Significant progress has been made in seasonal climate predictions based on general circulation models (GCMs). However, seasonal prediction of local heavy rain remains challenging due to limited ...resolution. A small signal‐to‐noise ratio also prevents meaningful predictions. In this study, 100‐member large‐ensemble sets of GCM simulations and high‐resolution downscaled products with a regional climate model were used to identify the unknown source of seasonal predictability for the risk of local heavy rainfall around Japan and Taiwan. The detected predictable signals depended on the location and the season. Highly predictable signals were found for events caused by typhoons and the stationary front. Further analyses of the large‐scale backgrounds simulated by the parent‐GCM revealed that each source of predictability comes from various flavors of El Niño/Southern Oscillation and anomalies in the Indian Ocean. The approach of this study potentially provides an opportunity to identify unknown predictable regional signals all over the world.
Plain Language Summary
Recently, significant progress has been made in seasonal‐scale climate predictions (forecasts of up to months) based on a global climate model. However, the spatial resolution of a commonly used global climate model is insufficient for simulating local heavy rainfall events. In addition, there are insufficient samples for analysis because of the rare occurrence of extreme events. Therefore, the seasonal prediction of local heavy rainfall remains challenging. In this study, we resolved these shortcomings by increasing the number of samples through repeated numerical simulations using a high‐resolution climate model, and examined whether this could improve predictions. Our analysis covers the regions of Japan, the Korean Peninsula, and Taiwan. We found that heavy rainfall frequency is highly predictable in Taiwan during the typhoon season and in western Japan during the rainy season. This is because each heavy rainfall event is strongly linked to different sea surface temperature anomalies in tropical oceans that can be predicted with high accuracy using a global climate model. Various phases of El Niño and La Niña and the related Indian Ocean fluctuations are the primary drivers of heavy rainfall in each region. Our approach potentially provides an opportunity to identify unknown predictable regional signals worldwide.
Key Points
This study employs high‐resolution large‐ensemble simulations to overcome shortcomings of seasonal prediction of heavy rain events
Large‐ensemble simulations with 20‐km grid spacing are essential to obtain high predictability of heavy rain frequency in Taiwan and Japan
The sources of the predictability come from sea surface temperature anomalies in the tropical Pacific and Indian Oceans
Portions of East Asia often experienced extremely heavy rainfall events over the last decade. Intense atmospheric rivers (ARs), eddy transports of moisture over the middle latitudes, contributed ...significantly to these events. Although previous studies pointed out that landfalling ARs will become more frequent under global warming, the extent to which ARs produce extreme rainfall over East Asia in a warmer climate remains unclear. Here we evaluate changes in the frequency and intensity of AR‐related extreme heavy rainfall under global warming using a set of high‐resolution global and regional atmospheric simulations. We find that both the AR‐related water vapor transport and rainfall intensify over the southern and western slopes of mountains over East Asia in a warmer climate. ARs are responsible for a large fraction of the increase in the occurrence of extreme rainfall in boreal spring and summer. ARs will bring unprecedented extreme rainfall over East Asia under global warming.
Plain Language Summary
In July 2018 and July 2020, East Asia suffered from extremely heavy rainfall events. The heavy rainfall was observed over a broad area because of organized water vapor flow associated with atmospheric rivers (ARs). ARs received increasing attention over the past decade because of such hazardous events. Under global warming, water vapor transports by ARs are enhanced. Using a set of global and regional atmospheric model simulations, we assessed the great role of ARs in the future extreme rainfall events. ARs with increased water vapor will bring record‐breaking extreme rainfall when they make landfall over China, the Korean Peninsula and Japan. Such a great importance of ARs may also be found over other mid‐latitude regions, including western North America and Europe.
