Prof Yang-Yi Sun received PhD at Graduate Institute of Space Science, National Central University, Taoyuan city of Taiwan, in 2014. He visited CU/CIRES-NOAA/SWPC, Boulder, Colorado, from March 2011 to February 2014 and Kyushu University, Fukuoka, Japan, from July 2016 to June 2017. He is currently a professor at Institute of Geophysics and Geomatics, China University of Geosciences (Wuhan), China, since 2017. His research specialties are ionospheric weather (e.g. geomagnetic storm, solar eclipse), modulation of long-term tropospheric variabilities (e.g. El Niño - Southern Oscillation, Pacific Decadal Oscillation) on the upper atmosphere, and impact of ground motions (e.g. earthquake, tsunami) on both the lower and upper atmosphere. He analyzed and assimilated ground- and space-based Global Navigation Satellite System (GNSS) observations for studying those scientific topics for several years.
"GNSS Helps Us Get Our Feet Back on the Ground from Ionosphere"
The Earth’s ionosphere (from ~70 to thousands km above the Earth) is central to our solar-terrestrial environment. Both solar activity (e.g. solar flare, solar wind, coronal mass ejection, and moon shadow of eclipse) and perturbations from lower atmosphere (e.g. cyclone, convection, and El Niño - Southern Oscillation) and ground motion (e.g. earthquake, tsunami, and volcanic eruption) leave many of shape footprints messy on the ionosphere. We do appreciate any novel technique being around to help us to investigate unexplained phenomena.
Dense Global Navigation Satellite System (GNSS) networks can globally scan ionospheric electron density structures in both horizontal and vertical directions with high temporal and spatial resolutions. Scientists have benefits from the ground- and space-based GNSS observations to comprehensively study ionospheric morphology response to solar activities in the recent two decades. This talk first briefly introduces the effect of the solar activities, such as geomagnetic storm and solar eclipse, on the change of ionospheric structures that critically impacts radio wave communication and navigation systems.
Other than the impact of solar activities, numerous ionospheric phenomena that may result from perturbations from lower atmosphere and ground remain unexplained. This talk pays attention to the influence of El Niño - Southern Oscillation (ENSO), which is considered to be the primary dynamical driver of the interannual variations in troposphere, on the quasi-biennial oscillation (QBO) in stratosphere (U30 index, the monthly mean of zonal wind at 30mb pressure level over Singapore), mesosphere, lower thermosphere, and even ionosphere. The ENSO signatures in the QBOs at various altitudes are observed by the FORMOSAT-3/COSMIC radio occultation (RO) sounding profiles of temperature and electron density. The RO technique records ENSO signals which are pertinent to the ongoing study attempting to establish the long-term change in the troposphere connection to the upper atmosphere.
Moreover, ground motions due to a large earthquake or tsunami can significantly perturb the ionosphere. The horizontal movement of seismo-traveling atmospheric disturbance (STAD) in the ionosphere have been comprehensively observed by dense ground-based GNSS networks. However, study for its vertical component is rare. This talk shows that the 2011 Mw9.0 Tohoku earthquake/tsunami can perturb the vertical structures of not only the ionosphere, but also the stratosphere. The RO-recorded vertical component of STADs allows a more comprehensive understanding of excitation, propagation, and dissipation of earthquake/tsunami-induced waves in the whole atmosphere. The waves detection in the lower atmosphere is benefit to earthquake/tsunami warning system.
The ground- and space-based GNSS is a powerful technique to capture atmospheric variabilities in both horizontal and vertical directions at various altitudes, that bring us a holistic view of dynamic interaction between the Earth's spheres and help us to seek a deeper understanding of our solar-terrestrial environment.