|
|
On a warm, sunny day we all like to go outside and enjoy the heat
and light the Sun provides. While you are sitting there enjoying
the sunshine, there are other products from the Sun that we do
not want to enter Earth’s atmosphere. These particles, in mass
quantities, would cause such intense radiation that life on Earth
would not exist as we know it.
When the solar wind comes to Earth it meets an obstacle more than
10 times the size of Earth - the Earth’s magnetosphere. This encompasses
Earth and causes most particles to flow around the Earth, similar
to a rock in a stream. Particles begin their encounter with Earth
by passing through a curved “Bow Shock”, a surface that slows,
heats, and partially deflects the particles around Earth. This
surface is similar to the bow wave formed as a boat moves through
water. The particles are now in a region referred to as the magnetosheath
and for the most part they stay in this region as they flow around
the hard barrier called the Earth’s magnetopause, a surface separating
the Earth’s magnetic fields from the Sun’s. The force of the solar
wind, which carries the Sun’s magnetic field with it, compresses
the Earth’s dayside magnetosphere and stretches the “tail” out
to a length over 100 times the radius of Earth. Most particles
travel down the length of this tail and out into interplanetary
space. However, some solar wind particles leak through the magnetic
barrier and are trapped inside. Solar wind particles also rush
through funnel-like openings (cusps) at the North and South Poles,
releasing tremendous energy when they hit the upper atmosphere.
The Northern and Southern Lights (auroras) are the evidence we
can see of this energy transfer from the Sun to the Earth.
Earth responds to the Sun’s varying energy output in different
ways. For example, episodic events such as fast coronal mass ejections,
which occur more frequently near the peak of the 11 year solar
activity cycle, can trigger major magnetospheric disturbances
known as nonrecurrent geomagnetic storms. Associated with such
large storms, and with more moderate recurrent storms as well,
are spectacular aurora displays as well as enhanced fluxes of
energetic particles and ionospheric disturbances that can damage
spacecraft, disrupt communications, and disable power grids. Variations
over the 11 year solar cycle in the intensity of the Sun’s electromagnetic
output at short (X-ray and ultraviolet) wavelengths significantly
affect the chemistry, structure, and dynamics of the Earth’s upper
atmosphere, while longer-term solar irradiance variations may
be linked to major shifts in the global climate.
- The Sun -Earth Connection program is one of the four principal
science themes of NASA’s Office of Space Sciences. It encompass
the scientific disciplines of solar and heliospheric physics,
magnetospheric physics, and aeronomy (the study of ionized and
neutral upper atmospheres of the Earth and other planets). The
predominant emphasis of the Sun-Earth Connection theme is on the
study of solar system plasmas, the current systems and magnetic
fields associated with them, and the ionospheres and tenuous upper
atmospheres of the Earth and planets. The Sun-Earth Connection
program seeks to understand the transfer of energy from the Sun
to the Earth and the response of the Earth’s coupled magnetosphere-ionosphere-atmosphere
system to this energy transfer.
NASA uses satellites with various instruments on board to collect
data throughout the Sun-Earth system. One of these satellites,
POLAR, has visible and ultraviolet imaging
|
|
- systems on board that provide views of the Aurora looking down.
VIS (Visible Imaging System) consists of three low light level
cameras that provide only night time aurora ovals. UVI (Ultraviolet
Imager) has a smaller field of view but provides continual coverage
of the auroral oval in ultraviolet light. These cameras along
with the other instruments on POLAR are used to quantitatively
assess the dissipation of magnetospheric energy into the aurora,
develop a model of energy flow within the magnetosphere, and determine
the responses of the magnetosphere to storms and the changing
(dynamic) solar wind.
Another NASA satellite, WIND, primarily monitors the solar wind
far upstream from Earth but occasionally comes back to sample
the near Earth environment and boundaries. Wind measures radio
and plasma wave phenomena which occur in the solar wind upstream
of the Earth’s magnetosphere and in key regions of the magnetosphere.
EPACT studies the particle acceleration in solar flares, the interplanetary
medium, and the planetary magnetospheres. The Solar Wind Experiment
(SWE) measures ions and electrons in the solar wind to reveal
properties of the plasma and their role in the transfer of mass,
momentum, and energy from the Sun to the Earth. The MFI (Magnetic
Field Investigation ) will study the structure and fluctuation
characteristics of the interplanetary magnetic field to determine
the influence of transfers of energy in the solar wind and the
effects on the Earth’s magnetosphere.
Geotail, a Japanese (ISAS) mission, was originally in Earth’s
deep magnetotail region (1992 - 1995) but then came in to sample
the magnetopause and bow shock boundaries (passing through each
twice in its five day orbit much of the year), and to sample the
near tail region. On board there is a magnetometer to measure
the in-situ magnetic fields (MGF) as well as a plasma instrument
measuring ions and electrons in the solar wind and magnetosheath
(CPI). EFD studies the electric field in the plasma sheet and
the electric field near the magnetopause.
Interball-Tail, a Russian satellite contributing data to NASA
through an international collaboration-the Inter-Agency Consultative
Group (IACG)-uses two mass spectrometers to measure ion mass and
energy ranges. This satellite crosses the same boundaries and
regions as Geotail but orbits at a higher latitude. INTERBALL
is also has an Auroral probe but its data are not yet available
to the public. When available, this data can be used to learn
more about auroras. Two different aurora imagers are installed
on the Auroral probe main satellite. These imagers provide the
two-dimensional global patterns of aurora phenomena and their
time development. INTERBALL also has a tail probe that measures
ions and their energy ranges. This satellite is a good boundary
satellite because it crosses both the bow shock and the magnetopause
during its orbit.
The study of the bow shock and the magnetosphere and their reaction
to the energy that is released from the sun is a relatively new
field of science since the launch of satellites in the 1960’s.
The combination of solar wind monitors and spacecraft at the boundaries
makes this area of research a most exciting time for scientists.
Researchers are now analyzing these data to see patterns and apply
those patterns to past and future events. There are many unanswered
questions. Perhaps, through your investigation, some of these
mysteries can be solved.
|
|
