Showing papers by "Lou-Chuang Lee published in 2020"

Earth’s Outgoing Longwave Radiation Variability Prior to M ≥6.0 Earthquakes in the Taiwan Area During 2009–2019

Abstract: This paper proposes an analysis method, using the National Oceanic and Atmospheric Administration satellite data, to trace variations in outgoing longwave radiation (OLR) for finding the precursors of earthquakes. The significance of these observations is investigated using data sets of recent M ≥ 6.0 earthquakes around the Taiwan area from 2009 to 2019. We suggest that the precursory signal could be an EIndex anomaly (EA) in the form of substantial thermal releases distributed near the epicenter. The consecutive appearances of OLR EAs are observed as precursors two to fifteen days before significant earthquakes, and we refer to this as a pre-earthquake OLR EIndex anomaly (POEA). We interpret these thermal sources as possibly originating from electromagnetics together with gas emissions associated with pre-seismic processes. This study highlights the potential of OLR anomalous changes in earthquake precursor studies, at least in the Taiwan region.

Fluid and kinetic aspects of magnetic reconnection and some related magnetospheric phenomena

Abstract: Magnetic field reconnection plays a key role in determining the magnetic field topology and in the conversion of magnetic energy into kinetic energy in cosmic plasmas. Magnetic reconnection was proposed by solar physicists in an attempt to explain solar flares. The concept of magnetic reconnection was extended to Earth’s magnetosphere to explain auroral substorms. In this review, we first briefly review the classical fluid steady models with small separatrix angle. We then report magnetic reconnection with a large separatrix angle, and the time-dependent multiple X line reconnection (MXR) associated with flux transfer events. The transition from a single X line reconnection to MXR is examined. Global three-dimensional (3-D) magnetic reconnection is reviewed. The particle pressure gradient associated mainly with the electron (ion) off-diagonal pressure tensor terms, $$P_{xy}$$ and $$P_{zy}$$ , is shown to play an important role for electron (ion) dynamics to balance the reconnection electric field ( $$E_{y}$$ ) near the X line. In addition, various plasma waves and instabilities may occur near the ion diffusion and electron diffusion regions, including the upper hybrid drift waves, lower hybrid drift waves, ion-ion beam instability, electron beam instability, whistler waves and kinetic Alfven waves. The layered structure of outflow region of magnetic reconnection is examined. These layered structures include slow shocks, rotation discontinuities, expansion waves and plasma jets. Recent satellite observations of magnetic reconnection in the Earth and planetary magnetospheres are also discussed. The polar cap electric field associated with magnetic reconnection at the Earth's magnetopause and the energy flow in the polar cap region are examined.

Plasma and magnetic-field structures near the Martian induced magnetosphere boundary - I. Plasma depletion region and tangential discontinuity

Abstract: The interaction between the solar wind and the Martian induced magnetosphere can lead to the formation of various regions with different plasma and magnetic-field characteristics. In this paper, these structures are investigated based on the plasma and magnetic-field measurements from Mars Atmosphere and Volatile EvolutioN (MAVEN). We find that the structures upstream of Mars are similar to those around Earth: both have a bow shock, magnetosheath, magnetopause, and a magnetosphere or induced magnetosphere. The inner part of Martian magnetosheath is called a plasma depletion region (PDR), similar to the plasma depletion layer upstream of the Earth’s magnetopause, in which the magnetosheath magnetic fields are piled up and the magnetosheath plasmas (including ions and electrons) are partially depleted. Several cases of PDRs are examined in detail. The hotter plasmas in PDRs are squeezed out along the enhanced magnetic field, resulting in the decrease of the plasma beta, the plasma density, and the ion temperature. The boundary between the magnetosheath and the induced magnetosphere is called the magnetopause, which can be identified as a magnetohydrodynamic discontinuity, either tangential discontinuity (TD) or rotational discontinuity, where the magnetic field changes its orientation. Tangential discontinuities with an insignificant normal component (B N ≈ 0) of the magnetic field are the focus of this study. This discontinuity separates the magnetosheath H+ ions from the heavy ions (e.g. O+ , O ) in the induced magnetosphere. Inside a TD, ions from both sides are mixed. There are 3332 boundary crossings by MAVEN in 2015, 1075 cases of which are identified as the TD (including the potential TD). Tangential discontinuities at Mars are at higher locations in the southern hemisphere and have an average thickness of ~200 km, mostly ranging from 50 to 400 km. The sample of TD is a decreasing function of θ (θ is the magnetic field rotation angle on the two sides of the TD). The PDRs in front of TDs are thicker in the northern hemisphere. From the sub-solar point to the Mars tail, PDR thickness increases and the proton number density and temperature decrease.

Multiple X-line Reconnection Observed in Mercury’s Magnetotail Driven by an Interplanetary Coronal Mass Ejection

Abstract: How magnetic reconnection drives Mercury's magnetospheric dynamics under extreme solar wind conditions is not well understood. Here we report MESSENGER observations of an active reconnection event in Mercury's magnetotail driven by an interplanetary coronal mass ejection on 2011 November 23. The primary Hall magnetic field, sequential passage of X-lines with Hall field perturbations, and flux ropes (FRs) provide unambiguous evidence of multiple X-line reconnection in an unstable ion diffusion region. In addition, large FRs consisting of multiple successive small-scale FRs are ejected tailward at quasi-periodic intervals of ~1 minute, which is comparable to the Dungey cycle time. We propose that these large FRs are generated by the interaction and coalescence of multiple ion-scale FRs. This is distinct from the commonly accepted Earth-like substorm process where plasmoids are created by widely separated X-lines in the magnetotail. These observations suggest that during extreme solar wind conditions multiple X-line reconnection may dominate the tail reconnection process and control the global dynamics of Mercury's magnetosphere.

Effects of Electron Temperature Anisotropy on Proton-beam Instability in the Solar Wind

Abstract: Effects of electron temperature anisotropy on proton beam instability in the solar wind L. Xiang, K. H. Lee, D. J. Wu, and L. C. Lee 1 School of Physics and Electronics, Hunan Normal University, Changsha, China 2 Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan 3 Purple Mountain Observatory, CAS, Nanjing, China 4 Space Science Institute, Macau University of Science and Technology, Macau, China e-mail (speaker): xiangliang@hunnu.edu.cn