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In early summer 2020, eastern China was hit by record-breaking Meiyu rainfall. The anomalous western Pacific subtropical high (WPSH) played a crucial role in this event. This paper exposes the abnormal features of the WPSH and its related vertical circulations and reveals its dynamical causes in this period, from the perspective of the three-pattern decomposition of global atmospheric circulation (3P-DGAC). Analyzing the anomalous spatial patterns of the three stream functions R, H, and W of the horizontal, meridional, and zonal circulations defined by the 3P-DGAC, we discovered that the WPSH described by R at 850 hPa was intensified and westward from the horizontal circulation. For the vertical circulations, the local meridional circulation along East Asia expressed by H manifested an abnormal downdraft at 20° N, which was beneficial to strengthening the WPSH. The zonal circulation in the tropical Pacific represented by W was anomalously far to the west, which was related to the westward extension of the WPSH. Then, to uncover the causes of the anomalous WPSH from the dynamics, we used the vorticity equation based on the 3P-DGAC and found that the negative relative vorticity advection anomaly over the western Pacific played a key role in this event. Due to the positive sea surface temperature (SST) anomaly and enhanced convection over the Maritime Continent (MC), local vertical circulations at low latitudes were significantly activated. The intense local meridional circulation along East Asia carried the relative vorticity from the MC to the western Pacific and strengthened the WPSH. The ascending branch of the zonal circulation in the tropical Pacific moved westward, which may favor the westward extension of the WPSH. This study represents a promising step in revealing the three-dimensional (3D) structure and internal dynamics of anomalous WPSH. [ABSTRACT FROM AUTHOR]

The western North Pacific subtropical high (WNPSH) is a critical atmospheric circulation system influencing weather and climate patterns in eastern China. Accurately predicting its activity is essential for anticipating and managing natural disasters such as droughts and floods in the region. In this study, we employ the decision tree (DT) as the fundamental model and devise a compatible framework to create an integrated model known as the Decision Tree Integration Model for Synthesizing Multiple External Forcing Signals (DTI-MS), to perform classification prediction of the WNPSH ridge line in summer. Within the construction of DTI-MS, the interpretability advantage of DT model is fully exploited. Three significant sources of external forcing signals, namely sea surface temperature in the Pacific, Tropical Indian Ocean and Atlantic Ocean, and snow depth across the Eurasian continent, are identified from distinct DT models, with clear physical meanings. Through the voting strategy, these signals are integrated, laying the groundwork for DTI-MS to synthesize multiple external forcing signals. Regarding prediction performance, DTI-MS achieves a high classification accuracy of 91% in the training set and 93% in the testing set, with recalls for the southerly and northerly positions of the WNPSH in the testing set also exceeding 80%. Compared with the commonly used machine learning models such as DT and Random Forests constructed through general modeling approaches, DTI-MS also demonstrates higher classification accuracy. Overall, DTI-MS not only shows promising potential in predicting the WNPSH ridge line, but its integration framework also provides a new paradigm for short-term climate prediction modeling. • Three categories of the WNPSH ridge line can markedly differentiate the summer precipitation in eastern China. • The DTI-MS model integrates three crucial sources of external forcing signals with clear physical meanings. • The DTI-MS model has superior interpretability. • The DTI-MS model has an excellent classification prediction performance. [ABSTRACT FROM AUTHOR]

