August 24-26, 1998; An exercise in "space weather" prediction

       An exercise in  "space weather" prediction was conducted by NOAA and
ISTP team members at NASA/GSFC during the August 24-26, 1998, event as follows.  
While the X1/3B LDE flare was still in its early stage, a NOAA/Boulder 
(M. Dryer and Z.K. Smith of the Space Environment Center) prediction of shock 
arrival at Earth was made.  Two models, STOA and ISPM (a modification of STOA 
and also using ground-based radio metric frequency drift as a shock "trigger"),
were used to provide an ex post facto window between 0535 - 2149 UT on August 
26.  The actual shock arrival, signaled by the SSC, was at 0651 UT on 26 August.

       An alternate prediction was made by ISTP team members at NASA/Goddard Space
Flight Center (M. Kaiser and M. Reiner of the WIND/WAVES team) while the shock
was enroute to 1 AU. The Type II radio bursts interplanetary emissions (due to 
plasma oscillations) gradually decrease in frequency as the shock encounters a 
decreasing solar wind density.  The predicted window was from 1900 UT, 
25 August, to 1600 UT on 26 August, depending on whether the emission was 
at the second harmonic or fundamental frequency, respectively.

      The exercise recounted above demonstrates the difficulties and
challenges faced by "real time" and "enroute" predictive techniques that are
based on ground-based observatories, space-based instruments, and models
that are based on kinematics, parametric MHD calculations, and remote
sensing.   Expected imminent (November 1998) use of SOHO/LASCO/EIT
observations are expected to add important "trigger" information such as
glancing shock, or 'head-on', impact at Earth's magnetosphere.

Murray Dryer 

• Daniel Berdichevsky - Raytheon STX Corporation at ISTP Science Planning and Operat ions Facility(SPOF) (berdi@istp1.gsfc.nasa.gov)

• NASA contact for these pages: W.H. Mish, Code 690, email: wmish@istp1.gsfc. nasa.gov