arXiv subjects

Kartika Sangal

Publications and source records attributed to Kartika Sangal.

6 recordsLinked to original sources

arXiv2026

Recurrent Coronal Jets and QPPs: Periodic Reconnection and Localized Heating Across Quiet-Sun to Active Regions

We analyze quasi-periodic pulsations (QPPs) in recurrent coronal jets driven by periodic magnetic reconnection associated with successive flux emergence in the fan-spine magnetic topologies. Using the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO), we investigate three long-lived recurring jets spanning quiet Sun to moderate-field-strength regions, each exhibiting recurrent eruptions linked to episodic reconnection. Wavelet analysis of multithermal AIA EUV jet-base light curves detects QPPs with periods of 6-13 min, exceeding typical p-mode oscillation periods. Distance-time analysis reveals quasi-periodic propagating ridges, interpreted as recurrent field-aligned plasma ejections, and morphological similarities to slow magnetoacoustic waves, which cannot be entirely excluded. However, the dominant photospheric unsigned flux periodicities of 10-32 min at the jet source regions favor the reconnection-driven interpretation. DEM analysis confirms multithermal plasma with the hottest emission concentrated near the jet base, and the QPP periods fall well below both radiative and conductive cooling timescales, implying persistent localized heating within the fan-spine configuration. These results demonstrate that periodic reconnection in fan-spine topologies drives recurrent jet eruptions and contributes to localized coronal heating across the quiet Sun, moderate-field strength regions, and active regions.

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arXiv2026

Chromospheric resonator model for sunspot revealed by multi-height observation of umbral wave

Sunspots are transient, magnetically intense features that host oscillations linked to magnetohydrodynamic (MHD) waves. These waves may contribute to plasma heating and drive mass flows in the solar wind. Beyond their energetic role, they serve as diagnostic tools for probing sunspot structure. In this study, we investigated chromospheric wave propagation in a sunspot using high-resolution, multi-wavelength observations from the Goode Solar Telescope at Big Bear Solar Observatory. Spectral analysis shows that the intensity at H$α$ line core and its wings exhibited oscillatory signal at about 3 min. We performed a cross-wavelet analysis to examine the phase relationship between the wing-integrated and line-core intensity oscillations of the H$α$ line and the centroid-derived H$α$ Doppler velocity. We also analyze the phase relationships between intensity pairs from different passband combinations of the H$α$ line. The results indicate the presence of slow magnetoacoustic modes manifesting standing waves along with upward propagating waves. The observed phase patterns suggest that umbral waves are confined within a non-ideal acoustic resonator, providing measurable wave properties that could serve as input for sunspot seismology and refine models of sunspot atmospheric structure.

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arXiv2024

Statistical investigation of wave propagation in the quiet-Sun using IRIS spectroscopic observations

In the current analysis, we use spectroscopic observations of the quiet-Sun made by IRIS instrument, and investigate wave propagation. We analyze various spectral lines formed in different atmospheric layers such as the photosphere, chromosphere, and transition region. We examine Doppler velocity time-series at various locations in the quiet-Sun to determine the dominant oscillation periods. Our results executing statistical analysis resemble those of the classical physical scenario, indicating that the photosphere is mainly characterized by the dominant 5-minute period, while the chromosphere is primarily associated with the 3-minute oscillation period. In the transition region, we observe a variety of oscillation periods, with dominant periods of 3, 8, and 12 minutes. We estimate the cut-off frequency by deducing phase difference between two Doppler velocity time-series obtained from spectral line pairs in different atmospheric layers formed at different temperatures. It reveals a significant correlation between 3-minute periods in TR and photospheric oscillations, suggesting that these oscillations in the TR might propagate from the photosphere. Additionally, we analyze the phase difference between chromospheric oscillations and photospheric oscillations, demonstrating that only the 3-minute oscillations propagate upwards. Based on the statistical analyses, we suggest the presence of magnetoacoustic waves in the solar atmosphere in which some are propagating from the lower solar atmosphere upward, while some others are propagating downward. TR carries both long-period oscillations generated in situ, and some photospheric oscillations which are also able to reach there from below.

