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R J Stening - One of the best experts on this subject based on the ideXlab platform.
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Lunar tide in the equatorial electrojet in relation to stratospheric warmings
Journal of Geophysical Research, 2011Co-Authors: R J SteningAbstract:[1] The relationship between sudden stratospheric warmings (SSWs) and large-amplitude Lunar Tides in the equatorial electrojet (EEJ) is studied. Analysis of ground magnetometer data shows that the Lunar tide in the EEJ is maximum during the northern winter season except in the Pacific Ocean region. Since SSWs are also a northern winter phenomenon, it is suggested that the relation between the large Lunar tide in the EEJ and the SSW may possibly be coincidental. The Lunar tide in the geomagnetic variations at Huancayo is anomalously large compared with other EEJ stations. An examination of geomagnetic variations at EEJ stations during SSW events shows that afternoon counter-electrojets are frequently present at new moon and full moon, though the relationship is sometimes broken. The observation of large Lunar EEJs when no SSW is present and of various different delay times suggests that other atmospheric processes are likely to be in play.
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Lunar Tides in the thermosphere ionosphere electrodynamics general circulation model
Journal of Geophysical Research, 1999Co-Authors: R J Stening, A D Richmond, R G RobleAbstract:Lunar semidiurnal Tides are introduced at the lower boundary of the National Center for Atmospheric Research Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM). The Tides are derived from the model of Vial and Forbes [1994] and interesting properties of these Tides are found when they are subjected to Hough decomposition; there is considerable hemispherical antisymmetry in the September Tides, and the March and September modal compositions are significantly different. A differencing method is used to isolate the Lunar tidal effects in the TIEGCM, and these are compared with Lunar tidal analyses of ionospheric data. The model reproduces the broad features of the Lunar tide in f0F2 (maximum frequency of the F region) with phase changes around 7° magnetic dip latitude during daytime. The model and data analysis both give variations of the amplitude and phase of the Lunar tide with local time. Near the equator the variation of phase with local time changes with latitude as the equatorial anomaly develops during the day. Comparison between the model predictions and analyses of data at observatories at midlatitudes produces mixed results. Here the effects of the Lunar components of both electrodynamic drifts and of neutral winds need to be taken into account. Several cases of day to night changes in the phase of the Lunar tide in f0F2 are noted. Large nighttime amplitudes of the Lunar tide in hmF2 (height of the maximum density), more than 4 km, seem to be due to inphase action of the electrodynamic and neutral wind effects while during daytime they are out of phase. The Lunar tide in the ratio of oxygen to nitrogen density [O]/[N2]is estimated and found to be of relatively minor importance. Amplitudes of the Lunar tide in f0F2 may be measured at more than 0.4 MHz at some local times, but the model values are less than this. Comparison is also made with ion drift measurements made by the San Marco D satellite. The several uncertainties which underlie this work are discussed in detail.
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Lunar Tides in the mesosphere over christmas island 2 n 203 e
Journal of Geophysical Research, 1997Co-Authors: R J Stening, D M Schlapp, R A VincentAbstract:This paper reports the first measurement of the Lunar tide in upper atmosphere winds at an equatorial site. Wind velocities have been measured at Christmas Island, in the Pacific Ocean, from 1990 to 1993 over the height range 82 to 98 km and hourly values have been used to deduce the Lunar tide using a least squares method. Amplitudes are 1 to 3 m/s with only small changes in phase with season. A large phase change over the early part of 1990 was found in the northward wind. Generally, the phase difference between northward and eastward winds was about 6 hours, and good agreement was obtained with a tidal model developed from that of Forbes [1982a].
