I. J. Kantor

Global Positioning System measurements of the ionospheric zonal apparent velocity at Cachoeira Paulista in Brazil

Ionospheric irregularities and their zonal apparent drift were studied using Global Positioning System (GPS) measurements at Cachoeira Paulista (22.41°S, 45.00°W, −26° dip angle) in Brazil during November 6–19, 1998. Radio scintillations at the GPS L1 frequency (1.575 GHz) were monitored using four GPS receivers spaced geomagnetically east–west and north–south. Total electron content (TEC) was measured through the ionospheric advance of the GPS L1 and L2 (1.227 GHz) phases. Strong amplitude scintillations coincided with TEC fluctuations associated with spread F bubbles elongated along the magnetic field. Movement of the Presnel-scale (400 m) ionospheric irregularity layers caused the scintillation to drift, and their zonal apparent drift velocities were measured using a cross-correlation technique. Our measurements show that the apparent eastward velocity varies from 200 m/s to 150 m/s at 2000 LT, and then it decreases to 100–50 m/s at midnight. On a magnetically disturbed day, reversal of the zonal apparent drift was observed just after midnight, and the apparent westward velocities observed at early in the morning showed large variations with location in the sky. From the receivers spaced in the geomagnetic north–south direction we measured near-zero time shifts, from which we conclude that the correlation length of several-hundred-meter-scale irregularities is much larger than 70-m separation between the north and south receivers.

Equatorial anomaly effects on GPS scintillations in brazil

In a collaborative study, INPE and Cornell University have installed several Global Positioning System (GPS) based scintillation monitors over the Brazilian territory in order to study L Band scintillation. These scintillation monitors were developed by Cornell University to measure the amplitude scintillation observed at L1 (1.575 GHz) GPS signal and are sensitive to ionospheric irregularities of about 400 meters scale size. This paper describes some characteristics of the intensity of scintillations observed at three observation sites in Brazil: (1) Sao Luis (2.33 ° S, 44 ° W, dip latitude 1.3 ° S), located at magnetic equator, (2) Sao Jose dos Campos (23.21 ° S, 45.86 ° W, dip latitude 17.8 ° S), located under the equatorial anomaly peak and (3) Cuiaba (15.33 ° S, 56.46 ° W, dip latitude 6.1 ° S), an intermediate observation site located in between the magnetic equator and the equatorial anomaly peak. Analysis of data from January to March of 2000 showed that the occurrence percentage as well as the magnitude of the L Band scintillation increase with latitude from the magnetic equator to the equatorial anomaly crest as previously reported by Basu et al. (1988). Strong scintillation with S4 index exceeding 0.5 only has been observed under equatorial anomaly peak while at magnetic equator scintillation intensity (S4 index) did not exceed 0.3. Such studies from the network of stations set up by INPE and Cornell University in Brazil, where the effect of large declination controls the ESF statistics, will be very useful for developing a regional scintillation model for use in IRI.

Ionospheric irregularity zonal velocities over Cachoeira Paulista

Abstract We have studied the zonal drift velocity of nighttime ionospheric irregularities from Cachoeira Paulista (22.41°S,45°W, dip latitude −17.43°), a station under the Equatorial Anomaly, from December 1998 to February 1999 using L1 band GPS receivers and OI 630 nm all-sky images. The average decimetric solar flux index for this period of increasing solar activity was about 145 and magnetically quiet days with ΣKp 55 m in the magnetic east–west direction and probed small scale plasma structures (scale size about 400 m ) at altitudes near 350 km . The zonal irregularity drift velocities measured by this technique were eastward with values of about 160 m / s at 20 LT, about 140 m / s around midnight, and decreased further in the post-midnight sector. The variability of these drifts decreased significantly after midnight. The zonal velocities of large scale plasma structure were obtained using OI 630 nm all-sky images from a region located about 24.1°S and 45°W at a nominal height of 250 km which corresponds to the bubble projection along the magnetic field lines to 350 km over Cachoeira Paulista. These all-sky imager derived zonal drifts are also eastward, but have magnitudes smaller than the spaced GPS eastward drifts, particularly in the pre-midnight sector. We will discuss these two drift measurement techniques and the interpretation of our results.

