Response Of Circulation Research Articles

Near-global summer circulation response to the spring surface temperature anomaly in Tibetan Plateau –– the GEWEX/LS4P first phase experiment

Subseasonal to seasonal (S2S) prediction of droughts and floods is one of the major challenges of weather and climate prediction. Recent studies suggest that the springtime land surface temperature/subsurface temperature (LST/SUBT) over the Tibetan Plateau (TP) can be a new source of S2S predictability. The project “Impact of Initialized Land Surface Temperature and Snowpack on Subseasonal to Seasonal Prediction (LS4P)” was initiated to study the impact of springtime LST/SUBT anomalies over high mountain areas on summertime precipitation predictions. The present work explores the simulated global scale response of the atmospheric circulation to the springtime TP land surface cooling by 16 current state-of-the-art Earth System Models (ESMs) participating in the LS4P Phase I (LS4P-I) experiment. The LS4P-I results show, for the first time, that springtime TP surface anomalies can modulate a persistent quasi-barotropic Tibetan Plateau-Rocky Mountain Circumglobal (TRC) wave train from the TP via the northeast Asia and Bering Strait to the western part of the North America, along with the springtime westerly jet from TP across the whole North Pacific basin. The TRC wave train modulated by the TP thermal anomaly play a critical role on the early summer surface air temperature and precipitation anomalies in the regions along the wave train, especially over the northwest North America and the southern Great Plains. The participant models that fail in capturing the TRC wave train greatly under-predict climate anomalies in reference to observations and the successful models. These results suggest that the TP LST/SUBT anomaly via the TRC wave train is the first order source of the S2S variability in the regions mentioned. Furthermore, the TP surface temperature anomaly can influence the Southern Hemispheric circulation by generating cross-equator wave trains. However, the simulated propagation pathways from the TP into the Southern Hemisphere show large inter-model differences. More dynamical understanding of the TRC wave train as well as its cross-equator propagation into the Southern Hemisphere will be explored in the newly launched LS4P phase II experiment.

Different responses of surface air temperature over Eurasia in early and late winter to the autumn Kara–Laptev Sea ice

The Arctic climate is changing rapidly, along with intensified melting of sea ice, which has significant impacts on surface air temperature (SAT) in Eurasia. This study reveals that the subseasonal response of SAT to the autumn Kara–Laptev Sea ice (KLSIC) differs significantly between early and late winter. The response of SAT to KLSIC forms a warm Arctic–cold Eurasia pattern in early winter. Conversely, the negative anomaly response of SAT to KLSIC in late winter is only distributed in the band range of Eurasia, without significant positive SAT anomaly over the Arctic Ocean. After further examination of the separate physical mechanisms involved in early and late winter, it is found that a decrease in KLSIC in autumn can lead to a strengthened Ural high and Siberian high in the Arctic–Eurasia region, which is conducive to cold events in the mid-latitudes of Eurasia in early winter. For late winter, a westward shift in the response of atmospheric circulation to KLSIC leads to a negative anomaly feedback of North Sea surface temperature, which triggers the propagation of Rossby waves to the Sea of Japan through the wave activity flux. Meanwhile, the deep trough of East Asia is strengthened and extends to the southeast, guiding northern cold air to the western Pacific. Our results highlight that different subseasonal effects of sea ice should be considered in Eurasian climate prediction, rather than only consider the effects in winter mean.

Enhanced spring warming of the Tibetan Plateau amplifies summer heat stress in Eastern Europe

The Tibetan Plateau (TP), often referred to as the “Roof of the World”, has experienced rapid warming in recent decades. This warming has had significant impacts on downstream regions, while its effects on upstream regions are less well-defined. This study explores the relationship between TP warming and the occurrence of summer heat stress days in Europe, with a particular focus on Eastern Europe (EEU). Our analysis reveals a robust correlation between TP warming in both the summer and the preceding spring, and the frequency of heat stress days in EEU, demonstrating a significant interannual connection. During the spring, pronounced warming in the southern TP generates a strong local Rossby wave source, triggering a substantial divergence anomaly that amplifies the warming effect. This mechanism weakens the subtropical jet and strengthens the polar jet during the summer, setting the stage for anticyclonic anomalies over EEU. Furthermore, anomalies induced by TP warming, characterized by local upward movement and divergence at upper levels, intensify convergence and sinking airflow in the upstream region, leading to increased adiabatic heating in EEU. The dynamic response of the summer circulation anomaly, exemplified by the anticyclone anomaly over EEU, to prior TP warming is further corroborated through numerical simulations.

