npj Climate and Atmospheric Science最新文献

The hurricane, with maximum wind speed over 64 kts, is among the most terrible calamities over the northern Atlantic (NATL). Previous studies identified a poleward migration of tropical cyclone (TC) genesis over the Pacific Ocean, but the shift over the NATL is statistically insignificant. The present study detects a robust southward migration in the genesis latitude of NATL TCs that later reach hurricane strength after 1979, which is consistent with a growth in hurricane frequency in the southern part (10°-20°N) of NATL. This increasing trend of hurricane frequency is intimately attributable to the decreasing vertical shear of zonal wind, resulting from a decreasing north-south temperature gradient. The reduced north-south temperature gradient is primarily caused by greater warming trend in tropospheric temperature in the subtropics, driven by intensified static stability. The present research suggests a potential increase in the hazards confronted by low-latitude islands and coastal nations in Northern America.

As a result of the high volume of maritime traffic along the coasts of Namibia and western South Africa, mariners recorded numerous in-situ wind observations since early times. Many of these historical data are currently available through the International Comprehensive Ocean-Atmosphere Data Set (ICOADS). Here, we make use of these historical data to develop an instrumental index for the characterization of the upwelling-favorable winds over the southern Benguela Upwelling System from 1833 to 2014. Our results suggest that upwelling in this region has increased since the mid-1980s, in good agreement with previous research. However, when the entire period is considered, our index does not evidence a long-term trend but a multidecadal variability with an oscillation period between 20 and 30 years. We found a significant influence of ENSO exerted through the modulation of the position of the South Atlantic high-pressure system. However, this teleconnection may be highly non-stationary.

The tropical cyclone (TC) generated orographic precipitation frequently causes severe floods and landslides over coastal and land areas, but its underlying processes remain largely unresolved. This study explored this issue using a high-density rain gauge network and Doppler radar observations to investigate an intense orographic precipitation event over Da-Tun Mountain (DT) in northern Taiwan associated with Typhoon Meari (2011). Detailed examination of observations and the quantification of precipitation enhancement showed that the seeder–feeder mechanism, rather than the widely known upslope lifting mechanism, was a primary contributor to heavy precipitation. Smaller-scale, landfalling convective elements embedded within TC background precipitation and their interactions with DT also influenced the degree of orographic enhancement of precipitation. These rapidly evolving scenarios represent a secondary contributor to the modulation of precipitation intensities. The results from the study provide important insights into the relative importance of the different processes of orographically enhanced precipitation for TCs.

The 2023/24 El Niño, emerging after a rare triple-dip La Niña, garnered global attention due to its potential to evolve into an extreme event, given the largest accumulation of warm water in the equatorial western Pacific since 1980. Despite initial expectations, its growth rate unexpectedly decelerated in mid-2023, preventing it from reaching the anticipated intensity. Here, we show through observational analyses that unusual easterly anomalies over the tropical western-central Pacific, persisting after the end of the preceding La Niña, significantly contributed to this slowdown. A prominent east‒west sea surface temperature gradient in the region has been identified as the crucial factor associated with these unusual and persistent easterly anomalies. This temperature gradient is directly attributed to a negative North Pacific Meridional Mode and a deepened thermocline over the Philippine Sea. These findings offer a deeper understanding of the atypical transition from a prolonged multi-year La Niña to an El Niño.

The Kumalak River, a typical alpine glacierized catchment in the Tianshan region, experiences complex flooding driven by glacier meltwater, snowmelt, and rainfall. However, the mechanisms driving these processes under climate change remain unclear. To address this, a SWAT-Glacier hydrological model and a degree–day factor model were used for snowmelt, glacier meltwater, and rainfall calculations. Two Long Short-Term Memory (LSTM) models (LSTM-SG and LSTM-DDF) were developed using these inputs, and additive decomposition and integrated gradient methods were applied to interpret flood mechanisms. Glacier meltwater was found to dominate annual maximum flood (AMF) events, while snowmelt drove annual spring maximum flood (AMFSp) events. For AMF events (1960–2018), contributions were 10.01–12.21% from snowmelt, 60.49–60.92% from glacier meltwater, and 26.86–29.50% from rainfall. For AMFSp events (1961–2018), contributions were 48.49–56.08% from snowmelt, 16.12–22.08% from glacier meltwater, and 27.79–29.42% from rainfall. These findings provide critical insights for enhancing flood prediction and optimizing water resource management.

The UK Met Office decadal prediction system DePreSys4 shows skill in predicting the number of tropical cyclones (TCs) and TC track density over the eastern Pacific and tropical Atlantic Ocean on the decadal timescale (up to ACC = 0.93 and ACC = 0.83, respectively, as measured by the anomaly correlation coefficient—ACC). The high skill in predicting the number of TCs is related to the simulation of the externally forced response, with internal climate variability also allowing the improvement in prediction skill. The Skill is due to the model’s ability to predict the temporal evolution of surface temperature and vertical wind shear over the eastern Pacific and tropical Atlantic Ocean. We apply a signal-to-noise calibration framework and show that DePreSys4 predicts an increase in the number of TCs over the eastern Pacific and the tropical Atlantic Ocean in the next decade (2023–2030), potentially leading to high economic losses.