Mapping and Survey of Plasma Bubbles over Brazilian Territory

Ionospheric plasma irregularities or bubbles, that are regions with depleted density, are generated at the magnetic equator after sunset due to plasma instabilities, and as they move upward they map along the magnetic field lines to low latitudes. To analyse the temporal and spatial evolution of the bubbles over Brazilian territory, the mapping of ionospheric plasma bubbles for the night of 17/18 March 2002 was generated using data collected from one GPS receiver array, and applying interpolation techniques. The impact on the performance of Global Navigation Satellites System (GNSS) and on the Space Based Augmentation System (SBAS) in the tropical regions of the GPS signal losses of lock and of the signal amplitude fades during ionospheric irregularities is presented.

Survey and prediction of the ionospheric scintillation using data mining techniques

[1] Irregularly structured ionospheric regions may cause amplitude and phase fluctuations of radio signals. Such distortion is called ionospheric scintillation. These ionospheric irregularities occur as part of depleted plasma density regions that are generated at the magnetic equator after sunset by equatorial ionospheric plasma instability mechanism. Also known as ionospheric bubbles, they drift upward to high altitudes at the equator and extend/expand to low latitudes along the Earth magnetic field lines. Ionospheric irregularities affect the space weather since they present large variations with the solar cycle and during solar flares and coronal mass ejections. In general, navigation systems such as the Global Positioning System and telecommunications systems are also affected by the scintillation. The aim of this work is to apply data mining for the prediction of ionospheric scintillation. Data mining can be divided into two categories: descriptive or predictive. The first one describes a data set in a concise and summarized way, while the second one, used in this work, analyzes the data to build a model and tries to predict the behavior of a new data set. In this study we employed data series of ionospheric scintillation and other parameters such as the level of solar activity, vertical drift velocity of the plasma at the magnetic equator, and magnetic activity. The results show that prediction of the ionospheric scintillation occurrence during the analyzed period was possible regardless of the high variability of the ionospheric parameters that affect the generation of such irregularities.

Rocket-borne measurements of equatorial ionospheric electron densities and their comparison with IRI-10 predictions

Abstract Three experiments were conducted using high frequency capacitance probes carried on board SONDA III rockets launched off the coast of Natal (6° S, 36\dgW), Brasil. Electron-density height profiles from two of the experiments, one daytime, and one nighttime, are representative of quiet equatorial ionospheric conditions whereas for the third experiment the rocket was launched into a nighttime ionosphere that was disturbed by a developing plasma hubble event. Agreement between experimental results and the IRI predictions for the quiet day and night densities varies with height. Comparisons are also made with electron densities obtained from the semi-empirical Low Latitude Ionospheric Model (SLIM).

Comparison of ionospheric electron temperature rocket measurements over Natal, Brazil, with the IRI model

Abstract A SONDA III rocket was launched from Natal on 11 December 1985, at 2030 LT, carrying a Langmuir probe that measured the kinetic electron temperature in the E and F regions of the equatorial ionosphere over Natal, Brazil. The rocket attained an altitude of 524 km. The electron temperature was determined through the derivative of the current versus voltage characteristics of the Langmuir probe and the detection of the floating potential. Results are compared with the IRI model, and the divergence of the results with the model is discussed.

Influence of the geomagnetic activity on the GPS signal

The Global Positioning System has been largely used to indicate the position of a receiver. The stability of this system depends on the medium propagation characteristics. In the present work we study the influence of 2 geomagnetic storms on the variations of the amplitude (scintillation) of the GPS signal in different periods of the year. This scintillation in the GPS signal is due to the presence of ionospheric irregularities. We verified that on the April 2000 storm, that occurred in a period of low incidence of ionospheric irregularities, the geomagnetic storms led to large scintillations of the GPS signal, while during November 2003 when the scintillations are usually high, the geomagnetic storms lead them to fall down. The storm main phase time of occurrence, that was different for each analysed storm, is proposed to be the cause of this different response of the ionospheric irregularities to the magnetic storms.