Modulation of the northward penetration of Antarctica intermediate waters into the eastern equatorial Indian Ocean under glacial and interglacial conditions

The Indo-Pacific warm pool is the warmest and most dynamic ocean–atmosphere-climate system on Earth and was subject to significant climate changes during the Pleistocene glacial-interglacial transitions. This has been shown to significantly affected the strength of surface waters that redistribute heat from the tropics to the southern part of the Indian Ocean. Here we investigate the response of the oceanic circulation at intermediate depth (1200 m) of the eastern equatorial Indian Ocean (EEIO) with neodymium (Nd) isotopes in the context of the climatic oscillation of the last 500 ka. The most striking feature of our new dataset is the seesaw Nd record that mimics glacial-interglacial cycles. While the interglacial periods are characterized by a higher contribution of the less radiogenic neodymium (~ − 7εNd) Antarctic Intermediate Water (AAIW), the glacial periods are characterized by more radiogenic water mass of Pacific origin (~ − 5εNd). To explain the increase in the εNd signature toward a more radiogenic signature as the Indo-Pacific connection is reduced under the low sea level of the glacial periods, we show that under global cooling, the AAIW advances northward into the tropics, which is a consequence of the general slowdown of the thermohaline circulation. Therefore, oceanic mixing at intermediate depth in the eastern tropical Indian intermediate water is modulated by the production rate of the AAIW in the Southern Ocean. Our study provides new evidence for the role that changes in the deep oceanic conditions play in amplifying externally forced climate changes that ultimately lead to drier/moister atmospheric conditions and weaker/stronger monsoons during glacial/interglacial periods over eastern tropical Indian Ocean.

The response of atmospheric blocking and East Asian cold extremes to future Arctic Sea ice loss

The effect of Arctic warming on cold extremes over middle latitude remains a controversial and unresolved issue, particularly considering potential enhanced Arctic amplification in future scenarios. Here we examine the possible responses of winter cold extremes to the projected sea ice loss under 2 °C global warming scenario in four models, based on the atmosphere-only experiments of the Polar Amplification Model Inter-comparison Project (PAMIP). We find agreement with the increased responses of extreme cold days over East Asia (EA), characterized by longer duration or stronger intensity of temperature drop during cold events. Accordingly, most models exhibit a weak response of the Ural blocking in the corresponding composite circulation fields, whereas the westward movement of an anomalous anticyclonic system from eastern Siberia before the maturing of the Ural blocking is notable in four models. We suggest that this westward shifting pattern may prolong the duration of Ural blocking or modulate the strength of the Northeast Asian cold vortex, resulting in longer or stronger cold anomalies in EA. Accordingly, increased blocking frequency with a more pronounced westward response of shipment signals is also found over eastern Siberia, where a reduced meridional potential vorticity gradient (PVy) exists. The background of weak PVy can enhance the atmospheric nonlinearity, resulting in the anticyclonic anomalies less prone to dispersion and presenting a westward characteristic. Our results highlight the impact of the nonlinear response of circulation to Arctic sea ice loss. In contrast to more concerned Ural blocking influence, it is suggested that the downstream impact of eastern Siberia blocking on cold extremes in EA may be more pronounced in an enhanced Arctic amplification climate.

Nonstationarity in the NAO–Gulf Stream SST Front Interaction

Abstract The interaction between the North Atlantic Oscillation (NAO) and the latitudinal shifts of the Gulf Stream sea surface temperature front (GSF) has been the subject of extensive investigations. There are indications of nonstationarity in this interaction, but differences in the methodologies used in previous studies make it difficult to draw consistent conclusions. Furthermore, there is a lack of consensus on the key mechanisms underlying the response of the GSF to the NAO. This study assesses the possible nonstationarity in the NAO–GSF interaction and the mechanisms underlying this interaction during 1950–2020, using reanalysis data. Results show that the NAO and GSF indices covary on the decadal time scale but only during 1972–2018. A secondary peak in the NAO–GSF covariability emerges on multiannual time scales but only during 2005–15. The nonstationarity in the decadal NAO–GSF covariability is also manifested in variations in their lead–lag relationship. Indeed, the NAO tends to lead the GSF shifts by 3 years during 1972–90 and by 2 years during 1990–2018. The response of the GSF to the NAO at the decadal time scale can be interpreted as the joint effect of the fast response of wind-driven oceanic circulation, the response of deep oceanic circulation, and the propagation of Rossby waves. However, there is evidence of Rossby wave propagation only during 1972–90. Here it is suggested that the nonstationarity of Rossby wave propagation caused the time lag between the NAO and the GSF shifts on the decadal time scale to differ between the two time periods.

