Despite its potential importance in the global climate system, mixing properties of the North Pacific low‐latitude western boundary current system (LLWBC) remained unsampled until very recently. We report here on the first measurements of turbulence microstructure associated with these currents, made in the western boundary region of the tropical North Pacific east of the Philippines. The results suggest that thermocline mixing in the North Pacific LLWBC is generally weak with the diapycnal diffusivity κρ∼O(10−6) m2 s−1. This is consistent with predictions from internal wave‐wave interaction theory that mixing due to internal wave breaking is significantly reduced at low latitudes. Enhanced mixing is found to be associated with a permanent cyclonic eddy, the Mindanao Eddy, but mainly at its south and north flanks. There, κρ is elevated by an order of magnitude due to eddy‐induced geostrophic shear. Mixing in the eddy core is at the background level with no indication of enhancement.

A comprehensive investigation using the air quality network and meteorological data of China in 2015 showed that PM2.5 driven by cold surges from the ground level could travel up to 2000 km from northern to southern China within two days. Air pollution is more severe and prominent during the winter in north China due to seasonal variations in energy usage, trade wind movements, and industrial emissions. In February 2015, two cold surges traveling from north China caused a temporary increase in the concentration of PM2.5 in Shanghai. Subsequently, the concentration of PM2.5 in Xiamen increased to a high of 80 µg/m3 , which is double the average PM2.5 concentration in Xiamen during the winter. This finding is a new long-range transport mechanism comparing to the well-established mechanism, with long-range transport more likely to occur in the upper troposphere than at lower levels. These observations were validated by results from the back trajectory analysis and the RAMS- CMAQ model. While wind speed was found to be a major facilitator in transporting PM2.5 from Beijing to Xiamen, more investigation is required to understand the complex relationship between wind speed and PM2.5 and how it moderates air quality in Beijing, Shanghai, and Xiamen.

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Internal solitary wave (ISW) reflection is rarely observed in satellite images, even in the South China Sea (SCS), where the strongest and most energetic ISWs in the world have been observed. Compared to the large number of satellite images showing shoaling ISW in the SCS, fewer than 10 satellite images have been reported showing ISW reflection. In this study, we collect recent satellite images and implement a numerical model to analyze ISW reflection near Dongsha Atoll, in the SCS. Satellite observations show that the reflection appears to be associated with the large‐amplitude ISWs generated by strong tidal currents in Luzon Strait. Numerical simulations show that ISWs break when reaching the sloping bottom. Part of ISW energy is reflected by mode‐1 waves and their trailing mode‐2 waves. The mode‐1 waves have two types: long inertia‐gravity waves and breaking ISW‐induced short waves. They propagate quickly but induce weak vertical velocity and surface imprints. Mode‐2 waves induce strong vertical velocity, showing visible signature in satellites. Horizontal distribution of the energy indicates that a maximum energy of about 2% of the incident energy is contained in a single reflected wave. This could explain why the reflected waves are rarely observed, because reflected waves must be sufficiently large to be detected in satellite images. Although individual wave's energy is small, in total up to 20% of the incident wave is reflected by the groups of mode‐1 and mode‐2 waves. This suggests that ISW reflection has a significant impact on energy distribution over the continental slopes.