Armstrong, C.M. Laird, D.L. Detrick, and A.T. Weatherwax, Correlation of solar energetic protons and polar cap absorption, J. Geophys. Res. 106(A1), 149-163, 2001.From its location at the Lagrangian point L1 about 1.5 million km from Earth and 148.5 million km from the Sun, ACE has a prime view of the solar wind, interplanetary magnetic field and higher-energy particles accelerated by the Sun, as well as particles accelerated in the heliosphere and the galactic regions beyond. ACE also provides near-real-time 24/7 continuous coverage of solar wind parameters and solar energetic particle intensities (space weather). When reporting space weather ACE provides an advance warning (about 1 hour) of geomagnetic storms that can overload power grids, disrupt communications on Earth, and present a hazard to astronauts. see http://www.srl.caltech.edu/ACE/ace_mission.html). More detail can be found in Stone et al., The Advanced Composition Explorer, Space Science Reviews 86, 1, 1998.SOHO also obits at the L1 Lagrangian point, where it continuously monitors the Sun with 12 different instruments. Of particular use for space weather warnings are EIT (Extreme Ultraviolet Imaging Telescope), which can detect eruptive solar flares, and LASCO (Large Angle and Spectrometric Coronagraph), which can detect coronal mass ejections that may impact Earth’s magnetosphere. See http://sohowww.nascom.nasa.gov/about/docs/SOHO_Fact_Sheet.pdf. Sample EIT and LASCO images are shown in Figure 5.5.

3. GLONASS is based on a constellation of active satellites that continuously transmit coded signals in two frequency bands, which can be received by users anywhere on Earth’s surface to identify their position and velocity in real time based on ranging measurements. The system is a counterpart to the U.S. GPS, and both systems share the same principles in their data transmission and positioning methods. GLONASS is operated by the Coordination Scientific Information Center (KNITs) of the Ministry of Defense of the Russian Federation. See http://www.spaceandtech.com/spacedata/constellations/glonass_consum.shtml.

4. Boscher, D.M., S.A. Bourdarie, R.H.W. Friedel, and R.D. Belian, Model for the geostationary electron environment: POLE, IEEE Trans. Nucl. Sci. 50(6), 2278-2283, 2003.

5. CRRES, Combined Release and Radiation Effects Satellite. See http://nasascience.nasa.gov/missions/crres.

6. GOES, Geostationary Operational Environment Satellite. GOES 13 is the most recent addition to the in orbit fleet of GOES satellites and carries the primary solar x-ray imager. These satellites provide continuous terrestrial weather monitoring (http://www.goes.noaa.gov/) and monitoring of solar activity and space weather (http://www.swpc.noaa.gov/).

7. SDO, Solar Dynamics Observatory. SDO is designed to improve understanding of the Sun’s influence on Earth and near-Earth space by studying the solar atmosphere on small scales of space and time and in many wavelengths simultaneously. See http://sdo.gsfc.nasa.gov/.