Responses of the Mean Thermosphere Circulation, O/N2 Ratio and Ne to Solar and Magnetospheric Forcing From Above and Tidal Forcing From Below

AbstractThe day‐to‐day variability (“weather”) associated with the diurnal‐ and zonal‐mean (DZM) circulation, O/N2 ratio and electron density (Ne) of the I‐T system due to tidal “forcing from below” and solar flux and magnetosphere (SM) “forcing from above” during 2021 are delineated, diagnosed and quantitatively compared using a series of model simulations designed to separate these responses with respect to their origins. The external forcings are driven by actual tidal, solar wind, and solar flux observations. Both circulation systems occupy the full extent of the I‐T, and the SM‐forced DZM circulation is 2–3 times more vigorous in terms of vertical and meridional wind magnitudes. Tidal‐driven DZM Ne reductions of up to 30%–40% with respect to those of the fully forced I‐T system occur, mainly between ±30° latitude, compared to SM‐driven increases of up to 15%–20%. In terms of annual variances over this latitude range, tidal‐driven DZM Ne variances exceed or equal those of the SM‐driven variances. The former is mainly controlled by O/N2 ratio vis‐a‐vis tidal‐forced temperature variations above 150 km. While a similar cause‐effect relation exists for the latter, this is superseded by Ne variability associated with solar production. However, DZM I‐T system variability forced from below is underestimated in the simulations in two respects: the effects of gravity waves are omitted, and tidal forcing is represented by 45‐day running means, as compared with the more realistic actual daily variability of SM forcing. These shortcomings should be ameliorated once multi‐satellite missions planned for the future come to fruition.

Storylines for Future Projections of Precipitation Over New Zealand in CMIP6 Models

AbstractLarge uncertainty exists in the sign of long‐term changes in regional scale mean precipitation across the current generation of global climate models. To explore the physical drivers of this uncertainty for New Zealand, here we adopt a storyline approach applying cluster analysis to spatial patterns of future projected seasonal mean precipitation change across CMIP6 models (n = 43). For the winter precipitation change signal, the models split roughly into two main groups: both groups have a very robust wet signal across the west coast of the South Island but differ notably in terms of the sign of precipitation change across the north of the North Island. These far north winter precipitation differences appear related to how far the Hadley cell edge and regional eddy‐driven jet shift across the models relative to their historical positions. In contrast, for summer, most models have a markedly weaker and spatially non‐uniform response, where internal variability often plays a large role. However, a small group of models predict a robust wet signal across most of the country in summer. This “wet model” group is characterized by a regional La Niña‐like increase in high pressure shifted further to the south‐east of New Zealand, associated with more frequent north‐easterly flow over the country and accompanied by significant warming of local sea surface temperatures. This regional circulation response appears related to changes in stationary Rossby wave paths as opposed to changes in La Niña occurrence frequency itself.

Manipulation of internal blockage in triangular triple quantum dot

We utilize the calculation of hierarchical equations of motion to demonstrate that the spin-dependent properties between adjacent quantum dots (QDs) can be changed by breaking the internal symmetry configuration, corresponding to the inversion of dominant chiral states. In the linear triple quantum dots (LTQDs) connected to two electron reservoirs, we can observe that the blockage appears at the triangle triple quantum dots (TTQDs) by gradually increasing the coupling strength between next-nearest double QDs. When the initial coupling between LTQDs has altered, the internal chiral circulation also undergoes the corresponding transform, thus achieving qualitative regulation and detection of the blocking region. We also investigate the response of the chiral circulation to the dot–lead coupling strength, indicating the overall robust chiral circulation of the TTQDs frustration.