Climate warming alters spatial and seasonal patterns of surface water availability (P-E), affecting runoff and terrestrial water storage. However, a comprehensive assessment of these changes across various hydroclimates remains lacking. We develop a multi-model ensemble approach to classify global terrestrial hydroclimate into four distinct regimes based on the mean and seasonality of P-E. P-E is projected to become increasingly variable across space and time. Wet regions with low and high seasonality are likely to experience more concentrated increases in wet-season runoff by up to 20%, highlighting potential increases in flood-related vulnerability. Low-seasonality regions exhibit faster wet-season increases and more rapid dry-season decreases in soil moisture, heightening the likelihood of water scarcity and drought. Conversely, dry regions with high seasonality are less sensitive to climate change. These findings underscore the multifaceted impacts of climate change on global water resources, necessitating the need for tailored adaptation strategies for different hydroclimate regimes.

Ozone is the primary air pollutant in eastern China during the warm season. Clarifying the differences in the spatio–temporal evolution of the ozone formation sensitivity between ozone polluted days and clean air days is key for the precise formulation of ozone prevention policies. By combining ground–and satellite–based remote sensing with ground station observations, we identified large spatio–temporal differences in the ozone formation sensitivity in eastern Chinese cities under different ozone pollution levels. Diurnally, the NO₂ concentration was higher in the morning and lower at noon on the ozone exceedance days. The HCHO concentration was higher throughout the day, and the transition limited regime or NO_x–limited regime contributed more to the ozone formation sensitivity on the ozone exceedance days. Vertically, the ratio of HCHO to NO₂ (FNR) was higher on ozone exceedance days, and the contributions of NO_x–limited regime at 0–2 km and the transition limited regime at 0–1 km on ozone exceedance days increased considerably. Spatially, HCHO in the North China Plain and middle–lower Yangtze River Plain was significantly increased on ozone exceedance days, while the NO₂ concentration in the southeast hills was increased on ozone exceedance days. The difference in FNR values between northern and southern cities in eastern China on O₃ exceedance days narrowed, and the ozone formation sensitivity in eastern China tended to be under a transition limited regime. The shifts in the ozone formation sensitivity under different ozone pollution levels implies that controlling only one of the precursors cannot achieve the best O₃ prevention effect, and the most appropriate ratio of O₃ precursor emission reductions should be designed according to ozone formation sensitivity in the different regions.

The amplified warming on the Tibetan Plateau (TA) is a distinctive characteristic of global climate change, leading to various climate responses with far-reaching implications. This study investigates the influence of interannual variation of TA on summer precipitation over East Asia (Pre_EA) using observational data and a Linear Baroclinic Model (LBM). When TA exceeds the Northern Hemisphere average, summer precipitation in the Yangtze River Valley significantly decreases, while it increases in North China and South China, resulting in a tripole Pre_EA pattern. Notably, the relationship between TA and Pre_EA is independent of the El Niño-Southern Oscillation (ENSO) and explains more variance in Pre_EA than ENSO. Our analysis reveals that TA enhances the tripole Pre_EA pattern by modulating moisture transport and vertical motion in the East Asia-North Pacific regions. Specifically, positive TA is linked to significant local tropospheric warming, which intensifies and eastward expands the South Asian High, creating a double-gyre meridional circulation over East Asia. Additionally, positive TA induces an eastward-propagating wave, reinforcing a midlatitude anomalous high-pressure belt over East Asia and the western North Pacific regions. These circulation changes weaken the East Asian subtropical jet, form a notable double jet configuration, and promote subsidence over mid-latitude East Asia. Moreover, anomalously warm sea surface temperatures in the Northwestern Pacific reinforce the TA-Pre_EA relationship by contributing to the mid-latitude East Asia-North Pacific high-pressure belt. Our LBM model experiments support these findings. Our study provides an in-depth understanding of the physical processes influencing summer precipitation variability in East Asia.

Winter Arctic sea ice is a crucial climate indicator, declining at an accelerated rate compared to the past and playing a significant role in Arctic amplification over recent decades. The sea-ice concentration (SIC) in the Greenland–Barents Sea (GBS) shows considerable interannual variability, yet the link between this variability and the El Niño–Southern Oscillation (ENSO) remains uncertain. Here, we identify a reversed relationship between the autumn Central Pacific (CP)-type ENSO and the winter GBS SIC around the mid-1980s. Observational and model experiments demonstrate that, before the mid-1980s, CP ENSO triggered a double wave pattern propagating toward the Arctic, generating a positive geopotential height anomaly in the Arctic. Such an anomaly, along with a northerly anomaly, favored cold-air advection and intrusion into the GBS, resulting in an increased SIC. After the mid-1980s, however, CP ENSO only induced a single wave train towards the Arctic, favoring a positive geopotential height anomaly over Iceland. As a result, the southerly anomaly transported abundant moisture into the GBS and consequently reduced the SIC. The variation in wave patterns can largely be attributed to the sea surface temperature anomaly in the tropical Atlantic induced by CP ENSO. Our findings highlight the unstable connection between tropical and polar regions, which provides a basis for better understanding the mechanisms of Arctic sea-ice changes.