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Wetterzentrale Forum Archiv 2000 2. Halbjahr

ASTRONOMIE: STD - AstroAlert über X5(engl./lang)

Geschrieben von: Peter, Frankfurt/M.
Datum: 14. Juli 2000, 21:54 Uhr


A s t r o A l e r t

Sun-Earth Alert

Solar Terrestrial Dispatch

http://www.spacew.com

14 July 2000

* Major Significant X5 Proton Flare Alert *

* Category S3 Solar Radiation Storm Alert *

* Middle Latitude Auroral Activity Warning *

* Low Latitude Auroral Activity Watch *

At 10:24 UTC on 14 July, the largest solar flare to be directly observed
so far this solar cycle was spawned by active sunspot Region 9077, which has
now exploded with a total of three major X-class flares. Todays flare was
the largest of all and the most serious, reaching an X5 category in x-rays
and accelerating very high energy protons toward the Earth.

Within minutes of the flare, very high energy (estimated much higher
than 100 MeV) protons impacted the Earth's magnetosphere and ionosphere at
near relativistic velocities (almost the speed of light). This is the most
significant energetic solar radiation storm since solar cycle 22. Energetic
proton densities at energies greater than 100 MeV have increased by a factor
of more than 3 magnitudes (1000 times higher than normal). Protons with
energies greater than 10 MeV, which are generally considered the lowest
energy protons capable of producing satellite anomalies, increased in density
by a factor almost 5 magnitudes (not quite 100,000 times) greater than normal
background levels.

This solar radiation storm is currently categorized as an S3 event and
is approaching a category S4 event (S1 being weak and S5 being extreme).
People on Earth are safe from the effects of these adverse space environment
conditions. Satellites and people in orbit are at highest risk. Here are some
of the possible effects of an S3/S4 radiation storm:

* Unavoidable biological radiation hazard to astronauts performing EVA

(spacewalk) activities.

* Elevated levels of radiation exposure to passengers and crew in

commercial jets travelling across the high and polar latitude regions

(lower latitude aircraft are not at risk). The increased radiation

exposure would be equivalent to receiving approximately 5 to 10 chest

x-rays.

* Satellites can experience memory upset problems, noise on imaging

systems, star-tracker orientation problems, and solar panel

degradation.

* Ionospheric radio signal propagation has been completely blacked out

for all communications paths that traverse through the high latitude

and polar latitude ionospheres. No high frequency (2 to 30 MHz) radio

communications through the high and polar ionospheres are expected

until later on 16 or 17 July.

There have already been numerous confirmed anomalies on spacecraft. The
SOHO spacecraft is experiencing significant noise on its imaging systems,
which is rendering scientists abilities to monitor solar activity more
difficult. The ACE spacecraft has suffered suspected contamination in its
ability to accurately measure the speed and density of the solar wind. And
the POLAR spacecraft (which images auroral activity and other important space
environment properties) is unable to produce images of auroral activity due
to suspected contamination of its imaging systems (these are just a few
examples).

Again, we must emphasize that people on Earth are at no risk to these
events. The Earth's magnetosphere, ionosphere and atmosphere protect life on
Earth from radiation exposure. Even people flying in aircraft really have
nothing to worry about. This is primarily a space-based radiation problem
that is of more concern to astronauts and satellite operators than anyone
else.

Today's major X5 solar flare was associated with a full halo coronal
mass ejection that is expected to make a near head-on collision with the
Earth. The velocity of the disturbance is not known precisely because of the
level of proton-induced image degradation in the SOHO cameras. Radio
observations of the flare revealed a strong inner-coronal shock wave that had
an estimated velocity of 1,300 kilometers per second. However, SOHO team
members determined a possible disturbance velocity (in the outer corona) as
high as perhaps 1,775 kilometers per second.

Predictions on the time of arrival of this disturbance will vary
depending on the type of data that is used. However, it appears that the
disturbance may arrive between approximately 19:00 UTC on 15 July (3 pm EDT
on 15 July) and 16:00 UTC on 16 July (noon EDT on 16 July). The arrival of
this disturbance is virtually certain to occur.

This disturbance is expected to have a potentially high impact on
space-based systems when it arrives. Spacecraft operating in geosynchronous
orbits near the noon-sector of their orbits (when they lie between the Sun
and the Earth, as viewed from the Earth) are expected to cross through the
protective shield of the Earth's magnetosphere into the magnetosheath region
when the higher pressure from the solar wind behind the disturbance
compresses the Earth's magnetosphere on the dayward side to altitudes inside
the orbit where geosynchronous spacecraft operate. This can produce
pointing-related anomalies on geosynchronous spacecraft and can increase
overall wear and tear on solar panels and other exposed equipment. There will
also be a chance for numerous spacecraft charging related anomalies that may
occur on orbiting spacecraft in general if the disturbance triggers a
significant geomagnetic storm. The Earth's atmosphere may also begin to bloom
outward and increase atmospheric drag on lower orbiting spacecraft -
particularly those with perigees below 500 kilometers.

A major to severe geomagnetic storm may be associated with the arrival
of the disturbance on 15/16 July. Hydro and electric power utilities may
observe induced electrical currents on their transmission lines caused by
electrical currents induced by rapid variations in the Earth's magnetic
field. These currents can produce damage to electrical transformers and other
equipment used by power companies to deliver electricity to end users. This
does NOT mean your computer will explode. Power companies protect end users
from the effects of induced electrical currents caused by geomagnetic storms.
A worst case scenario would be the temporary loss of power caused by perhaps
the failure of a power transformer or some other sensitive equipment. And the
chance of this happening is very low for any specific region.

A middle latitude auroral activity warning has been issued together with
a low latitude auroral activity watch for all middle and low latitude regions
of the Earth. This disturbance has the potential to produce intense displays
of auroral activity over these regions. Observers interested in watching for
these events on their home computers are encouraged to obtain a copy of the
free STD Aurora Monitor software package, which will provide near-realtime
updated information and imagery that you can use to monitor conditions as
they happen. The software is available at: http://www.spacew.com/aurora. It
is a relatively small download of only 2.5 megabytes but is an immensely
useful package for monitoring auroral activity. Sky & Telescope has
graciously agreed to serve as an additional mirror for this software. We
apologize for not having versions available for Macintosh or Linux systems.
Other users may visit: http://www.spacew.com/www/aurora.html.

WE WOULD APPRECIATE IT IF PEOPLE WOULD SUBMIT SIGHTINGS OF AURORAL
ACTIVITY TO THE AURORAL ACTIVITY OBSERVATIONS NETWORK AT:

http://www.spacew.com/www/subaurora.html

Or use the aforementioned software to submit your sightings to the
Network.

There is a chance active sunspot Region 9077 might spawn additional
energetic activity over the next several days. However, some decay has been
observed in the region which may reduce its ability to produce energetic
activity.

** End of AstroAlert *

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