Abstract
Abstract. We provide an event study of THEMIS observations of the low-latitude boundary layer in the dayside magnetosphere. Simultaneous multipoint observations obtained on 5 December 2008 show that the magnetosheath-like plasma in the low-latitude boundary layer is transferred earthward from the magnetopause. This earthward transport is accompanied by decrease in the density and fluctuating bulk flow. We calculate the eddy diffusion coefficients, which can be estimated from the observed velocity data, and found that the numbers are in good quantitative agreement with the spatial and time scales of the observed earthward transport signatures. It is shown that other possible plasma transport processes such as convection or diffusion induced by plasma wave turbulence are inconsistent with the observations. Our study strongly suggests that the observed transport is due to diffusive transport via turbulent eddy motions as is the case of an ordinary (Navier–Stokes) fluid.
Highlights
IntroductionUnderstanding the transport mechanism of material particles (e.g., constituent molecule or pollutant) in various fluid media (e.g., atmosphere or ocean) is important in many industrial and geophysical problems
Understanding the transport mechanism of material particles in various fluid media is important in many industrial and geophysical problems
The eddy diffusion coefficient obtained from the flow velocity data is consistent with the spatial and time scale characteristics seen by the multi-point observations
Summary
Understanding the transport mechanism of material particles (e.g., constituent molecule or pollutant) in various fluid media (e.g., atmosphere or ocean) is important in many industrial and geophysical problems. It is well known that turbulence can transfer those particles more efficiently than molecular diffusion This mode of transport is called eddy diffusion or turbulent diffusion (e.g., Hinze, 1975). Discussions on eddy diffusion in the magnetosphere have been based on coarse-grained datasets that have a time scale of hours and a spatial scale larger than 1 RE. The datasets of these characteristics have been subjected to statistical studies (Borovsky et al, 1998; Wang et al, 2010) or to single-spacecraft studies (Borovsky et al, 1998; Wing et al, 2006). The dataset has a time scale of ten minutes and a spatial scale less than 1 RE, from which we can make a more solid test regarding whether the observed signatures match the expectation from eddy diffusion framework
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