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Showing papers by "Michael P. Hickey published in 2010"


Journal ArticleDOI
TL;DR: In this article, a spectral full-wave model was used to study the upward propagation of a gravity wave disturbance and its effect on atmospheric nightglow emissions, and the response of the OH Meinel nightglows in the mesopause region (∼87 km altitude) produces relative brightness fluctuations.
Abstract: [1] A spectral full-wave model is used to study the upward propagation of a gravity wave disturbance and its effect on atmospheric nightglow emissions. Gravity waves are generated by a surface displacement that mimics a tsunami having a maximum amplitude of 0.5 m, a characteristic horizontal wavelength of 400 km, and a horizontal phase speed of 200 m/s. The gravity wave disturbance can reach F region altitudes before significant viscous dissipation occurs. The response of the OH Meinel nightglow in the mesopause region (∼87 km altitude) produces relative brightness fluctuations, which are ∼1% of the mean for overhead viewing. The wave amplitudes grow as the wave disturbance propagates upward, which causes the thermospheric nightglow emission responses to be large. For overhead viewing, the brightness fluctuations are ∼50% and 43% of the mean for the OI 6300 A and O 1356 A emissions, respectively. The total electron content fluctuation is ∼33% of the mean for overhead viewing. For oblique viewing, the relative brightness fluctuations are slightly smaller than those obtained for overhead viewing. In spite of this, the thermospheric nightglow brightness fluctuations are large enough that oblique viewing could provide early warning of an approaching tsunami. Thus, the monitoring of thermospheric nightglow emissions may be a useful augmentation to other observational techniques of tsunami effects in the thermosphere/ionosphere system.

50 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigate how the dynamics of the thermosphere is influenced by the dissipation of a tsunami-driven gravity wave disturbance, which can efficiently propagate to the upper atmosphere.
Abstract: [1] We investigate how the dynamics of the thermosphere is influenced by the dissipation of a tsunami-driven gravity wave disturbance. Unlike typical lower atmospheric sources, the tsunami generates a spectrum entirely of fast gravity waves that can efficiently propagate to the upper atmosphere. This disturbance transports momentum into the thermosphere while dissipation due to molecular viscosity and thermal conduction drives a downward sensible heat flux within the thermosphere. The divergence of the momentum flux forces a change in velocity of 150–200 m/s between 200 and 300 km altitude. A tsunami propagating for ∼10 h before making landfall will produce a secular change in the wind and temperature field that extends as much as 8000 km along the direction of wave propagation. The induced winds should be observable through a variety of methods. The thermal effects driven by the divergence of the sensible heat flux are more modest and would be difficult to observe. These simulations show that large tsunami events could have a pronounced dynamical effect in the thermosphere until conditions relax to their undisturbed state.

21 citations


21 Sep 2010
TL;DR: In this paper, ground-based Global Positioning System (GPS) measurements of ionospheric Total Electron Content (TEC) show variations consistent with atmospheric internal gravity waves caused by ocean tsunamis following two recent seismic events: the American Samoa earthquake of September 29, 2009, and the Chile earthquake of February 27, 2010.
Abstract: Ground-based Global Positioning System (GPS) measurements of ionospheric Total Electron Content (TEC) show variations consistent with atmospheric internal gravity waves caused by ocean tsunamis following two recent seismic events: the American Samoa earthquake of September 29, 2009, and the Chile earthquake of February 27, 2010. Fluctuations in TEC correlated in time, space, and wave properties with these tsunamis were observed in TEC estimates processed using JPL's Global Ionospheric Mapping Software. These TEC estimates were band-pass filtered to remove ionospheric TEC variations with wavelengths and periods outside the typical range of internal gravity waves caused by tsunamis. Observable variations in TEC appear correlated with the tsunamis in certain locations, but not in others. Where variations are observed, the typical amplitude tends to be on the order of 1% of the background TEC value. Variations with amplitudes ~ 0.1 - 0.2 TECU are observable with periods and timing affiliated with the tsunami. These observations are compared to estimates of expected tsunami-driven TEC variations produced by Embry Riddle Aeronautical University's Spectral Full Wave Model, an atmosphere-ionosphere coupling model, and found to be in good agreement in some locations, though there are cases when the model predicts an observable tsunami-driven signature and none is observed. These TEC variations are not always seen when a tsunami is present, but in these two events the regions where a strong ocean tsunami was observed did coincide with clear TEC observations, while a lack of clear TEC observations coincided with smaller tsunami amplitudes. There exists the potential to apply these detection techniques to real-time GPS TEC data, providing estimates of tsunami speed and amplitude that may be useful for early warning systems.