Unlike previous studies solely focused on the influences of low or mid-latitudes signals on regional extreme events, this paper used the three-pattern decomposition of global atmospheric circulation (3P-DGAC), taking the 2018 hot summer in East Asia for example, to quantitatively reveal the dynamic and synergistic effects of low and mid-latitudes signals on regional extreme events. By analyzing the anomalous three-dimensional structure of atmospheric circulations in 2018 hot summer, we discovered that the local meridional circulation at low latitudes and zonal circulation at mid-latitudes both produced abnormal downdrafts in East Asia, which were consistent with the anomalous anticyclone in this region. Then, we investigated the relative vorticity advection combined with 3P-DGAC to uncover the dominant circulation patterns, and found the horizontal circulation at mid-latitudes and local meridional circulation at low latitudes were the major contributor to the anomalous anticyclone, accounting for 56% and 44% respectively. This result indicated the 2018 hot summer might be influenced by the synergistic effect of low and mid-latitudes signals. Finally, by investigating sea surface temperature anomaly (SSTA) and mid-latitudes wave train, we considered the tripole-like SSTA pattern in the North Atlantic and positive SSTA in Kuroshio and its extension area (K-KE) as the main causes of horizontal circulation anomalies, and the anomalous meridional circulation was related to the extremely late onset of South China Sea summer monsoon (SCSSM). This study provided a novel way to quantitatively study synergistic effects of low and mid-latitudes signals on regional extreme events. • East Asia was hit by extreme heat event in the summer of 2018. • Horizontal circulations at mid-latitudes and meridional circulations at low latitudes contributed greatly to this event. • The combination of 3P-DGAC and dynamic variables can be applied to the study of dynamic causes of extreme climate events. [ABSTRACT FROM AUTHOR]

This paper reviews the three-pattern decomposition of global atmospheric circulation (3P-DGAC) developed in recent years, including the decomposition model and the dynamical equations of global horizontal, meridional, and zonal circulations. Compared with the traditional two-dimensional (2D) circulation decomposition method, the 3P-DGAC can effectively decompose the actual vertical vorticity into two components that are caused by the horizontal circulation and convergent/divergent movement (associated with the meridional and zonal circulations). It also decomposes the vertical velocity into the components of the meridional vertical circulation and the zonal vertical circulation, thus providing a new method to study the dynamical influences of convergent/divergent motions on the evolution of actual vertical vorticity and an accurate description of local vertical circulations. The 3P-DGAC is a three-dimensional (3D) circulation decomposition method based on the main characteristics of the actual atmospheric movements. The horizontal, meridional, and zonal circulations after the 3P-DGAC are the global generalization of Rossby waves in the middle-high latitudes and Hadley and Walker circulations in low latitudes. Therefore, the three-pattern decomposition model and its dynamical equations provide novel theoretical tools for studying complex interactions between middle-high and low latitude circulations as well as the physical mechanisms of the abnormal evolution of large-scale atmospheric circulations under the background of global warming. [ABSTRACT FROM AUTHOR]

This study reveals the causes of extreme high temperatures in China in August 2022 and the role of South Asian high (SAH) anomaly. The 2022 extreme heat events in the Tibetan Plateau (TP) and Yangtze River basin (YRB) are the strongest since 1979, accompanied by an anticyclonic anomaly in the northeastern part of the SAH. Six displacement indices of the SAH are defined by taking advantage of the stream function R of horizontal circulation in the three-pattern decomposition of the global atmospheric circulation (3P-DGAC) model, which can effectively remove the systematic errors in geopotential high caused by global warming. The results show an extreme northward shift of the eastern center of SAH occur in August 2022, with correlation coefficients 0.85 and 0.69 with the temperature anomaly indices of TP and YRB regions, respectively, for 1979–2022. In addition to the La Niña event, we find evidence that the soil moisture in the Indo-China Peninsula (ICP) region from January to August 2022 is extremely wet, linked to significant impacts on the northward movement of the eastern center of SAH response to land-air interactions. Further, the 3P-DGAC model helps us to reveal that the extreme northward shift of the eastern center of SAH brings extensive circulation adjustments, in which the local meridional circulation anomaly intensifies the high temperature in the YRB, while the local zonal circulation in the middle latitudes is the main cause of the high temperature in the TP. Meanwhile, the northward shift of the eastern center of SAH pushes the East Asian subtropical westerly jet (EAJ) northeastward, and the convergent downdraft to the right of EAJ exit also further aggravates the summer hot extremes in China in 2022. • An innovative application of stream function R in 3P-DGAC model to define the SAH indices. • In August 2022, The extreme northward shift of the eastern center of SAH was responsible for the high temperature in China. • Extremely wet soil moisture in Indo-China Peninsula in spring and summer 2022 exacerbates the displacement anomaly of SAH. [ABSTRACT FROM AUTHOR]

