1] Recent developments in tomographic imaging allow the use of GPS satellite data to image the Earth's ionosphere. Ground-based GPS receivers monitor the Earth's ionosphere continuously, and a comprehensive database of ionospheric measurements suitable for tomographic processing now exists. The tomographic inversion of these GPS data in a three-dimensional time-dependent inversion algorithm can reveal the spatial and temporal distribution of ionospheric electron density. This new technique is unique for studying ionospheric physics because it gives a time-continuous near-global view of the ionosphere. The tomographic algorithms have been under continuous development for several years and are now yielding new geophysical results. Two fundamentally different algorithms (Multi-instrument Data Analysis System and Ionospheric Data Assimilation Three-Dimensional) are presented. They show the ionospheric impact of two major space weather events during the recent solar maximum. Results obtained from these two algorithms are similar, which provides additional confidence in the accuracy of the images.
A new technique for ionospheric imaging is demonstrated during a severe geomagnetic storm of 15th July 2000. The three‐dimensional time‐dependent imaging algorithm is applied to multi‐directional ground‐based GPS data and yields spatial maps of electron concentration. This technique is demonstrated by showing a series of images of the mid‐latitude ionosphere over the USA during the storm of July 2000. A strong uplift in the height of the F‐layer is observed after 20 UT on 15th July, followed by a severe latitudinal electron concentration gradient. Independent verification of the images is provided by the ionosondes and incoherent scatter radar data. The GPS images reveal the large‐scale dynamics of the ionosphere during the disturbed conditions and show the potential of geophysical imaging for storm‐time ionospheric studies.
[1] On 5 April 2010 a coronal mass ejection produced a traveling solar wind shock front that impacted the Earth's magnetosphere, producing the largest geomagnetic storm of 2010. The storm resulted in a prolonged period of phase scintillation on Global Positioning System signals in Antarctica. The scintillation began in the deep polar cap at South Pole just over 40 min after the shock front impact was recorded by a satellite at the first Lagrangian orbit position. Scintillation activity continued there for many hours. On the second day, significant phase scintillation was observed from an auroral site (81 S) during the postmidnight sector in association with a substorm. Particle data from polar-orbiting satellites provide indication of electron and ion precipitation into the Antarctic region during the geomagnetic disturbance. Total electron content maps show enhanced electron density being drawn into the polar cap in response to southward turning of the interplanetary magnetic field. The plasma enhancement structure then separates from the dayside plasma and drifts southward. Scintillation on the first day is coincident spatially and temporally with a plasma depletion region both in the dayside noon sector and in the dayside cusp. On the second day, scintillation is observed in the nightside auroral region and appears to be strongly associated with ionospheric irregularities caused by E region particle precipitation.
Ionospheric imaging with GPS provides a near‐global view of the three‐dimensional time‐evolving ionosphere. This is of particular interest during storms. The focus of this paper is on the height redistribution of the plasma and in particular the longitudinal and latitudinal variations in the time of plasma uplifts. Three storms, 15 July 2000, 30 October 2003 and 20 November 2003, are studied here. Dramatic elevation of the F layer by more than one hundred kilometers was seen in the images during daytime over Europe and the USA for all three storms. All three showed an east‐west time delay of around one hour in the peak‐height elevation over some 85° longitude. The 20 November 2003 storm also showed a north‐south time delay in the change in the F‐region height with the uplift seen first at high latitudes and then low latitudes. Independent evidence from other instruments and techniques are provided as supporting evidence that the peak‐height uplifts occurred. Candidate mechanisms of the peak height changes are electric fields and neutral winds and the roles of these drivers will be investigated in future modelling studies.
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