專題演講 2024

This study encompasses three interrelated projects, each designed to enhance our comprehension of ionospheric profile variations and structures. The initial project leverages ground-based observations of 630.0 nm airglow emission intensities to assess atomic oxygen ion ([O⁺]) densities between 150 to 450 km altitude using photochemical models. This approach is corroborated by electron density measurements from the digisonde DPS-4 in Irkutsk, Russia, suggesting a method for employing airglow as global ionospheric indicators. Expanding on this fundamental understanding of ionospheric airglow emissions, the second project confronts the intricacies of adapting the inversion model for global satellite observations. Moreover, the application of deep learning to fine-tune Abel inversion significantly reduces the margin of error in reconstructing the previously unobservable upper segment (>300 km) of airglow intensity profiles, as captured by FORMOSAT-2. This advancement promises a marked improvement in the completeness and reliability of airglow data, opening new avenues for ionospheric study and operational forecasting. The final project delves into ionospheric scintillation during geomagnetic disturbances, particularly through an analysis of FORMOSAT-7/COSMIC-2 data in the context of a moderate geomagnetic event that led to the loss of 38 out of 49 SpaceX Starlink satellites in 2022. Our analyses identify a link between the S4 index behavior and the disturbance in the electron density profiles, underscoring the effects of prompt penetration electric (PPE) fields and disturbance dynamo (DD) on ionospheric irregularities. In conclusion, the collective endeavor of these projects offers a detailed and intricate perspective on the ionospheric profile’s variability and composition, encompassing both disruptive influences and functional mechanisms.

Keywords: Ionosphere, Airglow, Plasma irregularity, Geomagnetic storm, Deep learning.

https://www.asiaa.sinica.edu.tw/people/cv_c.php?i=tjthieme

(Monday)12:20-13:20(special time) Venue: NTNU Gongguan campus S801-2

Whistler-mode waves were first detected on the ground during WWI as the so-called lightning-generated whistlers, a type of electromagnetic wave in audio frequencies. The whistlers can travel through the ionosphere and magnetosphere, bringing back plasma distribution information. Satellites later also observed whistler-mode waves exhibiting various frequency-time patterns in spectrograms, including chorus and hiss. Satellite missions have also detected them on the Moon, other planets, and solar wind. These waves can exchange energies with electrons and cause electrons to precipitate into Earth’s upper atmosphere, playing a crucial role in space weather. This presentation will provide observational and audio examples, along with fundamental theory. We will also discuss our ongoing research on these waves observed by the ARTEMIS mission in lunar orbit.

Venue: NTNU Gongguan campus Conference Center 2F Meeting Room (師大公館校區 綜合館二樓交誼廳)

Stars are formed within molecular clouds, and the star formation processes in galaxies are greatly impacted by the environments at the galactic and large scales. Recent surveys that combine Integral Field Spectroscopy with millimeter observations offer excellent chances to examine the relationship between gas and star formation in galaxies at scales of (sub)kpc, effectively connecting the physics across different scales. During this presentation, I will introduce the ALMaQUEST survey, which I have been leading to investigate the role of molecular gas in star formation. Furthermore, I will also discuss the current understanding of the process of star formation suppression in galaxies.

https://www.asiaa.sinica.edu.tw/people/cv_c.php?i=lihwailin

(Tuesday)14:20(special time) Venue: NTNU Gongguan campus S102

As far as we know, our Earth and Solar System are unique. It could, in principle, be the only planetary system in the Universe to harbour intelligent life or even life at all. As such, attempting to reconstruct its history is one of the most fundamental pursuits in the natural sciences. Whereas astronomical observations and space missions provide a general framework for understanding the planet surfaces, more comprehensive information about the deep planets and deep time comes from the analyses of meteorites and space mission (e.g., Apollo, Hayabusa, and Chang’E missions) returning samples. These precious rocks come directly from solar system bodies such as the Moon, Mars and other asteroids, and carry important information about their formation and accretion histories. This talk focuses on using high-precision chromium isotope measurements to understand the 1 Earth differentiation time (very early), 2 the oldest volcanism in the solar system (predating the formation of Earth), and 3 the origin of water on early Mars (a blue Mars).

In recent years, the realm of space exploration has expanded significantly, garnering increased attention and utilization. The advent of companies like SpaceX, led by visionary Elon Musk, has propelled the popularity of applications such as low earth orbit (LEO) satellites. Taiwan, too, has embraced the Space Era, embarking on a journey of space science and industry development since 1991. Beginning from the ground up, Taiwan has progressed through two phases of indigenous space technology programs, laying the foundation for its current endeavors. As the Taiwan Space Agency (TASA) advances into its third phase, exciting developments are underway. Having joined TASA in 2023, I aim to provide a concise overview of TASA’s achievements and its aspirations to keep pace with global counterparts in the Space Era. Additionally, I will introduce fundamental concepts utilized by scientific payloads, such as GNSS-RO and GNSS-R, which measure atmospheric and sea level properties. Moreover, numerous universities possess the capabilities to plan, manufacture, and operate cubic satellites, further enriching Taiwan’s space endeavors. Through this presentation, we will delve into Taiwan’s historical and contemporary space missions, inviting you to embark on an engaging journey into space exploration.

[PHY colloquium]

Fast radio bursts (FRBs) are energetic millisecond transients of extragalactic origin, whose nature and emission mechanism remain mysteries. Despite >1000 FRBs having been detected, only a few dozens of them have host galaxies localized. Therefore, a radio telescope with wide field of view (FoV) and high angular resolution are required for accumulating the statistics and pinpoint host galaxies of FRBs. The BURSTT telescope are phased antenna arrays designed for the purpose, with multiple stations observing in the 300-800 MHz band, under construction in Taiwan, outlying islands and partner sites. After completion in 2024, BURSTT will have ~10,000 deg^2 instantaneous FoV with an event rate of ~1 FRB per day, and 1″ angular resolution. The wide FoV maximizes the chance of multi-wavelength/muti-messenger counterpart. BURSTT will help to understand the physics of FRBs, and clarify their application as cosmological probe.

[ES colloquium]

The Outer Planet Atmospheres Legacy (OPAL) program with Hubble was started in 2014 with the goal of studying time-domain phenomena in Jupiter, Uranus, and Neptune, with Saturn added in 2018 once the Cassini spacecraft was de-orbited. Once a year, the OPAL program images each of our four outer planets, producing pairs of global maps in multiple filters, which are made available at the MAST archive. The OPAL team (Simon, Wong, and Orton) have used the data to discover new dark spots on Neptune, discover a UV-dark oval in Jupiter’s southern polar haze cap, measure changes in Jupiter’s Great Red Spot over time, detect fine-scale waves, chronicle shifts in haze and cloud layers on all four planets, measure jet streams, and study the structure and evolution of convective storms. The data have also provided a valuable resource enhancing the science return from the Juno and New Horizons spacecraft missions, also supplementing observations from a growing list of observatories including JWST, Kepler, Spitzer, VLA, Keck, ALMA, IRTF, VLT, and Gemini.

Wong et al. (2022) https://doi.org/10.1016/j.icarus.2022.115123
Simon et al. (2022) https://doi.org/10.3390/rs14061518
Wong et al. (2021) https://doi.org/10.1029/2021GL093982

[ES colloquium]