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Recent Updates to the Predicted Space Weather at Saturn – Fair or Stormy Weather?

April 30, 2013

This animated movie shows the simulated solar wind velocity from  March 21 to  May 10, 2013.
This animated movie shows the simulated solar wind velocity from March 21 to May 10, 2013. Click here or on the image for a larger version and further description.
Scientists have updated their models based on recent observations of the Sun and are predicting what the space weather at Saturn will be during the auroral campaign. The solar wind is a fast-moving stream of charged particles emanating from the Sun that moves outwards towards the Earth and planets. Even during nominal conditions, the solar wind contains significant inhomogeneities, variations in density and speed. Due to the Sun's rotation (roughly 27 days), the solar wind bears a spiral appearance.

At irregular intervals, the solar wind flow is interrupted by episodic major solar eruptions known as coronal mass ejections (CMEs), which are propelled outwards into the ambient wind. Variations in the plasma density and speed within these solar storms can be much more dramatic than during quiet conditions. For both 'fair-weather' and 'storm' conditions, predicting the arrival at Earth of variations in the solar wind is important because these can lead to geomagnetic storms. Similarly, predicting the solar wind at Saturn is important as previous research results indicate Saturn’s aurora responds to solar wind dynamic pressure and enhancements from ICMEs (Interplanetary Coronal Mass Ejections) - the interplanetary counterpart of CMEs.

The model used to predict space weather at Saturn (referred to as WSA-Enlil and its variants) is a physics-based, global MHD (magnetohydrodynamic) model that is capable of simulating both types of solar wind conditions (fair or stormy).

Two CMEs that were actually observed leaving the Sun were included in the simulation. In the animation they can be identified as dark “blobs” leaving the Sun. The first CME was observed to leave the Sun on 2013-03-21T22:36Z (March 21, 2013 at 10:36 p.m. UTC) at a speed of roughly 1,400 miles per hour (633 kilometer per second ). Scientists categorize these events according to how unusual or common they are, and this was categorized as a rather common event. However a second CME left the Sun on 2013-04-11T07:36Z (April 11, 2013, at 7:36 a.m. UTC) with a higher speed of about about 2,200 miles per hour (1,000 kilometers per second) and was much larger in angular extent. CMEs of this type occur only occasionally and this one is expected to arrive at Saturn around May 11-12, 2013, shortly before the next round of coordinated auroral observations.

Yihua Zheng, Ph.D.
NASA Goddard Space Flight Center
Heliophysics Science Division

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