Abstract
Abstract. The energetic events on the sun, solar wind and subsequent effects on the Earth's geomagnetic field and upper atmosphere (ionosphere) comprise space weather. Modern navigation systems that use radio-wave signals, reflecting from or propagating through the ionosphere as a means of determining range or distance, are vulnerable to a variety of effects that can degrade the performance of the navigational systems. In particular, the Global Positioning System (GPS) that uses a constellation of earth orbiting satellites are affected due to the space weather phenomena. Studies made during two successive geomagnetic storms that occurred during the period from 8 to 12 November 2004, have clearly revealed the adverse affects on the GPS range delay as inferred from the Total Electron Content (TEC) measurements made from a chain of seven dual frequency GPS receivers installed in the Indian sector. Significant increases in TEC at the Equatorial Ionization anomaly crest region are observed, resulting in increased range delay during the periods of the storm activity. Further, the storm time rapid changes occurring in TEC resulted in a number of phase slips in the GPS signal compared to those on quiet days. These phase slips often result in the loss of lock of the GPS receivers, similar to those that occur during strong(>10 dB) L-band scintillation events, adversely affecting the GPS based navigation.
Highlights
The solar disturbances affecting the Earth’s magnetic field, cause geomagnetic storms
We report that the loss of lock of Global Positioning System (GPS) receiver signal may occur whenever there is a fast rate of change in the Total Electron Content (TEC) fluctuations, during the periods of geomagnetic storm activity
Studies on the two overlapping geomagnetic storms, that occurred during 8 to 12 November 2004, have clearly revealed the adverse affects on the GPS range delay measurements as inferred from the TEC measurements made from a chain of dual frequency GPS receivers in the Indian sector
Summary
The solar disturbances affecting the Earth’s magnetic field, cause geomagnetic storms. Changes in the electron density, due to space weather activity, can change the speed at which the radio waves travel, introducing a propagation delay in the GPS signal. These delays can vary with time, and such intervals of rapid change can last for several hours, especially in the polar and auroral. The maximum Dst value on 8 November 2004 was −383 nT, considerably stronger than −296 nT measured on 10 November 2004 These two storms have produced adverse affects in the communication and navigation systems such as GPS by introducing huge electron density gradients and scintillations. The maximum excursion of this geomagnetic storm is −296 nT and occurred at 14:00 IST on 10 November 2004
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