TEC

About: TEC is a research topic. Over the lifetime, 5119 publications have been published within this topic receiving 84696 citations.

Day-to-night transport in the Martian ionosphere: Implications from total electron content measurements

Abstract: The nightside Martian ionosphere is thought to be contributed by day-to-night transport and electron precipitation, of which the former has not been well studied. In this work, we evaluate the role of day-to-night transport based on the total electron content (TEC) measurements made by the Mars Advanced Radar for Subsurface and Ionospheric Sounding on board Mars Express. This is accomplished by an examination of the variation of nightside TEC in the time domain rather than the traditional solar zenith angle domain. Our analyses here, being constrained to the Northern Hemisphere where the effects of crustal magnetic fields can be neglected, reveal that day-to-night transport serves as the dominant source for the nightside Martian ionosphere from terminator crossing up to time in darkness of ≈5.3 × 103 s, beyond which it is surpassed by electron precipitation. The observations are compared with predictions from a simplified time-dependent ionosphere model. We conclude that the solid body rotation of Mars is insufficient to account for the observed depletion of nightside TEC but the data could be reasonably reproduced by a zonal electron flow velocity of ≈1.9 km s−1.

The Effects of Large Ionospheric Gradients on Single Frequency Airborne Smoothing Filters for WAAS and LAAS

Abstract: Both WAAS and LAAS receivers use carrier-smoothing filters to reduce the effects of multipath and thermal noise at the aircraft. For the majority of users this reduces the magnitude of the errors and leads to improved accuracy. However, the presence of a significant ionospheric gradient can introduce a bias into the output of this filter. If unmitigated, this bias can grow to be significantly larger than the noise and multipath effects the filter is employed to reduce. Such gradients are rare at midlatitudes; however, they are much more common in polarregions and sometimes a daily occurrence in equatorial regions. Therefore, this problem which may be rare in the United States or Europe will be much more significant in other parts of the world. The bias arises because the GPS code and carrier measurements are affected differently by the ionosphere. A positive delay for the code creates an equal, but opposite advance for the carrier. Therefore, as the ionospheric Total Electron Content (TEC) changes along a user’s line of sight to the satellite, the code and carrier measurements diverge from each other at twice the rate of ionospheric change. Nominally, the rate of change over a few hundred seconds is very small (less than a few millimeters per second) leading to decimeter-sized biases or less. However, if the user’s line of sight traverses a significant ionospheric gradient, the TEC can change by tens of meters in just a few minutes. This in turn can create a biased filter estimate of greater than 20 meters. This error is large compared to the overall error budget less than 0.4 m one-sigma. This paper investigates the combined effect of the TEC change and the filter bias on the WAAS/LAAS user’s differential range error and suggests a remedy to lessen the impact. This solution includes changes to the airborne algorithms to detect large differences between the code and carrier. The ability of the airborne receiver to detect this bias depends on the amount of thermal noise and multipath it experiences. This paper will review the current expected levels of noise and multipath and indicate level of performance that should be achievable.

Extreme enhancement in total electron content after sunset on 8 November 2004 and its connection with storm enhanced density

Abstract: [1] After sunset on 8 November 2004, the ionospheric total electron content (TEC) was observed to have anomalously increased following a severe daytime positive TEC storm at longitudes of Japan. The observation was made using a dense GPS receiver network, and covered a geographic latitudinal range of 27 to 45°N. There was a greater increase in TEC at higher latitudes in the evening, and the TEC reached 90 TEC units at 45°N (∼40°N magnetic latitude) at 1145 UT (2045 LT). The TEC enhancement exhibited features significantly different from those of positive TEC storms normally observed at Japan's longitudes. These features are interpreted as low-latitude signatures of a storm enhanced density (SED). Previously, SEDs were reported only at longitudes of America, and this led to the hypothesis that geomagnetic field configurations at these longitudes play a role in their formation. The present observations indicate that SEDs can be observed at other longitudes.