We present a full‐waveform tomographic model of the crust and upper mantle beneath the Japanese Islands region. This is based on the combination of GPU‐accelerated spectral‐element wavefield simulations, adjoint techniques, and nonlinear optimization. Our model explains complete seismic waveforms of events not used in the inversion in the period range from 20 to 80 s. Quantitative resolution analysis indicates that resolution lengths within the well‐covered areas are around 150 km in the horizontal and around 30 km in the vertical directions. In addition to the high‐velocity signatures of known lithospheric slabs in the region, our model reveals a pronounced low‐velocity anomaly beneath the volcanic island of Ulleung in the Sea of Japan, reaching −19% around 100 km depth. The Ulleung anomaly originates at or above the Pacific slab, rises vertically upward to the base of the Philippine Sea slab at ∼200 km depth, circumvents it in NW direction, and then significantly strengthens in the uppermost mantle above the Philippine Sea slab. Among the numerous hypotheses for the generation of low‐velocity anomalies in subduction systems, those invoking instabilities before or when a slab enters the transition zone seem most likely. The age and fast subduction of the Pacific slab may facilitate the transport of fluids into the transition zone. This may promote the reduction in viscosity and the onset of convective upwelling, aided by ambient mantle flow, such as return flow within the mantle wedge.

Occurrences of concurrent extreme atmospheric hazards represent a significant area of uncertainty for organizations involved in disaster mitigation and risk management. Understanding risks posed by natural disasters and their relationship with global climate drivers is crucial in preparing for extreme events. In this review we quantify the strength of the physical mechanisms linking hazards and atmosphere‐ocean processes. We demonstrate how research from the science community may be used to support disaster risk reduction and global sustainable development efforts. We examine peer‐reviewed literature connecting 16 regions affected by extreme atmospheric hazards and eight key global drivers of weather and climate. We summarize current understanding of multihazard disaster risk in each of these regions and identify aspects of the global climate system that require further investigation to strengthen our resilience in these areas. We show that some drivers can increase the risk of concurrent hazards across different regions. Organizations that support disaster risk reduction, or underwrite exposure, in multiple regions may have a heightened risk of facing multihazard losses. We find that 15 regional hazards share connections via the El Niño–Southern Oscillation, with the Indian Ocean Dipole, North Atlantic Oscillation, and the Southern Annular Mode being secondary sources of significant regional interconnectivity. From a hazard perspective, rainfall over China shares the most connections with global drivers and has links to both Northern and Southern Hemisphere modes of variability. We use these connections to assess the global likelihood of concurrent hazard occurrence in support of multihazard resilience and disaster risk reduction goals.

Historical anthropogenic aerosol (AA) changes are found to have caused a statistically significant negative Southern Annular Mode (SAM) trend (associated with an equatorward jet shift) in 14 out of 35 individual ensemble members from the fifth Coupled Model Intercomparison Project (CMIP5) since 1860. However, this response is not robust. The significance of the SAM response to aerosol is model dependent and not simply related to aerosol forcing. Multiple sources of uncertainty result in a nonrobust response that means that the model mechanism connecting remote Northern Hemisphere AA forcing remains unclear. Analysis of single forcing experiments suggests that assuming the climate response to individual model forcings to be linearly additive cannot be made without proper assessment. Our results suggest that AAs may have had a historical influence on the SAM, but its influence may be overstated by assuming linearity.

High resolution simulations at 4.4 km and 1.5 km resolution have been performed for 12 historical tropical cyclones impacting Bangladesh. We use the European Centre for Medium-Range Weather Forecasting 5th generation Re-Analysis (ERA5) to provide a 9-member ensemble of initial and boundary conditions for the regional configuration of the Met Office Unified Model. The simulations are compared to the original ERA5 data and the International Best Track Archive for Climate Stewardship (IBTrACS) tropical cyclone database for wind speed, gust speed and mean sea-level pressure. The 4.4 km simulations show a typical increase in peak gust speed of 41 to 118 knots relative to ERA5, and a deepening of minimum mean sea-level pressure of up to −27 hPa, relative to ERA5 and IBTrACS data. The downscaled simulations compare more favourably with IBTrACS data than the ERA5 data suggesting tropical cyclone hazards in the ERA5 deterministic output may be underestimated. The dataset is freely available from 10.5281/zenodo.3600201.