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Based on potential vorticity (PV) thinking, northeast China cold vortex (NCCV) corresponds to an upper‐level high PV anomaly from stratospheric PV downward intrusion. Within a vortex, latent heating from precipitation would produce a vertical dipole of PV anomalies that would affect structures and evolution of the vortex. In this paper, three‐dimensional structures and evolution of NCCV and, effects of latent heating from precipitation along bent‐back, cold and warm fronts on them are investigated based on convection‐allowing simulations for an intense NCCV case during 8–17 June 2012. Trajectory analysis shows that the negative upper‐level diabatic PV anomaly from bent‐back frontal precipitation, near the vortex center, is the dominant contributor to erosion of high PV in the vortex core region as it is advected in, leading to the weakening of the vortex. The negative PV anomalies along the cold and warm fronts, at the east‐to‐southeast side of the vortex, are mostly advected downstream away from the NCCV. In the middle troposphere, positive PV anomalies are primarily generated along fronts and the accumulated positive PV anomalies filling the vortex region help to reinforce the low‐level cyclonic circulation. The lower‐level PV is affected by surface heating and cooling through their effects on static stability, but such effects are periodic and create mainly diurnal variations. The NCCV eventually decays as the upper‐level vortex weakens due to significant PV erosion. Plain Language Summary: Northeast China cold vortex (NCCV) is responsible for much of the warm season precipitation in northeast China. Based on convection‐allowing simulations of a characteristic case, the distribution and effects of latent heating release from precipitation in bent‐back, cold and warm frontal regions on the structures and evolution of potential vorticity (PV) within the NCCV are studied. Negative upper‐level PV anomalies generated at the bent‐back front are primarily responsible for the filamentation and erosion of high PV in the core of NCCV, leading to the weakening of the vortex. At middle‐to‐low levels, positive PV anomalies generated reinforce the low‐level circulations. However, the lower‐level PV exhibits a significant diurnal cycle, which is mainly affected by the surface heating and cooling through reducing static stability at daytime and increasing static stability during night. The overall system eventually decays as the upper‐level vortex weakens. Key Points: Precipitation in northeast China cold vortex produces negative upper‐level potential vorticity (PV) anomaly that weakens the upper level cold vortexNegative PV anomaly produced at the bent‐back front is the dominant contributor to the erosion of upper‐level high PV in the vortex centerLower‐level vortex is enhanced by positive PV anomaly from precipitation, and the PV has diurnal variations due to surface heating/cooling [ABSTRACT FROM AUTHOR]

Precipitation accumulations, integrated over rainfall events, are investigated using hourly data across continental China during the warm season (May–October) from 1980 to 2015. Physically, the probability of precipitation accumulations drops slowly with event size up to an approximately exponential cutoff scale sL where probability drops much faster. Hence sL can be used as an indicator of high accumulation percentiles (i.e., extreme precipitation accumulations). Overall, the climatology of sL over continental China is about 54 mm. In terms of cutoff changes, the current warming stage (1980–2015) is divided into two periods, 1980–97 and 1998–2015. We find that the cutoff in 1998–2015 increases about 5.6% compared with that of 1980–97, with an average station increase of 4.7%. Regionally, sL increases are observed over East China (10.9% ± 1.5%), Northwest China (9.7% ± 2.5%), South China (9.4% ± 1.4%), southern Southwest China (5.6% ± 1.2%), and Central China (5.3% ± 1.0%), with decreases over North China (−10.3% ± 1.3%), Northeast China (−4.9% ± 1.5%), and northern Southwest China (−3.9% ± 1.8%). The conditional risk ratios for five subregions with increased cutoff sL are all greater than 1.0, indicating an increased risk of large precipitation accumulations in the most recent period. For high precipitation accumulations larger than the 99th percentile of accumulation s99, the risk of extreme precipitation over these regions can increase above 20% except for South China. These increases of extreme accumulations can be largely explained by the extended duration of extreme accumulation events, especially for "extremely extreme" precipitation greater than s99. [ABSTRACT FROM AUTHOR]

The characteristics of summer precipitation over northern central China (NC China) and its associated atmospheric circulation have been documented in many previous studies. However, the prediction of extreme precipitation events, which is vital for water resource management and agricultural yield, has received little attention. In this study, we attempted to establish a statistical model to predict mid‐summer extreme precipitation days (EPDs) over NC China, based on a year‐to‐year increment (DY) approach. Three variables—preceding early‐spring snow cover DY over western China, previous early‐summer sea surface temperature (SST) DY in the North Pacific, and SST DY differences between the equatorial western and eastern Pacific—were selected as potential predictors. The first predictor exerted an impact on precipitable water content anomalies, South Asian high and vertical movement anomalies over NC China through anomalous soil moisture over northern China. The latter two predictors affected the EPDs over NC China via modulating moisture transport originating from tropical oceans. Further results showed that the prediction model performed well in predicting the inter‐annual variation of EPDs, with respective correlation coefficients of.79/.67 between the predicted and observed EPDs DY/EPDs for 1980–2014. The agreement index of the prediction model was 0.67 and the Nash–Sutcliffe efficiency was 0.37, suggesting good capabilities of the prediction model. Both the one‐year‐out cross‐validation test for 1980–2014 and independent hindcast for 1995–2014 demonstrated that these three predictors showed skilful predictions of EPDs over NC China. The cross‐validation (hindcast) simulated EPDs DY achieved a significant correlation coefficient of.74 (.78) with the observations, along with positive Nash–Sutcliffe efficiency values. Notably, the decadal shift of EPDs around the 2000s was successfully replicated in both cross‐validation and hindcast results. [ABSTRACT FROM AUTHOR]

