modeling

Magnetic field and plasma diagnostics for solar coronal mass ejections: A case study using the forward modeling approach

whawkins — Fri, 03 Mar 2023 22:05:34 +0000

Magnetic field and plasma diagnostics for solar coronal mass ejections: A case study using the forward modeling approach whawkins Fri, 03/03/2023 - 15:05

Author:

whawkins

Mar 3, 2023

Synthesized results of the Fe xiii 10747 line, along with several POS cross section quantities in the model during CME eruption (a)-(e): Intensity (Stokes I), linear polarization degree(L/I), line width, Doppler velocity, and azimuth derived from synthesized signals. (f)-(h): Magnetic field, temperature, and density distributions in the POS. The arc-shaped contour in each panel represents ∇ · v = −0.05. Two leading fronts (LF) can be distinguished in panel (a). Each white arrow in panel (g) represents the POS projection of the deduced shock normals. The solar disk is indicated by the yellow curve in each panel. The region below 1.05R⊙ is masked.

Solar Physics: The proposed COronal Solar Magnetism Observatory (COSMO) Large Coronagraph (LC) will provide unique observations to study coronal mass ejections (CMEs) with its ability to diagnose the magnetic field and plasma properties in the solar corona. Here we take a realistic magnetohydrodynamic CME model, and synthesize the signals of several coronal emission lines (CELs) to perform forward modeling of COSMO LC observation of a CME. We use the Stokes parameters of the Fe xiii 10747 Angstrom line to diagnose the magnetic field and plasma properties of the CME flux rope. The results show that COSMO LC can provide magnetic field measurements of CME progenitors with a high spatial resolution (2′′ pixels). By using a worse resolution (6′′ pixels), the COSMO LC observation may also be used to qualitatively study the evolution of magnetic field during the CME eruption. We then use the synthetic signals of several other CELs to diagnose the physical conditions in the CME leading front, including the shock. The COSMO LC observations of the Fe xiii 10798/10747 Angstrom and Ar xiii 8300/10143 Angstrom line pair can provide density diagnostics of the front. By observing several CELs with different formation temperatures, the COSMO LC can be used to diagnose the temperature and ionization states in the front. We suggest that the Fe xiii 10747 Angstrom line should be given the highest priority when observing CMEs, while observations of the Fe xiii 10798 Angstrom, Fe xiv 5303 Angstrom, Fe xv 7062 Angstrom, and Ar xiii 10143 Angstrom lines can also provide valuable information on CMEs.

Equinoctial Asymmetry in the Upper Ionosphere: Comparison of Satellite Observations and Models

whawkins — Wed, 05 Oct 2022 17:16:46 +0000

Equinoctial Asymmetry in the Upper Ionosphere: Comparison of Satellite Observations and Models whawkins Wed, 10/05/2022 - 11:16

Author:

whawkins

Oct 5, 2022

JGR Space Phyics—L. Lomidze, D. J. Knudsen, M. Shepherd, J. D. Huba, and A. Maute

SAMI3 simulation results for electron density near noon using TIE-GCM neutral atmosphere as a model input, the bottom panel is the corresponding relative (in %) change for Ne. The wind effect on electron density is shown by the black dashed line and the neutral density by the turquoise line.

The terrestrial ionosphere displays significant equinoctial asymmetry despite the upper atmosphere receiving similar levels of solar ionization energy at a given location and local time in spring and fall during similar solar activity conditions. This intriguing feature is not well understood or modelled, particularly in the upper ionosphere, and causes of the asymmetry are not fully established and quantified. Yet, their study is important to provide better insights into the atmosphere-ionosphere coupling processes. Analysis of Langmuir probe data from ESA’s Swarm satellite at ~525 km altitude reveals that the daytime electron density is larger for all latitudes during March than during September, while the electron temperature shows inverted asymmetry except at low latitudes. Simultaneously obtained neutral density data from Swarm GPS accelerations indicate that the thermosphere is denser during the spring. The asymmetry seen by Swarm electron density observations is also present in electron densities obtained using GPS radio occultation measurements from the COSMIC satellites. Simulations were performed using physics-based ionosphere models (SAMI3, WACCM-X, and TIE-GCM) to determine their ability to produce the observed asymmetry, understand the generation mechanism(s), and establish the relative role of physical drivers. Modeling of the asymmetry by SAMI3 driven with the TIE-GCM neutral atmosphere shows that both neutral density and winds play a critical role, but the density has a greater effect.

