ACE News #18
July 24, 1998

NOAA Implements First Derived Product based on Real Time Solar Wind Data: A Predicted Kp for use in Space Weather Forecasting

The promise of Real Time Solar Wind data from ACE is the ability to predict increased geomagnetic activity up to one hour before interplanetary disturbances arrive at Earth. Prior to July 1, 1998 the operational center at NOAA’s Space Environment Center used ACE solar wind plasma and magnetic field data directly to determine when activity would increase, i.e., by looking to see if the magnetic field turned south in GSM coordinates. If it did, they knew that geomagnetic activity would increase, but had to guess by how much, which depends on the solar wind speed and the field magnitude. During the last few months SEC has imported and reworked a code written by Costello at Rice University to allow advance prediction of Kp using the latest two hours of solar wind plasma and magnetic field data from ACE. An algorithm to predict Kp was chosen because Kp and its derivatives are heavily used within the operations center as indicators of global geomagnetic activity and to derive warnings, alerts, and forecasts.

The actual Kp index, which varies from 0 for no activity to 9 for very high activity, is calculated every three hours during the day by averaging the maximum deviation of the field at each of a set of ground magnetometers. In order to get maximum value from the lead-time supplied by ACE data, the predicted Kp, indicated here by pKp, is calculated every 15 minutes. The Costello neural network model, using the most recent 2 hours of data, calculates a predicted value and the predicted time of arrival is calculated assuming simple convection in the X direction (t=X/Vsw). These values are seen in the figure above as stars in the top panel for pKp and stars in the bottom panel for the predicted time of arrival (Lead-Time, in minutes). The data are color coded to indicate the amount of data used in the calculation (green is all or most data present, orange is intermediate, and yellow indicates a small amount of data present). The display turns red if pKp>5, the threshold for major activity. The horizontal bar is the observed Kp derived by the USAF, called the estimated Kp. It arrives within 20 minutes after the end of each three-hour period. The above 24-hour period shows low activity, followed by minor (3 to 4) activity. On the right hand side of the plot several points fall beyond the vertical dashed line, which represents real time. These points represent a prediction of future geomagnetic activity.

This is the first time that an operational solar wind product has been derived in real time and used in the NOAA forecast center as an aid in issuing alerts, warnings, and forecasts.

Contributed by Ron Zwickl of NOAA's Space Environment Center.

Real time solar wind data from four ACE instruments is available within five minutes of acquisition at http://sec.noaa.gov/ace/ACErtsw_home.html

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Last modified 23 July 1998, Andrew Davis
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