A constant daylength during the Precambrian era?

The effects of the earth and ocean tides on the semi-diurnal lunar tide in the atmosphere have been ignored in nearly all studies of this air tide. Elementary arguments show that these boundary effects are not trivial. Using linear theory we calculated the combined effect of the lunar potential, the earth tide, and the ocean tide on a realistic model atmosphere. Love's theory was used to represent the earth tide. Numerical calculations by Bogdanov and Magarik and by Pekeris and Accad were used to represent the ocean tide. Our results indicate that the ocean tide has a significant and probably a dominant effect on the lunar air tide. The ocean tide of Pekeris and Accad yielded results that agreed better with the observations. We calculated the effect of a tide in a “small” or “point” ocean on the atmosphere and found that its effects were global. Hence, differences between the observations and our calculations of the lunar air tide cannot easily be reduced by simple manipulation of the forcing fun...

Thermal infrared imaging by Longwave Infrared Camera (LIR) aboard JAXA's Venus orbiter Akatsuki has revealed horizontal structures of large‐scale topographic gravity waves (mountain waves) and thermal tides in the Venusian atmosphere. For quantitative analysis of these waves, we developed a radiative transfer model for an atmosphere perturbed by a gravity wave, which represents the mountain waves and the thermal tides in the equatorial region. Combining the infrared images with temperature profiles from the Akatsuki radio occultation, the cloud particle scale height, as well as the vertical wavelengths and growth rates of mountain waves and the semidiurnal thermal tide were determined. The cloud particle scale height around the cloud top was estimated to be approximately equal to the atmospheric scale height, indicating a vertically well‐mixed layer of the cloud particles near the cloud top in low latitudes. It was demonstrated that the brightness temperature amplitude observed by LIR is approximately half of the atmospheric temperature amplitude at the cloud top. The waves' impact on the mean flow above the cloud top was assessed by estimating their momentum deposition. The results show that mountain waves can induce an intense but localized deceleration of tens of m s −1 /day or larger above 80 km, while the semidiurnal tide provides a global and persistent deceleration that increases with height to reach the order of 1 m s −1 /day at 80 km. These results reveal two important but distinct mechanisms that contribute to the momentum budget of the Venusian upper atmosphere.

Planets in the liquid-water habitable zone of low-mass stars experience large tidal forces, 103–104 times those on Earth, due to the small distance between the habitable zone and the host stars. Therefore, interior solid tides, ocean tides, and atmospheric tides on these planets could be much stronger than those on Earth, but little work has been done to explicitly simulate the ocean tides. Here, for the first time, we perform global ocean tide simulations and show that ocean tides on asynchronously rotating planets with large eccentricities can reach O ( 1000 ) m in height and O ( 10 ) m s − 1 in flow speed. Interactions between tide and bottom topography can induce large energy dissipation, ∼ O ( 100 ) W m − 2 in the global mean. This tidal energy dissipation can strongly accelerate orbital evolution by 1–2 orders of magnitude. However, for planets with small eccentricities, the ocean tides are much weaker but still comparable to those on modern Earth. Our results suggest that ocean tides on eccentric planets orbiting low-mass stars are orders of magnitude more powerful than those on Earth and can dramatically influence surface geography and orbital evolution.

Loading of the Earth’s crust due to variations in global atmospheric pressure can displace the position of geodetic stations. However, the station displacements induced by the diurnal and semidiurnal atmospheric tides (S1-S2) are often neglected during Global Positioning System (GPS) processing. We first studied the magnitudes of S1-S2 deformation in the Earth’s center of mass (CM) frame and compared the global S1-S2 grid models provided by the Global Geophysical Fluid Center (GGFC) and the Vienna Mapping Function (VMF) data server. The magnitude of S1-S2 tidal displacement can reach 1.5 mm in the Up component at low latitudes, approximately three times that of the horizontal components. The most significant difference between the GGFC and VMF grid models lies in the phase of S2 in the horizontal components, with phase discrepancies of up to 180° observed at some stations. To investigate the effects of S1-S2 corrections on GPS coordinates, we then processed GPS data from 108 International GNSS Service (IGS) stations using the precise point positioning (PPP) method in two processing strategies, with and without the S1-S2 correction. We observed that the effects of S1-S2 on daily GPS coordinates are generally at the sub-millimeter level, with maximum root mean square (RMS) coordinate differences of 0.18, 0.08, and 0.51 mm in the East, North, and Up components, respectively. We confirmed that part of the GPS draconitic periodic signals was induced by unmodeled S1-S2 loading deformation, with the amplitudes of the first two draconitic harmonics induced by atmospheric tide loading reaching 0.2 mm in the Up component. Moreover, we recommend using the GGFC grid model for S1-S2 corrections in GPS data processing, as it reduced the weighted RMS of coordinate residuals for 45.37%, 46.30%, and 53.70% of stations in the East, North, and Up components, respectively, compared with 39.81%, 44.44%, and 50.00% for the VMF grid model. The effects of S1-S2 on linear velocities are very limited and remain within the Global Geodetic Observing System (GGOS) requirements for the future terrestrial reference frame at millimeter level.