Effects of spectral resolution on simple magnetic field diagnostics of the Mg II h & k lines

whawkins — Fri, 23 Sep 2022 21:17:25 +0000

Effects of spectral resolution on simple magnetic field diagnostics of the Mg II h & k lines whawkins Fri, 09/23/2022 - 15:17

Author:

whawkins

Sep 23, 2022

The Astrophysical Journal: Rebecca Centeno, Matthias Rempel, Roberto Casini, and Tanausu del Pino Aleman study the effects of finite spectral resolution on the magnetic field values retrieved through the weak field approximation (WFA) from the cores of the Mg II h&k lines. The retrieval of the line-of-sight (LOS) component of the magnetic field, Blos, from synthetic spectra generated in a uniformly magnetized FAL-C atmosphere are accurate when restricted to the inner lobes of Stokes V. As we degrade the spectral resolution, partial redistribution (PRD) effects that more prominently affect the outer lobes of Stokes V, are brought into the line core through spectral smearing, degrading the accuracy of the WFA and resulting in an inference bias, which is more pronounced the poorer the resolution. When applied to a diverse set of spectra emerging from a sunspot simulation, we find a good accuracy in the retrieved Blos when comparing it to the model value at the height where the optical depth in the line core is unity. The accuracy is preserved up to field strengths of B~1700 G. Limited spectral resolution results in a bias toward weaker retrieved fields. The WFA for the transverse component of the magnetic field is also evaluated. We find the best estimates when the WFA is evaluated in the core of the line. Reduced spectral resolution degrades the accuracy of the inferences because spectral mixing results in the line effectively probing deeper layers of the atmosphere.

Scatter density plots of the retrieved value of Blos retrieved from Mg II h using the weak field approximation, against their MURaM model counterparts for the case of infinite spectral resolution (left), R = 45,000h (middle) and R = 30,000 (right). The model values are taken at the height where the core of the Mg II h line reaches optical depth unity. The darker the grey-level, the higher the number of samples in the bin. The bin size is 40 G. The red line represents the ideal solution and the blue line shows a linear fit through the data.

Scientific Motivations and Future Directions of Whole Atmosphere Modeling

whawkins — Fri, 16 Sep 2022 17:58:22 +0000

Scientific Motivations and Future Directions of Whole Atmosphere Modeling whawkins Fri, 09/16/2022 - 11:58

Author:

whawkins

Sep 16, 2022

Frontiers in Astronomy and Space Sciences: Dr.Nick Pedatella asserts that the recent development of whole atmosphere models that extend from the surface to the upper thermosphere represents a significant advance in modeling capabilities of the ionosphere-thermosphere. Whole atmosphere models have had an especially important influence on understanding the role of terrestrial weather on generating variability in the ionosphere-thermosphere. This paper provides an overview of the scientific motivations and contributions made by whole atmosphere modeling. This is followed by a discussion of future directions in whole atmosphere modeling and the science that they will enable.

Schematic of the various mechanisms through which lower-atmosphere processes influence the ionosphere-thermosphere. Whole atmosphere models are critical for understanding these processes.

Figure from the 2013 Solar and Space Physics Decadal Survey.

On the variability of total electron content over Europe during the 2009 and 2019 Northern Hemisphere SSWs

whawkins — Fri, 02 Sep 2022 16:51:20 +0000

On the variability of total electron content over Europe during the 2009 and 2019 Northern Hemisphere SSWs whawkins Fri, 09/02/2022 - 10:51

Author:

whawkins

Sep 2, 2022

JGR- Space Physics: T. A. Siddiqui, Y. Yamazaki, C. Stolle, A. Maute, J. Lastovicka , I. K. Edemskiy, Z. Mosna.