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n2 and m2 Lunar Tides atmospheric resonance revisited
Annales Geophysicae, 1996Co-Authors: D M Schlapp, J M Forbes, R J Stening, A H Manson, C E Meek, R A VincentAbstract:A numerical model has been used to calculate the atmospheric response to forcing at periods in the region of 12-13.5 h. The results show that the response is enhanced in the neighbourhood of 13 h. These results have been compared with Lunar tidal analyses of mesospheric wind data and geomagnetic variations at a number of stations. It is found that the N2 Lunar tidal component (period 12.66 h) is significantly enhanced relative to the main Lunar tidal component M2 (period 12.42 h) in both types of data, compared with what would be expected from the gravitational tidal potential. This supports the predictions of the numerical model. An appreciable phase shift is also found in the experimental data between the N2 and M2 Tides, agreeing in sense with what would be expected for a resonance at a period around 13 h.
Richard D Ray - One of the best experts on this subject based on the ideXlab platform.
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Lunar and solar torques on the oceanic Tides
2013Co-Authors: Richard D Ray, B G Bills, Benjamin F ChaoAbstract:A general framework for calculating Lunar and solar torques on the oceanic Tides is developed in terms of harmonic constituents. Axial torques and their associated angular momentum and earth-rotation variations are deduced from recent satellite-altimeter and satellite-tracking tide solutions. Torques on the prograde components of the tide produce the familiar secular braking of the rotation rate. The estimated secular acceleration is approximately -1300 sec/century(sup 2) (less 4% after including atmospheric Tides); the implied rate of change in the length of day is 2.28 milliseconds/century. Torques on the retrograde components of the tide produce periodic rotation variations at twice the tidal frequency. Interaction torques, e.g. solar torques on Lunar Tides, generate a large suite of rotation-rate variations at sums and differences of the original tidal frequencies. These are estimated for periods from 18.6 years to quarter-diurnal. At subdaily periods the angular momentum variations are 5 to 6 orders of magnitude smaller than the variations caused by ocean tidal currents.
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secular changes in the solar semidiurnal tide of the western north atlantic ocean
Geophysical Research Letters, 2009Co-Authors: Richard D RayAbstract:[1] An analysis of twentieth century tide gauge records reveals that the solar semidiurnal tide S2 has been decreasing in amplitude along the eastern coast of North America and at the mid-ocean site Bermuda. In relative terms the observed rates are unusually large, of order 10% per century. Periods of greatest change, however, are inconsistent among the stations, and roughly half the stations show increasing amplitude since the late 1990s. Excepting the Gulf of Maine, Lunar Tides are either static or slightly increasing in amplitude; a few stations show decreases. Large changes in solar, but not Lunar, Tides suggest causes related to variable radiational forcing, but the hypothesis is at present unproven.
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tidal models in a new era of satellite gravimetry
Space Science Reviews, 2003Co-Authors: Richard D Ray, David D Rowlands, Gary D EgbertAbstract:The high precision gravity measurements to be made by recently launched (and recently approved) satellites place new demands on models of Earth, atmospheric, and oceanic Tides. The latter is the most problematic. The ocean Tides induce variations in the Earth's geoid by amounts that far exceed the new satellite sensitivities, and tidal models must be used to correct for this. Two methods are used here to determine the standard errors in current ocean tide models. At long wavelengths these errors exceed the sensitivity of the GRACE mission. Tidal errors will not prevent the new satellite missions from improving our knowledge of the geopotential by orders of magnitude, but the errors may well contaminate GRACE estimates of temporal variations in gravity. Solar Tides are especially problematic because of their long alias periods. The satellite data may be used to improve tidal models once a sufficiently long time series is obtained. Improvements in the long-wavelength components of Lunar Tides are especially promising.
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global ocean tide models on the eve of topex poseidon
IEEE Transactions on Geoscience and Remote Sensing, 1993Co-Authors: Richard D RayAbstract:Global ocean tide models that can provide tide corrections to TOPEX/Poseidon altimeter data are described. Emphasis is given to the Schwiderski and Cartwright-Ray models, as these are the most comprehensive, highest resolution models, but other models that will soon appear are mentioned. Differences between models for M/sub 2/ often exceed 10 cm over vast stretches of the ocean. Comparisons to 80 selected pelagic and island gauge measurements indicate the Schwiderski model is more accurate for the major solar Tides, the Cartwright-Ray for the major Lunar Tides. The adequacy of available tide models for studying basin-scale motions is probably marginal at best, although rapid advancement is expected over the next several years. >
V I Perminov - One of the best experts on this subject based on the ideXlab platform.
