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Gunter Stober - One of the best experts on this subject based on the ideXlab platform.
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Semidiurnal Solar Tide differences between fall and spring transition times in the Northern Hemisphere
2018Co-Authors: J. Federico Conte, Gunter Stober, Hauke Schmidt, Jorge L. Chau, Fazlul I. Laskar, Peter BrownAbstract:Abstract. We present a study of the semidiurnal Solar Tide (S2) during the fall and spring transition times in the Northern Hemisphere. The Tides have been obtained from wind measurements provided by three meteor radars located at: Andenes (69° N, 16° E), Juliusruh (54° N, 13° E) and Tavistock (42° N, 81° W). During the autumn, S2 is characterized by a sudden and pronounced decrease occurring every year and at all height levels. The spring transition also shows a decrease of S2, but not sudden and that ascends from lower to higher altitudes during an interval of ~ 15 to 40 days. To assess contributions of different semidiurnal tidal components, we have examined a 20-year free run simulation by the Hamburg Model of the Neutral and Ionized Atmosphere (HAMMONIA). We found that the differences exhibited by the S2 Tide between equinox times are mainly due to distinct behaviors of the migrating semidiurnal and the non-migrating westward propagating wave number 1 tidal components (SW2 and SW1, respectively). Specifically, during the fall both, SW2 and SW1 decrease, while during the spring time SW2 decreases but SW1 remains approximately constant or decreases only slightly. The decrease shown by SW1 during the fall occurs later than that of SW2 and S2, which indicates that the behavior of S2 is mainly driven by the migrating component. Nonetheless, the influence of SW1 is necessary to explain the behavior of S2 during the spring. In addition, a strong shift in the phase of S2 (of SW2 in the simulations) is also observed during the fall. Our meteor radar wind measurements show more gravity wave activity in the autumn than during the spring, which might be indicating that the fall decrease is partly due to interactions between SW2 and gravity waves.
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upper mesospheric lunar Tides over middle and high latitudes during sudden stratospheric warming events
Journal of Geophysical Research, 2015Co-Authors: J L Chau, N M Pedatella, Vivien Matthias, Peter Hoffmann, Gunter StoberAbstract:In recent years there have been a series of reported ground- and satellite-based observations of lunar Tide signatures in the equatorial and low latitude ionosphere/thermosphere around sudden stratospheric warming (SSW) events. This lower atmosphere/ionosphere coupling has been suggested to be via the E region dynamo. In this work we present the results of analyzing 6 years of hourly upper mesospheric winds from specular meteor radars over a midlatitude (54°N) station and a high latitude (69°N) station. Instead of correlating our results with typical definitions of SSWs, we use the definition of polar vortex weaking (PVW) used by Zhang and Forbes (2014). This definition provides a better representation of the strength in middle atmospheric dynamics that should be responsible for the waves propagating to the E region. We have performed a wave decomposition on hourly wind data in 21 day segments, shifted by 1 day. In addition to the radar wind data, the analysis has been applied to simulations from Whole Atmosphere Community Climate Model Extended version and the thermosphere-ionosphere-mesosphere electrodynamics general circulation model. Our results indicate that the semidiurnal lunar Tide (M2) enhances in northern hemispheric winter months, over both middle and high latitudes. The time and magnitude of M2 are highly correlated with the time and associated zonal wind of PVW. At middle/high latitudes, M2 in the upper mesosphere occurs after/before the PVW. At both latitudes, the maximum amplitude of M2 is directly proportional to the strength of PVW westward wind. We have found that M2 amplitudes could be comparable to semidiurnal Solar Tide amplitudes, particularly around PVW and equinoxes. Besides these general results, we have also found peculiarities in some events, particularly at high latitudes. These peculiarities point to the need of considering the longitudinal features of the polar stratosphere and the upper mesosphere and lower thermosphere regions. For example, during SSW 2009, we found that M2 enhances many days before PVW which is not in agreement with most of our results.
Daniel J. Scheeres - One of the best experts on this subject based on the ideXlab platform.
