Diagnostics of equatorial and low latitude ionosphere by TEC mapping over Brazil

The total electron content (TEC) in the equatorial and low-latitude ionosphere over Brazil was monitored in two dimensions by using 2011 data from the ground-based global navigation satellite system (GNSS) receiver network operated by the Brazilian Institute for Geography and Statistics. It was possible to monitor the spatial and temporal variations in TEC over Brazil continuously during both day and night with a temporal interval of 10 min and a spatial resolution of about 400 km. The daytime equatorial ionization anomaly (EIA) and post-sunset plasma enhancement (PS-EIA) were monitored over an area corresponding to a longitudinal extension of 4000 km in South America. Considerable day-to-day variation was observed in EIA and PS-EIA. A large latitudinal and longitudinal gradient of TEC indicated a significant ionospheric range error in application of the GNSS positioning system. Large-scale plasma bubbles after sunset were also mapped over a wide range. Depletions with longitudinally separated by more than 800 km were observed. They were extended by more than 2000 km along the magnetic field lines and drifted eastward. It is expected that 2-dimensional TEC mapping can serve as a useful tool for diagnosing ionospheric weather, such as temporal and spatial variation in the equatorial plasma trough and crest, and particularly for monitoring the dynamics of plasma bubbles.     

Cross Field Diffusion of Cosmic Rays in a Two-Dimensional Magnetic Field Turbulence

Cross field diffusion of energetic particles (cosmic rays) in a two-dimensional static magnetic field turbulence is studied performing test particle simulations. Qualitatively different diffusion processes are observed depending on the ratio of Larmor radius (ρ) to the correlation length (λ) of the magnetic field fluctuations. The diffusion is found to be composed of several regimes with distinct statistical properties, which can be characterized using Levy statistics. This revised version was published online in August 2006 with corrections to the Cover Date.     

Overview of Nighttime Ionospheric Instabilities at Low- and Mid-Latitudes: Coupling Aspects Resulting in Structuring at the Mesoscale

We present a review of the current state of understanding regarding two classes of irregularities causing mesoscale structuring (hundreds of kilometers) in the nighttime ionosphere at low- and mid-latitudes. Additionally, current state of understanding of equatorial plasma bubbles at low latitudes, and medium-scale traveling ionospheric disturbances at mid latitudes and their relationship to possible seeding from lower altitudes are described. In each case, well-developed linear theories exist to explain the general properties of the irregularities. However, these linear theories have growth rates too low to explain the actual observations, giving rise to the need to invoke seeding mechanisms. We describe the observational databases that have been compiled over the decades and discuss possible coupling and seeding mechanisms that would overcome the low growth rate and explain the observed structuring at the mesoscale. Future research directions are also briefly discussed.