Multi-decadal pacemaker simulations with an intermediate-complexity climate model

Abstract. In this paper, we first describe the main features of a new version of the International Centre for Theoretical Physics global atmospheric model (SPEEDY) with improved simulation of surface fluxes and the formulation of a three-layer thermodynamic ocean model (TOM3) suitable to explore the coupled extratropical response to tropical ocean variability. Then, we present results on the atmospheric model climatology, highlighting the impact of the modifications introduced in the model code, and show how important features of interdecadal and interannual variability are simulated in a “pacemaker” coupled ensemble of 70-year runs, where portions of the tropical Indo-Pacific are constrained to follow the observed variability. Despite the very basic representation of variations in greenhouse forcing and heat transport to the deep ocean (below the 300 m domain of the TOM3 model), the coupled ensemble reproduces the variations in surface temperature over land and sea with very good accuracy, confirming the role of the Indo-Pacific as a “pacemaker” for the natural fluctuations of global-mean surface temperatures found in earlier studies. Atmospheric zonal-mean temperature trends over 50 years are also realistically simulated in the extratropical lower troposphere and up to 100 hPa in the tropics. On the interannual scale, sea-surface temperature (SST) variability in sub-tropical and tropical regions not affected by SST relaxation is underestimated (mostly because of the absence of dynamically induced variability), while extratropical SST variability during the cold seasons is comparable to that observed. Atmospheric teleconnection patterns and their connections with SST are reproduced with high fidelity, although with local differences in the amplitude of regional features (such as a larger-than-observed response of extratropical SST to North Atlantic Oscillation variability). The SPEEDY-TOM3 model also reproduces the observed connection between averages of surface heat fluxes over the oceans and land surface air temperature in the wintertime northern extratropics. Overall, as in earlier versions of SPEEDY, the fidelity of the simulations (both in terms of climatological means and variability) is higher near the surface and in the lower troposphere, while the negative impacts of the coarse vertical resolution and simplified parameterizations are mostly felt in the stratosphere. However, the improved simulation of surface heat fluxes and their impact on extratropical SST variability in this model version (obtained at a very modest computational cost) make the SPEEDY-TOM3 model a suitable tool to investigate the coupled response of the extratropical circulation to interannual and inter-decadal changes of tropical SST in ensemble experiments.

Last Glacial Maximum climate and atmospheric circulation over the Australian region from climate models

Abstract. The Last Glacial Maximum (LGM; ∼21 kyr ago) was the most recent time that the Earth experienced global maximum ice volume and minimum eustatic sea level. The climate changes over the Australian region at the LGM remain uncertain, including the extent of cooling in the arid interior, changes in the regional atmospheric circulations such as the tropical monsoon and mid-latitude westerlies, and changes in the balance between precipitation and evaporation. In this study, 13 climate model simulations that were included in the Paleoclimate Modelling Intercomparison Project (PMIP) Phases 3 and 4 are used to investigate regional climate (temperature, precipitation, and wind) over Australia at the LGM. The model simulations are compared with existing proxy records and other modelling studies. All models simulate consistent annual and seasonal cooling over the Australian region (defined as 0–45° S, 110–160° E) at the LGM compared to pre-industrial, with a multi-model mean 2.9 °C decrease in annual average surface air temperature over land at the LGM compared to pre-industrial. Models simulate a range of LGM precipitation anomalies over the region. Simulated precipitation changes over tropical Australasia appear to be driven by changes in circulation and moisture transport, which vary greatly between models. Surface moisture balance calculated from precipitation minus evaporation shows little change over much of the Australian land area at the LGM. Changes in the strength and position of the mid-latitude westerlies are uncertain, with wide model disagreement. These results indicate that climate model simulations do not show a robust response in either tropical or mid-latitude circulation to LGM boundary conditions, suggesting that caution is required when interpreting model output in this region. Further analysis based on model evaluation and quantitative model–proxy comparison is required to better understand the drivers of LGM climate and atmospheric circulation changes in this region.

