اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدPlasma flow vs. magnetic feature-tracking speeds in the Sun
172
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We simulate the magnetic feature tracking (MFT) speed using advective-diffusive transport models in both one and two dimensions. By depositing magnetic bipolar regions at different latitudes at the Suns surface and following their evolution for a prescribed meridional circulation and magnetic diffusivity profiles, we derive the MFT speed as a function of latitude. We find that in a one dimensional surface-transport model the simulated MFT speed at the surface is always the same as the meridional flow-speed used as input to the model, but is different in a two-dimensional transport model in the meridional (r,theta) plane. The difference depends on the value of the magnetic diffusivity and on the radial gradient of the latitudinal velocity. We have confirmed our results with two different codes in spherical and Cartesian coordinates.
قيم البحث
اقرأ أيضاً
Recent observations revealed that small magnetic elements abundant at the solar surface move poleward with a velocity which seems to be lower than the plasma velocity $U_{theta}$. Guerrero et al. (2011) explained this discrepancy as a consequence of
diffusive spreading of the magnetic elements due to a positive radial gradient of $|U_{theta}|$. As the gradients sign (inferred by local helioseismology) is still unclear, cases with a negative gradient are studied in this paper. Under this condition, the velocity of the magnetic tracers turns out to be larger than the plasma velocity, in disagreement with the observations. Alternative mechanisms for explaining them independently are proposed. For the turbulent magnetic pumping it is shown that it has to be unrealistically strong to reconcile the model with the observations.
We perform radiative magnetohydrodynamic calculations for the solar quiet region to investigate the dependence of statistical flow on magnetic properties and the three-dimensional (3D) structure of magnetic patches in the presence of large-scale flow
that mimics differential rotation. It has been confirmed that strong magnetic field patches move faster in the longitudinal direction at the solar surface. Consequently, strong magnetic patches penetrate deeper into the solar interior. The motion of the deep-rooted magnetic patches is influenced by the faster differential rotation in the deeper layer. In this study, we perform realistic radiative magnetohydrodynamic calculations using R2D2 code to validate that stronger patches have deeper roots. We also add large-scale flow to mimic the differential rotation. The magnetic patches are automatically detected and tracked, and we evaluate the depth of 30,000 magnetic patches. The velocities of 2.9 million magnetic patches are then measured at the photosphere. We obtain the dependence of these values on the magnetic properties, such as field strength and flux. Our results confirm that strong magnetic patches tend to show deeper roots and faster movement, and we compare our results with observations using the point spread function of instruments at the Hinode and Solar Dynamics Observatory (SDO). Our result is quantitatively consistent with previous observational results of the SDO.
Spicules are the most ubuiquitous type of jets in the solar atmosphere. The advent of high-resolution imaging and spectroscopy from the Interface Region Imaging Spectrograph (IRIS) and ground-based observatories has revealed the presence of very high
apparent motions of order 100-300 km/s in spicules, as measured in the plane of the sky. However, line-of-sight measurements of such high speeds have been difficult to obtain, with values deduced from Doppler shifts in spectral lines typically of order 30-70 km/s. In this work we resolve this long-standing discrepancy using recent 2.5D radiative MHD simulations. This simulation has revealed a novel driving mechanism for spicules in which ambipolar diffusion resulting from ion-neutral interactions plays a key role. In our simulation we often see that the upward propagation of magnetic waves and electrical currents from the low chromosphere into already existing spicules can lead to rapid heating when the currents are rapidly dissipated by ambipolar diffusion. The combination of rapid heating and the propagation of these currents at Alfvenic speeds in excess of 100 km/s leads to the very rapid apparent motions, and often wholesale appearance, of spicules at chromospheric and transition region temperatures. In our simulation, the observed fast apparent motions in such jets are actually a signature of a heating front, and much higher than the mass flows, which are of order 30-70 km/s. Our results can explain the behavior of transition region network jets and the very high apparent speeds reported for some chromospheric spicules.
We investigate the fine structure of magnetic fields in the atmosphere of the quiet Sun. We use photospheric magnetic field measurements from {sc Sunrise}/IMaX with unprecedented spatial resolution to extrapolate the photospheric magnetic field into
higher layers of the solar atmosphere with the help of potential and force-free extrapolation techniques. We find that most magnetic loops which reach into the chromosphere or higher have one foot point in relatively strong magnetic field regions in the photosphere. $91%$ of the magnetic energy in the mid chromosphere (at a height of 1 Mm) is in field lines, whose stronger foot point has a strength of more than 300 G, i.e. above the equipartition field strength with convection. The loops reaching into the chromosphere and corona are also found to be asymmetric in the sense that the weaker foot point has a strength $B < 300$ G and is located in the internetwork. Such loops are expected to be strongly dynamic and have short lifetimes, as dictated by the properties of the internetwork fields.
We present a visual determination of the number of bright points (BPs) existing in the quiet Sun, which are structures though to trace intense kG magnetic concentrations. The measurement is based on a 0.1 arcsec angular resolution G-band movie obtain
ed with the Swedish Solar Telescope at the solar disk center. We find 0.97 BPs/Mm^2, which is a factor three larger than any previous estimate. It corresponds to 1.2 BPs per solar granule. Depending on the details of the segmentation, the BPs cover between 0.9% and 2.2% of the solar surface. Assuming their field strength to be 1.5 kG, the detected BPs contribute to the solar magnetic flux with an unsigned flux density between 13 G and 33 G. If network and inter-network regions are counted separately, they contain 2.2 BPs/Mm^2 and 0.85 BPs/Mm^2, respectively.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
