Comparison of the Tidal Signatures in Sporadic E and Vertical Ion Convergence Rate, Using FORMASAT-3/COSMIC Radio Occultation Observations and GAIA Model

Sporadic E or Es is a transient phenomenon where thin layers of enhanced electron density appear in the ionospheric E region (90-120 km altitude). The neutral wind shear caused by atmospheric tides can lead ions to converge vertically at E-region heights and form the Es layers. This research aims to determine the role of atmospheric solar and lunar tides in Es occurrence. For this purpose, radio occultation data of FORMASAT-3/COSMIC have been used, which provides complete global coverage of Es events. Moreover, GAIA model simulations have been employed to evaluate the vertical ion convergence induced by solar tides. The results show both migrating and non-migrating solar tidal signatures and the semidiurnal migrating lunar tidal signature in Es occurrence. The seasonal variation of the migrating solar tidal components of Es is in good agreement with those in the vertical ion convergence derived from GAIA. Furthermore, some non-migrating components of solar tides, including semidiurnal westward wavenumbers 1 and 3 and diurnal eastward wavenumbers 2 and 3, also significantly affect the Es occurrence rate.

Effect of Semidiurnal Lunar Tides Modulated by Quasi-2-Day Wave on Equatorial Electrojet during Three Sudden Stratospheric Warming events

<p>We present an analysis of the perturbations and wave characteristics in equatorial electrojet (EEJ) and equatorial zonal winds in the mesosphere and lower thermosphere region during three sudden stratospheric warming (SSW) events, based on the wind observations by two meteor radars in Indonesia and the geomagnetic field observations in India. During three SSWs, the shifting semidiurnal perturbations are consistently observed in the EEJ and accompanied with strong 2-day periodic perturbations simultaneously. The semidiurnal lunar (L2) tidal amplitudes in the EEJ and zonal winds show the prominent enhancements during the episodes of EEJ perturbations. The time-period spectra of the L2 tidal amplitudes in both the EEJ and zonal winds present the obvious quasi-2-day wave (QTDW) amplification with good agreement during these periods. Our results firstly reveal the important contributions of QTDW to EEJ perturbations during SSWs and the semidiurnal lunar tides modulated by QTDW serve as the main forcing agent therein</p>

The 1970–1984 lunar laser ranging observations in the Crimean Astrophysical Observatory

The Lunar Laser Ranging (LLR) has been the main method of study of the dynamics of the Sun-Earth-Moon system since 1969 to present. Lunar parts of the three modern high-precision ephemerides of the Solar system bodies are based solely on LLR measurements: DE (USA), EPM (Russia), INPOP (France). LLR measurements allow to determine parameters of lunar orbital and rotational motion, as well as some parameters related to terrestrial and lunar tides, and also fundamental relativistic parameters. Those parameters were determined from LLR with high accuracy by different authors. In USSR, LLR measurements were performed in the Crimean Astrophysical Observatory (CrAO) in Nauchny, on the 2.6 m Shajn’s Zenith telescope (ZTSh) with an automated laser ranging system developed by the Russian Lebedev Physical Institute (LPI). Within the time span of 1969–1984, 1400 measurements were obtained. Unlike LLR measurements done in other observatories, they were eventually forgotten and have not made their way into the dataset that is used by scientists worldwide to build lunar ephemerides and conduct other lunar research. The main reason for writing this paper was the discovery by Tryapitsyn, a researcher at the Katziveli station of CrAO, of old printouts containing the 1970–1984 LLR observations made with the ZTSh 2.6 m telescope. Some details were missing from the printouts, which required careful restoration work. In this paper the history of those LLR observations with surrounding historical events is presented, and some details of the analysis these observations are described. Of particular interest is the finding related to the three normal points of Lunokhod-1 ranges obtained in 1974 that allowed Odile Calame to determine the rover’s position with a few kilometers accuracy. Unfortunately, the accuracy was not sufficient for other researchers to confirm and pin down the location of the rover.

Comparing the ionospheric response to the 2008/2009 and 2018/2019 SSW events

<p>It is now well accepted that the ionosphere and thermosphere are sensitive to forcing from the lower atmosphere (troposphere-stratosphere) owing mainly to the progress that have been made in the last decade in understanding the vertical coupling mechanisms connecting these two distinct atmospheric regions. In this regard, the studies linking the upper atmosphere (mesosphere-lower thermosphere-ionosphere) variability due to sudden stratospheric warming (SSW) events have been particularly important. The change of stratospheric circulation due to SSW events modulate the spectrum of vertically upward propagating atmospheric waves (gravity waves, tides, and planetary waves) resulting in numerous changes in the state of the upper atmosphere. Much of our understanding about the upper atmospheric variability associated due to the SSWs events have been gained by studying the 2008/2009 SSW event, which occurred under extremely low solar flux conditions. Recently another SSW event in 2018/2019 occurred under similar low solar flux conditions. In this study we simulate both these SSW events using Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM-X) and present the findings by comparing the ionospheric and thermospheric response to both these SSW events. The tidal characteristics of the semidiurnal solar and lunar tides and the thermospheric composition for both these SSW events are compared and the causes of varying responses are investigated.</p>

Geomagnetic field variations due to Solar and Lunar tides in the Brazilian Sector

<p><strong>Abstract</strong></p><p>Geomagnetic field variations in 2018 due to solar and lunar tides in the Brazilian sector were studied using data provided by magnetometers installed at São José dos Campos (23.21<sup>o</sup>S, 0345.97<sup>o</sup>W; Dip latitude 20.9<sup>o</sup>S), Eusébio, Ceará (3.89° S, 38.46° W) and São Luís, Maranhão (2.53° S, 44.30° W). Variations associated with these tides were identified using the horizontal component of the geomagnetic field, H(nT). Least square fit method was employed in determining the monthly amplitudes and phases of the diurnal, semidiurnal and ter-diurnal solar tides. The monthly amplitudes and phases of the lunar tide were then calculated using the residual measurements (obtained after subtracting the solar tidal components from each day), converting the solar local time to lunar time and subjecting the residuals to harmonic analysis. The maximum solar tide amplitude recorded was 23.96nT(diurnal) in March, at Eusébio whereas the minimum amplitude was 0.45nT(terdiurnal) recorded in December at São José dos Campos. The lunar tide recorded a maximum amplitude of 4.33nT(semidiurnal) in February, at São Luís and a minimum amplitude of 0.13nT(diurnal) in August, at Eusébio.</p><p> </p><p> </p><p><strong>Keywords</strong>: Solar tides, Lunar tides, Geomagnetic field, Magnetometer.</p><p> </p>

On the variability of the semidiurnal solar and lunar tides of the equatorial electrojet during sudden stratospheric warmings

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 Fúquene 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.