The sun. For as long as man has been on the Earth, the sun has been a source of wonderment. Many legends and myths have been written about it, it has been worshipped as a god, and studied as to its origin and its effect on our solar system. Now with the use of satellites both inside and outside the Earth’s magnetosphere (glossary), scientists are learning more about solar activity and the effect on the Earth.
The sun is a not a quiet body as it appears from the Earth. The storm has storms but not like the ones here on Earth. When the Sun has a storm, it is a violent series of explosions and may result in tremendous releases of material into the solar system. Sometimes that material and energy comes toward the Earth. When this happens, there are effects on the magnetosphere, the protective shield around the Earth, and sometimes there are effects on the atmosphere which may result in effects to man and the satellites that we rely on for communications. There is also evidence that shows that the activity on the sun may affect the power systems on the Earth. We do not know all of the effects and that is one of the reasons that this area is being studied.
Solar Activity and Effects on the Earth
Sunspots are found in the photosphere of the sun. Click here to see an image of sunspots http://www.exploratorium.edu/sunspots/. Sunspots data has been recorded as early as 28 BC by the ancient Chinese. Sunspots appear as dark spots on the sun. They tend to follow an eleven year cycle from solar minimum, a time of low sunspot numbers, to solar maximum, a time of high solar numbers. Sunspots are darker because they are cooler because the strong magnetic fields inhibit the transport of heat by the convective motion of the sun. Sunspots are made of two parts- the umbra which is the darker center, and the penumbra, which is the lighter outer area. Sunspots are usually located near the solar equator, but never below 5 or above 40 degrees north and south latitude. Sunspots themselves do not seem to have an effect on the Earth but they do seem to correlate with an increase in activity on the sun that does.
Solar flares occur in the chromosphere and are associated with regions of sunspot activity. Click here for an image of a solar flare. During solar maximum, solar flares occur at an average of one flare per week. The flares can last for hours for large events to only tens of seconds for impulsive events. A solar flare heats the solar gases to tens of millions of degrees Kelvin and accelerate protons and electrons streaming toward Earth. The abrupt release of energy contains ultraviolet light, x-radiation, and sometimes gamma radiation. Solar flares appear as a sudden brightening of a small area on the sun. The particles from a solar flare are able to react with the magnetosphere and some of those particle are able to enter the magnetosphere and reach the ionosphere to produce auroras and affect our communication systems.
Solar wind is the plasma of charged particles (protons, electrons, and ionized atoms) coming out of the sun in all directions. The solar wind is constantly streaming toward the Earth but its speed is always changing. The average speed of the solar wind is 400 km/s or almost one million miles per hour. Solar wind originates due to the expansion of the corona, the sun’s outer atmosphere. The solar wind composition reflects the composition of the corona. High velocity solar wind originate from coronal holes found at the poles of the sun. The solar wind is affects by sunspot activity. During times of high sunspot activity, the strong magnetic fields do not allow the atmosphere to expand thus cutting off the high velocity solar wind. Solar wind has an effect on the Earth’s magnetosphere compressing it on the sun side and expanding it on the tail side.
CME (coronal mass ejections) are large ejections of matter from the corona. Just as solar flare, these occur more often during solar maximum. Click here for an image of a CME. The ejection is usually made of millions of tons of material in the form of charged particles. These particles move at a speed of about 1 million miles per hour which means they can make the trip to the Earth in just 3 or 4 days. Researchers are studying areas on the sun that exhibit a S- shaped pattern called a sigmoid. They believe that these sites may be where coronal mass ejections occur. The hope of this research is to be able to warn of impending danger from a CME heading toward Earth by identifying these areas. When the cloud of matter collides with the Earth, it can produce a geomagnetic storm which disturbs the Earth’s magnetic fields. This disruption of the magnetic fields can cause problems with satellites orbiting the Earth.
How we study the activity on the Sun
There are many different satellites and ground-based instruments that study the sun.
The data collected from each instrument can be used to try to explain the sun- earth connection.
