A study on the nighttime midlatitude ionospheric trough

Abstract

[1] Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) electron density profiles are used to investigate the nighttime midlatitude ionospheric trough (MIT). We find that at midnight the longitudinally deepest MIT occurs to the west of the geomagnetic pole in both the Northern and Southern Hemispheres during the equinox seasons and local summer. The deepest MIT could be ascribable to the enhanced depletion caused by horizontal neutral wind. In the early evening, the eastward neutral wind prevails in the midlatitude F region, which blows the plasma downward where the declination is eastward in the Northern Hemisphere but westward in the Southern Hemisphere, both lying to the west of the geomagnetic pole. The downward drift would enhance the plasma depletion for more molecular composition at lower altitude. In addition, we find for the first time that the location of nighttime MIT minimum oscillated with a periodicity of 9 days and an amplitude of about 1°-1.5°geomagnetic latitude during 2007-2008, associated with the recurrent high-speed solar wind. Our results shed new light on the empirical description and numerical simulation of MIT.

Modelling the main ionospheric trough using the Electron Density Assimilative Model (EDAM) with assimilated GPS TEC

“…After the Harang discontinuity near local magnetic midnight the trough may be a fossil from the earlier time in the eastward flow in the dawn sector as mentioned by Pryse et al (2006), although the continuing decrease evident after 03:00 UT may be attributed to continuing chemical loss (Lee et al, 2011). The statistical study of He et al (2011) considered NmF2 for magnetic activity Kp of less than 3 and categorized the data by season and hemisphere. They concluded that the depth of the midnight trough showed longitudinal dependency in the equinox seasons and summer, and related this to the neutral winds and the configuration of the geomagnetic field.…”

“…Bates et al (1973) focussed on the poleward edge of the trough under quiet geomagnetic activity, where the maximum electron density at the trough wall in the F region was some 1 • latitude equatorward of the visible aurora. In later years, the dependencies of the trough on other parameters have been investigated, for example on season and solar activity (Ishida et al, 2014), geomagnetic conditions (Werner and Prölss, 1997) and longitude (He et al, 2011;Whalen, 1989). Many studies have aimed to characterize trough production and properties.…”

Statistical analysis of ionospheric mid-latitude trough over the Northern Hemisphere derived from GPS total electron content data

“…The GPS-TEC In this study, we examined the trough structure averaged longitudinally over the course of a day. The longitudinal average of the trough structure depends not only on the longitude effect of the trough occurrence rate (He et al 2011) but also on the longitude effect of the trough structure (Karpachev 2003). The occurrence rate of the trough shows significant variations depending on the season, solar activity, and MLT (Ishida et al 2014).…”

“…The trough has been investigated using various data and methods such as data from satellites, tomography, total electron content (TEC), incoherent scatter radar (ISR), and models (Muldrew 1965;Nilsson et al 2005;Pryse et al 2006;Middleton et al 2008;He et al 2011;Lee et al 2011;Ishida et al 2014). Currently, due to the fast-growing number of ground-based GPS receivers, GPS-TEC measurements have been increasingly used for upper atmospheric research.…”

Statistical analysis of the mid-latitude trough position during different categories of magnetic storms and different storm intensities

“…Throughout the current paper, 'trough' refers specifically to the mid-latitude trough. The trough has been studied for several decades (Muldrew 1965;Horvath and Essex 2003;Nilsson et al 2005;Pryse et al 2006;Middleton et al 2008;He et al 2011;Lee et al 2011;Ishida et al 2014). Most studies have displayed the quiet-time features of the trough (e.g., Rodger et al 1992;Scali 1992;Rodger 2008).…”