Previous studies have suggested that tropical cyclone (TC) seasons over the western North Pacific (WNP) in the decaying years of El Niño events are generally less active than normal. The two ...strongest El Niño events on record were 1997/98 and 2015/16, but TC activities over the WNP displayed a sharp contrast between the decaying years of the two events. In 1998, consistent with previous studies, the WNP witnessed an extremely quiet season with no TC genesis in the preseason (January–June) and with only 10 named TCs observed in the typhoon season (July–October), making 1998 the most inactive season in the basin on record. In 2016, no TC formed in the preseason, similar to 1998; however, the basin became remarkably active in the typhoon season with above-normal named TCs observed. Further analyses indicate that the absence of TCs in the preseason in both 1998 and 2016 and the less active typhoon season in 1998 were attributed to the strong western Pacific anomalous anticyclone associated with the super El Niño events. However, the pattern of sea surface temperature anomalies (SSTAs) in the Pacific in 2016 showed features distinct from that in 1998. During July–August, the extremely positive phase of the Pacific meridional mode (PMM) triggered an anomalous cyclonic circulation and negative vertical wind shear over the WNP, favorable for TC geneses, while during September–October, the combined effect of the equatorial western Pacific warming and the weak La Niña event enhanced TC geneses over the WNP.
Spatial patterns of climate response to changes in anthropogenic aerosols and well-mixed greenhouse gases (GHGs) are investigated using climate model simulations for the twentieth century. The ...climate response shows both similarities and differences in spatial pattern between aerosol and GHG runs. Common climate response between aerosol and GHG runs tends to be symmetric about the equator. This work focuses on the distinctive patterns that are unique to the anthropogenic aerosol forcing. The tropospheric cooling induced by anthropogenic aerosols is locally enhanced in the midlatitude Northern Hemisphere with a deep vertical structure around 40°N, anchoring awesterly acceleration in thermal wind balance. The aerosol-induced negative radiative forcing in the Northern Hemisphere requires a cross-equatorial Hadley circulation to compensate interhemispheric energy imbalance in the atmosphere. Associated with a southward shift of the intertropical convergence zone, this interhemispheric asymmetric mode is unique to aerosol forcing and absent in GHG runs. Comparison of key climate response pattern indices indicates that the aerosol forcing dominates the interhemispheric asymmetric climate response in historical all-forcing simulations, as well as regional precipitation change such as the drying trend over the East Asian monsoon region. While GHG forcing dominates global mean surface temperature change, its effect is on par with and often opposes the aerosol effect on precipitation, making it difficult to detect anthropogenic change in rainfall from historical observations.
Anthropogenic aerosols partially mask the greenhouse warming and cause the reduction in Asian summer monsoon precipitation and circulation. By decomposing the atmospheric change into the direct ...atmospheric response to radiative forcing and sea surface temperature (SST)-mediated change, the physical mechanisms for anthropogenic-aerosol-induced changes in the East Asian summer monsoon (EASM) and South Asian summer monsoon (SASM) are diagnosed. Using coupled and atmospheric general circulation models, this study shows that the aerosol-induced troposphere cooling over Asian land regions generates anomalous sinking motion between 20° and 40°N and weakens the EASM north of 20°N without SST change. The decreased EASM precipitation and the attendant wind changes are largely due to this direct atmospheric response to radiative forcing, although the aerosol-induced North Pacific SST cooling also contributes. The SST-mediated change dominates the aerosol-induced SASM response, with contributions from both the north–south interhemispheric SST gradient and the local SST cooling pattern over the tropical Indian Ocean. Specifically, with large meridional gradient, the zonal-mean SST cooling pattern is most important for the Asian summer monsoon response to anthropogenic aerosol forcing, resulting in a reorganization of the regional meridional atmospheric overturning circulation. While uncertainty in aerosol radiative forcing has been emphasized in the literature, our results show that the intermodel spread is as large in the SST effect on summer monsoon rainfall, calling for more research into the ocean–atmosphere coupling.
The authors investigate the relationship between sea surface temperature (SST) in the tropical Indian Ocean (TIO) and the seasonal atmosphere circulation in the Asian monsoon region (AMR) using the ...maximum covariance analyses (MCAs). The results show that the Asian monsoon circulation is significantly correlated with two dominant SST anomaly (SSTA) modes: the Indian Ocean Basin mode (IOB) and the Indian Ocean dipole mode (IOD). The peak SSTA of the IOB appears in spring and has a much stronger relationship with the Asian summer monsoon than the peak of the IOD does, whereas the peak SSTA for the IOD appears in fall and shows a stronger link to the Asian winter monsoon than to the Asian summer monsoon. In addition, the IOB in spring has a relatively stronger link with the atmospheric circulation in summer than in other seasons.