Sudden Stratospheric Warming events are a polar winter phenomena which mainly occurs in the northern hemisphere. They are associated with large scale changes in the stratosphere which modify significant the solar and lunar tide with a 12 hr period, coupling into the upper atmosphere. One of the observed changes is in middle and low latitudes total electron content (TEC). In this study the variations of the TEC over Europe is investigated during two northern hemisphere SSWs events in 2009 and 2019. TEC variations can be caused by the vertical coupling to lower atmosphere and by geomagnetic forcing. Delineating the two cause of TEC variability in observations is challenging. We investigated the dominant drivers and their respective contributions to TEC changes during both SSW events. We simulate the SSWs using the Whole Atmosphere Community Climate Model eXtended version (WACCM-X) and compare the SSW effect on the semidiurnal solar and lunar tidal variabilities in the mesosphere-lower thermosphere (MLT) region. Further, in order to assess the mechanisms responsible for the TEC variability during the SSWs, we analyze the difference between simulations with the Thermosphere-Ionosphere Electrodynamics General Circulation Model (TIE-GCM) driven by WACCM_X fields at the lower boundary with and without geomagnetic forcing. The TIE-GCM simulations allow us to isolate the geomagnetic and lower atmospheric forcing effects on the TEC. We find that there was a major enhancement in daytime TEC over Europe during the 2019 SSW event, which was predominantly geomagnetically forced (∼80%), while for the 2009 SSW, the major variability in TEC was accounted for by lower atmospheric forcing.

Daily averaged TEC over Europe for TIE-GCM forced at the lower boundary by WACCM-X and (a) S1 with geomagnetic forcing and (b) S2 without geomagnetic forcing, as a function of universal time for the 2019 SSW. The TEC increase attributed to the geomagnetic forcing is illustrated in (c) by the difference of (a) and (b). The filled contour lines in (c) are only plotted when absolute TEC difference exceeds 1 TECU. The dashed black and blue open contour lines mark the contribution of geo- magnetic forcing to the TEC variability at 40 and 80% levels, respectively. The vertical black dashed lines mark the day of PVW.

The Multiscale Atmosphere-Geospace Environment (MAGE) model

kolinski — Mon, 11 Jul 2022 21:20:33 +0000

The Multiscale Atmosphere-Geospace Environment (MAGE) model kolinski Mon, 07/11/2022 - 15:20

The effects of IMF By on the middle thermosphere during a geomagnetically “quiet” period at solar minimum

kolinski — Mon, 11 Jul 2022 21:02:35 +0000

The effects of IMF By on the middle thermosphere during a geomagnetically “quiet” period at solar minimum kolinski Mon, 07/11/2022 - 15:02

Publication: JR Space Physics; Authors: Xuguang Cai, Wenbin Wang, Alan Burns, Liying Qian, Richard W. Eastes

Author:

kolinski

Jul 11, 2022

The polar view of the percentage difference of simulated ∑O/N2 and GOLD observed ∑O/N2 between DOY 111 and 110 at 15:10 UT in 2019. The perimeter latitude is 30°N

Numerical simulations using the National Center for Atmospheric Research (NCAR) thermosphere-ionosphere-electrodynamics general circulation model (TIE-GCM) are performed to elucidate the effects of the interplanetary magnetic field (IMF) on the middle thermosphere composition during a “geomagnetically quiet” period from the day of year (DOY) 110-111 in 2019 (when the Auroral electrojet (AE) index never exceeded 300 nT and the Kp never exceeded 2). In particular, this paper aims to examine how the Global-scale Observations of the Limb and Disk (GOLD) mission observed daytime thermospheric O and N2 column density ratio (∑O/N2) depletion at mid-latitudes originated under such a “geomagnetically quiet” condition. A comparison of electric potential, Joule heating rate per unit mass, ion velocity, neutral temperature and winds in the middle thermosphere (∼160 km) between real IMF and without the IMF east-west component (By) indicates that a By dominant condition can enhance their strengths under this “geomagnetically quiet” condition. Consequently, ∑O/N2 depletion with a stronger magnitude (30% compared with ∼8% without By) and larger disturbed area was introduced in the post-midnight sector at high-latitudes due to strong and localized upwelling associated with the enhanced Joule heating rate per unit mass. The ∑O/N2 depletion was transported equatorward and corotated from local post-midnight to early morning, and was observed by GOLD at middle latitudes during daytime.