Key Points
Atmospheric rivers bring extreme rainfall over East Asia in current and future climates
Atmospheric rivers are responsible for a large fraction of the increase in extreme rainfall over East Asia under global warming
Intensified water vapor transports by atmospheric rivers cause record‐breaking extreme rainfall events in a warmer climate
An earth system model (MIROC-ESM 2010) is fully described in terms of each model component and their interactions. Results for the CMIP5 (Coupled Model Inter-comparison Project phase 5) historical ...simulation are presented to demonstrate the model's performance from several perspectives: atmosphere, ocean, sea-ice, land-surface, ocean and terrestrial biogeochemistry, and atmospheric chemistry and aerosols. An atmospheric chemistry coupled version of MIROC-ESM (MIROC-ESM-CHEM 2010) reasonably reproduces transient variations in surface air temperatures for the period 1850-2005, as well as the present-day climatology for the zonal-mean zonal winds and temperatures from the surface to the mesosphere. The historical evolution and global distribution of column ozone and the amount of tropospheric aerosols are reasonably simulated in the model based on the Representative Concentration Pathways' (RCP) historical emissions of these precursors. The simulated distributions of the terrestrial and marine biogeochemistry parameters agree with recent observations, which is encouraging to use the model for future global change projections.
We report laser operation of two Tb
-activated gain media, Tb:LiYF
and LiTbF
, in yellow or/and green spectral region. A record-high slope efficiency of 63% among Tb
-lasers and maximum output power ...of 1.17 W (incident power of 2.79 W) at around 544 nm were obtained with a c-cut 15%Tb:LiYF
crystal. The yellow laser characteristics in σ-polarization were studied. A slope efficiency of 21% at 582 nm was achieved. More importantly, we succeeded in laser operation of LiTbF
for the first time to the best of our knowledge. Laser oscillation at around 544 nm yielded a maximum slope efficiency of 45%. This points toward the possibility of producing high-energy pulsed lasers using LiTbF
, which features a high active-ion concentration as well as relatively long lifetime.
The single-station microtremor horizontal-to-vertical spectral ratio (MHVSR) method was initially proposed to retrieve the site amplification function and its resonance frequencies produced by ...unconsolidated sediments overlying high-velocity bedrock. Presently, MHVSR measurements are predominantly conducted to obtain an estimate of the fundamental site frequency at sites where a strong subsurface impedance contrast exists. Of the earthquake site characterization methods presented in this special issue, the MHVSR method is the furthest behind in terms of consensus towards standardized guidelines and commercial use. The greatest challenges to an international standardization of MHVSR acquisition and analysis are (1) the
what
— the underlying composition of the microtremor wavefield is site-dependent, and thus, the appropriate theoretical (forward) model for inversion is still debated; and (2) the
how
— many factors and options are involved in the data acquisition, processing, and interpretation stages. This paper reviews briefly a historical development of the MHVSR technique and the physical basis of an MHVSR (the
what
). We then summarize recommendations for MHVSR acquisition and analysis (the
how
). Specific sections address MHVSR interpretation and uncertainty assessment.
The effect of the helically-trapped energetic-ion-driven resistive interchange modes (EICs) on energetic ion confinement is studied in the Large Helical Device deuterium plasmas. Neutron diagnostics ...such as the neutron flux monitor and the vertical neutron camera (VNC) are used in order to measure neutrons mainly created by beam-plasma reactions. The line-integrated neutron profiles are obtained by VNC in magnetohydrodynamic-quiet plasma with various neutral beam (NB) injection patterns. The profiles are consistent with that expected by the beam ion density calculated using orbit-following simulations. Significant decreases of the total neutron emission rate (Sn) and the neutron counting rate of the VNC (Cn) in central cords are observed to be synchronized with EIC bursts with perpendicular-NB injection. The drop rates of both Sn and Cn increase with EIC amplitude and reach around 50%. The line-integrated neutron profiles before and after EIC burst show that in the central cords, Cn decrease due to EIC burst whereas there is almost no change in the other cords. The experimental results suggests that the effect of EIC on helically-trapped beam ion is substantial, however the effect of passing beam ion is not significant.
