The Experts below are selected from a list of 96 Experts worldwide ranked by ideXlab platform
Sean Bruinsma - One of the best experts on this subject based on the ideXlab platform.
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wave driven variability in the ionosphere thermosphere mesosphere system from timed observations what contributes to the wave 4
Journal of Geophysical Research, 2011Co-Authors: J Oberheide, J M Forbes, Xiaoli Zhang, Sean BruinsmaAbstract:[1] Numerous observations and model studies made during the past 5 years have unequivocally revealed that the ionosphere and thermosphere owe a considerable amount of their longitudinal, local time, seasonal latitudinal and day-to-day variability to waves originating in the lower part of the atmosphere. The most prominent pattern is the four-peaked (“wave 4”) longitudinal structure frequently observed by (quasi-) Sun-Synchronous Satellites in a variety of ionospheric and thermospheric parameters. The “wave 4” has often been attributed to the diurnal, eastward, wave number 3 (DE3), nonmigrating tide alone. A more detailed analysis of TIMED observations, supported by physics-based empirical modeling and data from the CHAMP satellite, now indicates that this interpretation needs to be revised. Secondary wave generation due the nonlinear interaction between the migrating diurnal tide and the DE3 leads to a large stationary planetary wave 4 (SPW4) and a large semidiurnal, eastward wave number 2 (SE2) tide in the equatorial zonal wind at E-region heights. Combined amplitudes can equal those of the DE3. SE2 penetrates into the upper thermosphere with transequatorial wind speeds in excess of 10 m/s. This paper discusses the resulting implications for electric field generation in the E-region and tidal-ionosphere coupling in the F-region and provides observational constraints for future modeling efforts.
Yongcun Cheng - One of the best experts on this subject based on the ideXlab platform.
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multimission empirical ocean tide modeling for shallow waters and polar seas
Journal of Geophysical Research, 2011Co-Authors: Yongcun Cheng, Ole Baltazar AndersenAbstract:[1] A new global ocean tide model named DTU10 (developed at Technical University of Denmark) representing all major diurnal and semidiurnal tidal constituents is proposed based on an empirical correction to the global tide model FES2004 (Finite Element Solutions), with residual tides determined using the response method. The improvements are achieved by introducing 4 years of TOPEX–Jason 1 interleaved mission into existing 18 years (1993–2010) of primary joint TOPEX, Jason 1, and Jason 2 mission time series. Hereby the spatial distribution of observations are doubled and satellite altimetry should be able to recover twice the spatial variations of the tidal signal which is particularly important in shallow waters where the spatial scale of the tidal signal is scaled down. Outside the ±66° parallel combined Envisat, GEOSAT Follow-On, and ERS-2, data sets have been included to solve for the tides up to the ±82° parallel. A new approach to removing the annual sea level variations prior to estimating the residual tides significantly improved tidal determination of diurnal constituents from the Sun-Synchronous Satellites (e.g., ERS-2 and Envisat) in the polar seas. Extensive evaluations with six tide gauge sets show that the new tide model fits the tide gauge measurements favorably to other state of the art global ocean tide models in both the deep and shallow waters, especially in the Arctic Ocean and the Southern Ocean. One example is a comparison with 207 tide gauge data in the East Asian marginal seas where the root-mean-square agreement improved by 35.12%, 22.61%, 27.07%, and 22.65% (M2, S2, K1, and O1) for the DTU10 tide model compared with the FES2004 tide model. A similar comparison in the Arctic Ocean with 151 gauge data improved by 9.93%, 0.34%, 7.46%, and 9.52% for the M2, S2, K1, and O1 constituents, respectively.
Jean-luc Margot - One of the best experts on this subject based on the ideXlab platform.
