Patterns of variation in plant and animal diversity along precipitation gradients have been extensively studied, but much less is known about how and to what extent precipitation affects the biogeographic distribution of microbial diversity in arid areas across large spatial scales. Here we collected soils from 54 sites along a 3700 km transect covering a wide range of grassland ecosystems with distinct aridity gradients. We quantified the bacterial community diversity and the effects of climate, edaphic parameter and geographic distance on the bacterial community structure using high-throughput 16S rRNA gene sequencing. Of the 35 phyla detected, 6 were dominant: Actinobacteria, Acidobacteria, Alphaproteobacteria, Deltaproteobacteria, Bacteroidetes and Planctomycetes. Aridity was a major factor influencing bacterial diversity, community composition and taxon abundance. Although the pattern of bacterial species richness is markedly different from that of plant species richness, most soil bacteria were endemic to particular bioregions like macro-organisms. Community similarity significantly declined with environmental distance and geographic distance (r = -0.579 and -0.773, respectively). Geographic distance (historical contingencies) contributed more to bacterial community variation (36.02%) than combined environmental factors (24.06%). Overall, our results showed that geographic distance and climatic factors concurrently govern bacterial biogeographic patterns in arid and semi-arid grassland.

Previous studies reported that the summer western Pacific subtropical high (WPSH) has extended westward since the late 1970s and the change has affected summer rainfall over China and tropical cyclone prevailing tracks in the western North Pacific. The authors show that the 500-hPa geopotential height in the midlatitudes of the Northern Hemisphere has trended upward in the warming climate and the westward extension of the WPSH quantified with the 500-hPa geopotential height is mainly a manifestation of the global rising trend. That is, the summer 500-hPa WPSH has not remarkably extended westward since the late 1970s when the global trend is removed. It is suggested that the index that indicates the west–east shift of the summer 500-hPa WPSH should be redefined and that further investigation is needed to understand the observed climate change in the summer rainfall over China and tropical cyclone prevailing tracks in the western North Pacific.

The east-west migration of the tropical upper-tropospheric trough (TUTT) on the interannual time scale and its influence on tropical cyclone (TC) formation over the western North Pacific (WNP) is investigated in this study. Climatologically, the TUTT can be identified from 100 to 400 hPa with a relative vorticity maximum between 150 and 200 hPa. In addition to the strong westerly vertical wind shear in the south flank of the TUTT, this study shows that the cold-core system is associated with low relative humidity and subsidence to the east of the trough axis. As a result, the TC formation is enhanced (suppressed) in the eastern portion of the WNP when the TUTT shifts eastward (westward) on the interannual time scale. The interannual TUTT shift is closely associated with the SST anomalies in the central and eastern tropical Pacific or ENSO phases. The warm (cold) phase of ENSO corresponds to the eastward (westward) shift of the TUTT. The physical factors found to be responsible for the influence of ENSO on TC formation can be associated with the east-west shift of the TUTT. It is shown that the interannual variations of TC formation in the eastern part of the WNP basin are closely associated with the east-west shift of the TUTT due to the associated environmental conditions that are generally not favorable for TC formation.

The WNP tropical cyclone (TC) activity peaks in July-August-September, accounting for about 60% of the annual TC count (Chan, 2005;Lander, 1994). TCs in this study are defined as those in the data sets with maximum wind speed exceeding the tropical storm intensity (17.2 m s −1 or 34 knots). Climatologically, about four TCs form in July and it usually takes a northward-recurved track and exerts great impacts on subtropical East Asia. However, no TC formation in July 2020 over the WNP was recorded in July 2020 (Figure 1a), which is the first time in the available historical records since 1945. The unprecedented absence of TC formation suggests its possible unique driving factors.It is well known that El Niño-Southern Oscillation (ENSO) is an important factor modulating TC activity over the WNP (Chan, 1985;Lander, 1994;Wang & Chan, 2002). During the El Niño decaying summer, an anomalous anticyclonic circulation is a recurrent pattern in the WNP, which acts to suppress TC genesis over the WNP (