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coupled orbit attitude dynamics and relative state estimation of spacecraft near small Solar system bodies
Advances in Space Research, 2016Co-Authors: Gaurav Misra, Maziar Izadi, Amit K Sanyal, Daniel J. ScheeresAbstract:The effects of dynamical coupling between the rotational (attitude) and translational (orbital) motion of spacecraft near small Solar System bodies is investigated. This coupling arises due to the weak gravity of these bodies, as well as Solar radiation pressure. The traditional approach assumes a point-mass spacecraft model to describe the translational motion of the spacecraft, while the attitude motion is considered to be completely decoupled from the translational motion. The model used here to describe the rigid-body spacecraft dynamics includes the non-uniform rotating gravity field of the small body up to second degree and order along with the attitude dependent terms, Solar Tide, and Solar radiation pressure. This model shows that the second degree and order gravity terms due to the small body affect the dynamics of the spacecraft to the same extent as the orbit–attitude coupling due to the primary gravity (zeroth order) term. Variational integrators are used to simulate the dynamics of both the rigid spacecraft and the point mass. The small bodies considered here are modeled after Near-Earth Objects (NEO) 101955 Bennu, and 25143 Itokawa, and are assumed to be triaxial ellipsoids with uniform density. Differences in the numerically obtained trajectories of a rigid spacecraft and a point mass are then compared, to illustrate the impact of the orbit–attitude coupling on spacecraft dynamics in proximity of small bodies. Possible implications on the performance of model-based spacecraft control and on the station-keeping budget, if the orbit–attitude coupling is not accounted for in the model of the dynamics, are also discussed. An almost globally asymptotically stable motion estimation scheme based solely on visual/optical feedback that estimates the relative motion of the asteroid with respect to the spacecraft is also obtained. This estimation scheme does not require a model of the dynamics of the asteroid, which makes it perfectly suited for asteroids whose properties are not well known.
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orbit mechanics about asteroids and comets
Journal of Guidance Control and Dynamics, 2012Co-Authors: Daniel J. ScheeresAbstract:Space missions to small Solar system bodies such as asteroids and comets must deal with multiple perturbations acting on the spacecraft. These include strongperturbations from the gravityfield and Solar Tide, but for small bodies, the most important perturbations may arise from Solar radiation pressure acting on the spacecraft. Previous research has generally investigated the effect of the gravity field, Solar Tide, and Solar radiation pressure acting on a spacecraft trajectory about an asteroid in isolation and has not considered their joint effect. In this paper, a more general theoretical discussion of the joint effects of these forces will be given. Specific criteria are found for when it is possible for a spacecraft to orbit about a small body in a bound orbit. In the casewhere such boundmotion is possible, a general solution for the averaged motion of a spacecraft subject to Solar radiation pressure perturbations is given. Finally, interactions between Solar radiation pressure and gravity field perturbations are investigated.
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Solar Radiation Pressure: Exact Analysis
Orbital Motion in Strongly Perturbed Environments, 2012Co-Authors: Daniel J. ScheeresAbstract:Moving beyond gravity-only dynamics about small bodies, we first consider the combined effect of Solar radiation and Solar Tide perturbations on a spacecraft orbiting about an asteroid or comet. In this section we assume the central body can be modeled as a sphere, and neglect gravitational perturbations. This situation models orbital dynamics when far from asteroids or comets where the dominant perturbation will be from Solar effects. We shall also see that for large enough bodies, such as Eros, Solar radiation pressure only plays a minimal role. For missions to bodies whose sizes are on the order of a few kilometers or less, however, Solar radiation pressure is the principal concern for orbital stability. It is interesting to note that the Solar Tide is generally negligible when compared to Solar radiation pressure, yet it is included in this discussion for completeness. From a direct analysis of the equations of motion and their equilibrium points specific limits can be derived on orbit semi-major axis for when Solar radiation can strip a spacecraft out of orbit. The analysis given here is based on some earlier work by Dankowicz [27] and the analysis given in [171].
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Orbit Mechanics about Small Asteroids
2007Co-Authors: Daniel J. ScheeresAbstract:Space missions to small Solar system bodies must deal with multiple perturbations acting on the spacecraft. These include strong perturbations from the gravity field and Solar Tide, but for small bodies the most important perturbations may arise from Solar radiation pressure (SRP) acting on the spacecraft. Previous research has generally investigated the effect of the gravity field, Solar Tide, and SRP acting on a spacecraft trajectory about an asteroid in isolation and has not considered their joint effect. In this paper a more general theoretical discussion of the joint effects of these forces is given.