<p>Observations of the Venus Climate Orbiter “Akatsuki” provide us with horizontal distributions of the horizontal winds derived from cloud tracking of the Ultraviolet Imager (UVI) and of temperature observed by the Longwave Infrared Camera (LIR). However, these observations are limited in altitude, local time (day or night side), and frequency. Then it is difficult to elucidate the general circulation of the Venus atmosphere, including various temporal and spatial scales, only from observations. In this study, we produced a Venus dataset (analysis) that has high temporal and spatial resolutions by assimilating horizontal winds derived by the Akatsuki observations. At the top of the cloud layer of Venus, there are planetary-scale atmospheric waves that are excited by the solar heating and move with the sun, called the thermal tides. In this presentation, we focused on thermal tides to verify the analysis.</p> <p>We use the Venus atmospheric data assimilation system “ALEDAS-V" (Sugimoto et al., 2017) [1] for assimilation and the Venus atmospheric general circulation model “AFES-Venus" (Sugimoto et al., 2014) [2] for ensemble forecasts. AFES-Venus is a full nonlinear dynamical GCM on the assumption of hydrostatic balance, designed for the Venus atmosphere. ALEDAS-V uses the Local Ensemble Transform Kalman Filter, and is the first data assimilation system for the Venus atmosphere. We assimilated the cloud top (~70km) zonal and meridional winds obtained by tracking morphology, using Akatsuki UVI data (Horinouchi et al., 2021) [3] from September 1st to December 31st, 2018. The assimilation data (analysis) from October 1st to November 30th, 2018, is analyzed, because the root-mean-square-deviations (RMSD) from FR (free run; the case without data assimilation) are stable.</p> <p>Figures (a) and (d) show the observed zonal and meridional winds, respectively. The zonal wind has a local minimum near 11 LT (local time) around the equator (Figure a). The meridional wind is the weakest at the equator and increases with latitude, and the amplitude is maximum around noon (Figure d) in the local time direction. Note that these winds obtained from observations exist only the dayside equatorward of 50° latitudes (Figure a and d).</p> <p>Figures (b) and (e) show the deviations from the zonal means of zonal and meridional winds at an altitude of 70 km in the FR, respectively. For zonal wind, diurnal (zonal wavenumber 1) and semidiurnal (zonal wavenumber 2) tides are dominant at latitudes poleward and equatorward of 30, respectively (Figure b). The zonal wind deviation has a local minimum at 14-15LT, which is ~ 2 hours behind the observation (Figures a and b). The meridional wind deviation is polar and equatorial on the dayside and nightside, respectively (Figure e), and this distribution is consistent with Akatsuki's observation (Figure d).</p> <p>Figures (c) and (f) show the zonal and meridional winds as a result of assimilation, respectively. The zonal wind in the equatorial region have a local minimum near 11 LT. The assimilation improved the semidiurnal tide closer to the observations (Figures a and c). The meridional wind is not so different from FR. This is probably because FR was originally very similar to observations (Figures d and f). These results are consistent with a previous study by Sugimoto et al. (2019) [4]. In addition, while the observed winds exist only on the dayside, the results of assimilation show that the horizontal winds field is modified significantly even on the nightside. It is suggested that spatially limited data assimilation can improve the general circulation of GCM.</p> <p>In the future work, we are planning to release the assimilation dataset as the “objective analysis data” of Venus for the first time in the world.</p> <p><img src="" alt="" width="743" height="482" /></p> <p>[1] Sugimoto, N., et al. Development of an ensemble Kalman filter data assimilation system for the Venusian atmosphere. Scientific Reports 7(1), 9321 (2017).</p> <p>[2] Sugimoto, N., et al. Baroclinic instability in the Venus atmosphere simulated by GCM. J. Geophys. Res. Planets 119, 1950–1968 (2014).</p> <p>[3] Horinouchi, T., et al. Venus Climate Orbiter Akatsuki Cloud Motion Vector Data Set v1.0, JAXA Data Archives and Transmission System (2021).</p> <p>[4] Sugimoto, N., et al. Impact of data assimilation on thermal tides in the case of Venus Express wind observation. Geophys. Res. Lett. 46, 4573–4580 (2019).</p>

