Description: The inner core boundary (ICB), where melting and solidification of the core occur, plays a crucial role in the dynamics of the Earth's interior. To probe temporal changes near the ICB beneath the eastern hemisphere, I analyze differential times of PKiKP (dt(PKiKP)), double differential times of PKiKP‐PKPdf, and PKiKP coda waves from repeating earthquakes in the southwest Pacific subduction zones. dt(PKiKP) values are mostly within ±30 ms of one another, without systematic temporal dependence. Some observations of PKiKP coda waves have absolute time shifts of 〉50 ms relative to their main phases. The combination of temporal changes in PKiKP coda arrivals and negligible changes in PKiKP arrivals favors a smooth ICB with fine‐scale structures in the upper inner core. dt(PKiKP) values are interpreted in the context of melting‐ or growth‐induced ICB topography, based on dynamic models. Uncertainties in dt(PKiKP) prevent verification of ICB melting or growth on decadal time scales.

Description: This study examines time-dependent inner core structures using waveforms and double differential times of the PKP(bc–df) and PKP(ab–df) phases measured from repeating earthquakes in the southwest Pacific subduction zones. Repeating earthquakes can eliminate potential artefacts of interevent distance and improve the measurement precision of temporal changes in PKPdf phases due to differential rotation of the Earth's inner core. PKPdf waves from the southwest Pacific primarily sample the eastern hemisphere of the inner core along equatorial paths. Time separation of repeating earthquakes ranges from 4 to 14.4 yr. Most observed double differential times of PKP(bc–df) and PKP(ab–df) are within ±70 ms, with no systematic changes as a function of time separation or calendar time. Null temporal changes of the PKPdf wave could indicate a smooth regional-scale lateral velocity gradient in the eastern hemisphere of the inner core. Uncertainties in the data prohibit statistically meaningful estimates of the lateral velocity gradient, temporal trend, inner core differential rotation rate, or decadal oscillations. Synthetic seismograms are used to test the effects of several possible artefacts and to quantify the magnitudes of velocity perturbations relative to previous estimates. These artefacts are quantitatively assessed to determine their expected effects on the measurements.

Description: We report complex seismic anisotropy in the top 80 km of the Earth's inner core beneath Africa. The anisotropy in the top 80 km of the inner core is constrained using differential travel times, amplitude ratios, and waveforms of the PKiKP-PKIKP phases sampling Africa along various directions. The differential PKiKP-PKIKP time residuals (relative to the Preliminary Reference Earth Model [PREM]) along the polar paths are larger than those along the equatorial paths by 0–1.4 s, indicating the presence of seismic anisotropy in the top 80 km of the inner core. Furthermore, the observations along the polar paths show complex regional variations beneath Africa: the differential PKiKP-PKIKP travel time residuals vary from 1.2 s beneath eastern Africa, to −0.1 s beneath central Africa, and to −0.2 to 0.8 s beneath western Africa. A correlation between small PKIKP/PKiKP amplitude ratios and large differential PKiKP-PKIKP travel time residuals is observed. The waveform data are spatially binned into six groups to constrain the regional dependence of velocity and attenuation anisotropy in the top 80 km of the inner core. Overall, the seismic data can be explained by an isotropic upper inner core (UIC) overlying an anisotropic lower inner core (LIC) in the top 80 km of the inner core across Africa. The thickness of the isotropic UIC varies from 0 to 50 km, and the P velocity transition from the isotropic UIC to the anisotropic LIC is sharp, with velocity increases laterally varying from 1.6% to 2.2%. The attenuation structure along the polar paths has a Q value of 600 for the isotropic UIC and Q values varying from 150 to 400 for the anisotropic LIC. The complex seismic anisotropy in the top of the inner core is found in a region where a rapid change of the inner core boundary (ICB) between 1993 and 2003 was discovered (Wen, 2006) and may be explained by complex alignments of iron crystals, resulting from a localized anomalous solidification of the inner core.