ACE was launched on August 1997. It is located at the L1 point in space. Two of the instruments used to study the solar wind are the SWICS and SWEPAM. SWICS (Solar Wind Ion Composition Spectrometer) measures the chemical and isotopic composition of solar matter. It also measures the temperatures and mean speeds of all major solar wind ions, from H to Fe, travelling at an average of over 400 km/s. This data along with other data sets will be used to help increase the understanding of the solar wind in the area of solar and heliospheric physics. SWEPAM (Solar Wind Electron, Proton, and Alpha Monitor) measures the solar wind plasma electron and ion fluxes (rates of particle flow) as a function of direction and energy. This data along with data from three other ACE instruments is used to determine real-time solar wind conditions that are sent to the Earth for space weather broadcast purposes. Click here for further information on ACE role in space weather .
SOHO is a project of international cooperation between ESA and NASA. It was launched on December 2, 1995 and is part of the Solar Terrestrial Science Program (STSP) comprising of SOHO and CLUSTER and the International Solar Terrestrial Physics Program (ISTP) with Geotail, Wind, and Polar. Three of the instruments used to study the solar wind and other activities on the sun are LASCO, EIT, and SUMER. LASCO has three coronagraphs that image the corona. Each coronagraph has a different size occulting disk so that you can see fainter and fainter corona as you go away from the sun’s surface. C1 has the smallest view and C3 has the largest view. A coronograph is a telescope that can block the light coming from the solar disk so the corona can be seen. LASCO images are taken in black and white but color is added to make the images look nicer and also to be able to identify images from the different coronagraphs. Click here for images. LASCO is designed to investigate the transport of mass, momentum, and energy through the coronal and into the solar wind. It also helps to try to investigate the conditions that trigger events in the corona such as CME’s, and the interaction of coronal plasma and the dust in the area near the sun. EIT (Extreme Ultraviolet Imaging Telescope) has shown where the high speed solar wind originates. In the false color image, the lighter area indicates a strong magnetic field whereas the area of the open magnetic field where high speed solar wind originate appears dark. The images from the EIT are different colors due to the filters used. The different filters show different wavelengths of light and the specific chemicals that emit at that wavelength. To view the different images click here. SUMER (Solar Ultraviolet Measurements of Emitted Radiation) spectrometer analyzes UV light which is given off by the hot gases in the sun’s atmosphere. Analysis will include measuring profiles and intensities of extreme ultraviolet in the solar atmosphere, Doppler shifts in the atmosphere, and also SUMER obtains full images of the sun and the inner corona.
Yohkoh ( sunbeam in Japanese), a Japanese satellite, was launched on August 31, 1991 from Kagoshima, Japan. Yohkoh is a project of the Institute for Space and Astronautical Sciences. Yohkoh is intended to study the x-ray and gamma rays of the sun. Two of the instruments on Yohkoh are the SXT ( soft x-ray telescope) and the HXT (hard x-ray telescope) study the high energy solar flares and other coronal activities. Since x-rays do not penetrate the Earth’s atmosphere, information must be collected from outside of our atmosphere. The SXT produces images at low energy and the HXT produces images at a higher energy level. For images click here. The goal of Yohkoh is to try to find explanation for solar phenomena that is seen in the x-ray range.
WIND was launched in November 1994. The satellite carries an array of scientific instruments for monitoring solar wind conditions near the Earth. One of the instruments on WIND is the SWE. SWE consists of five integrated sensors/electronic boxes and a data processing unit. The instruments measure the velocity, density, temperature and heat flux of the solar wind. The velocity and measurement of electrons and ions may reveal properties of plasma and the role it plays in the movement of mass, momentum, and energy from the sun to the Earth. These measurements also hope to enhance the understanding of the interaction of the solar wind and the magnetosphere.
SAMPEX was lunched in July 1, 1992 into a high inclination shuttle orbit. SAMPEX contains four instruments that measure energetic nuclei and electrons as well as ion composition. It was designed to study energetic particles of solar, interplanetary and magnetospheric origin thought to be accelerated in the solar wind. One of the instruments, HILT, is designed to measure heavy ions from He to Fe in the energy range from 8 to 220 MeV ( medium energy solar energetic ions). These measurements along with measurements of other instruments are used to determine the origin of these particles. The measurements of the particles can also be used to identify effects on particles within the magnetosphere due to the solar wind or solar events.
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.
With all of the satellites tracking the solar wind and solar events from the L1 point to low shuttle orbit, scientists are now being able to accurately track and interpret the particles and energies from the sun and their impact on the Earth. There is still more research that must be done to help accurately predict the impacts of solar events on the Earth.