The Molecular Oxygen Density Structure of the Lower Thermosphere as Seen by GOLD and Models

kolinski — Mon, 11 Jul 2022 20:39:20 +0000

The Molecular Oxygen Density Structure of the Lower Thermosphere as Seen by GOLD and Models kolinski Mon, 07/11/2022 - 14:39

Publication: Geophysics Research Letters; Author's: K. R. Greer, F. Laskar, R. Eastes, J. Lumpe, H.-L. Liu, and N. Pedatella

Author:

kolinski

Jul 11, 2022

Comparisons of local time structure of molecular oxygen at 21°N, 170 km altitude. Red dots are for the longitude of 33°E, while blue dots are for the longitude of 128°W. Panel (a) shows molecular oxygen densities as observed by the GOLD instrument for one star, HD74280, between January 2019 and July 2021. Panel (b) are results from the MSISE-00 empirical model sampled for the same locations and conditions as the GOLD observations. Panel (c) is as panel (b) but for the MSIS2.0 empirical model. Panel (d) shows the SD-WACCM-X model sampled for the GOLD observations. The observations show a distinctly diurnal structure in local time, while all the model results indicate a semidiurnal structure.

This paper compares new observations from the Global-scale Observations of Limb and Disk (GOLD) mission of molecular oxygen (O2) in the lower thermosphere (130 - 200 km in altitude) to widely used models in the aeronomy community. The main finding is that the local time structure of the observed molecular oxygen has a minimum at 6 hours local time and a peak near 18 hours local time while the models all show a structure that has peaks at both 6 and 18 hours local time. This significant difference not only influences the total neutral thermospheric density results from the models, but may ultimately impact the calculated ionospheric plasma density and its temporal variability. Understanding ionospheric plasma densities is vital for the proper modeling of the propagation of communications and navigational signals.

Efficient numerical treatment of ambipolar and Hall drift as hyperbolic system

kolinski — Thu, 03 Mar 2022 22:06:31 +0000

Efficient numerical treatment of ambipolar and Hall drift as hyperbolic system kolinski Thu, 03/03/2022 - 15:06

Publication: Astrophysical Journal; Authors: M. Rempel and D. Przybylski

Author:

kolinski

Mar 3, 2022

Snapshot from a two-dimensional test simulation setup with a 8x8Mm domain reaching from the upper convection zone into the transition region. Presented are a) temperature, b) density, c) magnetic field strength, d) ambipolar diffusivity, e) ambipolar drift velocity, and f) ambipolar heating. The latter two were computed using the hyperbolic treatment introduced in this publication.

Partially ionized plasmas, such as the solar chromosphere, require a generalized Ohm's law including the effects of ambipolar and Hall drift. While both describe transport processes that arise from the multifluid equations and are therefore of hyperbolic nature, they are often incorporated in models as a diffusive, i.e. parabolic process. While the formulation as such is easy to include in standard MHD models, the resulting diffusive time-step constraints do require often a computationally more expensive implicit treatment or super-time-stepping approaches. In this paper we discuss an implementation that retains the hyperbolic nature and allows for an explicit integration with small computational overhead. In the case of ambipolar drift, this formulation arises naturally by simply retaining a time derivative of the drift velocity that is typically omitted. This alone leads to time-step constraints that are comparable to the native MHD time-step constraint for a solar setup including the region from photosphere to lower solar corona. We discuss an accelerated treatment that can further reduce time-step constraints if necessary. In the case of Hall drift we propose a hyperbolic formulation that is numerically similar to that for the ambipolar drift and we show that the combination of both can be applied to simulations of the solar chromosphere at minimal computational expense.

