Abstract
In this paper, we employ electron density profiles derived by the GPS radio occultation experiment aboard the FORMOSAT-3/COSMIC (F3/C) satellites to examine the electron density on geographic latitudes of 40° to 80° in the Southern hemisphere and 30° to 60° in the Northern hemisphere at various global fixed local times from February 2009 to January 2010. The results reveal that an eastward shift of a single-peak plasma density feature occurs along the Weddell Sea Anomaly (WSA) latitudes, while a double-peak plasma density feature appears along the northern Mid-latitude Summer Nighttime Anomaly (MSNA) latitudes. A cross-comparison between three-dimensional F3/C electron density and HWM93 simulation confirms that the magnetic meridional effect and vertical effect caused by neutral winds exhibit the eastward shifts. Furthermore, we find that the eastward shift of the peaks when viewed as a function of local time suggests that they could be interpreted as being comprised of different tidal components with distinct zonal phase velocities in local time.
Highlights
The Weddell Sea Anomaly (WSA) was first observed by ground-based ionosondes over Antarctica during the International Geophysical Year in 1957 (Bellchambers and Piggott 1958)
The WSA and northern Mid-latitude Summer Nighttime Anomaly (MSNA) have been well known as anomalous enhancements of the nighttime electron density
The two eastward phase shifts 91 and 121 m/s are computed by averaging three-time-point fitting shift by 1 point in 135° E–115° W and 50° W–100° E latitudinal zone, respectively the F3/C observations in this study show that the anomalous enhancements along the WSA and northern MSNA latitudes in both hemispheres are not specific nighttime features but exist over the whole day
Summary
The Weddell Sea Anomaly (WSA) was first observed by ground-based ionosondes over Antarctica during the International Geophysical Year in 1957 (Bellchambers and Piggott 1958). Remote sensing and in situ observations (Burns et al 2008; Lin et al 2009, 2010; Jee et al 2009; He et al 2009; Liu et al 2010) indicate that the WSA extends over a much larger region than originally thought: spanning between South America and Antarctica and extending to the central Pacific region. De Larquier et al (2011) observed the MSNA feature using
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