Editing Space weather (section)

===Ground-based===
Space weather is monitored at ground level by observing changes in the Earth's magnetic field over periods of seconds to days, by observing the surface of the Sun, and by observing radio noise created in the Sun's atmosphere.

The [[Wolf number|Sunspot Number]] (SSN) is the number of [[sunspot]]s on the Sun's photosphere in visible light on the side of the Sun visible to an Earth observer. The number and total area of sunspots are related to the brightness of the Sun in the [[extreme ultraviolet|EUV]] and X-ray portions of the [[sunlight|solar spectrum]] and to solar activity such as solar flares and coronal mass ejections<!-- (CMEs) -->.

The 10.7&nbsp;cm radio flux (F10.7) is a measurement of RF emissions from the Sun and is roughly correlated with the solar EUV flux. Since this RF emission is easily obtained from the ground and EUV flux is not, this value has been measured and disseminated continuously since 1947. The world standard measurements are made by the [[Dominion Radio Astrophysical Observatory]] at Penticton, BC, Canada and reported once a day at local noon<ref>{{Cite web|url=http://www.swpc.noaa.gov/ftpdir/lists/radio/7day_rad.txt |title=Last 7 days of solar radio flux |url-status=dead |archive-url=https://web.archive.org/web/20141006071524/http://www.swpc.noaa.gov/ftpdir/lists/radio/7day_rad.txt |archive-date=October 6, 2014 }}</ref> in solar flux units (10<sup>−22</sup>W·m<sup>−2</sup>·Hz<sup>−1</sup>). F10.7 is archived by the National Geophysical Data Center.<ref>[ftp://ftp.ngdc.noaa.gov/STP/SOLAR_DATA/SOLAR_RADIO/FLUX/  NOAA/NGDC F10.7 archive]{{dead link|date=May 2018 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

Fundamental space weather monitoring data are provided by ground-based magnetometers and magnetic observatories. Magnetic storms were first discovered by ground-based measurement of occasional magnetic disturbance. Ground magnetometer data provide real-time situational awareness for postevent analysis. Magnetic observatories have been in continuous operations for decades to centuries, providing data to inform studies of long-term changes in space climatology.<ref>{{cite journal|author=Love, J. J.|year= 2008|title= Magnetic monitoring of Earth and space|journal= Physics Today|volume=61|issue= 6|pages=31–37|url=http://geomag.usgs.gov/downloads/publications/pt_love0208.pdf|doi=10.1063/1.2883907|bibcode=2008PhT....61b..31H}}</ref><ref>{{cite journal|author=Love, J. J.|year= 2011|author2=Finn, C. A. |title= The USGS Geomagnetism Program and its role in space weather monitoring|journal= Space Weather|volume=9|issue= 7|pages= 07001|doi=10.1029/2011SW000684|url=http://geomag.usgs.gov/downloads/publications/2011SW000684.pdf|bibcode=2011SpWea...9.7001L|doi-access=free}}</ref>

[[Disturbance storm time index<!-- |Dst index -->]] (Dst index) is an estimate of the magnetic field change at the Earth's magnetic equator due to a ring of electric current at and just earthward of the [[geosynchronous orbit]].<ref>{{Cite web|title = Bulletin 40 |first1=Masahisa |last1=SUGIURA |first2=Toyohisa |last2=KAMEI|url = http://wdc.kugi.kyoto-u.ac.jp/dstdir/dst2/onDstindex.html|website = wdc.kugi.kyoto-u.ac.jp|access-date = 2015-07-24}}</ref> The index is based on data from four ground-based magnetic observatories between 21° and 33° [[Geomagnetic latitude|magnetic latitude]] during a one-hour period. Stations closer to the magnetic equator are not used due to ionospheric effects. The Dst index is compiled and archived by the World Data Center for Geomagnetism, Kyoto.<ref name="kyoto">[http://wdc.kugi.kyoto-u.ac.jp/wdc/Sec3.html Geomagnetic Data Service] World Data Center for Geomagnetism, Kyoto</ref>

[[K-index|Kp/ap]] index: 'a' is an index created from the geomagnetic disturbance at one midlatitude (40° to 50° latitude) geomagnetic observatory during a 3-hour period. 'K' is the quasilogarithmic counterpart of the 'a' index. Kp and ap are the average of K and an over 13 geomagnetic observatories to represent planetary-wide geomagnetic disturbances. The Kp/ap index<ref>[http://www.gfz-potsdam.de/kp-index Helmholtz Centre PotsdamGFZ German Research Centre for Geosciences]</ref> indicates both geomagnetic storms and substorms (auroral disturbance). Kp/ap data are available from 1932 onward.

AE index is compiled from geomagnetic disturbances at 12 geomagnetic observatories in and near the auroral zones and is recorded at 1-minute intervals.<ref name="kyoto" /> The public AE index is available with a lag of two to three days that limits its utility for space weather applications. The AE index indicates the intensity of geomagnetic substorms except during a major geomagnetic storm when the auroral zones expand equatorward from the observatories.

Radio noise bursts are reported by the Radio Solar Telescope Network to the U.S. Air Force and to NOAA. The radio bursts are associated with solar flare plasma that interacts with the ambient solar atmosphere.

The Sun's photosphere is observed continuously<ref>[http://www.swpc.noaa.gov/solar_sites.html List of solar observatories] {{webarchive|url=https://web.archive.org/web/20110410190312/http://www.swpc.noaa.gov/solar_sites.html |date=2011-04-10 }}</ref> for activity that can be the precursors to solar flares and CMEs. The Global Oscillation Network Group (GONG)<ref>[http://gong.nso.org Global Oscillation Network Group home page]</ref> project monitors both the surface and the interior of the Sun by using [[helioseismology]], the study of sound waves propagating through the Sun and observed as ripples on the solar surface. GONG can detect sunspot groups on the far side of the Sun. This ability has recently been verified by visual observations from the ''[[STEREO]]'' spacecraft.

[[Neutron monitor]]s on the ground indirectly monitor cosmic rays from the Sun and galactic sources. When cosmic rays interact with the atmosphere, atomic interactions occur that cause a shower of lower-energy particles to descend into the atmosphere and to ground level. The presence of cosmic rays in the near-Earth space environment can be detected by monitoring high-energy neutrons at ground level. Small fluxes of cosmic rays are present continuously. Large fluxes are produced by the Sun during events related to energetic solar flares.

[[Total Electron Content]] (TEC) is a measure of the ionosphere over a given location. TEC is the number of electrons in a column one meter square from the base of the ionosphere (around 90&nbsp;km altitude) to the top of the ionosphere (around 1000&nbsp;km altitude). Many TEC measurements are made by monitoring the two frequencies transmitted by [[Global Positioning System|GPS]] spacecraft. Presently, GPS TEC is monitored and distributed in real time from more than 360 stations maintained by agencies in many countries.

Geoeffectiveness is a measure of how strongly space weather magnetic fields, such as coronal mass ejections, couple with the Earth's magnetic field. This is determined by the direction of the magnetic field held within the plasma that originates from the Sun. New techniques measuring [[Faraday effect|Faraday rotation]] in radio waves are in development to measure field direction.<ref>{{cite web|title=Under Sunveillance|url=http://www.physics.org/featuredetail.asp?id=73|publisher=physics.org|access-date=12 September 2012}}</ref><ref>{{cite web|title=Solar-Heliospheric-Ionospheric Science|url=http://www.haystack.mit.edu/mwa/Science%20Goal/Solar-Heliospheric-Ionospheric%20Science/solar.html|publisher=MIT Haystack Observatory|access-date=12 September 2012}}</ref>