Michael P. Hickey

Bio: Michael P. Hickey is an academic researcher from Embry-Riddle Aeronautical University, Daytona Beach. The author has contributed to research in topics: Gravity wave & Thermosphere. The author has an hindex of 28, co-authored 86 publications receiving 2495 citations. Previous affiliations of Michael P. Hickey include Marshall Space Flight Center & Clemson University.

Lower thermospheric response to atmospheric gravity waves induced by the 2011 Tohoku tsunami

Abstract: Previous GPS observations have revealed that while ionospheric TIDs were seen propagating in all directions away from the 2011 Tohoku earthquake epicenter, the total electron content (TEC) fluctuations associated with the subsequent tsunami were largest for waves propagating toward the northwest of the epicenter. Ionospheric motions observed approximately 10 min after the earthquake were attributed to fast acoustic waves directly produced by the earthquake. Waves that first appeared about 40 min after the tsunami onset in TEC measurements were attributed to atmospheric gravity waves. In this paper, we conjecture that the remarkably different responses observed for the eastward and westward propagating waves noted in previous observations can be explained by the different ocean depths associated with the two directions of travel and by the effects of the mean winds. The former has consequences for the generated gravity waves (wave spectrum), while their combination has consequences for the ability of the waves to propagate to higher altitudes. Because the ocean depth to the east of the epicenter is greater than that to the west, the eastward propagating tsunami travels faster than the westward propagating tsunami; and hence, the eastward propagating gravity waves that are generated will be faster than the westward waves. We demonstrate that the faster eastward waves encounter regions of evanescence that inhibits their upward propagation, with the result that the westward propagating waves reach the lower thermosphere sooner and with much larger amplitudes than those of the eastward propagating waves. However, at much higher altitudes the slower westward propagating waves are severely damped by viscosity, with the result that only the eastward propagating waves survive to F region altitudes. These results are clearly seen in our full-wave model simulations and also in the evolution of the wave momentum flux calculated using our 2-D, time-dependent model.

Wave‐modified mean exothermic heating in the mesopause region

Abstract: We employ a model of wave-driven OH nightglow fluctuations to calculate the effects of gravity waves on the chemical exothermic heating due to reactions involving odd hydrogen and odd oxygen species in the mesopause region. Using a model based on time means and deviations from those means, it is demonstrated that gravity waves contribute to the time-average exothermic heating. The effect can be significant because the fractional fluctuations in minor species density can be substantially greater than the fractional fluctuation of the major gas density. Our calculations reveal that the waves mitigate the exothermic heating, demonstrating their potential importance in the heat budget of the mesopause region.

Ionospheric Electron Density Perturbations Driven by Seismic Tsunami-Excited Gravity Waves: Effect of Dynamo Electric Field

Abstract: The effect of an ionospheric dynamo electric field on the electron density and total electron content (TEC) perturbations in the F layer (150–600 km altitudes) is investigated at two arbitrarily selected locations (noted as 29° N and 60° N in latitudes) in the presence of seismic tsunami-excited gravity waves propagating in a stratified, nondissipative atmosphere where vertical gradients of atmospheric properties are taken into consideration. Generalized ion momentum and continuity equations are solved, followed by an analysis of the dynamo electric field (E). The E -strength is within several mV/m, determined by the zonal neutral wind and meridional geomagnetic field. It is found that, at the mid-latitude location, n0 e is dominated by the atmospheric meridional wind when E = 0, while it is determined by the zonal wind when E ≠ 0. The perturbed TEC over its unperturbed magnitude lies in around 10% at all altitudes for E = 0, while it keeps the same percentage at most altitudes for E ≠ 0, except a jump to >25% in the F2-peak layer (300–340 km in height). By contrast, at the low-latitude location, the TEC jump is eliminated by the locally enhanced background electron density.

On nonlinear response of minor species with a layered structure to gravity waves

Abstract: [1] We investigate the temporal and spatial variations of the local and integrated response of minor species and OH emission to a small-scale gravity wave. A Chapman-like function is used to model the unperturbed profiles of minor species like ozone, hydrogen, and OH emission. Because the gravity waves that we simulate do not violate the nonacceleration conditions, the waves will not cause a secular variation in the minor species concentrations. We therefore use the Krylov-Bogoliubov-Mitropolsky averaging method to remove the higher-order secular terms in our perturbation expansion. A vertical drift velocity, second order in nature, is required to remove the secular terms. The equivalence of this vertical drift velocity to the Eulerian drift is demonstrated. Using the perturbation method to treat the response of minor species to a small-scale gravity wave, we compute the first- and second-order perturbation terms and find that the second-order terms will also be important for narrow minor species profiles having large gradients (or small-scale heights).

Atmospheric Gravity Waves and Effects in the Upper Atmosphere Associated with Tsunamis