The three-pattern decomposition of global atmospheric circulation (TPDGAC) partitions three-dimensional (3D) atmospheric circulation into horizontal, meridional and zonal components to study the 3D structures of global atmospheric circulation. This paper incorporates the three-pattern decomposition model (TPDM) into primitive equations of atmospheric dynamics and establishes a new set of dynamical equations of the horizontal, meridional and zonal circulations in which the operator properties are studied and energy conservation laws are preserved, as in the primitive equations. The physical significance of the newly established equations is demonstrated. Our findings reveal that the new equations are essentially the 3D vorticity equations of atmosphere and that the time evolution rules of the horizontal, meridional and zonal circulations can be described from the perspective of 3D vorticity evolution. The new set of dynamical equations includes decomposed expressions that can be used to explore the source terms of large-scale atmospheric circulation variations. A simplified model is presented to demonstrate the potential applications of the new equations for studying the dynamics of the Rossby, Hadley and Walker circulations. The model shows that the horizontal air temperature anomaly gradient (ATAG) induces changes in meridional and zonal circulations and promotes the baroclinic evolution of the horizontal circulation. The simplified model also indicates that the absolute vorticity of the horizontal circulation is not conserved, and its changes can be described by changes in the vertical vorticities of the meridional and zonal circulations. Moreover, the thermodynamic equation shows that the induced meridional and zonal circulations and advection transport by the horizontal circulation in turn cause a redistribution of the air temperature. The simplified model reveals the fundamental rules between the evolution of the air temperature and the horizontal, meridional and zonal components of global atmospheric circulation. [ABSTRACT FROM AUTHOR]

In order to study the interactions between the atmospheric circulations at the middle-high and low latitudes from the global perspective, the authors proposed the mathematical definition of three-pattern circulations, i.e., horizontal, meridional and zonal circulations with which the actual atmospheric circulation is expanded. This novel decomposition method is proved to accurately describe the actual atmospheric circulation dynamics. The authors used the NCEP/NCAR reanalysis data to calculate the climate characteristics of those three-pattern circulations, and found that the decomposition model agreed with the observed results. Further dynamical analysis indicates that the decomposition model is more accurate to capture the major features of global three dimensional atmospheric motions, compared to the traditional definitions of Rossby wave, Hadley circulation and Walker circulation. The decomposition model for the first time realized the decomposition of global atmospheric circulation using three orthogonal circulations within the horizontal, meridional and zonal planes, offering new opportunities to study the large-scale interactions between the middle-high latitudes and low latitudes circulations. [ABSTRACT FROM AUTHOR]

This study investigates the differences and connections between the three-pattern decomposition of global atmospheric circulation, the representation of the horizontal vortex circulation in the middle-high latitudes and the local partitioning of the overturning circulation in the tropics. It concludes that the latter two methods are based on the traditional two-dimensional (2D) decomposition of the vortex and divergent circulations in the fluid dynamics and that the three-pattern decomposition model is not a simple superposition of the two traditional methods but a new three-dimensional (3D) decomposition of global atmospheric circulation. The three-pattern decomposition model can decompose the vertical vorticity of atmosphere into three parts: one part is caused by the horizontal circulation, whereas the other two parts are induced by divergent motions, which correspond to the zonal and meridional circulations. The diagnostic results from the decomposed vertical vorticities accord well with the classic theory: the atmospheric motion at 500 hPa is quasi-horizontal and nondivergent and can represent the vertical mean state of the entire atmosphere. The analysis of the climate characteristics shows that the vertical vorticities of the zonal and meridional circulations are the main cause of the differences between the three-pattern circulations and traditional circulations. The decomposition of the vertical vorticity by the three-pattern decomposition model offers new opportunities to quantitatively study the interaction mechanisms of the Rossby, Hadley and Walker circulations using the vorticity equation. [ABSTRACT FROM AUTHOR]

