SEC Navigation Systems Loran-C Page

Loran-C operations are hampered when the sky wave arrives at a receiver at the same time as the ground wave. This occurs when the reflecting height of the ionosphere drops, as it does during times of increased activity in the space environment.

This activity can be of different types:

• Solar flare x-rays, with the effect most acute on the dayside of the earth;
• Solar energetic particles, impacting Loran-C operations at all local times, but strongest at high latitudes;
• Geomagnetic storm activity, hampering operations at all local times and at all latitudes.

The net effect of each of these three types of geophysical activity is a lowering of the reflection height of the ionosphere.

Check Today's Space Weather to see if any of these three conditions have occurred. If the x-ray flux, as measured by the long wavelength (1.0 - 8.0 A) channel on either of the GOES spacecraft, exceeded "M" level (>1.0E-5 W-sq. m.), dayside Loran-C users may have been affected.

Solar energetic particle fluxes are available on the Proton Flux Plot. If the red trace surpassed a flux of 1.0E+1, enhanced fluxes of protons were observed at geosynchronous orbit and have the potential of impacting Loran-C in the polar regions.

The state of the Earth's magnetic field can be determined from the Planetary K-Index Plot . Red bars denote periods during which the magnetic field was sufficiently disturbed to affect the proper function of the Loran-C system.

Forecasts of Solar and Geophysical activity for the next several days can be helpful in planning future Loran-C operations. The Joint USAF/NOAA Report of Solar and Geophysical Activity contains information on solar x-ray activity (parts I and III), solar energetic particles (part II), and geomagnetic activity (parts II, V, and VI).

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