On the (In)stability of Sunspots

kolinski — Thu, 03 Mar 2022 21:55:08 +0000

On the (In)stability of Sunspots kolinski Thu, 03/03/2022 - 14:55

Publication: Astronomy & Astrophysics; Authors: H. Strecker, W. Schmidt, R. Schlichenmaier, M. Rempel

Author:

kolinski

Mar 3, 2022

The stability of sunspots is one of the long-standing unsolved puzzles in the field of solar magnetism and the solar cycle. The thermal and magnetic structure of the sunspot beneath the solar surface is not accessible through observations, thus processes in these regions that contribute to the decay of sunspots can only be studied through theoretical and numerical studies.

Aims: We study the effects that destabilise and stabilise the flux tube of a simulated sunspot in the upper convection zone. The depth-varying effects of fluting instability, buoyancy forces, and timescales on the flux tube are analysed.

Maps of the magnetic field strength at depth of z = −7.5 Mm beneath the solar photosphere at different times (indicated in red in each panel). The boundary of the sunspot (red line) is defined by the contour value Bc = 4781 G. At the beginning of the analysis, at t = 0 h, panel (a), the inner part of the flux tube is mainly undisturbed. Within 6 hours, regions of weaker field appear in the innermost part of the flux tube while the outer structure becomes more ragged, as is shown in panel (b). The increasing raggedness causes a degradation of the flux tube. This degradation process continues in time, as panels (c–e) show. At 29.75 h, the roundish structure of the flux tube has completely vanished. The degradation process takes place in all regions deeper than 1 Mm below the surface.

Methods: We analysed a numerical simulation of a sunspot calculated with the MURaM code. The simulation domain has a lateral extension of more than 98 Mm × 98 Mm and extends almost 18 Mm below the solar surface. The analysed data set of 30 hours shows a stable sunspot at the solar surface. We studied the evolution of the flux tube at defined horizontal layers (1) by means of the relative change in perimeter and area, that is, its compactness; and (2) with a linear stability analysis.

Results: The simulation shows a corrugation along the perimeter of the flux tube (sunspot) that proceeds fastest at a depth of about 8 Mm below the solar surface. Towards the surface and towards deeper layers, the decrease in compactness is damped. From the stability analysis, we find that above a depth of 2 Mm, the sunspot is stabilised by buoyancy forces. The spot is least stable at a depth of about 3 Mm because of the fluting instability. In deeper layers, the flux tube is marginally unstable. The stability of the sunspot at the surface affects the behaviour of the field lines in deeper layers by magnetic tension. Therefore the fluting instability is damped at depths of about 3 Mm, and the decrease in compactness is strongest at a depth of about 8 Mm. The more vertical orientation of the magnetic field and the longer convective timescale lead to slower evolution of the corrugation process in layers deeper than 10 Mm.

Conclusions: The formation of large intrusions of field-free plasma below the surface destabilises the flux tube of the sunspot. This process is not visible at the surface, where the sunspot is stabilised by buoyancy forces. The onset of sunspot decay occurs in deeper layers, while the sunspot still appears stable in the photosphere. The intrusions eventually lead to the disruption and decay of the sunspot.

modeling

Magnetic field and plasma diagnostics for solar coronal mass ejections: A case study using the forward modeling approach

Recent News

Equinoctial Asymmetry in the Upper Ionosphere: Comparison of Satellite Observations and Models

Recent News

Effects of spectral resolution on simple magnetic field diagnostics of the Mg II h & k lines

Recent News

Scientific Motivations and Future Directions of Whole Atmosphere Modeling

Recent News

On the variability of total electron content over Europe during the 2009 and 2019 Northern Hemisphere SSWs

Recent News

The Multiscale Atmosphere-Geospace Environment (MAGE) model

Recent News

The effects of IMF By on the middle thermosphere during a geomagnetically “quiet” period at solar minimum

Recent News

The Molecular Oxygen Density Structure of the Lower Thermosphere as Seen by GOLD and Models

Recent News

Efficient numerical treatment of ambipolar and Hall drift as hyperbolic system

Recent News

On the (In)stability of Sunspots

Recent News