Ionospheric Disturbances and Their Impact on IPS Using MEXART Observations

We study the impact of ionospheric disturbances on the Earth’s environment caused by the solar events that occurred from 20 April to 31 May 2010, using observations from the Mexican Array Radio Telescope (MEXART). During this period of time, several astronomical sources presented fluctuations in their radio signals. Wavelet analysis, together with complementary information such as the vertical total electron content (vTEC) and the Dst index, were used to identify and understand when the interplanetary scintillation (IPS) could be contaminated by ionospheric disturbances (IOND). We find that radio signal perturbations were sometimes associated with IOND and/or IPS fluctuations; however, in some cases, it was not possible to clearly identify their origin. Our Fourier and wavelet analyses showed that these fluctuations had frequencies in the range ≈?0.01 Hz?–?≈?1.0 Hz (periodicities of 100 s to 1 s).     

Some Characteristics of the Ionospheric Behavior During the Solar Cycle 23 – 24 Minimum

The Solar Cycle 23?–?24 minimum has been considered unusually deep and complex. In this article we study the ionospheric behavior during this minimum, and we have found that, although observable, the ionosphere response is minor and marginally exceeds the range of normal geophysical variability of the system. Two main ionospheric parameters have been studied: vertical TEC (vTEC, total electron content) and NmF2 (peak concentration of the F region). While vTEC showed a consistent modest decrease of the mean value, NmF2 behavior was less clear, with instances where the mean value for the minimum 23?–?24 was even higher that for the minimum 22?–?23. More extensive work is required to gain a better understanding of the ionospheric behavior under conditions similar to those presented in the last minimum.     

Evaluation of the STORM-Time Ionospheric Empirical Model for the Bastille Day event

Recent theoretical model simulations of the ionospheric response to geomagnetic storms have provided the understanding for the development of an empirical storm-time ionospheric model (STORM). The empirical model is driven by the previous time-history of a _p, and is designed to scale the quiet-time F-layer critical frequency (f _o F ₂) to account for storm-time changes in the ionosphere. The model provides a useful, yet simple tool for modeling of the perturbed ionosphere. The quality of the model prediction has been evaluated by comparing with the observed ionospheric response during the Bastille Day (July 2000) storm. With a maximum negative D _st of −290 nT and an a _p of 400, this magnetic perturbation was the strongest of year 2000. For these conditions, the model output was compared with the actual ionospheric response from all available stations, providing a reasonable latitudinal and longitudinal coverage. The comparisons show that the model captures the decreases in electron density particularly well in the northern summer hemisphere. In winter, the observed ionospheric response was more variable, showing a less consistent response, imposing a more severe challenge to the empirical model. The value of the model has been quantified by comparing the root mean square error (RMSE) of the STORM predictions with the monthly mean. The results of this study illustrate that the STORM model reduces the RMSE at the peak of the disturbance from 0.36 to 0.22, a significant improvement over climatology.