1. Planetary waves in the equatorial mesosphere and ionosphere measurements Lourivaldo Mota Lima (UEPB) Luciana R. Araújo, Maxwelton F. Silva (UEPB) H. Takahashi, P. P. Batista, I. S. Batista (INPE) ( lourivaldo_mota@yahoo.com.br )

2. Motivation IONOSPHERE Middle Low Atmosphere Magnetosphere The possible causes of the ionospheric variability includes: Solar ionizing radiation, solar wind, geomagnetic activity, neutral atmosphere and electrodynamics. Part of F2-layer variability has been attributed to meteorological sources in the neutral atmosphere. The purpose of this work is to study the presence of mesosphere-ionosphere coupling throughout the identification of oscillatory signatures with planetary scale wave periods in the equatorial meteor winds, geomagnetic field and in the evening F region vertical plasma drift measurements.

3. Ionosphere MLT Region Low Atmosphere Introduction When global-scale waves propagate from lower atmosphere to ionosphere it is possible to cause disturbances in the electrical current system whose periods are the same of the planetary waves. The current system will produce perturbations in the geomagnetic field measurements. Day-to-day variations in the ionospheric current from magnetometer data obtained during quiet geomagnetic conditions can be interpreted as being due to planetary and gravity wave propagation up to dynamo region or due atmospheric tidal modulation with planetary waves periods.

4. Recent Studies Gurubaran et al. (2001) identified the signatures of the quasi-2-day variability in the equatorial electrojet using magnetometers; Abdu et al. (2006) found planetary wave modulation in the equatorial F-layer vertical drift. Pancheva et al. (2006) have analyzed the 2-day wave coupling of the low-latitude atmosphere-ionosphere system. Planetary 5–6-day waves coupling in the low-latitude atmosphere– ionosphere system have been investigated by Pancheva et al. (2008) Takahashi et al. (2012) also have analyzed 2-day wave using meteor winds and ionospheric parameters for equatorial region.

5. In this work were used equatorial measurements of the bottom-side virtual height of the ionospheric F layer h’F, meteor winds and magnetometer data. Data used in this study The h’F ionospheric measurements were obtained from a digital ionospheric sounder (DPS-4), which is operated at Fortaleza. The winds have been collected from a “SKiYMET” all-sky VHF radar at São João do Cariri in northeast Brazil region.

6. The geomagnetic data used in the present study were obtained from 6 stations around geographic equatorial region, which were downloaded from International Real-time Magnetic Observatory Network (www.intermagnet.org). Ascencion Island, ASC - 8  S, 345.6  W; Addis Ababa, AAE - 9  S, 38.7  E; Guam, GUA - 13.6  N, 144.86  E; Huancayo, HUA - 12  S, 284.7  E; Kourou, KOU - 2.2  N, 307.3  E; Mbour, MBO - 14.4  N, 343  E Data used in this study

7. Data Series The evening F region vertical plasma drift have been calculated from were Δh' F is the F bottom-side virtual height variations and Δt is the time interval. The wind measurements were obtained by SKiYMET meteor radar from radial velocity which is determined for each meteor echo from the Doppler shift. Zonal and meridional wind components are estimated by assuming that they are uniform and constant for specific height-time bins.

8. Thermal Tide Solar Radiation Thermal Tide Sq Current The dynamics of the MLT region establishes the lower thermospheric wind system, which generates electric fields and currents through of the ionospheric dynamo mechanism, when the electrically charged environment is moved through the geomagnetic field. Data Series The electric fields and dynamo currents produced by the interaction between the wind system and ionospheric plasma, drive the electrodynamical processes of the thermosphere-ionosphere system at low latitudes during magnetically quiet times (Pancheva et al., 2006).

9. For investigating the variability in the hourly X, Y and Z components of the geomagnetic field with periods of planetary waves, the method described by Pancheva et al. (2006) has been applied in the geomagnetic data analysis. Data Series The method use time series of relative scale coefficient obtained from geomagnetic field components, in which the 24-hour periodicity together with all harmonics are removed in advance. The method represents a special single-component decomposition of data, where instead of using a standard sine function we use a concrete diurnal course, which is treated as periodic, but which is not a simple sinusoid.

10. Results (Sep-Dec/2004) S-Transform amplitude spectra for Cariri zonal wind at 90-km for Sep – Dec 2004. 20 Sept - 23 Oct quiet and weak activities 6 days Lomb-Scargle periodograms for 28-day sequences of the relative scale coefficient obtained from geomagnetic data. The horizontal line represents the 95% confidence level. 6 days

11. Results (Sep-Dec/2004) Evening F region vertical plasma drift, obtained from h’F variations over Fortaleza; Filtered time series (band pass filter - 5.8 - 7.5 days): for vertical plasma drift; relative scale coefficient obtained from Y geomagnetic component at Addis Ababa; for zonal wind at Cariri for 90 km.

12. Results (Jan-Feb/2005) S-Transform amplitude spectra for Cariri zonal and meridional winds at 90-km. 24 Jan - 07 Feb quiet activities 2 days Lomb-Scargle periodograms for 10-day sequences of the relative scale coefficient obtained from geomagnetic data. The horizontal line represents the 95% confidence level.

13. Results (Jan-Feb/2005) Evening F region vertical plasma drift, obtained from h’F variations over Fortaleza; Filtered time series (band pass filter - 1.6 – 2.4 days): for vertical plasma drift; relative scale coefficient obtained from Y geomagnetic component at Addis Ababa; for meridional wind at Cariri for 90 km.

14. Results (Sep-Dec/2005) Lomb-Scargle periodograms for 28-day sequences of the relative scale coefficient obtained from geomagnetic data. The horizontal line represents the 95% confidence level. 7 days 6 days 1st Nov – 11 Dec quiet and weak activities S-Transform amplitude spectra for Cariri zonal wind at 90-km for Sep – Dec 2005.

15. Results (Sep-Dec/2005) Evening F region vertical plasma drift, obtained from h’F variations over Fortaleza; Filtered time series (band pass filter - 5.8 - 7.5 days): for vertical plasma drift; relative scale coefficient obtained from Y geomagnetic component at Addis Ababa; zonal wind at Cariri for 90 km.

16. Modulation of tides by planetary waves The atmospheric tides propagate freely upward in the thermosphere and then participate in the dynamo generation of electric fields at higher levels. If the tidal amplitudes are modulated with a ~6-day wave period, then they can induce 6-day variability of the electric fields as well.

17. Modulation of tides by planetary waves Likewise, tidal amplitudes modulated by a 2-day wave period, can induce a 2-day variability of the electric fields. The PW oscillations in zonal winds at E- layer height could be a more likely cause of the observed PW scale oscillations in the evening zonal electric field /F-region vertical plasma drift (Abdu et al., 2006).

18. Acknowledgements The authors gratefully acknowledge the financial assistance provided by the CNPq and PROPESQ/UEPB. Thank you for your attention!