Responses of hydrodynamic circulation to the climatic change of wind forcing in a subtropical estuary

Under the background of climate change, long-term trends in atmospheric-marine processes have been observed over the past decades. Being a subtropical estuary influenced by East Asian monsoon wind, the Pearl River Estuary (PRE) is chosen as a prototype to investigate the response of estuarine hydrodynamics to the local climatic regime shift in wind forcing. Analyses from ERA5 wind data and local meteorological observations have revealed that summer wind over PRE (prevailed by the up-estuary wind) was decreasing in magnitude and shifting anticlockwise from southwesterly to southeasterly over the past 42 years (1979–2020). Using a fully calibrated three-dimensional numerical model, the hydrodynamic circulation of PRE were simulated for 42 years with realistic daily wind forcing and repeated annual cycles for other forcing fields. Both the least-squares fitting and the EOF analysis demonstrate that the summertime longitudinal flow was strengthened while the lateral circulation was weakened over the past 42 years. Comparative analyses of the results obtained from the process-oriented numerical experiments revealed that the decreasing wind speed is the dominant factor for the strengthening of the longitudinal circulation, while the shifting wind direction is the dominant factor for the weakening of the lateral circulation. Using calculated long-term trends in wind forcing, wind conditions are predicted for 2100. The model results indicate that by 2100, there will be a further strengthening of the longitudinal circulation and a further weakening of the lateral circulation during the summer. The momentum budget reveals that the baroclinic pressure gradient and the diffusion term are the dominant terms modulating the changes of hydrodynamic circulation. The water mass in the PRE will become saltier, and the exchange between the deep channel and shallow shoals of the estuary will be slowed down in the future. The impact of these changes on brackish water habitats and local ecosystems needs further study.

Tropical Cyclogenesis Bias over the Central North Pacific in CMIP6 Simulations

Abstract Current coupled climate models contain large biases in simulating tropical cyclogenesis, reducing the confidence in tropical cyclone (TC) projection. In this study, we investigated the influence of sea surface temperature (SST) biases on TC genesis in the Coupled Model Intercomparison Project phase 6 simulations from 1979 to 2014. Positive TC genesis biases were found over the tropical central North Pacific (CNP) in most of climate models, including the high-resolution models. Compared to coupled models, TC genesis density (TCGD) simulations over CNP in uncoupled models forced by observational SST improved obviously. A warm SST bias over the tropical CNP in the coupled models is the main cause of TC genesis biases. The SST bias–induced diabatic heating leads to an anomalous Gill-type atmospheric circulation response, which contributes to a series of favorable environmental conditions for TC formation over the CNP. Numerical experiments were also performed with HiRAM to demonstrate the influence of SST biases on the TCGD simulation, further confirming our conclusion. The current results highlight the importance of improving TC simulation in state-of-the-art climate models by reducing SST simulation bias.

Exertional Stress-induced Pathogenic Luminal Content Translocation - Friend or Foe?

The incidence of perturbed gastrointestinal integrity, as well as resulting systemic immune responses and gastrointestinal symptoms, otherwise known as exercised-induced gastrointestinal syndrome (EIGS), is common among individuals who partake in prolonged exercise. EIGS may cause the translocation of pathogenic material, including whole bacteria and bacterial endotoxins, from the lumen into circulation, which may progress into clinical consequences such as sepsis, and potentially subsequent fatality. However, further investigation is warranted to assess the possibility of food allergen and/or digestive enzyme luminal to circulatory translocation in response to exercise, and the clinical consequences. Findings from this narrative literature review demonstrate evidence that whole bacteria and bacterial endotoxins translocation from the gastrointestinal lumen to systemic circulation occurs in response to exercise stress, with a greater propensity of translocation occurring with accompanying heat exposure. It has also been demonstrated that food allergens can translocate from the lumen to systemic circulation in response to exercise stress and initiate anaphylaxis. To date, no research investigating the effect of exercise on the translocation of digestive enzymes from the lumen into systemic circulation exists. It is evident that EIGS and consequential pathogenic translocation presents life-threatening clinical implications, warranting the development and implementation of effective management strategies in at-risk populations.

