Storms In Space By Ramon E. Lopez Department of Astronomy, University of Maryland, College Park   Figure 1. The space near Earth is controlled by Earth's magnetic field. The solar wind pushes Earth's field into a comet-shaped object called the magnetosphere. Image credit: of the Space Science Institute. Artwork by Steve Mercer. When we think of weather, we normally think about rain or shine, or snow during the winter months. However, there is another kind of weather that is beginning to make an impact on people's lives: space weather. What is space weather, and how does it affect us here on Earth? To answer these questions we have to begin with a few basic aspects of the space environment. 1. Space is not empty. Most people find this statement surprising since we generally think of space as a vacuum. To a certain degree this is true, but space is not an absolute vacuum. It is filled with very thin electrically charged gas consisting mostly of protons and electrons. The gas is so thin that a thimbleful of air holds as many atoms as does a cube 2 miles on each side in space. Pretty thin, but it is still there.   Figure 2. Earth's magnetic field traps energetic particles to form donut- shaped belts around Earth called the Van Allen radiation belts. 2. Earth is a magnet. Earth's magnetism is what makes a compass needle point north (or south), and it is this same magnetic field that plays an important part in space weather. Since the gases in space are electrically charged, magnetic fields can influence their motion, even trapping high-energy particles (like in the Van Allen radiation belts in Figure 2). Also, as electrically charged gases flow past magnetic fields, they generate electric currents. 3. The Sun produces an electrically charged gas called the solar wind that flows out from the Sun in all directions. When this solar wind hits Earth's magnetic field, it creates a comet-shaped magnetic cavity called the magnetosphere (see Figure 1). Electric currents are carried by the thin gas in space and flow down along Earth's magnetic field into our atmosphere. If these currents are intense enough, the atmosphere glows like a neon tube. This glow is the mysterious aurora, which appears both in the northern and southern polar regions. During big magnetic storms the aurora can be seen in Washington.   An aurora photographed in Alaska on September 6, 1996. Photo copyright Jan Curtis. So the space environment near Earth is dominated by Earth's magnetic field, but powered by the solar wind. And as in any environment, there can be disturbances which we can call "storms." Storms in the space environment are caused by gusts of solar wind that strike the magnetosphere. The magnetic field of the solar wind also plays a big role in storms by becoming connected to Earth's magnetic field. This allows the solar wind energy to get into the magnetosphere. The extra burst of energy drives big currents (millions of amps) in Earth's upper atmosphere, creates brilliant auroras, and causes fluctuations in the magnetic field. It also energizes the protons and electrons trapped in the Earth's magnetic field, raising the radiation levels in space. How do these "magnetic storms" impact us on Earth? To begin, more of what we do on Earth depends on our space systems. Just think about telephone and television. They both depend to an amazing degree on satellites to beam signals back and forth. During magnetic storms, communication satellites can be damaged by the radiation these storms produce. On January 11, 1997, the Telstar 401 satellite was lost during the height of a major magnetic storm that started a day earlier. The traffic Telstar 401 was carrying had to be quickly rerouted, and the satellite itself never recovered. Several other satellites have been lost during magnetic storms. At more than $200 million per lost satellite, big magnetic storms can be expensive. Magnetic storms can also directly disrupt electrical power here on Earth, causing blackouts over large regions. In March 1989, major storm caused 1/3 of Canada and part of upstate New York to lose power. Damages ran into the millions. Some experts think that now we may be more vulnerable to big magnetic storms because our electrical power grids are becoming more interconnected to improve efficiency. While big, dramatic events as described above are rare, space weather is something that will have an increasing impact on our lives. We are becoming more dependent on satellite technology, and the environment where these satellites operate does experience storms. Fortunately, scientists are studying space weather and are learning to predict at least some things. Who knows, before too long you may hear on the television, " ... and here's tonight's space weather update."