The large-scale atmospheric circulation and SSTA patterns of the covariability of the first two dominant MCA modes are described. For the first MCA mode, a warm IOB, persists from spring to summer, and the atmospheric circulation is enhanced by the establishment of the climatological summer monsoon. The increased evaporative moisture associated with the warm IOB is transported to South Asia by the climatological summer monsoon, which increases the moisture convergence toward this region, leading to a significant increase in summer monsoon precipitation. For the second MCA mode, a positive IOD possibly corresponds to a weaker Indian winter monsoon and more precipitation over the southwestern and eastern equatorial TIO.
El Niño–Southern Oscillation (ENSO) induces climate anomalies around the globe. Atmospheric general circulation model simulations are used to investigate how ENSO-induced teleconnection patterns ...during boreal winter might change in response to global warming in the Pacific–North American sector. As models disagree on changes in the amplitude and spatial pattern of ENSO in response to global warming, for simplicity the same sea surface temperature (SST) pattern of ENSO is prescribed before and after the climate warming. In a warmer climate, precipitation anomalies intensify and move eastward over the equatorial Pacific during El Niño because the enhanced mean SST warming reduces the barrier to deep convection in the eastern basin. Associated with the eastward shift of tropical convective anomalies, the ENSO-forced Pacific–North American (PNA) teleconnection pattern moves eastward and intensifies under the climate warming. By contrast, the PNA mode of atmospheric internal variability remains largely unchanged in pattern, suggesting the importance of tropical convection in shifting atmospheric teleconnections. As the ENSO-induced PNA pattern shifts eastward, rainfall anomalies are expected to intensify on the west coast of North America, and the El Niño–induced surface warming to expand eastward and occupy all of northern North America. The spatial pattern of the mean SST warming affects changes in ENSO teleconnections. The teleconnection changes are larger with patterned mean warming than in an idealized case where the spatially uniform warming is prescribed in the mean state. The results herein suggest that the eastward-shifted PNA pattern is a robust change to be expected in the future, independent of the uncertainty in changes of ENSO itself.
Previous studies have suggested that global ocean circulation would be significantly changed under global warming, while the change of North Equatorial Countercurrent (NECC) and its mechanisms are ...still unclear. Here, we investigate the location and intensity changes of NECC under global warming based on CESM1 high‐resolution long‐term simulations from the perspective of the Inter‐Tropical Convergence Zone (ITCZ), considering the close connection between NECC and ITCZ and well‐established changes of ITCZ. It is found that the annual‐mean NECC shifts equatorward of 0.39° and weakens by 21.71% in the RCP8.5 scenario at the end of 21st century. The NECC change is seasonally dependent, with maximum shift and weakening during spring, consistent with the changes of ITCZ. Both the location and intensity changes of ITCZ are important in the NECC changes, especially for spring. The weakening and equatorward shift of ITCZ contributes almost equally to the strongest decrease of spring NECC (47.63%).
Plain Language Summary
Global ocean circulation is suggested to exhibit significant changes under global warming, but whether and why the North Equatorial Countercurrent (NECC) would change is still unclear. It is well known that the NECC and Inter‐Tropical Convergence Zone (ITCZ) are closely coupled through air‐sea interaction. Under global warming, previous studies found that the ITCZ would move closer to the equator with maximum shift in spring and the annual‐mean NECC would be weakened in response to the enhanced equatorial warming. Hence, it is important to investigate whether the NECC would change following the ITCZ change. Here, based on long‐term simulations from a high‐resolution climate model, it is found that the NECC will indeed move closer to the equator under global warming following the equatorward shift of ITCZ. The NECC also gets weakened under global warming following the weakened ITCZ convergence, although the ITCZ precipitation gets stronger due to more moisture under warming. In spring, the largest equatorward shift of ITCZ has a comparable contribution to the largest decrease of NECC.