The viscosity of Venus’ mantle inferred from its rotational state

Venus’s cloud-top superrotation, characterized by equatorial zonal winds of ~100 m/s, is sustained by the atmospheric angular momentum (AM) induced by atmospheric waves, especially thermal tides, and meridional circulation. However, the overall patterns of thermal tides and their individual components’ contribution to superrotation remain poorly understood. Recent Akatsuki observations and semispectral model simulations suggest that the semidiurnal tide is the dominant driving force behind cloud-top superrotation. Using a 16-year radio occultation dataset observed by Venus Express and Akatsuki, we have, for the first time, revealed the thermal tide structure from the cloud base to mesopause (50-90 km) in the southern hemisphere and validated the tidal patterns simulated by the Venus Planetary Climate Model. The simulation indicates that diurnal tide-induced AM flux divergence is the primary driving force for the equatorial cloud-top superrotation, contrary to the previously held belief that the semidiurnal tide was dominant.

Heat conduction in the subsurface environment is the result of internal and external impacts and is governed by different forces in the short and long term. Externally, this phenomenon is related to daily temperature variations, terrestrial, oceanic, and atmospheric tides, and vegetation activity. However, beyond depths of up to 30 meters, thermal conduction is not applied. The transpiration of the vegetation plays a key role in this dynamic by being the connection point between the soil and the atmosphere. The main objectives of this thesis are (1) to identify the variation of groundwater microtemperature at daily and seasonal level, (2) to compare the variation of groundwater microtemperature with different meteorological parameters, (3) with terrestrial tides, (4) with vegetation activities, and (5) to analytically compare the groundwater microtemperature variation with land use changes in the studied area. Daily and annual variations in groundwater microtemperature were compared to variations in meteorological parameters and electrical potential of plants. A decrease of 2 mK was observed in daily subsurface temperature when the surface temperature exceeded 9 ºC. This diurnal temperature variation occurs during the phenological growing season of the vegetation. The same pattern was also observed during summer. However, this relationship does not always occur. At high temperatures (+30 °C) the decrease amounts to just 1 mK. This fact is related to the change in transpiration of plants, decreased or even suspended at high surface temperatures. With an increase in surface temperature an increase in tree electrical potential can be observed. This increase in electrical potential is concomitant with a change in groundwater temperature of approximately 2 mK. A frequency analysis of all data showed a daily frequency of high magnitude in all parameters. The lag time between changes in electric potential and subsurface microtemperature changes amounts to 17 hours, a result of the electrical potential difference between the northern and the southern exposure of the stem (N – S), and 5 hours, the result of the change in electrical potential difference between the southern and the northern stem exposure side (S – N). A comparison between potential changes and the computed change in gravity resulting from earth tidal effects showed that the correlation between the subsurface temperature variation with up to 2 mK and the change in surface temperature variation does not match directly. Atmospheric tides can be correlated with the changes in north and south electric potentials. Annually, a linear decrease of 0.0407 K/year was estimated, and model calculation applying a linear decrease in surface temperature of 2 K as a boundary condition was simulated. Comparing the results with the trend it is realistic to assume that when an apparent thermal diffusivity of 1.8*10-6 m2/s is applied an event starting between 10 and 20 years ago is responsible for the detected decrease in temperature. However, with this thermal diffusivity the conductive annual temperature variation reaches an amplitude of 1.1 mK instead of the measured 5.4 mK at 40 m, showing that the vegetation causes additional convective heat transport triggered by the annual surface temperature.

