NASA Technical Reports Server (NTRS) 20020090260: Under the Weather: Space Weather. The Magnetic Field of the Heliosphere

6 Pages·4.2 MB·English

by  NASA Technical Reports Server (NTRS)

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From the Sun to the Earth
can enjoy the dancing beauty of the
ormally, only people in the far north Eruptions in the outer atmosphere of the Sun are
aurora borealis; however, an intense
the usual source of "space weather"phenomena.
collision of charged solar particles with the
These eruptions, called coronal mass ejections
Earth's magnetic field can magnify the Northern
(CMEs), are related to the changes in magnetic
Lights so much that they are visible in the south-
fields that the Sun produces. This activi:ty is
ern United States. Behind the light show lies
cyclical. Every 11years, the frequency of erup-
enough flux of energetic particles carried by
tions spikes at what is known as a solar
solar wind to render our planet uninhabitable.
maximum.
The Earth's magnetic field, also known as the
magnetosphere, is the only thing that shields us
CMEs propel plasmas, or superheated ionized
from the Sun.
gases, into space through the background solar
wind plasma. The solar wind plasma mostly
Even the magnetosphere cannot fully guard us
consists of hydrogen atoms that have been fully
from the wrath of the Sun. In March 1989, a
ionized into protons and electrons. As the elec-
powerful solar flare hit Earth with such energy
trically charged particles move through space,
that it burned out transformers in Quebec's elec-
they generate their own magnetic field. During a
trical grid, plunging Quebec and the eastern
CME, the wind drags solar magnetic field lines
United States into darkness for more than
into space to form the heliosphere. Because of
9 hours.
the rotation of the Sun, the radially flowing solar
wind produces spiral magnetic field lines
Northern lights and energy grid overloads are
known as the Parker spiral.
not the only ways that a solar wind can affect us.
A solar storm in July 1999 interrupted radio
Rushing at speeds approaching 3 million miles
broadcasts. Solar activity can disorient radars
per hour, a CME takes roughly 2 to3 :days to hit
and satellite sensors, break up cell phone con-
the Earth. The bombardment of Earth with solar
nections, and threaten the safety of astronauts. A
protons is called a solar proton event. When the
large bombardment of solar particles can even
magnetic fields from the solar wind collide with
reduce the amount of ozone in the upper atmos-
the Earth's magnetosphere, the fields constantly
phere. Magnetohydrodynamics (MHD), the study
twist and turn. Occasionally, they break apart
of magnetic fields in magnetized plasmas, can
and reform rapidly. This process of magnetic
help scientists predict, and therefore prepare for,
reconnection transfers large amounts of heat and
the harmful side effects of solar weather in the
energy from the solar wind to the
magnetosphere.
magnetosphere.
67
Eye ion the solar wi nd Sciences (ISAS)formed the Intemafional Solar ....
Terrestrial Physics (ISTP)project inthe 1980s.
For the past 35 years, the Space Environment
The ISTP has launched severa! missions tOs_dy
Center in BoUlder, Colorado, has been the .... solar wind and its interaction with the Earth. ....
United States' official space weather forecas_ng
center: The organiza_on collects images of the A number of satellites can detect disturbances on
surface of the Sun, issues space wea_er advisory the Sun's surface up to3 days before aCME hits
bulle_ns, and develops mathematical models for the Earth:
the activity of ions in outer space. The National
Oceanic and Atmospheric Administration Both the Solar and Heliospheric
(NOAA) and the U.S. Air Force operate the Observatory (SOHO)and the
Center jointly. Other major centers of space Advanced Composition Explorer
weather study in the United States include the (ACE) satellites are positioned
NASA Goddard Space Flight Center and educa- 1.5 million miles awa)_ in an orbit
tional institutions such as UCLA, Dartmouth that keeps them. at a constant position
between the Earth and the Sun.
College, the University of Maryland at College