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near earth asteroid satellite spins under spin orbit coupling
The Astronomical Journal, 2015Co-Authors: Shantanu P Naidu, Jean-luc MargotAbstract:We develop a fourth-order numerical integrator to simulate the coupled spin and orbital motions of two rigid bodies having arbitrary mass distributions under the influence of their mutual gravitational potential. We simulate the dynamics of components in well-characterized binary and triple near-Earth asteroid systems and use surface of section plots to map the possible spin configurations of the Satellites. For aSynchronous Satellites, the analysis reveals large regions of phase space where the spin state of the satellite is chaotic. For Synchronous Satellites, we show that libration amplitudes can reach detectable values even for moderately elongated shapes. The presence of chaotic regions in the phase space has important consequences for the evolution of binary asteroids. It may substantially increase spin synchronization timescales, explain the observed fraction of asychronous binaries, delay BYORP-type evolution, and extend the lifetime of binaries. The variations in spin rate due to large librations also affect the analysis and interpretation of light curve and radar observations.
Ole Baltazar Andersen - One of the best experts on this subject based on the ideXlab platform.
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multimission empirical ocean tide modeling for shallow waters and polar seas
Journal of Geophysical Research, 2011Co-Authors: Yongcun Cheng, Ole Baltazar AndersenAbstract:[1] A new global ocean tide model named DTU10 (developed at Technical University of Denmark) representing all major diurnal and semidiurnal tidal constituents is proposed based on an empirical correction to the global tide model FES2004 (Finite Element Solutions), with residual tides determined using the response method. The improvements are achieved by introducing 4 years of TOPEX–Jason 1 interleaved mission into existing 18 years (1993–2010) of primary joint TOPEX, Jason 1, and Jason 2 mission time series. Hereby the spatial distribution of observations are doubled and satellite altimetry should be able to recover twice the spatial variations of the tidal signal which is particularly important in shallow waters where the spatial scale of the tidal signal is scaled down. Outside the ±66° parallel combined Envisat, GEOSAT Follow-On, and ERS-2, data sets have been included to solve for the tides up to the ±82° parallel. A new approach to removing the annual sea level variations prior to estimating the residual tides significantly improved tidal determination of diurnal constituents from the Sun-Synchronous Satellites (e.g., ERS-2 and Envisat) in the polar seas. Extensive evaluations with six tide gauge sets show that the new tide model fits the tide gauge measurements favorably to other state of the art global ocean tide models in both the deep and shallow waters, especially in the Arctic Ocean and the Southern Ocean. One example is a comparison with 207 tide gauge data in the East Asian marginal seas where the root-mean-square agreement improved by 35.12%, 22.61%, 27.07%, and 22.65% (M2, S2, K1, and O1) for the DTU10 tide model compared with the FES2004 tide model. A similar comparison in the Arctic Ocean with 151 gauge data improved by 9.93%, 0.34%, 7.46%, and 9.52% for the M2, S2, K1, and O1 constituents, respectively.
J Oberheide - One of the best experts on this subject based on the ideXlab platform.
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wave driven variability in the ionosphere thermosphere mesosphere system from timed observations what contributes to the wave 4
Journal of Geophysical Research, 2011Co-Authors: J Oberheide, J M Forbes, Xiaoli Zhang, Sean BruinsmaAbstract:[1] Numerous observations and model studies made during the past 5 years have unequivocally revealed that the ionosphere and thermosphere owe a considerable amount of their longitudinal, local time, seasonal latitudinal and day-to-day variability to waves originating in the lower part of the atmosphere. The most prominent pattern is the four-peaked (“wave 4”) longitudinal structure frequently observed by (quasi-) Sun-Synchronous Satellites in a variety of ionospheric and thermospheric parameters. The “wave 4” has often been attributed to the diurnal, eastward, wave number 3 (DE3), nonmigrating tide alone. A more detailed analysis of TIMED observations, supported by physics-based empirical modeling and data from the CHAMP satellite, now indicates that this interpretation needs to be revised. Secondary wave generation due the nonlinear interaction between the migrating diurnal tide and the DE3 leads to a large stationary planetary wave 4 (SPW4) and a large semidiurnal, eastward wave number 2 (SE2) tide in the equatorial zonal wind at E-region heights. Combined amplitudes can equal those of the DE3. SE2 penetrates into the upper thermosphere with transequatorial wind speeds in excess of 10 m/s. This paper discusses the resulting implications for electric field generation in the E-region and tidal-ionosphere coupling in the F-region and provides observational constraints for future modeling efforts.