Key Points
The North Equatorial Countercurrent (NECC) would be southward shift and weakened under global warming
The future changes of NECC are seasonally dependent, with maximum southward shift and weakening in spring
The NECC changes are closely related to the location and intensity changes of Inter‐Tropical Convergence Zone, especially in spring
While modelling studies suggest that mesoscale eddies strengthen the subduction of mode waters, this eddy effect has never been observed in the field. Here we report results from a field campaign ...from March 2014 that captured the eddy effects on mode-water subduction south of the Kuroshio Extension east of Japan. The experiment deployed 17 Argo floats in an anticyclonic eddy (AC) with enhanced daily sampling. Analysis of over 3,000 hydrographic profiles following the AC reveals that potential vorticity and apparent oxygen utilization distributions are asymmetric outside the AC core, with enhanced subduction near the southeastern rim of the AC. There, the southward eddy flow advects newly ventilated mode water from the north into the main thermocline. Our results show that subduction by eddy lateral advection is comparable in magnitude to that by the mean flow--an effect that needs to be better represented in climate models.
The response of the Indian Ocean dipole (IOD) mode to global warming is investigated based on simulations from phase 5 of the Coupled Model Intercomparison Project (CMIP5). In response to increased ...greenhouse gases, an IOD-like warming pattern appears in the equatorial Indian Ocean, with reduced (enhanced) warming in the east (west), an easterly wind trend, and thermocline shoaling in the east. Despite a shoaling thermocline and strengthened thermocline feedback in the eastern equatorial Indian Ocean, the interannual variance of the IOD mode remains largely unchanged in sea surface temperature (SST) as atmospheric feedback and zonal wind variance weaken under global warming. The negative skewness in eastern Indian Ocean SST is reduced as a result of the shoaling thermocline. The change in interannual IOD variance exhibits some variability among models, and this intermodel variability is correlated with the change in thermocline feedback. The results herein illustrate that mean state changes modulate interannual modes, and suggest that recent changes in the IOD mode are likely due to natural variations.
Following an El Niño event, a basin‐wide warming takes place over the tropical Indian Ocean, peaks in late boreal winter and early spring, and persists through boreal summer. Our observational ...analysis suggests that this Indian Ocean warming induces robust climatic anomalies in the summer Indo‐West Pacific region, prolonging the El Niño's influence after tropical East Pacific sea surface temperature has returned to normal. In response to the Indian Ocean warming, precipitation increases over most of the basin, forcing a Matsuno‐Gill pattern in the upper troposphere with a strengthened South Asian high. Near the ground, the southwest monsoon intensifies over the Arabian Sea and weakens over the South China and Philippine Seas. An anomalous anticyclonic circulation forms over the subtropical Northwest Pacific, collocated with negative precipitation anomalies. All these anomaly patterns are reproduced in a coupled model simulation initialized with a warming in the tropical Indian Ocean mixed layer, indicating that the Indian Ocean warming is not just a passive response to El Niño but important for summer climate variability in the Indo‐West Pacific region. The implications for seasonal prediction are discussed.
Purpose
Coexistence of frailty and hemodialysis is related to higher risk of hospitalization, falls and mortality. Given the potential reversibility of frailty, reaching the epidemiology of frailty ...in hemodialysis is of great importance. However, estimates of the prevalence of frailty in patients on hemodialysis vary widely. We tried to synthesize the existing body of literature on the prevalence of frailty in patients on hemodialysis.
Methods
We searched Pubmed, Embase, Web of Science and Cochrane for studies of the prevalence in patients on hemodialysis. The prevalence of frailty was synthesized across eligible studies using a random-effects model. We explored potential origin of heterogeneity in the estimates by meta-regression analysis.
Results
Prevalence range from 6.0 to 82.0% and the pooled prevalence of frailty in patients on dialysis was 34.3% (95% confidence interval (CI) 24.5–44.1%;
z
= 6.87;
p
= 0.00). The pooled estimates of prevalence for patients aged < 55, 55–65, and ≥ 65 were 56.0% (95% CI 28.9–83.2%;
z
= 4.04;
p
= 0.00), 32.3% (95% CI 22.9–41.7%;
z
= 6.74;
p
= 0.00), and 20.3% (95% CI 7.9–32.8%;
z
= 3.2;
p
= 0.00), respectively. There were no significant relationships between frailty in hemodialysis and factors such as years of publication, sample size (continuous), sample size(> 500 vs ≤ 500), diagnostic method (the Fried Frailty vs other), country (Europe & USA vs Asia) and duration of hemodialysis.
Conclusions
Frailty influences almost three in ten patients on hemodialysis. Understanding the underlying pathophysiology mechanisms and weakening the impacts of frailty in patients on hemodialysis are called on to action in the future work.
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