On the Variability of the Solar Mean Magnetic Field: Contributions from Various Magnetic Features on the Surface of the Sun

Bose, Suchismita; Nagaraju, K.

doi:10.3847/1538-4357/aaccf1

Cited by 21 publications

(23 citation statements)

References 38 publications

(59 reference statements)

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“…It has contribution from both the large scale magnetic field structure (i.e., ambient magnetic field) and the active regions on Sun. In recent study Bose & Nagaraju (2018) have shown that the variations in solar magnetic field has major (89%) contribution from the ambient magnetic field and the contribution from other features is insignificant (11%). It may be noted that SMED has undergone considerable gradual decrease from SC 22 to SC 24 (it is discussed in Sect.…”

Section: Data Sets and Energy Estimatesmentioning

confidence: 99%

Diminishing activity of recent solar cycles (22–24) and their impact on geospace

Kakad

Ramesh

et al. 2019

J. Space Weather Space Clim.

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This study examines the variation of different energies linked with the Sun and the Earth’s magnetosphere-ionosphere systems for solar cycles (SCs) 22–24 for which the gradual decrease in the solar activity is noticed. Firstly, we investigated the variation of solar magnetic energy density (SMED) for SCs 21–24 and its relation to the solar activity. We observed distinct double peak structures in SMED for the past four SCs, 21–24. This feature is consistent with noticeable asymmetry in their two peaks. For SCs 22–24 a significant decrease is observed in the integrated SMED of each SC. This reduction is 37% from SCs 22 to 23 and 51% from SCs 23 to 24, which indicates substantial weakening of Sun’s magnetic field for SC 24. Also, the magnetic, kinetic, and thermal energy densities at the Earth’s bow-shock nose are found to be considerably low for the SC 24. We examined the solar wind Alfven speed, magnetosonic Mach number, solar wind-magnetosphere energy coupling parameter (ε), and the Chapman-Ferraro magnetopause distance (LCF) for the SCs 22–24. The estimated maximum stand-off magnetopause distance is larger for SC 24 (LCF ≤ 10.6 RE) as compared to SC 23 (LCF ≤ 10.2 RE) and SC 22 (LCF ≤ 9.8 RE). The solar wind Alfven speeds during SCs 22 and 23 are in the same range and do not exceed ≈73 km/s whereas, it is below 57 km/s for SC 24. A lower bound of solar wind magnetosonic Mach number for SC 24 is larger (M ≥ 6.9) as compared to SC 22 (M ≥ 5.9) and SC 23 (M ≥ 6). We noticed weakening in the energy coupling parameter for SC 24, which resulted in substantial (15%–38%) decrease in average strength of high latitude ionospheric (AE), low latitude magnetospheric (Dst) and equatorial ionospheric (EEJ) current systems in comparison with SC 23. Subsequently, a reduction of ≈30% is manifested in the high latitude Joule heating for SC 24. Overall this study indicates the significant step down in various energies at Sun, Earth’s bow-shock, and near Earth environment for current SC 24, which will have important implication on our Earth’s atmosphere-ionosphere-magnetosphere system.

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Section: Data Sets and Energy Estimatesmentioning

confidence: 99%

Diminishing activity of recent solar cycles (22–24) and their impact on geospace

Kakad

Ramesh

et al. 2019

J. Space Weather Space Clim.

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“…This resulted in a binary mask in which 1 corresponded to the pixels of interest, and 0 the rest. This minimum chosen value of the magnetic flux density is close to the noise level of the HMI_720s magnetograms (Liu et al 2012;Bose & Nagaraju 2018). Finally, we used this mask to extract the cospatial quiet-Sun (less active) pixels from each AIA channel and computed the respective 1D histograms of the intensity values as shown in Fig.…”

Section: Baseline Modelmentioning

confidence: 96%

Multichannel autocalibration for the Atmospheric Imaging Assembly using machine learning

Santos

Bose

Salvatelli

et al. 2021

A&A

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Context. Solar activity plays a quintessential role in affecting the interplanetary medium and space weather around Earth. Remote-sensing instruments on board heliophysics space missions provide a pool of information about solar activity by measuring the solar magnetic field and the emission of light from the multilayered, multithermal, and dynamic solar atmosphere. Extreme-UV (EUV) wavelength observations from space help in understanding the subtleties of the outer layers of the Sun, that is, the chromosphere and the corona. Unfortunately, instruments such as the Atmospheric Imaging Assembly (AIA) on board the NASA Solar Dynamics Observatory (SDO), suffer from time-dependent degradation that reduces their sensitivity. The current best calibration techniques rely on flights of sounding rockets to maintain absolute calibration. These flights are infrequent, complex, and limited to a single vantage point, however. Aims. We aim to develop a novel method based on machine learning (ML) that exploits spatial patterns on the solar surface across multiwavelength observations to autocalibrate the instrument degradation. Methods. We established two convolutional neural network (CNN) architectures that take either single-channel or multichannel input and trained the models using the SDOML dataset. The dataset was further augmented by randomly degrading images at each epoch, with the training dataset spanning nonoverlapping months with the test dataset. We also developed a non-ML baseline model to assess the gain of the CNN models. With the best trained models, we reconstructed the AIA multichannel degradation curves of 2010–2020 and compared them with the degradation curves based on sounding-rocket data. Results. Our results indicate that the CNN-based models significantly outperform the non-ML baseline model in calibrating instrument degradation. Moreover, multichannel CNN outperforms the single-channel CNN, which suggests that cross-channel relations between different EUV channels are important to recover the degradation profiles. The CNN-based models reproduce the degradation corrections derived from the sounding-rocket cross-calibration measurements within the experimental measurement uncertainty, indicating that it performs equally well as current techniques. Conclusions. Our approach establishes the framework for a novel technique based on CNNs to calibrate EUV instruments. We envision that this technique can be adapted to other imaging or spectral instruments operating at other wavelengths.

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“…Especially it is seen in areas of dark spots [29]. According to numerous data, B 0 has a value of several gauss (see, for example, [30] and references therein). (In this paper, we will assume B 0 ∼ 10 G for estimates.)…”

Section: Convection In Astrophysicsmentioning

confidence: 99%

Notes about collapse in magnetohydrodynamics

Kuznetsov,

Mikhailov

2022

Preprint

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We discuss a problem about magnetic collapse as a possible process for singularity formation of the magnetic field in a finite time within ideal magneto-hydrodynamics for incompressible fluids. This process is very important from the point of view of various astrophysical applications, in particular, as a mechanism of magnetic filaments formation in the convective zone of the Sun. The collapse possibility is connected with compressibility of continuously distributed magnetic field lines. A wellknown example of the formation of magnetic filaments in the kinematic dynamo approximation with a given velocity field, first considered by Parker in 1963 [1], rather indicates that the increase in the magnetic field is exponential in time. In the case of the kinematic approximation for the induction equation, the magnetic filaments formation is shown to occur in areas with a hyperbolic velocity profile.

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On the Variability of the Solar Mean Magnetic Field: Contributions from Various Magnetic Features on the Surface of the Sun

Cited by 21 publications

References 38 publications

Diminishing activity of recent solar cycles (22–24) and their impact on geospace

Diminishing activity of recent solar cycles (22–24) and their impact on geospace

Multichannel autocalibration for the Atmospheric Imaging Assembly using machine learning

Notes about collapse in magnetohydrodynamics

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