In contrast to previous studies that mainly focused on the influence of the polar vortex in the horizontal circulation on the local cold air, this study uses the three-pattern decomposition of global atmospheric circulation (3P-DGAC) to reveal the dynamic synergistic effects of horizontal circulation, local meridional circulation, and local zonal circulation on cold waves, by examining the record-breaking extreme cold wave (ECW) in February 2021 across North America. In terms of horizontal circulation, this ECW is preceded by the strengthening of blocking highs over the North Pacific and North Atlantic that force the tropospheric polar vortex edge toward North America, resulting in the development of the North American trough. The strongly northwesterly wind caused by the North American trough strengthens the local meridional circulation over North America, transporting cold Arctic air to the mid-low latitudes. Meanwhile, the local meridional circulation over North America strengthens the ascending motion and subsequently promotes the development of local zonal circulation over the North Atlantic. In turn, the developed local zonal circulation reinforces the blocking highs over the two oceans, slowing the movement of the trough and ridge systems eastward and leading to a long duration for this ECW. The composite analysis further conforms that the vertical sinking motion corresponding to blocking highs over the two oceans is mainly contributed by the local zonal circulation, and the strong local zonal circulation over the North Atlantic could lengthen the duration of the cold wave by strengthening the blocking highs. This study suggests that 3P-DGAC is an effective tool for investigating the three-dimensional structural characteristics of anomalous circulations in ECWs. • North America was hit by a record-breaking extreme cold wave in February of 2021. • Dynamic synergistic effects of large scale three-dimensional circulation anomalies on extreme cold waves was studied. • The mid-high latitude local meridional circulation and local zonal circulation played a vital role in this extreme event. [ABSTRACT FROM AUTHOR]

China was hit by extreme precipitation in July and August of 2021 along with significant monthly variation. The positive precipitation anomalies observed in July were mainly located in eastern China, but these anomalies shifted to the middle and lower reaches of the Yangtze River (MLYR) in August. In this study, we investigated the July and August precipitation anomaly dynamics based on the three-pattern decomposition of global atmospheric circulation (3P-DGAC) method. The results showed that the mid-latitude zonal circulation played a dominant role in July 2021, causing anomalous positive relative vorticity advection over the center of the positive precipitation anomalies, thus providing strong convective activity for the anomalous precipitation. Nevertheless, the August anomalies could be better explained from a climate perspective. The anomalous relative vorticity distribution patterns recorded in August were often accompanied by extreme precipitation in the MLYR, and the negative relative vorticity anomalies identified in Northeast Asia also played a crucial role. In conclusion, the mechanisms of precipitation anomalies in July and August 2021 were almost completely disparate. In this study, we emphasized the role of the mid-latitude zonal circulation in extreme precipitation events, and suggested that the impact of mid-latitude zonal circulation will be further accentuated under global warming. • China was hit by extreme precipitation event in July and August of 2021. • A new method of global atmospheric circulation was used to study dynamic mechanism. • The mid-latitude zonal circulation played a vital role in this extreme event. [ABSTRACT FROM AUTHOR]

The tropical Pacific Walker circulation (PWC) is fundamentally important to global atmospheric circulation, and changes in it have a vital influence on the weather and climate systems. A novel three-pattern decomposition of a global atmospheric circulation (3P-DGAC) method, which can be used to investigate atmospheric circulations including the PWC, was proposed in our previous study. Therefore, the present study aims to examine the capability of this 3P-DGAC method to acquire interdecadal variations in the PWC and its connection to inhomogeneous air temperature changes in the period from 1961–2012. Our findings reveal that interdecadal variations in the PWC, i.e., weakening (strengthening) between the periods 1961–1974 and 1979–1997 (1979–1997 and 1999–2012), can be observed using the zonal stream function (ZSF) derived from the 3P-DGAC method. Enhancement of the PWC is also associated with the strengthening and weakening of zonal circulations in the tropical Indian Ocean (IOC) and Atlantic (AOC), respectively, and vice versa, implying a connection between these zonal overturning circulations in the tropics. The interdecadal variations in the zonal circulations correspond well to inhomogeneous air temperature changes, i.e., an enhancement of the PWC is associated with a warming (cooling) of the air temperature from 1000 to 300 hPa in the western (mid–eastern) Pacific Ocean and a cooling (warming) of the air temperature in the tropopause in the western (mid–eastern) Pacific Ocean. Furthermore, a novel index for the PWC intensity based on air temperature is defined, and the capability of the novel index in representing the PWC intensity is evaluated. This novel index is potentially important for the prediction of the PWC by using dynamic equations derived from the 3P-DGAC method. [ABSTRACT FROM AUTHOR]