Abstract.A latitudinal-distributed network of GPS receivers has been operating within Colombia, Peru and Chile with sufficient latitudinal span to measure the absolute total electron content (TEC) at both crests of the equatorial anomaly. The network also provides the latitudinal extension of GPS scintillations and TEC depletions. The GPS-based information has been supplemented with density profiles collected with the Jicamarca digisonde and JULIA power maps to investigate the background conditions of the nighttime ionosphere that prevail during the formation and the persistence of plasma depletions. This paper presents case-study events in which the latitudinal extension of GPS scintillations, the maximum latitude of TEC depletion detections, and the altitude extension of radar plumes are correlated with the location and extension of the equatorial anomaly. Then it shows the combined statistics of GPS scintillations, TEC depletions, TEC latitudinal profiles, and bottomside density profiles collected between September 2001 and June 2002. It is demonstrated that multiple sights of TEC depletions from different stations can be used to estimate the drift of the background plasma, the tilt of the plasma plumes, and in some cases even the approximate time and location of the depletion onset. This study corroborates the fact that TEC depletions and radar plumes coincide with intense levels of GPS scintillations. Bottomside radar traces do not seem to be associated with GPS scintillations. It is demonstrated that scintillations/depletions can occur when the TEC latitude profiles are symmetric, asymmetric or highly asymmetric; this is during the absence of one crest. Comparison of the location of the northern crest of the equatorial anomaly and the maximum latitude of scintillations reveals that for 90% of the days, scintillations are confined within the boundaries of the 50% decay limit of the anomaly crests. The crests of the anomaly are the regions where the most intense GPS scintillations and the deepest TEC depletions are encountered. In accord with early results, we observe that GPS scintillaCorrespondence to: C. E. Valladares (valladar@bc.edu) tions/TEC depletions mainly occur when the altitude of the magnetic equator F-region is above 500 km. Nevertheless, in many instances GPS scintillations and TEC depletions are observed to exist when the F-layer is well below 500 km or to persist when the F-layer undergoes its typical nighttime descent. Close inspection of the TEC profiles during scintillations/depletions events that occur when the equatorial F-layer peak is below 500 km altitude reveals that on these occasions the ratio of the crest-to-equator TEC is above 2, and the crests are displaced 10 • or more from the magnetic equator. When the equatorial F-layer is above 500 km, neither of the two requirements is needed, as the flux tube seems to be inherently unstable. We discuss these findings in terms of the RayleighTaylor instability (RTI) mechanism for flux-tube integrated quantities. We advance the idea that ...

Abstract. Measurements of total electron content (TEC) using 263 GPS receivers located in the North and South America continents are presented to demonstrate the simultaneous existence of traveling ionospheric disturbances (TID) at high, mid, and low latitudes, and in both Northern and Southern Hemispheres. The TID observations pertain to the magnetically disturbed period of 29-30 October 2003 also known as the Halloween storm. The excellent quality of the TEC measurements makes it possible to calculate and remove the diurnal variability of TEC and then estimate the amplitude, wavelength, spectral characteristics of the perturbations, and the approximate velocity of the AGW.

[1] Five GPS receivers have been deployed near the 74°W longitude meridian to measure the variability of total electron content (TEC) latitudinal profiles and to study the relation of this variability with the onset and evolution of spread F plasma structures. These five GPS receivers, together with two others that form part of the International GPS Service (IGS) network, three more that belong to the South Andes Project network, and an additional receiver located at Ancon, Peru, provide TEC values between 8°N and 40°S geographic latitude. In addition, all five GPS receivers managed by Boston College give the amplitude scintillation on a near-real time basis. This fact allows us to know the maximum latitude to which the irregularities extend and to infer the maximum altitude of the plasma bubbles. We have calculated TEC latitudinal profiles using the TEC values obtained by all the receivers between 1998 and 2001. We found that during the equinoxes, UHF scintillations occur when the ratio of the crest to the trough of the anomaly is 2 or larger. During the December solstice the crest is not very pronounced, but a sharp decrease of TEC at the magnetic equator precedes the onset of 1-km scale irregularities. We have also examined a longitudinal variability of scintillations by partitioning the sky in two sectors separated at the 74°W meridian. We consistently observe a greater number of GPS scintillation events at the eastern longitudes over the Amazon rain forest. This intriguing finding could well be explained by a larger population of gravity waves at longitudes east of the Andes.

Total electron content (TEC) values measured with several arrays of dual-frequency GPS receivers operating continuously and simultaneously at equatorial and low latitudes are used to construct regional maps of TEC over South and Central America and the Caribbean region. This extended database comprises TEC values collected by 126 stations that operated in South America in 2008, 181 stations in 2009, and 324 stations in 2010.The latter year includes GPS stations in Central America and the Caribbean region, extending the TEC coverage from the southern tip of South America to the northern boundary of Mexico (~30°N latitude). The TEC maps contain high (0.5°× 0.5°) spatial resolution and good (30 min) temporal resolution. The most prominent feature of these maps is the day-to-day variability that is observed during all seasons and under quiet and active magnetic conditions. Single station plots display TEC variations with time scales of few hours and the appearance of TEC enhancements near-midnight that can be accounted for by electric fields associated with disturbed magnetic conditions and the reverse fountain effect, respectively. To assess the TEC dependencies upon season, solar flux, magnetic activity, and local time over South and Central America, two statistical procedures were employed. First, we constructed monthly averages of TEC values along three field lines that intersect the magnetic equator at 70°, 60°, and 50°W longitudes that show a complex pattern of variability and symmetry/asymmetry of the equatorial anomaly depending on the season, the longitude, and the solar flux. Our second analysis consists of a non-linear least-square fit to simultaneously extract the solar flux, magnetic, and seasonal dependencies of TEC for each square cell (0.5°× 0.5°) of the regional maps and for each 30-min time sector. It is found that during low solar flux conditions, the anomaly is weak or non-existent. When the solar flux F10.7 index increases to 85 units the anomaly shows to be fully developed but contains a pronounced longitudinal/ seasonal dependence. During the equinoxes and afternoon hours, the northern crest extends across the South American continent, but the southern crest prevails in the eastern side of South America. It is found that the non-linear numerical fitting of the TEC distributions can reproduce only 70% of the TEC variability.

We applied multi–temporal 1D magnetotelluric (MT) surveys to identify space–time anomalies of apparent resistivity (ρa) in the upper lithosphere in the Antarctic Peninsula (the border between the Antarctic and the Shetland plates). We used time series over several weeks of the natural Earth’s electric and magnetic fields registered at one MT station of the Universidad Nacional de Colombia (RSUNAL) located at Seymour–Marambio Island, Antarctica. We associated resistivity anomalies with contrasting earthquake activity. Anomalies of ρa were detected almost simultaneously with the beginning of a seismic crisis in the Bransfield Strait, south of King George Island (approximately 85.000 events were reported close to the Orca submarine volcano, with focal depths < 20 km and MWW < 6.9). We explained the origin of these anomalies in response to fluid migration near the place of the fractures linked with the seismic swarm, which could promote disturbances of the pore pressure field that reached some hundreds of km away.