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Lunar Tides in the mesopause region obtained from summer temperature of the hydroxyl emission layer
Geomagnetism and Aeronomy, 2021Co-Authors: N. Pertsev, P. A. Dalin, V I PerminovAbstract:The summer mesopause region (altitudes of 82–92 km) is the coldest place in the Earth’s atmosphere; it is influenced by external effects, including Lunar Tides. In this study, we isolate the Lunar tidal harmonics from the temperature series of the hydroxyl emission layer (OH*) obtained from spectrophotometric measurements at the Zvenigorod scientific station of the Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences, in the summer seasons of 2000–2016. The OH* temperatures are the weighted average in a layer of ~9 km thick, which has a maximum at an altitude of ~87 km. The analysis made it possible to distinguish Lunar oscillations, among which two harmonics in the temperature of the mesopause region are identified for the first time. These oscillations are recognized as the second harmonic of the anomalistic Lunar tide (the mean period is ~13.78 days) and the Lunar tide with a period of 8 h 17 min, or, interpreting alternatively, the third harmonic of the Lunar synodic month (~9.84 days).
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influence of solar and Lunar Tides on the mesopause region as observed in polar mesosphere summer echoes characteristics
Journal of Geophysical Research, 2017Co-Authors: P Dalin, N. Pertsev, S Kirkwood, V I PerminovAbstract:Long-term observations of polar mesosphere summer echoes (PMSE) from 2002 to 2012 are investigated with the aim to statistically study the effects of solar thermal migrating and Lunar gravitational Tides on aerosol layers and their environment at altitudes 80–90 km. The solar and Lunar tidal periodicities are clearly present in PMSE data. For the first time, both amplitudes and phases of solar and Lunar Tides are estimated using PMSE data from the ESRAD radar located at Esrange (Sweden). The diurnal, semidiurnal, and terdiurnal solar migrating Tides show pronounced periodicities in the PMSE strength and wind velocity components. Lunar Tides demonstrate clear oscillations in the PMSE strength and wind velocities as well. “canonical” Lunar gravitational Tides, corresponding to the Lunar gravitational potential, produce rather large amplitudes and are comparable to the solar thermal Tides, whereas “noncanonical” Lunar oscillations have minor effects on PMSE layers, but are still statistically significant. The influence of diurnal/semidiurnal Tides and monthly/semimonthly tidal components is studied separately. Our estimations of solar thermal and Lunar tidal amplitudes are in good agreement with those of previous model and experimental studies. A new mechanism of quadratic demodulation of the solar semidiurnal and Lunar semidiurnal Tides is shown to be valid at the summer mesopause and can explain periodical PMSE oscillations due to the Lunar synodic semimonthly tide with period of 14.77 days. Two harmonics with periods of 27.0 and 13.5 days supposedly representing the solar rotation cycle are also clearly present in PMSE data.
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Influence of semidiurnal and semimonthly Lunar Tides on the mesopause as observed in hydroxyl layer and noctilucent clouds characteristics
Geomagnetism and Aeronomy, 2015Co-Authors: N. Pertsev, P. A. Dalin, V I PerminovAbstract:New results of research on Lunar Tides in the midlatitude mesopause region are presented. According to observational data on noctilucent clouds and spectrophotometric measurements of hydroxyl radiation, among the semimonthly and semidiurnal Lunar tidal harmonics under consideration, the semimonthly zonal tide (13.66 days), semimonthly synodic tide (14.77 days), and semidiurnal tide (12 h 25 min) were proven to be statistically significant. The temperature oscillations in the summer hydroxyl layer and the brightness of noctilucent clouds turned out to be nearly out of phase. For the first time, we considered two possible mechanisms of the generation of the synodic semimonthly harmonic. Here, statistical analysis of the hydroxyl data shows that the nonlinear demodulation of the superposition of solar and Lunar semidiurnal tidal harmonics is the most probable process.
