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Research output: Contribution to Journal/Magazine › Journal article › peer-review
Research output: Contribution to Journal/Magazine › Journal article › peer-review
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TY - JOUR
T1 - A theory of ionospheric response to upward-propagating tides
T2 - electrodynamic effects and tidal mixing effects
AU - Yamazaki (YY), Yosuke
AU - Richmond, Arthur
N1 - ©2013. American Geophysical Union
PY - 2013/9
Y1 - 2013/9
N2 - The atmospheric tide at ionospheric heights is composed of those locally generated and those propagated from below. The role of the latter in producing the variability of the daytime ionosphere is examined using the National Center for Atmospheric Research Thermosphere-Ionosphere-Electrodynamics General Circulation Model. The impact of upward-propagating tides is evaluated by running simulations with and without tidal forcing at the lower boundary (approximately 96 km), which imitates the effect of tides from below. When migrating diurnal and semidiurnal tides at the lower boundary is switched on, the intensity of E region currents and the upward velocity of the equatorial F region vertical plasma drift rapidly increase. The low-latitude ionospheric total electron content (TEC) first increases, then gradually decreases to below the initial level. The initial increase in the low-latitude TEC is caused by an enhanced equatorial plasma fountain while the subsequent decrease is due to changes in the neutral composition, which are characterized by a global-scale reduction in the mass mixing ratio of atomic oxygen O1. The results of further numerical experiments indicate that the mean meridional circulation induced by dissipating tides in the lower thermosphere is mainly responsible for the O1 reduction; it acts like an additional turbulent eddy and produces a “mixing effect” that enhances net downward transport and loss of O1. It is stressed that both electrodynamic effects and mixing effects of upward-propagating tides can be important in producing the variability of ionospheric plasma density. Since the two mechanisms act in different ways on different time scales, the response of the actual ionosphere to highly variable upward-propagating tides is expected to be complex.
AB - The atmospheric tide at ionospheric heights is composed of those locally generated and those propagated from below. The role of the latter in producing the variability of the daytime ionosphere is examined using the National Center for Atmospheric Research Thermosphere-Ionosphere-Electrodynamics General Circulation Model. The impact of upward-propagating tides is evaluated by running simulations with and without tidal forcing at the lower boundary (approximately 96 km), which imitates the effect of tides from below. When migrating diurnal and semidiurnal tides at the lower boundary is switched on, the intensity of E region currents and the upward velocity of the equatorial F region vertical plasma drift rapidly increase. The low-latitude ionospheric total electron content (TEC) first increases, then gradually decreases to below the initial level. The initial increase in the low-latitude TEC is caused by an enhanced equatorial plasma fountain while the subsequent decrease is due to changes in the neutral composition, which are characterized by a global-scale reduction in the mass mixing ratio of atomic oxygen O1. The results of further numerical experiments indicate that the mean meridional circulation induced by dissipating tides in the lower thermosphere is mainly responsible for the O1 reduction; it acts like an additional turbulent eddy and produces a “mixing effect” that enhances net downward transport and loss of O1. It is stressed that both electrodynamic effects and mixing effects of upward-propagating tides can be important in producing the variability of ionospheric plasma density. Since the two mechanisms act in different ways on different time scales, the response of the actual ionosphere to highly variable upward-propagating tides is expected to be complex.
KW - upward-propagating tide
KW - ionosphere-thermosphere coupling
KW - ionospheric wind dynamo
KW - tidal dissipation
KW - thermosphere composition
KW - mean flow
U2 - 10.1002/jgra.50487
DO - 10.1002/jgra.50487
M3 - Journal article
VL - 118
SP - 5891
EP - 5905
JO - Journal of Geophysical Research: Space Physics
JF - Journal of Geophysical Research: Space Physics
SN - 2169-9402
IS - 9
ER -