Improving the Timing of Space Weather Predictions Using Solar Wind and Interplanetary Magnetic Field Measurements

Details Improving the Timing of Space Weather Predictions Using Solar Wind and Interplanetary Magnetic Field Measurements Improving the Timing of Space Weather Predictions Using Solar Wind and Interplanetary Magnetic Field Measurements

May 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm..sm61b07w&link_type=abstract

American Geophysical Union, Spring Meeting 2001, abstract #SM61B-07

Other

2134 Interplanetary Magnetic Fields, 2722 Forecasting, 2784 Solar Wind/Magnetosphere Interactions

Scientific paper

Most investigations of terrestrial ``space weather'' rely on measurements of particles and fields in the upstream solar wind at the L1 orbit. The calculated delay time between the measurement and the impact on the Earth's magnetosphere/ionosphere system is often determined only by the velocity and separation distance along the Earth-Sun line. However, the ``phase front'' of the fluctuations in the Interplanetary Magnetic Field (IMF) often is tilted at an angle, which can lead to significant errors in the timing of the predictions. This error increases with the separation of the L1 orbit from the Earth-Sun line. The investigation reported here uses data from the times when four spacecraft, ACE, Wind, IMP-8, and Geotail, had all obtained simultaneous measurements of the IMF at their various locations. We have devised a technique whereby the exact, actual propagation delay time between ACE (at L1) and each of the other three, nearer spacecraft can be derived from these measurements. The propagation delay is determined as a smoothly varying function of time; when this measured delay is applied to all components of the IMF measured by ACE they are seen to match the target satellite's IMF to a degree that is much better than expected. These results give a high confidence that the IMF that is measured at L1 will most likely impact that Earth. The question is exactly when, as our results show that the actual time delays can vary by nearly an hour in either direction from the expected delays, due to the effects of the tilt. We have used these delay measurements between the multiple satellite to calculate the orientation of the phase front as a function of time. Four satellites are used in order to check the reality of the solution. Time animations of the phase front show surprising variations. We can further check the results by calculating the precise delay of the IMF from ACE to the Earth's magnetosphere, using the phase angle determined from our measurements, and then comparing this IMF with the effects measured by high-latitude ground magnetometers.

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