Park Rice University, and the University of The ISAS launched the Yohkoh satel-
Michigan.
lite in 1991. Yohkoh carries x-ray tele-
scopes and other sensors that were
The United States has also joined internation.al
contributed by the United States and
efforts to study theSun-Earth space environ-
Great Britain.
ment. NASA, the European Space Agency (ESA),
and Japan's Institute of Space and Astronautical In addition, a large fleet of spacecraft measures
the effects of the solar wind and CMEs on the
magnetosphere:
• NASA's Imager for Magnetopause-to-
Aurora Global Exploration (IMAGE),
launched in 2000, is the first satellite
dedicated to obtaining global images
of the magnetosphere.
• The ISTP launched GEOTAIL to
measure global energy flow and
transformation in the magnetic field
lines that spread out from Earth's
The aurora australis shines over the Southern Hemisphere.
68
This illustration shows the Earth's magnetosphere deflecting aCME cloud. A CME takes 2 to 4days to leave the Sun and reach Earth.
Image credi_:..T]'e SOHO proj_'ct ...
polar caps. Other ISTP spacecraft that monitor the development of
include WIND, POLAR, and space weather.
Cluster II.
The Los Alamos National Laboratory _f_ ['_ Flees
(LANL) created a series of satellites
Burch, J. L., "The fury of space storms," Scientific
that analyze magnetospheric plasma
American, Vol. 284, No. 4, April 2001
and measure spaceborne electrons,
Glanz, J., "Unlocking secrets of magnetic fields'
NOAA and NASA developed the
power," New York Times, October 24, 2000
Geostationary Operational
Environmental Satellites (GOES).
Seuss, S. T., and Tsurutani, B. T. (Eds.), From the
Among the many instruments on
Sun, American Geophysical Union, 1998
GOES satellites are a magnetometer,
an x-ray sensor, and other sensors
69
Researc,h Profile: The Magnetic Field of the Heliosphere
Investigators:
Aaron Roberts and Me!vyn Go!dstein, NASA Goddard Space _Flight Center, Interplanetary
Physics Branch ......
sphere to deepen our understanding of the fluctuations in the soiar wind.: Therefore, scien-
approach of solar winds toward Earth. The study tists can use the simulatiOn code to study realis-
focused on various sources of field line distor- tic field configurations and their important _
tions. effects on the propagation of potentially damag-
ing energetic particles coming from the Sun. The
The researchers calculated solar wind conditions investigators are currently optimizing the MHD
with a Flux-Corrected Transport MHD code. code for a higher resolution and greater realism
The code used a spherical-coordinate grid with than before.
general boundary conditions. A comparison with
data from the Helios deep space probe showed
that the code results were realistic.
The simulations showed that the ideal Parker
spiral field lines are easily modified, even in
uniform flow conditions. In particular, the mag-
netic field deviates from the Parker spiral at a
sector boundary, that is, the location near the
ecliptic at which the field changes polarity. Here,
loops of field form where the two polarities
connect.
Another project simulated the presence of Alfv6n
waves in the heliosphere. An Al,fvdn wave is the
movement of particles in a direction perpendicu-
lar to a magnetic field that bends the field lines ...........................................................................................................................................................................
The simulation introduced Alfv6n waves into a
The yellow and red lines in this illustration represent simulated
standard heliospheric flow, inwhich a high- magnetic field lines from the Sun. The blue region on the green
sphere indicates the sector boundary that separates magnetic polar-
speed solar wind surrounds a low-speed wind. ities, lmGe .,..".,'editi:_.',._,c:,'p!a_z_-'_Pa:h,'yysics t.h"ar_ch,NASA God&rd Space
Fi,)?htC:e_tt,.'"_,
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The top figure shows magnetic field values for the solar wing calculated in this
research project's simulation. For comparison, the bottom figure shows magnetic field
recordings from the Helios 2satellite, which was developed by NASA and the Federal
Republic of Germany.
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