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arXiv2023

Origin of Quasi-Periodic Pulsation at the Base of Kink Unstable Jet

We study a blowout jet that occurs at the west limb of the Sun on August 29$^{th}$, 2014 using high-resolution imaging/spectroscopic observations provided by SDO/AIA and IRIS. An inverse $γ$-shape flux-rope appears before the jet{--} morphological indication of the onset of kink instability. The twisted field lines of kink-unstable flux-rope reconnect at its bright knot and launch the blowout jet at $\approx$06:30:43 UT with an average speed of 234 km s$^{-1}$. Just after the launch, the northern leg of the flux rope erupts completely. The time-distance diagrams show multiple spikes or bright dots, which is the result of periodic fluctuations, i.e., quasi-periodic fluctuations (QPPs). The wavelet analysis confirms that QPPs have a dominant period of $\approx$ 03 minutes. IRIS spectra (Si~{\sc iv}, C~{\sc ii}, and Mg~{\sc ii}) may also indicate the occurrence of magnetic reconnection through existence of broad $\&$ complex profiles and bi-directional flows in the jet. Further, we have found that line broadening is periodic with a period of $\approx$ 03 minutes, and plasma upflow is always occurs when the line width is high, i.e., multiple reconnection may produce periodic line broadening. The EM curves also show the same period of $\approx$ 03 minutes in different temperature bins. The images and EM show that this jets spire is mainly cool (chromospheric/transition region) rather than hot (coronal) material. Further, line broadening, intensity, and EM curves have a period of $\approx$03 minutes, which strongly supports that multiple magnetic reconnection triggers QPPs in the blowout jet.

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arXiv2022

Spectroscopic study of solar transition region oscillations in the quiet-Sun observed by IRIS using Si IV spectral line

In the present paper, we use Si IV 1393.755 Å spectral line observed by the Interface Region Imaging Spectrograph (IRIS) in the quiet-Sun to determine physical nature of the solar transition region (TR) oscillations. We analyze the properties of these oscillations using wavelet tools (e.g., power, cross-power, coherence, and phase difference) along with the stringent noise model (i.e., power-law + constant). We estimate the period of the intensity and Doppler velocity oscillations at each chosen location in the quiet-Sun (QS) and quantify the distribution of the statistically significant power and associated periods in one bright and two dark regions. In the bright TR region, the mean periods in intensity and velocity are 7 min, and 8 min respectively. In the dark region, the mean periods in intensity and velocity are 7 min, and 5.4 min respectively. We also estimate the phase difference between the intensity and Doppler velocity oscillations at each location. The statistical distribution of phase difference is estimated, which peaks at -119\degree $\pm$ 13\degree, 33\degree $\pm$ 10\degree, 102\degree $\pm$ 10\degree\ in the bright region, while at -153\degree $\pm$ 13\degree, 6\degree $\pm$ 20\degree, 151\degree $\pm$ 10\degree\ in the dark region. The statistical distribution reveals that the oscillations are caused by propagating slow magnetoacoustic waves encountered with the TR. Some of these locations may also be associated with the standing slow waves. Even, in the given time domain, several locations exhibit presence of both propagating and standing oscillations at different frequencies.

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arXiv2021

Role of Non-Ideal Dissipation with Heating-Cooling Misbalance on the Phase Shifts of Standing Slow Magnetohydrodynamic Waves

We analyse the phase shifts of standing, slow magnetohydrodynamic (MHD) waves in solar coronal loops using a linear MHD model taking into account the role of thermal conductivity, compressive viscosity, radiative losses, and heating-cooling misbalance. We estimate the phase shifts in time and space of density and temperature perturbations with respect to velocity perturbations and also calculate the phase difference between density and temperature perturbations. The overall significance of compressive viscosity is found to be negligible for most of the loops considered in the study. For loops with high background density and/or low background temperature, the role of radiative losses (with heating-cooling misbalance) is found to be more significant. Also the effect of heating-cooling misbalance with a temperature- and density-dependent heating function is found to be more significant in the case of longer loop lengths ($L=500$\, Mm). We derived a general expression for the polytropic index [$γ_{\rm eff}$] and found that under linear MHD the effect of compressive viscosity on polytropic index is negligible. The radiative losses with constant heating lead to a monotonic increase of $γ_{\rm eff}$ with increasing density whereas the consideration of an assumed heating function [$H(ρ,T) \propto ρ^{a}T^{b}$, where $a=-0.5$ and $b=-3$] makes the $γ_{\rm eff}$ peak at a certain loop density. We also explored the role of different heating functions by varying the free parameters $a$ and $b$ for a fixed loop of $ρ_0 = 10^{-11}$\, kg $\text{m}^{-3}$, $T_0 = 6.3$\, MK and loop length $L= 180$\, Mm. We find that the consideration of different heating functions [$H(ρ,T)$] leads to a significant variation in the phase difference between density and temperature perturbations; however, the polytropic index remains close to a value of 1.66.

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