Climate Response to Vegetation Removal on Different Continents

AbstractUnderstanding the climatic effect of vegetation in different regions is important for understanding the climate impact of vegetation change in both the past and future. Here we quantify the climate response to vegetation removal on each continent, except Antarctica, using CESM1.2.2 under pre‐industrial climate condition, and the associated mechanisms are analyzed. Results show that removing the global vegetation lowers the global mean surface temperature (GMST) by 3.65°C. Removing vegetation over Eurasia and North America lowers GMST by 1.83°C and 0.88°C, respectively. They also reduce the global precipitation, but at a much slower rate than that would be caused in the CO2 perturbation experiments. Removing vegetation on all other continents has negligible influence on global climate, but has significant local warming effect due to weakening of evapotranspiration. The removal of low‐latitude vegetation tends to reduce the local precipitation, but increase the precipitation over nearby oceans, especially to the west. The feedbacks of thermodynamic sea ice and oceans amplify the initial direct cooling due to vegetation removal by a factor of >5. The response of ocean circulation has a negligible impact on GMST, but has a significant influence on the pattern of temperature changes by redistributing heat. Without the ocean‐circulation feedback, the Northern Hemisphere would be 1.30°C colder while the Southern Hemisphere 1.17°C warmer when the global vegetation is removed.

Response of winter climate and extreme weather to projected Arctic sea-ice loss in very large-ensemble climate model simulations

Very large (~2000 members) initial-condition ensemble simulations have been performed to advance understanding of mean climate and extreme weather responses to projected Arctic sea-ice loss under 2 °C global warming above preindustrial levels. These simulations better sample internal atmospheric variability and extremes for each model compared to those from the Polar Amplification Model Intercomparison Project (PAMIP). The mean climate response is mostly consistent with that from the PAMIP multi-model ensemble, including tropospheric warming, reduced midlatitude westerlies and storm track activity, an equatorward shift of the eddy-driven jet and increased mid-to-high latitude blocking. Two resolutions of the same model exhibit significant differences in the stratospheric circulation response; however, these differences only weakly modulate the tropospheric response. The response of temperature and precipitation extremes largely follows the seasonal-mean response. Sub-sampling confirms that large ensembles (e.g. ≥400) are needed to robustly estimate the seasonal-mean large-scale circulation response, and very large ensembles (e.g. ≥1000) for regional climate and extremes.

Aquaplanet simulations with winter and summer hemispheres: model setup and circulation response to warming

Abstract. To support further understanding of circulation changes in a warming climate, an idealised aquaplanet model setup containing summer and winter hemispheres is presented, and the results of circulation changes under warming are discussed. First, a setup is introduced that enables aquaplanet simulations with a warmer and a colder hemisphere, including realistic-looking summer and winter jet streams, storm tracks, and precipitation patterns that are fairly similar to observations, as well as a more intense and equatorward storm track in the winter compared to the summer hemisphere. The sea surface temperature (SST) distribution used here is inspired by the June–July–August zonal mean SST found in reanalysis data and is flexible to allow control of the occurrence of a single or double intertropical convergence zone (ITCZ). The setup is then used to investigate circulation changes under uniform warming, as motivated by recent research. For example, the stronger poleward shift of the storm tracks during summer compared to winter is reproduced. Furthermore, the jet waviness decreases under warming when compared on isentropes with maximum wind speed or isentropes at similar heights in pressure space. Jet stream waviness increases under warming when compared at similar-valued isentropes but primarily because the corresponding isentrope is closer to the surface in the warmer climate and waviness climatologically increases downwards in the atmosphere. A detailed analysis of the changes in wave amplitude for different wavenumbers confirms that the amplitude of large waves increases with warming, while that of short waves decreases with warming. The reduction in wave amplitude of short synoptic waves is found to dominate in the jet core region, where jet waviness also decreases and is more pronounced on the equatorward side of the jet. Long waves increase in amplitude on the poleward side of the jet and at upper stratospheric levels, which is consistent with increased jet waviness at these levels. The projected increased amplitude of planetary waves and the reduced amplitude of synoptic waves are thus clear in our aquaplanet simulations and do not require zonal asymmetries or regional warming patterns. During so-called high-amplitude wave events, there is no evidence for a preferential phase of Rossby waves of wavenumbers 5 or 7, indicating the crucial role of stationary waves forced by orography or land–sea contrast in establishing previously reported preferential phases. We confirm that feature-based block detection requires significant tuning to the warmer climate to avoid the occurrence of spurious trends. After adjustment for changes in tropopause height, the block detection used here shows no trend in the summer hemisphere and an increase in blocking in the colder hemisphere. We also confirm previous findings that the number of surface cyclones tends to decrease globally under warming and that the cyclone lifetimes become shorter, except for very long-lived cyclones.