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Temporary orbital capture of ejecta from comets and asteroids: Application to the Deep Impact experiment
Astronomy and Astrophysics, 2000Co-Authors: Daniel J. Scheeres, Francesco MarzariAbstract:The trajectories of dust particles ejected from the sur- face of a comet or asteroid after a cratering impact are influenced by the interplay of Solar radiation pressure, Solar Tide, cometary outgassing (for comets) and the body's irregular gravity field. In this paper we evaluate the ability of these forces to cause ejecta to become captured in temporary orbits about the parent body. We concentrate on the effect of Solar radiation pressure and com- pute conditions in which particles can be caught in temporary orbits. The first order effects of the Solar Tide, comet outgassing, and body gravity field are also discussed. Our analysis uses the approximation introduced by Richter & Keller (1995) which gives an analytical solution of the averaged equations of motion under the assumption that the radiation pressure is the dominant perturbative force. We validate that this approximation works properly under the special orbital conditions which ejecta have - characterized by high eccentricities and large semimajor axes. As a specific example, we use the theory to analyze the trapping of particles following the Deep Impact experiment, which will send a man-made impactor into the comet Tempel 1. The theory can be extended to other small Solar system bodies as well.
Baiqi Ning - One of the best experts on this subject based on the ideXlab platform.
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coupling between mesosphere and ionosphere over beijing through semidiurnal Tides during the 2009 sudden stratospheric warming
Journal of Geophysical Research, 2013Co-Authors: Jiangang Xiong, Feng Ding, Baiqi NingAbstract:[1] Sudden stratospheric warming (SSW) in the winter of 2008/2009 is the strongest recorded SSW event. The enhancement in semidiurnal variation of ionospheric TEC (total electron content) with phase shift forward is shown during 22 to 27 January 2009, based on the TEC observations in Beijing (40.30°N, 116.19°E geographic, 39.73°N dip latitude). We focus on finding the reason for the TEC variation. Winds observed by an all-sky meteor radar in the same observatory are used to study mesospheric variation. The semidiurnal Solar Tide in the mesosphere starts to increase before the SSW and maintains oscillation with period 16–20 days during the SSW. The semidiurnal lunar Tides in TEC and wind start to increase on 17 and 15 January, respectively. Although the semidiurnal lunar Tide in TEC over Beijing almost dies out on 1 February, that over equatorial ionospheric anomaly crest does not vanish until 15 February when lunar Tide in wind tends to be very weak. The maximum of lunar Tide in wind appears on 2 February at 96 km with amplitudes of 15 m/s and 21 m/s for zonal and meridional winds. The phase comparison shows that lunar Tides in TEC and zonal wind reach their maxima at almost the same time, which is 2–4 h lag behind the meridional wind. The coupling between the mesosphere and ionosphere contributes to the semidiurnal variation of TEC through both Solar and semidiurnal lunar Tides. The enhancement in semidiurnal lunar Tide is responsible for the TEC peak shift forward during the SSW.
Jean-loup Bertaux - One of the best experts on this subject based on the ideXlab platform.
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Influence of Solar-related effects and topography on the cloud top circulation above Aphrodite Terra from VMC/Venus Express wind fields
2019Co-Authors: M. V. Patsaeva, I. V. Khatuntsev, L. V. Zasova, Alain Hauchecorne, D.v. Titov, Jean-loup BertauxAbstract:A set of UV (365 nm) images obtained by the Venus Monitoring Camera [3] onboard ESA's Venus Express orbiter from 2006 to 2013 was used to study the circulation of the mesosphere. It was found that the surface topography influences on the behavior of the horizontal flow above Aphrodite Terra to at least 30°S. A maximum deceleration of the mean zonal flow is observed at noon above Ovda Regio (the highest region of Aphrodite Terra). We attributed the observed wind deceleration to interaction of the gravity (mountain) waves generated by Aphrodite Terra with the atmospheric circulation. The mean zonal and meridional flows at cloud top level in the equatorial region are perturbed by a Solar Tide at 13-14 h.
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Solar‐Related Variations of the Cloud Top Circulation Above Aphrodite Terra From VMC/Venus Express Wind Fields
Journal of Geophysical Research. Planets, 2019Co-Authors: M. V. Patsaeva, I. V. Khatuntsev, L. V. Zasova, Alain Hauchecorne, D.v. Titov, Jean-loup BertauxAbstract:Winds derived by a digital tracking technique from UV (365 nm) images captured by the Venus Monitoring Camera onboard the Venus Express spacecraft from 2006 through 2013 were used to study the atmospheric circulation at cloud top level (70±2 km). This data set allows variations of the wind speed with both latitude and longitude to be studied and establishes their correlation with surface topography as well as local time dependence. Both zonal and meridional wind components show some correlation with topography. The minimum zonal wind speed was found at noon above Ovda Regio (10° S, 93° E), the highest region of Aphrodite Terra, one of the largest highlands in the equatorial region. The area of slow zonal wind extends to at least 30° S and shifts in the direction of superrotation in the afternoon and with increasing latitude (poleward). The observed deceleration of cloud top wind was recently attributed to the interaction of the gravity (mountain) waves generated by Aphrodite Terra with the atmospheric circulation. The present study was performed for different local time over the mountainous longitudes. The deceleration pattern in the zonal wind field is mainly conserved within a few hours around noon. Systematic longitude shift is observed in the afternoon in the direction of the evening terminator. Another area of perturbation of both zonal and meridional wind components is observed in the equatorial region around LT=13‐14 h and may be explained by the Solar Tide.
