Simulations Of High-latitude Ionosphere-magnetosphere region plasma density structures and the Alfvén waves effects

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Title: Simulations Of High-latitude Ionosphere-magnetosphere region plasma density structures and the Alfvén waves effects
Author: Jaafari, Fajer Bitar
Abstract: O+ density structures in the polar cap ionosphere -magnetosphere region near 6000 km altitude have been observed with numerous spacecraft , with O+ densities ranging from above 10 cm -3 to lower than 0 .01 cm -3 . Regions with densities in the low range have been referred to as O+ density troughs [Zeng et al . , 2004] , or ion depletion zones [Horita et al . , 1993] . Regions with high O+ densities are likely caused by processes such as soft auroral electron precipitation and transverse wave heating . In this simulation work , we use the UT Arlington Dynamic Fluid -Kinetic (DyFK ) ionospheric plasma transport model to model O+ density profiles and other aspects of the ionosphere -magnetosphere plasma distribution under various conditions for two different studies . The first type of situation concerns the O+ troughs in the polar cap , which were observed by the Thermal Ion Dynamics Experiment (TIDE ) on the Polar spacecraft . We use solar wind parameters and IMF conditions as inputs to drive a time -varying high -latitude electric potential model [Weimer , 2001] . We also incorporate auroral processes involving the effects of soft electron precipitation and wave -driven transverse ion heating , we simulate the ionosphere -magnetosphere plasma transport and the associated O+ bulk parameter profiles of different flux tubes convecting in the high -latitude region . The simulation results for realistic parameters and specific geophysical conditions agree reasonably well with the O+ density variations observed . The second study involves examination of the effects of inertial Alfvén waves propagating along auroral field lines producing parallel electric fields which accelerate auroral precipitating electrons . We examine the propagation of Alfvén waves within O+ auroral ionosphere -magnetosphere density profiles . For the Alfvén wave description , a linear one -dimensional Gyro -Fluid code [Jones et al . , 2003] is used , in which electron inertia , electron pressure gradient and finite ion gyroradius effects are incorporated . This Alfvén wave propagation code determines the characteristics of propagating Alfvén waves which generate the inertial parallel electric field responsible for energizing electrons . A test particle model developed by Su et al [2004] is then used to simulate the response of a distribution of electrons to these Alfvén wave electric fields . The integrated energy flux of the resulting precipitating electrons will be obtained to link back with DyFK model , which shows the effect of such Alfvénic electrons on the plasma evolution in the DyFK code and on Alfvénic phase speed profile .
URI: http : / /hdl .handle .net /10106 /1755
Date: 2009-09-16

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Simulations Of High-latitude Ionosphere-magnetosphere region plasma density structures and the Alfvén waves effects. Available electronically from http : / /hdl .handle .net /10106 /1755 .

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