Nonlinearity and Asymmetry of the ENSO Stratospheric Pathway to North Atlantic and Europe, Revisited

AbstractNonlinearities and asymmetries of El Niño Southern Oscillation (ENSO) stratospheric pathway to the North Atlantic and Europe are examined in large ensembles conducted with fully coupled climate models during wintertime. The analysis is centered on historical experiments of the Max Planck Institute Grand Ensemble (MPI‐GE, 95 members) and expanded to six other ensembles of more limited size. In MPI‐GE, significant responses are obtained for each ENSO phase and three different intensities (weak, moderate and strong). Overall, linear relationships are found for either El Niño or La Niña key diagnostics that characterize the pathway. These relationships are generally weaker for the cold La Niña than for the warm El Niño so that asymmetries between them develop as the events intensify. Specifically for strong events, the extra‐tropical North Pacific and stratospheric responses are asymmetric, with larger responses for El Niño. In addition, the stratospheric asymmetry in strong events seems to contribute to the asymmetry in strong events in the North Atlantic—Europe response in the troposphere in late winter. The extra‐tropical North Pacific response shows general agreement between MPI‐GE and the other large ensembles. However, this agreement is not as large when other parts of the pathway are compared. Relatively high inter‐model response spread confirms the typical model uncertainty found when examining atmospheric circulation responses which include the stratosphere in state‐of‐the‐art climate models.

Hepatocyte growth factor as indicator for subclinical atherosclerosis.

Background: Hepatocyte growth factor (HGF) is a pleiotropic cytokine mainly produced by mesenchymal cells. After endothelial damage by oxidized low-density lipoprotein (LDL), HGF is produced and released into the circulation in response. Due to this mechanism HGF has been proposed as possible clinical biomarker for clinical as well as subclinical atherosclerosis. Patients and methods: The conducted study is an observational, single centre, cohort study, including 171 patients with at least one cardiovascular risk factor or already established cardiovascular disease (CVD). Each patient underwent 3D plaque volumetry of the carotid and femoral arteries as well as physical examination and record of the medical history. Additionally, plasma HGF and further laboratory parameters like high sensitivity C-reactive protein and LDL-cholesterol were determined. Results: 169 patients were available for statistical analysis. In bivariate correlation, HGF showed a highly significant correlation with total plaque volume (TPV, r=0.48; p<0.001). In receiver operating characteristic (ROC) analysis for high TPV, HGF showed an area under the curve (AUC) of 0.68 (CI 95%: 0.59-0.77, p<0.001) with a sensitivity of 78% and a specificity of 52% to predict high TPV at a cut-off of 959 ng/ml. In the ROC-analysis for the presence of CVD, HGF demonstrated an AUC of 0.65 (95% CI 0.55-0.73; p=0.01) with a sensitivity of 77% and a specificity of 52%. Conclusions: Higher plasma levels of HGF are associated with higher atherosclerotic plaque volume as measured by 3D-ultrasound.

De-stabilizing innate immunity in COVID-19: effects of its own positive feedback and erratic viraemia on the alternative pathway of complement.

Complement provides powerful, fast responses in the human circulation to SARS-CoV-2 (COVID-19 virus) infection of the lower respiratory tract. COVID-19 effects were investigated in a revised human in silico Mass Action model of complement's alternative pathway (AP) responses. Bursts of newly circulating virions increased the fission of Complement protein C3 into C3a and C3b via stimulation of the lectin pathway or inhibited complement factor H. Viral reproduction sub-models incorporated smoothly exponential or step-wise exponential growth. Starting complement protein concentrations were drawn randomly from published normal male or female ranges and each infection model run for 10 days. C3 and factor B (FB) syntheses driven by Lectin Pathway stimulation led to declining plasma C3 and increasing FB concentrations. The C3-convertase concentration, a driver of viral elimination, could match viral growth over three orders of magnitude but near-complete exhaustion of circulating C3 was more prevalent with step-wise than with 'smooth' increases in viral stimulation. C3 exhaustion could be prolonged. Type 2 Diabetes and hypertension led to greatly increased peak C3-convertase concentrations, as did short-term variability of COVID-19 viraemia, pulmonary capillary clotting and secondary acidosis. Positive feedback in the AP greatly extends its response range at the expense of stability.