اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدOn the Origin of Otho-Gardenhose Heliospheric Flux
64
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
Parker spiral theory predicts the heliospheric magnetic field (HMF) will have components of opposite polarity radially toward the Sun and tangentially antiparallel to the solar rotation (i.e. in GSE coordinates, with Bx/By<0). This theory explains the average orientation of the HMF very well but does not predict orthogardenhose (OGH) flux with BX/BY>0 that is often observed. We here study the occurrence and structure of OGH flux, as seen in near-Earth space (r=1AU) and by the Helios spacecraft at 0.29<r<1AU, in order to evaluate the contributions to OGH flux generation of the various mechanisms and factors that are not accounted for in Parker spiral theory. We study the loss of OGH flux with increasing averaging timescale between 16 seconds and 100 hours and so determine its spectrum of scale sizes. OGH flux at sunspot minimum is shown to be more common than at sunspot maximum and caused by smaller-scale structure in the HMF, with a mode temporal scale at a fixed point of 10hrs compared to 40hrs. OGH generated by rotating the HMF through the radial direction is also shown to differ in its spectrum of scale sizes from that generated by rotating the HMF through the tangential direction: the former does not contribute to the excess open heliospheric flux at a given r but the latter does. We show that roughly half of the HMF deflection from the ideal Parker spiral giving OGH at Earth occurs at r below 0.3AU. We highlight some questions which can be addressed by the Parker Solar Probe mission which will study the HMF down to r=0.046AU.
قيم البحث
اقرأ أيضاً
Solar and heliospheric cosmic rays provide a unique perspective in cosmic ray research: we can observe not only the particles, but also the properties of the plasmas in which the they are accelerated and propagate, using in situ and high-resolution r
emote sensing instruments. The heliospheric cosmic ray observations typically require space missions, which face stern competition against planetary and astrophysics missions, and it can take up to decades from the initial concept proposal until the actual observing of the cosmic rays can commence. Therefore it is important to have continuity in the cosmic ray mission timeline. In this overview, we review the current status and the future outlook in the experimental solar and heliospheric research. We find that the current status of the available cosmic ray observations is good, but that many of the spacecraft are near the end of their feasible mission life. We describe the three missions currently being prepared for launch, and discuss the future outlook of the solar and heliospheric cosmic ray missions.
Maps of the radial magnetic field at a heliocentric distance of ten solar radii are used as boundary conditions in the MHD code CRONOS to simulate a 3D inner-heliospheric solar wind emanating from the rotating Sun out to 1 AU. The input data for the
magnetic field are the result of solar surface flux transport modelling using observational data of sunspot groups coupled with a current sheet source surface model. Amongst several advancements, this allows for higher angular resolution than that of comparable observational data from synoptic magnetograms. The required initial conditions for the other MHD quantities are obtained following an empirical approach using an inverse relation between flux tube expansion and radial solar wind speed. The computations are performed for representative solar minimum and maximum conditions, and the corresponding state of the solar wind up to the Earths orbit is obtained. After a successful comparison of the latter with observational data, they can be used to drive outer-heliospheric models.
A major challenge in solar and heliospheric physics is understanding how highly localized regions, far smaller than 1 degree at the Sun, are the source of solar-wind structures spanning more than 20 degrees near Earth. The Suns atmosphere is divided
into magnetically open regions, coronal holes, where solar-wind plasma streams out freely and fills the solar system, and closed regions, where the plasma is confined to coronal loops. The boundary between these regions extends outward as the heliospheric current sheet (HCS). Measurements of plasma composition imply that the solar wind near the HCS, the so-called slow solar wind, originates in closed regions, presumably by the processes of field-line opening or interchange reconnection. Mysteriously, however, slow wind is also often seen far from the HCS. We use high-resolution, three-dimensional magnetohydrodynamic simulations to calculate the dynamics of a coronal hole whose geometry includes a narrow corridor flanked by closed field and which is driven by supergranule-like flows at the coronal-hole boundary. We find that these dynamics result in the formation of giant arcs of closed-field plasma that extend far from the HCS and span tens of degrees in latitude and longitude at Earth, accounting for the slow solar wind observations.
In this study, we evaluate a coronal mass ejection (CME) arrival prediction tool that utilizes the wide-angle observations made by STEREOs heliospheric imagers (HI). The unsurpassable advantage of these imagers is the possibility to observe the evolu
tion and propagation of a CME from close to the Sun out to 1 AU and beyond. We believe that by exploiting this capability, instead of relying on coronagraph observations only, it is possible to improve todays CME arrival time predictions. The ELlipse Evolution model based on HI observations (ELEvoHI) assumes that the CME frontal shape within the ecliptic plane is an ellipse, and allows the CME to adjust to the ambient solar wind speed, i.e. it is drag-based. ELEvoHI is used to perform ensemble simulations by varying the CME frontal shape within given boundary conditions that are consistent with the observations made by HI. In this work, we evaluate different set-ups of the model by performing hindcasts for 15 well-defined isolated CMEs that occurred when STEREO was near L4/5, between the end of 2008 and the beginning of 2011. In this way, we find a mean absolute error of between $6.2pm7.9$ h and $9.9pm13$ h depending on the model set-up used. ELEvoHI is specified for using data from future space weather missions carrying HIs located at L5 or L1. It can also be used with near real-time STEREO-A HI beacon data to provide CME arrival predictions during the next $sim7$ years when STEREO-A is observing the Sun-Earth space.
Over the solar-activity cycle, there are extended periods where significant discrepancies occur between the spacecraft-observed total (unsigned) open magnetic flux and that determined from coronal models. In this article, the total open heliospheric
magnetic flux is computed using two different methods and then compared with results obtained from in-situ interplanetary magnetic-field observations. The first method uses two different types of photospheric magnetic-field maps as input to the Wang Sheeley Arge (WSA) model: i) traditional Carrington or diachronic maps, and ii) Air Force Data Assimilative Photospheric Flux Transport model synchronic maps. The second method uses observationally derived helium and extreme-ultraviolet coronal-hole maps overlaid on the same magnetic-field maps in order to compute total open magnetic flux. The diachronic and synchronic maps are both constructed using magnetograms from the same source, namely the National Solar Observatory Kitt Peak Vacuum Telescope and Vector Spectromagnetograph. The results of this work show that the total open flux obtained from observationally derived coronal holes agrees remarkably well with that derived from WSA, especially near solar minimum. This suggests that, on average, coronal models capture well the observed large-scale coronal-hole structure over most of the solar cycle. Both methods show considerable deviations from total open flux deduced from spacecraft data, especially near solar maximum, pointing to something other than poorly determined coronal-hole area specification as the source of these discrepancies.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
