Solar Activity Monitoring

With A Look At Auroral Activity

   Auroral Activity

Read The Space Environment Center's Paper On The Aurora

Aurora is caused by interaction between the Earth's magnetic field and the solar wind (a mix of charged particles blowing away from the sun).  During solar storms, enough of these charged particles make it through to the Earth's upper atmosphere that they interact with the earths natural magnetic field lines.  When enough of these particles collide, energy is released in the form of auroral light.  In addition to creating a pretty light show (mostly in upper latitudes), radio signals scatter off of these particles and can greatly enhance propagation on 6 meters and above. High levels of aurora can also make HF propagation via polar routes difficult.

Instruments on board the NOAA Polar-orbiting Operational Environmental Satellite (POES) continually monitor the power flux carried by the protons and electrons that produce aurora in the atmosphere. SEC has developed a technique that uses the power flux observations obtained during a single pass of the satellite over a polar region (which takes about 25 minutes) to estimate the total power deposited in an entire polar region by these auroral particles. The power input estimate is converted to an auroral activity index that ranges from 1 to 10.

Over 100,000 satellite passes comprise the NOAA POES historical database that was used to construct statistical patterns of auroral power flux for each of the 10 levels of auroral activity as defined by total power dissipation as illustrated in the following table.

Real-Time Northern Hemisphere Auroral Activity	Real-Time Southern Hemisphere Auroral Activity

When displayed in geographic coordinates, the statistical patterns of auroral particle power input provide a "best-guess" estimate of the locations, geographic extents, and intensities of aurora at the time of the satellite pass that provided the estimate of auroral activity. Energetic auroral particles (primarily electrons) not only produce the visible aurora but also greatly influence the properties of the ionosphere and are connected with strong electrical currents (as much as several million amperes) that flow in the ionosphere and connect along the geomagnetic field to dynamo processes at high altitude in the magnetosphere. Thus, this same display provides a similar "best-guess" estimate of the geographic locations that may be subject to geomagnetic fluctuations that result from electrical currents flowing in the ionosphere, or the radio propagation paths that may be degraded because of increased absorption of the radio signal by the disturbed ionosphere

When geomagnetic activity is low, the aurora typically is located, in the hours around midnight, at about 67 degrees magnetic latitude*. As activity increases, the region of aurora expands toward the equator. When geomagnetic activity is very high, the aurora may be seen at mid and low latitude locations around the earth that would otherwise rarely experience the polar lights.

Kp map of midnight equatorward boundaries

* Corrected magnetic latitude
**The Handbook of Geophysics and the Space Environment, Air Force Geophysics Laboratory, 1985

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