Abstract: Tsunamis propagate at the surface of the deep ocean horizontal phase speeds of approximately 200 m/s, which is about two-thirds of the lower atmospheric sound speed. They have large horizontal wavelengths that are typically of a few hundred kilometers, and they remain coherent over large propagation distances. They also have large horizontal extents (sometimes a few thousand kilometers) parallel to their wave fronts. They can traverse great distances over a span of several hours, so that large areas of the oceanatmosphere interface are impacted. Typical dominant wave periods associated with tsunamis are a few tens of minutes. In the deep ocean their amplitudes are usually quite small with surface displacements being only a few centimeters, but occasional large events can have amplitudes of a few tens of cm. The speeds, wavelengths and periods of tsunamis lie within the range of those of atmospheric gravity waves. These are vertically transverse waves with motions of air parcels mainly influenced by gravity and buoyancy. The vertical displacement of the water acts like a moving corrugation at the base of the atmosphere and so very effectively generates atmospheric gravity waves. In general a spectrum of waves will be produced by a tsunami. Most of the power in the spectrum resides in internal gravity waves, with acoustic waves and evanescent waves being less efficiently generated. Internal waves can transport energy and momentum vertically through the atmosphere. Due to the decrease of mean atmospheric density with increasing altitude, the amplitude of these waves increases as they propagate upward in order to conserve wave energy. At sufficiently high altitudes molecular viscosity and thermal conductivity damp the waves, and their amplitudes then decrease with increasing altitude. Because the waves have high phase speeds (commensurate with the tsunami speed), they are deep waves with vertical wavelengths of ~ 100 km. This allows them to reach the middle thermosphere (~ 250 km altitude) before the molecular dissipation becomes severe. Atmospheric winds also influence the upward propagation of atmospheric gravity waves. Because the winds vary with height the waves may be propagating with the wind at some heights and against the wind at other heights. In the former case the vertical wavelengths are shortened, which increases the velocity shears and thereby increases the viscous damping rate. In the latter case the vertical wavelengths are increased, which decreases the velocity shears and decreases the viscous damping rate. At these heights the tsunami-driven atmospheric gravity waves have large amplitudes so that their interaction with the ionosphere is likely to produce detectable traveling

Gravity wave dynamics and effects in the middle atmosphere

Abstract: [1] Atmospheric gravity waves have been a subject of intense research activity in recent years because of their myriad effects and their major contributions to atmospheric circulation, structure, and variability. Apart from occasionally strong lower-atmospheric effects, the major wave influences occur in the middle atmosphere, between ∼ 10 and 110 km altitudes because of decreasing density and increasing wave amplitudes with altitude. Theoretical, numerical, and observational studies have advanced our understanding of gravity waves on many fronts since the review by Fritts [1984a]; the present review will focus on these more recent contributions. Progress includes a better appreciation of gravity wave sources and characteristics, the evolution of the gravity wave spectrum with altitude and with variations of wind and stability, the character and implications of observed climatologies, and the wave interaction and instability processes that constrain wave amplitudes and spectral shape. Recent studies have also expanded dramatically our understanding of gravity wave influences on the large-scale circulation and the thermal and constituent structures of the middle atmosphere. These advances have led to a number of parameterizations of gravity wave effects which are enabling ever more realistic descriptions of gravity wave forcing in large-scale models. There remain, nevertheless, a number of areas in which further progress is needed in refining our understanding of and our ability to describe and predict gravity wave influences in the middle atmosphere. Our view of these unknowns and needs is also offered.

The molecular identification of organic compounds in the atmosphere : state of the art and challenges

Abstract: Atmosphere: State of the Art and Challenges Barbara Nozier̀e,*,† Markus Kalberer,*,‡ Magda Claeys,* James Allan, Barbara D’Anna,† Stefano Decesari, Emanuela Finessi, Marianne Glasius, Irena Grgic,́ Jacqueline F. Hamilton, Thorsten Hoffmann, Yoshiteru Iinuma, Mohammed Jaoui, Ariane Kahnt, Christopher J. Kampf, Ivan Kourtchev,‡ Willy Maenhaut, Nicholas Marsden, Sanna Saarikoski, Jürgen Schnelle-Kreis, Jason D. Surratt, Sönke Szidat, Rafal Szmigielski, and Armin Wisthaler †Ircelyon/CNRS and Universite ́ Lyon 1, 69626 Villeurbanne Cedex, France ‡University of Cambridge, Cambridge CB2 1EW, United Kingdom University of Antwerp, 2000 Antwerp, Belgium The University of Manchester & National Centre for Atmospheric Science, Manchester M13 9PL, United Kingdom Istituto ISAC C.N.R., I-40129 Bologna, Italy University of York, York YO10 5DD, United Kingdom University of Aarhus, 8000 Aarhus C, Denmark National Institute of Chemistry, 1000 Ljubljana, Slovenia Johannes Gutenberg-Universitaẗ, 55122 Mainz, Germany Leibniz-Institut für Troposphar̈enforschung, 04318 Leipzig, Germany Alion Science & Technology, McLean, Virginia 22102, United States Max Planck Institute for Chemistry, 55128 Mainz, Germany Ghent University, 9000 Gent, Belgium Finnish Meteorological Institute, FI-00101 Helsinki, Finland Helmholtz Zentrum München, D-85764 Neuherberg, Germany University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States University of Bern, 3012 Bern, Switzerland Institute of Physical Chemistry PAS, Warsaw 01-224, Poland University of Oslo, 0316 Oslo, Norway

Global probabilistic projections of extreme sea levels show intensification of coastal flood hazard.

Abstract: Global warming is expected to drive increasing extreme sea levels (ESLs) and flood risk along the world's coastlines. In this work we present probabilistic projections of ESLs for the present century taking into consideration changes in mean sea level, tides, wind-waves, and storm surges. Between the year 2000 and 2100 we project a very likely increase of the global average 100-year ESL of 34-76 cm under a moderate-emission-mitigation-policy scenario and of 58-172 cm under a business as usual scenario. Rising ESLs are mostly driven by thermal expansion, followed by contributions from ice mass-loss from glaciers, and ice-sheets in Greenland and Antarctica. Under these scenarios ESL rise would render a large part of the tropics exposed annually to the present-day 100-year event from 2050. By the end of this century this applies to most coastlines around the world, implying unprecedented flood risk levels unless timely adaptation measures are taken.