N M Pedatella - One of the best experts on this subject based on the ideXlab platform.
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On the variability of the semidiurnal Solar and lunar Tides of the equatorial electrojet during sudden stratospheric warmings
Annales Geophysicae, 2018Co-Authors: T. A. Siddiqui, N M Pedatella, Astrid Maute, Y. Yamazaki, Hermann Lühr, Claudia StolleAbstract:Abstract. The variabilities of the semidiurnal Solar and lunar Tides of the equatorial electrojet (EEJ) are investigated during the 2003, 2006, 2009 and 2013 major sudden stratospheric warming (SSW) events in this study. For this purpose, ground-magnetometer recordings at the equatorial observatories in Huancayo and Fuquene are utilized. Results show a major enhancement in the amplitude of the EEJ semidiurnal lunar Tide in each of the four warming events. The EEJ semidiurnal Solar tidal amplitude shows an amplification prior to the onset of warmings, a reduction during the deceleration of the zonal mean zonal wind at 60∘ N and 10 hPa, and a second enhancement a few days after the peak reversal of the zonal mean zonal wind during all four SSWs. Results also reveal that the amplitude of the EEJ semidiurnal lunar Tide becomes comparable or even greater than the amplitude of the EEJ semidiurnal Solar Tide during all these warming events. The present study also compares the EEJ semidiurnal Solar and lunar tidal changes with the variability of the migrating semidiurnal Solar (SW2) and lunar (M2) Tides in neutral temperature and zonal wind obtained from numerical simulations at E-region heights. A better agreement between the enhancements of the EEJ semidiurnal lunar Tide and the M2 Tide is found in comparison with the enhancements of the EEJ semidiurnal Solar Tide and the SW2 Tide in both the neutral temperature and zonal wind at the E-region altitudes.
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upper mesospheric lunar Tides over middle and high latitudes during sudden stratospheric warming events
Journal of Geophysical Research, 2015Co-Authors: J L Chau, N M Pedatella, Vivien Matthias, Peter Hoffmann, Gunter StoberAbstract:In recent years there have been a series of reported ground- and satellite-based observations of lunar Tide signatures in the equatorial and low latitude ionosphere/thermosphere around sudden stratospheric warming (SSW) events. This lower atmosphere/ionosphere coupling has been suggested to be via the E region dynamo. In this work we present the results of analyzing 6 years of hourly upper mesospheric winds from specular meteor radars over a midlatitude (54°N) station and a high latitude (69°N) station. Instead of correlating our results with typical definitions of SSWs, we use the definition of polar vortex weaking (PVW) used by Zhang and Forbes (2014). This definition provides a better representation of the strength in middle atmospheric dynamics that should be responsible for the waves propagating to the E region. We have performed a wave decomposition on hourly wind data in 21 day segments, shifted by 1 day. In addition to the radar wind data, the analysis has been applied to simulations from Whole Atmosphere Community Climate Model Extended version and the thermosphere-ionosphere-mesosphere electrodynamics general circulation model. Our results indicate that the semidiurnal lunar Tide (M2) enhances in northern hemispheric winter months, over both middle and high latitudes. The time and magnitude of M2 are highly correlated with the time and associated zonal wind of PVW. At middle/high latitudes, M2 in the upper mesosphere occurs after/before the PVW. At both latitudes, the maximum amplitude of M2 is directly proportional to the strength of PVW westward wind. We have found that M2 amplitudes could be comparable to semidiurnal Solar Tide amplitudes, particularly around PVW and equinoxes. Besides these general results, we have also found peculiarities in some events, particularly at high latitudes. These peculiarities point to the need of considering the longitudinal features of the polar stratosphere and the upper mesosphere and lower thermosphere regions. For example, during SSW 2009, we found that M2 enhances many days before PVW which is not in agreement with most of our results.