ALBERT

Description: Equatorial thermosphere-ionosphere has several singular processes: Equatorial Ionization Anomaly (EIA), F-layer Pre-reversal enhancement (PRE), Equatorial Plasma Bubbles (EPBs) and Midnight Temperature Maximum (MTM). All these processes are related to interaction of the thermospheric winds and ionospheric plasma. Over the South American continent, we are observing dynamical processes of the atmosphere by multi-instrumental means, optical airglow imager, ionosonde, GNSS receiver network, together with available satellite data. In some cases, we observed large scale gravity waves propagating in the MLT region (80-100 km altitudes), then a few hours later we observed a similar wave structure propagating in the ionosphere. Investigating characteristics of the two waves we found that these waves have their origin in the troposphere where a deep convection spot was going on. Also found that detrended total electron content (TEC) map indicated a concentric wave structure in the ionosphere. However, the center of the concentric wave did not coincide with the convection spot, indicating that this concentric wave is not a primary wave but a secondary generated wave. The other phenomenon of interaction of thermosphere-ionosphere is Midnight Temperature Maximum (MTM) and plasma bubbles. We, some occasions, observed OI 630 nm enhancement inside the bubble when the MTM passed over the bubbles. This interaction must be related to coupling of the thermospheric winds and plasma bubbles. In this talk, we present observational evidence of these coupling processes and to discuss the source and propagation mechanism.

Description: The Rayleigh-Taylor instability growth rate (γRT) was estimated in order to investigate the impact of physical parameters that control the equatorial plasma bubbles (EPBs) development and compare the values with the EPBs occurrence data. γRT was estimated by using ionosonde data at Fortaleza (3.9°S, 38.45°W; dip angle: 9°S) and atmospheric models (IRI-2016, MSISE-00 and HWM-14). The EPBs occurrence was obtained by observing the rate of change of total electron content index (ROTI) using the ground-based global navigation satellite systems (GNSS) receivers in the northeast of Brazil. One year of data was used (2014). The comparison of γRT and the EPBs occurrence data indicates that the relationship between these two parameters could be characterized by a continuous probability distribution function. The results also indicate that background zonal and meridional winds, with the strength of the pre-reversal enhancement, are important factors to control EPB occurrence. The EPB occurrence probability is small when the γRT reaches negative values and becomes larger than 80% when the γRT is greater than 3 x 10-4 s-1. Some main features of the relation between the occurrence rate and from the point of view of the space weather concern will be presented.

Description: Equatorial plasma bubble (EPB) development was studied using detrended total electron content (dTEC) data over Brazil and a numerical model. The EPB characteristics were estimated using dTEC data from January 2012 to February 2016. Six hundred fifty-five nights with EPB occurrence were analyzed. In 30% of the nights, the EPBs presented an interhemispheric asymmetry. Simulations based on the effect of a transequatorial meridional wind suggested that it could reduce the EPB growth rate, forcing them to become fossil. During the fossil stage, the EPBs can drift under the influence of background neutral winds and then exhibit an asymmetric meridional development regarding the geomagnetic equator. Monthly averaged meridional wind and F-layer virtual height measurements were also analyzed and were consistent with the simulated results.

Description: High-precision geophysical observations are necessary to observe minute variations occurring in the Earth's deep interior. In many cases, only very long-period fluctuations are observable because short-period fluctuations are attenuated during the propagation from deep to the earth's surface. Therefore, the instruments are required to have ultra-wide bandwidth and high accuracy. In recent years, instruments capable of such ultra-broadband and high-precision observations have become available. ROIS-DS joint project [015RP2021, 018RP2022] has enabled us to start trying to develop a method to detect interested deep phenomena from the ultra-wide bandwidth observation recordings. We try to apply a signal extraction method based on the Hilbert-Huang transform (HHT) combined with strain analysis. We present here a laser extensometer with 1500 m baseline length 10-13 accuracy (e.g., Araya, 2017), a multi-component borehole strainmeter (e.g., Okubo et al., 2005 and Itaba et al., 2018), and a superconducting gravimeter (Yokoyama et al., 2017) as an example of high S/N. Acknowledgement: We would like to express their gratitude to the following organizations for their support: ROIS-DS joint [No. 015RP2021, 018RP2022] supports to conduct this research. The crustal deformation database operated by Hokkaido University was used to obtain the gravimetric data.