Statistics – Computation
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsm51a1606k&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #SM51A-1606
Statistics
Computation
2109 Discontinuities (7811), 2134 Interplanetary Magnetic Fields, 2164 Solar Wind Plasma, 7924 Forecasting (2722)
Scientific paper
Interaction between the solar wind and the Earth's magnetic field influences several phenomena on Earth and as a result is the subject of many studies. These studies often require accurate, "raw" solar wind parameters just before the solar wind interacts with Earth's magnetosphere. One widely used technique for determining interplanetary magnetic field (IMF) and solar wind parameters shifts the measurements at some distant point on the Earth-Sun line. The Advanced Composite Explorer (ACE) orbiting the L1 Lagrange point is the primary resource for collecting these measurements. The time delay for the shift is calculated using a simple kinematic approach: the time is equal to the distance from the satellite divided by the measured velocity of the solar wind. This approach can be relatively accurate due to the short distance to the L1 point compared to the distance to the Sun and in many situations it is acceptable based on the assumption that solar wind parameters do not change significantly before reaching the magnetosphere. However, measurements provided by satellites such as ACE are never taken exactly on the line connecting the Earth and the Sun. Because IMF is not homogeneous in any direction, the solar wind particles that actually reach the Earth are different from those that pass the satellite. As a result, IMF and solar wind measurements near the L1 point are usually different from IMF at the Earth. Theoretical considerations as well as simultaneous observations from different satellites show that IMF consists of current layers and wave fronts along which changes in magnetic induction are minimal at such a short scale as a diameter of ACE orbit. This work compares different methods for time delay calculation based on determination of orientation of such planar stationary structures in the solar wind by measurements of IMF vector at ACE satellite using 1 seconds magnetic field data and compares them with WIND 3 seconds magnetic field observations. This includes a determination of different IMF and solar wind parameters that influence each method. Each method is tuned using free parameters presented in the algorithm. Parameters that influence the quality of forecast for the methods are investigated. The tuning procedure uses sets of continuous data 1--15 days in length from different time periods between 1998 and 2001. Analysis of applicability of different methods has been made. Computations needed for analysis of these methods and data were performed on high performance computers at the Arctic Region Supercomputing Center. This research was initiated in response to the need for better IMF prediction in real-time during the application of the University of Alaska Fairbanks Eulerian Polar Ionosphere Model (UAF EPPIM).
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