Abstract Reduced Arctic sea‐ice has been proposed to induce severe Eurasian cold events. However, the physical mechanisms for this connection, particularly the relative importance of tropospheric and stratospheric processes, remain unclear. Using ERA‐Interim reanalysis data and WACCM‐SC simulations, we show that the Eurasian cooling induced by reduced sea‐ice centers over eastern Asia and northern Europe. Tropospheric and stratospheric processes contribute roughly equally to the cooling over eastern Asia, while the stratospheric and tropospheric contributions are 60% and 40%, respectively, over northern Europe. In the tropospheric pathway, weakened meridional temperature gradient due to reduced sea‐ice strengthens the Ural blocking and enhances the Siberian High. The enhanced Siberian High favors two streams of cold air‐mass, reaching northern Europe and eastern Asia. In the stratospheric pathway, enhanced upward‐propagating planetary wave 1 causes a shift of the stratospheric polar vortex toward Eurasia and consequently, tropospheric cyclonic anomalies are induced that enhance surface cold anomalies.
 Using the ERA5 reanalysis data, we identify seven easily calculable indices of the strength of theArctic stratospheric vortex: zonal winds at 10 hPa and temperature or height anomalies at 10 , 50, and 100 hPa.We then compare the climatological statistics and meteorological properties of strong and weak events basedon these indices. We particularly consider the sensitivity of the event statistics to the choice of thresholds, theuse of these indices in capturing stratosphere–troposphere coupling, and meteorological conditions relevant tochemical ozone depletion. The frequency, seasonal distribution, and interdecadal variability of strong eventsis more sensitive to threshold or index choice compared to weak events. Composites of polar-cap geopotentialheight anomalies are found to differ significantly based on the choice of index. In particular, height-basedevents reveal a strong and immediate barotropic response near the central date due to surface pressurefluctuations, making it more difficult to regard central dates of height-based events as purely stratosphericin origin. We further characterize the relationship of all indices to conditions relevant to chemical ozonedepletion, finding that temperature-based indices in the lower stratosphere perform best. Finally, we presentfour dynamical benchmarks used to assess and compare the representation of strong events in climate models.Our results highlight the challenges in determining the optimal definition for strong events and emphasizethe implications of different choices, providing valuable insights for guiding future studies in defining strong events. 
This study analyzed mechanism of saponins regulating fatty alcohol oxidase (FAO) to reduce myocardial remodeling and control heart failure. 30 Sprague-Dawley (SD) rats were randomly and equally assigned into control group, model group, and saponin group, followed by analysis of myocardial tissue pathology, cyclic guanosine monophosphate (cGMP), Recombinant Human Protein (PKG), Peroxisome proliferator-activated receptors (PPAR- α ) expression levels, and cell apoptosis. Compared to control group, cGMP, PKG, PPAR- α , uncoupling protein 3 (UCP3), and cluster of differentiation 36 (CD36) mRNA levels in the model group were significantly decreased ( P <0.001) and elevated in the saponin group ( P <0.05). Oxidation rates of adenosine triphosphate (ATP), phosphocreatine/ATP, and palmitic acid in the model group were significantly decreased ( P <0.001) and elevated in the saponin group ( P <0.05). Apoptosis and level of Cleaved caspase-3 were significantly reduced in the model group ( P <0.001) and increased in the saponin group ( P <0.05). Levels of cGMP, PKG, PPAR- α , UCP3 and CD36 in the model group decreased ( P <0.001) and increased in the saponin group ( P <0.001), but lower than in the control group. Relative to the model group, Brain Natriuretic Peptide (BNP) level was significantly increased in the inhibitor group and decreased in the agonist group ( P <0.001). Saponins activate cGMP-PKG signaling pathway, up-regulating cGMP and PKG, promoting PPAR- α expression, inhibiting myocardial cell necroptosis, thereby reducing inflammatory infiltration of myocardial cells, improving connective tissue hyperplasia, and reducing myocardial injury and myocardial remodeling, thus play an anti-heart failure role.
Abstract Using the ERA5 reanalysis data, we identify seven easily calculable indices of the strength of the Arctic stratospheric vortex: zonal winds at 10 hPa and temperature or height anomalies at 10 , 50, and 100 hPa. We then compare the climatological statistics and meteorological properties of strong and weak events based on these indices. We particularly consider the sensitivity of the event statistics to the choice of thresholds, the use of these indices in capturing stratosphere–troposphere coupling, and meteorological conditions relevant to chemical ozone depletion. The frequency, seasonal distribution, and interdecadal variability of strong events is more sensitive to threshold or index choice compared to weak events. Composites of polar‐cap geopotential height anomalies are found to differ significantly based on the choice of index. In particular, height‐based events reveal a strong and immediate barotropic response near the central date due to surface pressure fluctuations, making it more difficult to regard central dates of height‐based events as purely stratospheric in origin. We further characterize the relationship of all indices to conditions relevant to chemical ozone depletion, finding that temperature‐based indices in the lower stratosphere perform best. Finally, we present four dynamical benchmarks used to assess and compare the representation of strong events in climate models. Our results highlight the challenges in determining the optimal definition for strong events and emphasize the implications of different choices, providing valuable insights for guiding future studies in defining strong events.
Abstract Using the NCEP–NCAR reanalysis dataset, this study classifies stratospheric northern annular mode (NAM) anomalies during the negative or positive phase into two categories—anomalies extending into the troposphere [trop event (TE); referred to as negative or positive TEs] and those not extending into the troposphere [nontrop event (NTE); referred to as negative or positive NTEs], and the corresponding tropospheric environments during the TEs and NTEs are identified. Compared with that for the negative NTEs, the upward wave fluxes entering the stratosphere are stronger and more persistent during the negative TEs. Furthermore, the stronger and more persistent upward wave fluxes during the negative TEs are due to more favorable conditions for upward wave propagation, which is manifested by fewer occurrences of negative refractive index squared in the mid- to high-latitude troposphere and stronger wave intensity in the mid- to high-latitude troposphere. However, the tropospheric wave intensity plays a more important role than the tropospheric conditions of planetary wave propagation in modulating the upward wave fluxes into the stratosphere. Stronger and more persistent upward wave fluxes in the negative TEs, particularly wave-1 fluxes, are closely related to the negative geopotential height anomalies over the North Pacific and positive geopotential height anomalies over the Euro-Atlantic sectors. These negative (positive) geopotential height anomalies over the North Pacific (Euro-Atlantic) are related to the positive (negative) diabatic heating anomalies and the decreased (increased) blocking activities in the mid- to high latitudes. The subtropical diabatic heating could also impact the strength of the mid- to high-latitude geopotential height anomalies through modulating horizontal wave fluxes. For positive NAM events, the results are roughly similar to those for negative NAM events, but with opposite signal.
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