Complex demodulation in VLBI estimation of high frequency Earth rotation components

A key controller of a planet's rotational evolution, and hence habitability, is tidal dissipation, which on Earth is dominated by the ocean tides. Because exoplanet or deep‐time Earth topographies are unknown, a statistical ensemble is used to constrain possible tidal dissipation rates on an Earth‐like planet. A dedicated tidal model is used together with 120 random continental configurations to simulate Earth's semidiurnal lunar tide. The results show a possible ocean tidal dissipation range spanning 3 orders of magnitude, between 2.3 GWto 1.9 TW (1 TW=1012 W). When model resolution is considered, this compares well with theoretical limits derived for the energetics of Earth's present‐day deep ocean. Consequently, continents exert a fundamental control on tidal dissipation rates and we suggest that plate tectonics on a planet will induce a time‐varying dissipation analogous to Earth's. This will alter rotational periods over millions of years and further complicate the role of tides for planetary evolution.

Planets with a dense atmosphere present not only traditional gravitational and thermal tides, but also combined effects resulting from these two: gravitational torque upon pressure bulge, pressure torque upon tidal bulge, and pressure torque upon pressure bulge. Here we give a complete description of these effects and evaluate their relative contributions to the secular evolution of the planet's spin. In particular, we discuss the importance of determining the exact transfer mechanism of angular momentum from the atmosphere to the surface. It is shown that alternative atmospheric tides may play an important role if this transfer rate is not very effective, although this does not seem to be the present case on Earth or Venus.

Earth rotation deceleration/acceleration due to semidiurnal oceanic/atmospheric tides: Revisited with new calculation

Today with increased availability of data of middle atmospheric winds and temperature, modelling of middle atmospheric tides has acquired greater importance. The theory of atmospheric tides has two main parts: (i) Investigation of the sources of periodic excitation, and (ii) calculation of the atmospheric response to the excitation. Other than stratospheric ozone and tropospheric water vapour absorption, the thermal energy available from the absorption in Schumann–Runge (SR) continuum leading to photo-dissociation of O2 is important energy source for tides in the lower thermosphere. PHODIS radiative transfer model is capable of providing tidal forcing due to combined effect of solar and chemical heating in the wavelength region 116 to 850 nm. In this paper, we present an atmospheric tidal model based on classical tidal theory and the prime objective is to obtain the tidal structure due to conventional ozone and water vapour heating in conjunction with the O2 absorption. Mean wind and dissipation mechanisms are not considered. The present tidal model reveals that the diurnal amplitude peaks in mid to low latitudes, whereas semidiurnal component is stronger at higher latitudes. The semidiurnal tide is about an order of magnitude weaker than the diurnal tide. Also, semidiurnal wave has longer vertical wavelength than diurnal tide. The results of present model are qualitatively in good agreement with the other tidal models, which utilize more sophisticated parameterization. Thus, the salient features of the tidal structure are obtained using basic computations without considering the effects of background winds and dissipation processes. Further refinements to the model can serve as an inexpensive substitute to the presently available tidal models.

Satellite wind observations from the High Resolution Doppler Interferometer (HRDI) instrument on the Upper Atmosphere Research Satellite (UARS) are used to describe the latitudinal structure and seasonal variation of the terdiurnal (8 hour) atmospheric tide at 95 km. The amplitude of the annual average tide is 5 m/s (meridional) and 15 m/s (zonal). Within the range observed (60°S to 60°N), the maximum amplitudes are found during fall and winter at midlatitudes. Only weak temporal correlations with the diurnal and semidiurnal tides are seen on the monthly time scales resolved.

The technique to process the temperature data obtained in the COSMIC experiment is presented. The results obtained on the basis of COSMIC sounding data and reanalyses of ERA5 and MERRA-2 have been compared for the amplitudes of waves traveling westward with zonal wave numbers 1 and 2, as well as for diurnal and semidiurnal tides. The possibility of studying planetary waves and atmospheric tides considering their variability has been shown