Status Report

Space Weather Bulletin #01-6 Major Proton Event Underway

By SpaceRef Editor
August 16, 2001
Filed under , ,

Official Space Weather Advisory issued by NOAA Space Environment Center
Boulder, Colorado, USA


2001 August 15 at 11:10 p.m. MDT (2001 August 16 0510 UT)


A category S2 (Moderate) Solar Radiation Storm is in progress. This
event began with high energy proton flux above event levels at 7:05
p.m. Mountain Daylight Time (MDT) on August 15, 2001.

Current proton fluxes are at a level equivalent to S2 (Moderate) on the
NOAA Solar Radiation Storm scale. Effects may include, but are not
limited to, single-event upsets on satellites in earth orbit, and
degradation of high frequency radio communications at polar latitudes,
also known as Polar Cap Absorption (PCA). The NOAA S-scale is defined
by the lower energy proton flux (10 MeV), but because this event also
includes a significant higher energy flux component (100 MeV), other
effects are also possible, including increased radiation exposure for
manned space flight operations, more widespread radio communication
effects, and a wider range of potential impacts on satellites, such as
“snow” in imaging systems and degradation of satellite components due
to radiation exposure.

Major proton events generally follow energetic x-ray flares from active
sunspot regions on the visible side of the sun. This event was
somewhat unusual in that no notable x-ray enhancement was seen on
satellite monitors prior to its occurrence, suggesting a more unusual
“backside” event, from a sunspot region that has rotated beyond the
side of the sun facing Earth.

Subsequent imagery received from the LASCO instrument on the SOHO
satellite, operated by NASA/ESA, confirm that a major coronal mass
ejection (CME) emerged from a backside source starting at about 5:54
p.m. MDT on August 15th. Proton enhancements were first observed on
the SOHO SIS instrument at 6:25 p.m. MDT, indicating that these
particles were ejected from the sun at a velocity near 30% of the speed
of light. By 7:05 p.m. MDT, the flux of energetic protons observed on
the NOAA GOES-8 satellite had risen to the threshold for a major proton
event (as determined by 100 MeV proton flux). A second threshold for
lower energy protons (10 MeV proton flux) was reached at 7:35 p.m. MDT.
An associated Polar Cap Absorption (PCA) began at 8:10 pm MDT.

The last S2 (Moderate) event with flux levels similar to the one in
progress occurred on 18 April 2001, and lasted for about two days.
Interestingly, that event was also caused by a backside CME.

Data used to provide space weather services are contributed by NOAA,
USAF, NASA, NSF, USGS, the International Space Environment Services
and other observatories, universities, and institutions. More
information is available at SEC’s Web site or
(303) 497-5127. The NOAA Public Affairs contact is Barbara McGehan
at or (303) 497-6288.

SpaceRef staff editor.