This study unveils the evolution of two major early signals in the North Pacific atmosphere-ocean system that heralded abnormal high-pressure blockings and cold-vortex activities across Northeast China, based on an analysis of the configurations of major modes including the polar vortex, the North Pacific Oscillation (NPO), and SST in the preceding winter and spring and atmospheric low-frequency disturbances in Northeast China. We analyzed these aspects to understand the atmosphere-ocean physical coupling processes characterized by the two early signals, and here we explain the possible mechanisms through which dipole circulation anomalies affect the summer low-temperature processes in Northeast China. We further analyzed the interdecadal variation background and associated physical processes of the two early signals. [ABSTRACT FROM AUTHOR]

In recent years, there has been an increasing occurrence of compound heat-humidity (HH) events worldwide, leading to excessive morbidity and mortality. Southeast China has been particularly affected by HH events over the past decade. However, the seasonal prediction of HH events in Southeast China remains a considerable challenge. Based on the year-to-year increment (DY) approach and the empirical orthogonal function analysis, a robust prediction model is developed in this study for the midsummer HH events in Southeast China during 1981–2022. Three prediction models are individually constructed for the first three principal components (PCs) of the DY for HH events (hereafter referred to as HH_DY). The correlation coefficients (CCs) between the predicted and observed PCs exceed 0.75 in the cross-validation test for 1981–2022 and 0.80 in independent hindcasts for 2013–2022. The predicted graphical maps of HH_DY are reconstructed by the projecting the fitted three PCs onto the observed first three empirical orthogonal function modes, and the geographical patterns of HH events are obtained by adding the simulated HH_DY to the observed HH events for the preceding year. In the cross-validation test, the spatial features of the predicted HH events are highly accordant with those of the observations in nine extreme compound HH years, with area CC values ranging from 0.89 to 0.95. In the independent hindcasts for the past decade, the area CC values exceed 0.76 in all years and are >0.80 in eight years. Moreover, the predicted high-incidence areas of HH events are highly consistent with the observations in both the cross-validation test and independent hindcasts. The reliable prediction for geographical distributions of HH events in Southeast China is of great significance for human adaptation to future climate warming. • Using interannual increment methods, we developed a prediction model of midsummer compound HH events in Southeast China. • The area CCs range from 0.89 to 0.95 in nine extreme years of compound HH years in cross-validation test. • The predicted high-incidence areas of HH events agree with the observations in cross-validation and independent hindcasts. [ABSTRACT FROM AUTHOR]

• The southwesterly and northeasterly paths dominate the moisture transport. • Interannual variations of precipitation and moisture transport are closely linked. • Contribution of southwesterly path and the Indian Ocean increase during wet years. • The northeasterly path ranks the most important path during the dry years. • Flood variation is linked to moisture contribution from the Indian Ocean. This study used the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model to examine the moisture sources and pathways associated with warm-season precipitation over the Sichuan Basin (SCB), southwestern China, with emphasis on the long-term mean state and interannual variability. Four groups of moisture pathways were identified over the period 1981–2017; i.e., the southwesterly, northeasterly, northwesterly, and westerly paths. With respect to the long-term mean state, the southwesterly path made the largest moisture contribution (36.0%) and, in combination with the northeasterly path (the importance of which has received little attention in previous studies), provided 70.2% of the total moisture. The Indian Ocean serves as the most important moisture source, accounting for 36.3% of the total moisture. In terms of interannual variability, compared with dry years, in wet years, the moisture contributions from the southwesterly path and the Indian Ocean increase by 18.6% (38.3% vs. 32.3%) and 20.71% (38.38% vs. 31.80%), but the contributions from the other moisture pathways and other major sources decrease. During the dry years, the northeasterly path, rather than the southwesterly path, provides the most moisture (34.6%). There are significant positive correlations between variations in runoff over the central and northern SCB and the moisture contribution from the Indian Ocean, which is associated with anomalous precipitation patterns over the SCB induced by fluctuations in the moisture contributions from the Indian Ocean. [ABSTRACT FROM AUTHOR]