed the Martian dayside and nightside profiles of ionospheric species during each of the CME and CIR events. We have selected those orbit plasma density profiles which showed significant differences from the mean quiet-time profile during each event. The primary focus of this paper is to provide a comparative average scenario of the variation of Martian ionospheric species during CMEs and CIRs events. A significant difference can be observed in the profiles of the Martian dayside and nightside ionospheric species (O+, O2+, CO2+, NO+, C+, N+, & OH+) during CMEs and CIRs in comparison to mean quiet-time profile. The difference is more prominent on the nightside compared to the dayside ionosphere. During CIRs, the nightside ion density is nearly one order of magnitude less (above 250 km) in comparison to CMEs. The mean peak altitude and density of the lighter ions (O+, C+, N+, & OH+) were at lower altitudes during the CIRs compared to CMEs. Therefore, this study suggests that during the declining phase of solar cycle (SC 24), the impact of CIRs on the Martian ionospheric species is more prominent compared to CMEs.

physics.space-ph↗