Xiaoli Luan - Global morphology of electron density and neutral winds in the upper atmosphere/ionosphere
The Earth's ionosphere is one part of the upper atmosphere, starting at about 60 km to about 1000 km, which is overlapped with the thermosphere. The ionosphere is strongly ionised and it contains the ions, electrons (these two are nearly equal in density), and neutral compositions. Only less than 1% of the upper atmosphere becomes ionised, but those charged particles completely changes the characteristics of the upper atmosphere due to electric-magnetic and ion-neutral interaction. The F2-layer in the ionosphere (200-500 km) is the region where the largest electron density located. At the F2-layer, the status of the charged particles (ions and electrons) and the neutral background that interacts with them are of great concern, because the ionosphere can carry electrical currents and can reflect, deflect and scatter the wireless radio waves.
The ions and neutral winds are closely coupled due to ion-neutral drag effects. Xiaoli’s work focuses on the morphology of the ionospheric electron density and meridional winds in the F2-layer, and is aimed to discussion the mechanism that causes their morphology. In NCAR, Xiaoli is focusing on the global geographic variations (Latitudinal and longitudinal) of the F2-layer electron density and neutral wind and their related mechanism. The global observation of electron density profile form the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) and the self-consistent TIEGCM provide good tools for her study. Thus morphology of winds and electron density at the oceanic areas in the northern hemisphere, and at areas in the southern hemisphere, where the observational data are sparse or not available in the past, can be better understood. The longitudinal variations of the meridional winds at the magnetic meridian are marked and similar between the winds derived from COSMIC and TIEGCM. Therefore the TIEGCM simulation is applied to further discuss the mechanism and the study found the effects of the magnetic declination (DEC) are largely responsible for the longitudinal variations of the meridional winds at the magnetic meridian (Figure 1). Both the peak electron density of the F2-layer and the way of its enhancements during the night-time are found to be distinctly different among the majority of the longitudes (~45-245°E), the Atlantic Ocean sector, the eastern part of the North American sectors (Figure 2). Several mechanisms can cause these longitudinal variations, including the separation between the geographic and geomagnetic axes, the difference of the magnetic field intensity at different longitudes and also the longitudinal variation of the magnetic meridional winds.
The ionosphere/thermosphere disturbance under geomagnetic storm condition is her another research project. Under the geomagnetic storm conditions, large energy coming from the solar winds can deposit to the polar region and induce significant changes in the ionosphere/thermosphere. The recent work she involves is to study the variations of the energy depositing to the polar region under various geophysical conditions, such as the variation of the total energy in different solar activity, interplanetary magnetic field (IMF) and geomagnetic activity conditions. The principal goal of these research works is to validate and improve the NCAR HAO GCMs, and also try to understand the involved mechanism of some physical process.
Figure 1. The effect of the magnetic declination (DEC) on the longitudinal variations of the meridional winds (unit: m/s) from TIEGCM simulation at 40ºN. The Magnetic Meridional Wind (bottom, right panel) is the horizontal wind in the magnetic meridian. The North-South wind (positive equatorward) and Zonal Winds (positive eastward) are in geographic coordinates. The contour interval is 20 m/s for all winds.
Figure 2. F2-layer peak density (NmF2) during night at different longitudinal sectors: North America (230ºE and 290ºE), North Atlantic Ocean (340ºE) and East Asia (120ºE). Note different contour scales in each longitudinal sector.
ASP Spotlight September 2008
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