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
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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.
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