Gunter Stober - One of the best experts on this subject based on the ideXlab platform.
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Climatology of semidiurnal Lunar and solar Tides at middle and high latitudes: Interhemispheric comparison
Journal of Geophysical Research: Space Physics, 2017Co-Authors: J. Federico Conte, N M Pedatella, Peter Hoffmann, Gunter Stober, Astrid Maute, Jorge L. Chau, Diego Janches, David C. Fritts, Damian J. MurphyAbstract:The semidiurnal Lunar and solar Tides obtained from meteor radar measurements spanning from 2009 until 2013 observed at Davis (69°S) and Rio Grande (54°S) are presented and compared to the northern hemisphere ones at Andenes (69°N) and Juliusruh (54°N). Mean tidal differences for both intra- and inter-hemispheric scenarios are analyzed. Tidal behavior is also compared against numerical simulations during 2009 and 2013 sudden stratospheric warming (SSW) time periods. Possible influences in the southern hemisphere from the local stratosphere are also investigated using Modern Era Retrospective analysis for Research and Applications, version 2 (MERRA-2) datasets. The main features of the mean zonal wind are similar in both hemispheres, i.e. stronger amplitudes over mid latitude locations; eastward winds during winter and westward below 90 km with eastwards higher up during corresponding summer times. On the other hand, the semidiurnal solar Tides observed in the southern hemisphere show clear differences when compared to the northern hemisphere and between mid and high latitude locations at the same hemisphere. These differences are even larger for the semidiurnal Lunar tide, which shows stronger amplitudes from October to March, and March to October, over Davis and Rio Grande, respectively. Our results indicate that the Lunar Tides over the southern hemisphere mid latitudes are more prone to react to the northern hemisphere stratospheric polar vortex influences, in agreement with numerical simulations, particularly for the time of the 2013 SSW.
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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.
Paul A. Rydelek - One of the best experts on this subject based on the ideXlab platform.
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Long-period Lunar Earth Tides at the geographic South Pole and recent models of ocean Tides
Geophysical Journal International, 2000Co-Authors: Machiel Bos, T. F. Baker, Florent Lyard, W. E. Zürn, Paul A. RydelekAbstract:For many years the ocean tide models of Schwiderski (1980) were the standards used by the Earth tide community to interpret deviations of observed Earth Tides from predictions on the basis of earth models constructed by seismologists. Recently, the TOPEX/POSEIDON altimeter mission provided new and improved information on pelagic ocean Tides, which led several research groups to generate new models of the major oceanic Tides. This in turn renewed our own interest in the observations of long-period Lunar Tides at the geographic South Pole that were reported many years ago with an attempt to interpret the deviation from predictions using the Schwiderski models. We used four different models of the fortnightly (Mf) and monthly (Mm) ocean Tides to calculate their attraction and loading effects at the South Pole and compared the results with the observed gravity Tides. In our earlier interpretation we did not realize that for long-period ocean Tides the so-called ‘Greenwich’ phase does not refer to the phase of these Tides at the latitude of Greenwich, but to the phase at the equator. This resulted in a mistake in the relative phases of Earth tide and ocean effect at the South Pole. For Mf we now find that all models predict the phase lead of the observed versus theoretical Tides within the formal uncertainties; however, the amplitude is still underpredicted by 1.5–2 per cent. This could be due to several reasons: instrument calibration, errors in the body and/or ocean tide models, relaxation of the Earth's elastic properties, and the huge ice sheet of Antarctica. These possibilities are discussed. For the Mm tide the observed amplitude is well predicted within error; however, the uncertainties in the measurements are rather large.
