كليدواژه :
ميدان مغناطيسي , ماهواره كلاستر , مغناطوسپهر , لايه گذار آلفوني
چكيده فارسي :
اخيرا با مطالعۀ آماري مشاهدات ماهوارۀ كلاستر (CLUSTER satellite system) يك لايۀ گذار در داخل غلاف مغناطيسي گزارش شده است. اين لايه با (MA=1 (Alfven Mach به جريان كلي ذرات (Bulk flow) اجازه مي‌دهد كه از فراآلفوني به فروآلفوني از طرف خارج كاسپ (Cusp) بيروني به سمت داخل كاسپ تبديل شود و در حالت باد خورشيدي با جهت ميدان مغناطيسي بين سياره‌اي (Interplanetary Magnetic Field (IMF) شمالي مشاهده شود، اما نتايج شبيه‌سازي وجود آن را در شرايط باد خورشيدي با جهت ميدان مغناطيسي بين سياره‌اي جنوبي در طول تمام مرز مغناطوسپهر نيز نشان مي‌دهد. نقش اين لايه به‌منظور درك تغييرات جريان كلي ذرات در نزديكي مرز كاسپ بيروني مهم است. به منظور تحليل اين لايه، از يك شبيه‌سازي سه‌بعدي ذره‌اي با اندازۀ بزرگ‌مقياس براي برهم‌كنش باد خورشيدي با مغناطوسپهر زمين استفاده شده است. ما IMF را از جهت شمال به سمت جنوب چرخانده‌ايم تا ديناميك لايۀ گذار آلفوني (ATL) را با توجه به چرخش IMF بررسي كنيم. اگرچه در مطالعات آماري كلاستر (CLUSTER) تنها منطقۀ محدودي از مغناطوسپهر براي اين لايۀ آلفوني مطالعه شده است، ما اين لايه را براي كل مغناطوسپهر بررسي كرده و ديناميك آن را با توجه به چرخش IMF از شمال به سمت جنوب بررسي كرده‌ايم و در نهايت نتايج به‌دست‌آمده از شبيه‌سازي را با مشاهدات تجربي مقايسه كرده‌ايم. نتايج حاصل از شبيه‌سازي براي جريان‌هاي موازي ذرات و انتقال به ارتفاعات كمتر لايۀ گذار آلفوني با مشاهدات حاصل از ماهوارۀ كلاستر براي حالت IMF جنوبي سازگار است.
چكيده لاتين :
Space weather is the concept of changing environmental conditions in the space from the solar atmosphere to the geospace. Much of space weather is driven by energy carried by solar wind through the interplanetary space from regions near the surface of Sun and Sun’s atmosphere. Space weather has two focal points: scientific research and applications. Space weather research touches upon the large-scale energy and matter eruptions from the solar activity region, the propagation and evolution of the interplanetary disturbances, the response of the geospace to the interplanetary disturbances, the significant changes of the geospace environment, and finally the impact on the human activities. The magnetosphere is the outermost layer of the geospace, and the interaction of solar wind with the magnetosphere is the key element of the space weather cause-and-effect chain process from Sun to Earth, which is one of the most challenging scientific problems in the geospace weather study. The nonlinearity, multiple component, and time-dependent nature of the geospace make it very difficult to describe in terms of the physical process in geospace using traditional analytic analysis approach. Numerical simulations, a new research tool developed in recent decades, have a deep impact on the theory and application of the geospace. The low- and middle-altitude cusp regions of Earth’s magnetosphere have been widely studied in the past. However, the high-altitude cusp region was not explored extensively in the early days of space science, with the notable exception of the HEOS-2 spacecraft which undertook the first detailed investigations of this part of the magnetosphere. More recently, major advances on the role of this key region, which is in direct interaction with the solar wind, have been provided by the Polar and four-spacecraft Cluster missions. Much of this work has been focused on analysis of individual crossings, but a few statistical studies of the high-altitude cusp region have been undertaken using data from the HEOS-2, Hawkeye, Polar and Interball data set. The actual flow pattern of the exterior cusp region is poorly known. A transition layer inside the magnetosheath near the outer boundary of cusp has been clearly evident during statistical experimental observation of the cusp boundaries from CLUSTER mission. Because of its high-quality data and its suitable orbit the four-spacecraft Cluster mission is perfectly adapted for high-altitude cusp investigations and therefore for large scale statistical studies. This layer characterized by MA=1 (Alfvenic Mach) allows the bulk flow to transit from super-Alfvenic to sub-Alfvenic from the exterior to the interior side of the outer cusp and has been observed experimentally mainly during Northward IMF case, however our simulation results show its existence during southward IMF as well. The role of this layer is important in order to understand the flow variations near the outer cusp boundary. In order to analyze this layer, we have used a large 3D PIC simulation of solar wind-magnetosphere interaction. We turned the IMF from Northward to southward direction to investigate Alfvenic Transition Layer (ATL) dynamics according to the IMF rotations. Although, in CLUSTER statistical studies, only a limited area of magnetosphere studied for ATL, we reported this layer for the whole magnetosphere during all simulation and have investigated its dynamics with IMF rotation. Finally we compared our results with experimental observations. Our results had a good agreement with the observational data for the parallel currents and also ATL observed in lower altitudes for the southward IMF case.