Strong cold air outbreaks caused heavy snowfall over the inland areas of the Sea of Japan coast of Japan in mid‐December 2020. The 48‐hr accumulated snowfall during the term broke a snowfall record ...at some observational stations of the Japan Meteorological Agency (JMA). We investigated the impacts of atmospheric and oceanic temperature changes due to historical global warming since the pre‐industrial period on this heavy snowfall event. Hindcast and pseudo non‐warming experiments were conducted using the nonhydrostatic model developed by the JMA. The historical climatic differences were obtained from the database for policy decision‐making for future climate change (d4PDF). Our experiments indicated that historical global warming enhanced precipitation over the whole region and enhanced heavy snowfall over the inland areas on the Sea of Japan side. In this event, the contribution of conversion from snowfall to rainfall due to warming was limited over coastal areas. The enhancement of precipitation was mainly caused by oceanic warming, which increased latent heat flux over the Sea of Japan and made the low‐level atmosphere less stable. Historical atmospheric warming suppressed precipitation due to atmospheric stabilization. Our results indicated that the heavy snowfall was caused by the cold air outbreaks under the warm sea surface temperatures in December and enhanced by historical global warming.
Plain Language Summary
Heavy snowfall occurs over the inland areas of the Sea of Japan coast in mid‐December 2020. The 48‐hr accumulated snowfall broke a snowfall record at some observational stations. The numerical simulations indicate that historical global warming since the pre‐industrial period enhanced the heavy snowfall over the inland areas on the Sea of Japan side. The oceanic warming is more important for the enhancement of snowfall than atmospheric warming only, because oceanic warming supplies more moisture to the atmosphere and makes the low‐level atmosphere less stable. Since the sea surface temperature in December is warmer than that in other month in winter, it widely enhances snowfall over the inland areas along the Sea of Japan.
Key Points
Historical global warming enhanced heavy snowfall occurring over inland areas along the Sea of Japan in central Japan in mid‐December 2020
Sensitivity experiments indicate that warming of the Sea of Japan mainly contributed to the enhancement of heavy snowfall
Oceanic warming supplies more moisture to the atmosphere and makes the low‐level atmosphere less stable, which enhances precipitation
Results of comprehensive long‐term simulations of surface all‐sky and clear‐sky ultraviolet (UV) radiation through 1960–2100 are presented. A new earth system model, MIROC‐ESM‐CHEM, is used for the ...simulation, which considers key processes that change the surface UV radiation: atmospheric dynamics and chemistry affecting ozone in the stratosphere and troposphere, aerosols and clouds in the troposphere, and changes in surface albedo with sea ice and snow cover. In contrast to previous assessments considering only the effect of long‐term change in stratospheric ozone, the simulated long‐term behavior of UV radiation in this study is strongly affected by other processes. In one of two simulations, all‐sky UV radiation in the northern midlatitudes is projected to increase in the 21st century despite the expected recovery of the stratospheric ozone layer. Reductions in aerosols and clouds are expected to overcompensate for the effect of ozone recovery. The results are sensitive to the future socioeconomic scenario, describing GHG concentrations and emissions of aerosol and ozone precursors in the troposphere. The interannual variability of UV radiation associated with the 11 year solar cycle and local processes is also discussed.
Key Points
Future all‐sky UV‐B radiation at the Earth's surface is projected by an ESM
The UV‐B is dramatically affected by the future socioeconomic scenarios
Tropospheric/stratospheric ozone, aerosols, clouds, and albedo affect the result
A deuterium experiment was initiated to achieve higher-temperature and higher-density plasmas in March 2017 in the Large Helical Device (LHD). The central ion temperature notably increases compared ...with that in hydrogen experiments. However, an energetic particle mode called the helically-trapped energetic-ion-driven resistive interchange (EIC) mode is often excited by intensive perpendicular neutral beam injections on high ion-temperature discharges. The mode leads to significant decrease of the ion temperature or to limiting the sustainment of the high ion-temperature state. To understand the effect of EIC on the energetic ion confinement, the radial transport of energetic ions is studied by means of the neutron flux monitor and vertical neutron camera newly installed on the LHD. Decreases of the line-integrated neutron profile in core channels show that helically-trapped energetic ions are lost from the plasma.
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