Description: Numerous studies have indicated that the atmospheric heat source (AHS) over the Tibetan Plateau (TP) is highly correlated with the western North Pacific anomalous anticyclone (WNPAC) in summer. However, such an interannual relationship has been weakened since the late 1990s. The present work shows that the TP AHS was significantly and positively correlated with the WNPAC in 1979–1999 (P1), while this relationship became insignificant hereafter (2000–2020; P2). We identify that the long-term change in the upper-level atmospheric circulation over the TP is responsible for weakening the relationship. An obvious upper-level anticyclonic trend occurred over the northeastern TP in the past four decades, with an easterly trend on the anticyclone’s southern flank, representing anomalous westerlies during P1 but anomalous easterlies during P2 over the main portion of the TP. With the anomalous upper-level westerlies in P1, the abnormal high pressure induced by the TP heating (i.e. AHS) extended downstream in the upper troposphere. Subsequently, anomalous descending motions formed over the northwestern Pacific due to the eastward-extended high pressure, together with the vertical transport of negative relative vorticity, favorable for the enhancement of the WNPAC. Whereas in P2, the TP heating-induced abnormal high pressure was confined over the southern TP due to the anomalous easterlies, suppressing its downstream influence and finally breaking the connection between the TP AHS and the WNPAC. Modeling results from both LBM sensitivity experiments and CESM large ensemble dataset further confirm the important role of the change in background circulation in weakening the relationship.

Description: An extreme drought occurred over Southeast China (SEC) in August 2019. We demonstrate synergistic effects of mid-latitude and tropical circulation on this extreme event and highlight the impacts of the coupling and locking of two cyclones at different latitudes, which are otherwise ignored. We propose the relaying roles of the Tibetan Plateau (TP) and western North Pacific in connection with the tropical convection and SEC precipitation. The equivalent-barotropic anticyclone over the TP and low-tropospheric cyclone over the western North Pacific both resulted from the positive Indian Ocean dipole and El Niño Modoki. The equivalent-barotropic cyclone over Northeast China originated from the dispersion of Rossby waves upstream along the subtropical waveguide associated with the North Atlantic tripole sea surface temperature anomaly pattern and the Rossby wave response to the TP precipitation deficiency. Further, they jointly contributed to this drought by inducing strong northerly wind anomalies in the entire troposphere over East China. These anomalous northerly winds led to decreased warm moisture from the south and substantial sinking motions, which inhibited the occurrence of the SEC local convection and precipitation. The SEC precipitation is closely related to convection over the Maritime Continent from a climate perspective. This relationship is verified by observations, linear baroclinic model experiments, and general circulation model sensitivity experiments with and without the TP, in which precipitation anomalies over the southern TP and Philippine Sea play important bridge roles. The results will advance the prediction of the SEC extreme drought events.

Description: The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on NASA’s TIMED (Thermosphere Ionosphere Mesosphere Energetics Dynamics) satellite measure vertical profiles of kinetic temperature, pressure, geopotential height and volume mixing ratios of minor species such as CO2, H2O (two important greenhouse gases) since January 2001. With its two-solar-cycle record, we can quantify the long term changes of global temperature, CO2, and H2O and distinguish their solar cycle variations. In this talk, we will review the SABER measured linear trends of temperature, CO2 and H2O. Global temperature in the stratosphere and mesosphere has been cooling due to anthropogenic greenhouse gas, i.e., CO2. CO2 and H2O have also been observed to increase due to anthropogenic CO2 and CH4 emission and warming tropopause. Meanwhile, we will discuss the lessons we learnt while calculating the trends from SABER.

Description: Super typhoons (SuperTYs) generated in the Northwest Pacific (WNP) constantly undergo a sharp weakening after crossing the Philippines-Taiwan into the South China Sea (SCS), thus acting as a natural “buffer” to protect the south-eastern coast of China from severe typhoons due to the blockage of the mountains and the unique atmospheric and oceanic environmental fields. This study examines the determinants of this buffer zone and speculates on the response of this part of the SuperTYs in future climate change. Here, we show that the strong vertical wind shear accompanying the South China Sea summer monsoon is a determining factor in the weakening of SuperTYs into the buffer zone, with a linear correlation up to 0.71. Although most studies suggest that the risk of severe typhoons will increase with global warming, our diagnosis of the latest Sixth Coupled Model Intercomparison Project (CMIP6) multi-model ensemble shows that the decisive factor, vertical wind shear, will not change in trend even in the worst scenario. Therefore, the risk of a severe typhoon making landfall off the southeast coast of China is not getting any worse in future global warming.

Description: Understanding the evolution of Coronal Mass Rejections is a challenging endeavor. Imagers provide snapshots of the eruptions, in-situ instruments provide a one-dimensional time series during encounters, theories are not up to date with current observations, and there is a lack of dedicated missions providing multi-spacecraft measurements. All of these factors are severely impacting our understanding of the ever-changing dynamics of CMEs during evolution. However, a wealth of valuable data exist and novel techniques to extract information are always needed. In this work, we discuss different approaches to making the most of the available data, through data analysis techniques, improving fitting techniques, and utilizing different spacecraft configurations. We also present recommendation on the needed measurements to adequately study and probe the structure and evolution of CMEs.