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East Asian winter monsoon (EAWM) is one of the most crucial circulation systems in the Northern Hemisphere during winter, significantly influencing the weather and climate of East Asia. Therefore, predicting EAWM variations is considered as a key issue in winter climate prediction. The EAWM intensity index, as defined by Liu Shi (ISA) has shown a strong and consistent correlation with the interannual and interdecadal variations of winter temperature in Northeast China. However, the precursors influencing the EAWM (ISA) changed significantly with the decadal shift of the EAWM in the late 1990s. Predictions of EAWM have become less effective, and it is necessary to identify new predictors. Therefore, correlation analysis is conducted to identify the key factors influencing ISA based on the sea-ice-air system using reanalysis data produced by the National Centers for Environmental Prediction (NCEP) and the National Center for Atmospheric Research (NCAR), as well as optimum interpolation SST V2 data from the National Oceanic and Atmospheric Administration (NOAA). EAWM precursor factors are established and their possible interactions are discussed. Factors are used to construct a statistical prediction model using multiple linear regression method, which is evaluated through cross-validation. Results reveal a significant positive correlation between ISA and the horseshoe-shaped sea surface temperature (SST) pattern over the tropical Pacific autumn, as well as SST over the Gulf Stream and the Eurasian mid-high latitude circulation pattern in stratosphere. ISA shows a stronger and more consistent negative correlation with the sea ice concentration of the Barents Sea than that of the Kara Sea and Laptev Sea. These precursors influence ISA through land/sea thermal differences, winter atmospheric circulation patterns such as the East Asian trough, Ural blocking, and the East Asian subtropical westerly jet. The aforementioned prediction model demostrates a good fit and can be utilized to predict EAWM intensity under the current interdecadal background, with a consistency in the anomaly sign rate of 81.8% (9/11) during 11-year hindcast from 2012 to 2022. An analysis of two years of prediction failures reveals that the winter Arctic Oscillation (AO) forecasts, as well as the abrupt transition of the AO from autumn to winter, should be considered in the EAWM prediction process.

This study investigates the major patterns of large-scale tilted ridges (LSTRS) over the Eurasian continent and their connections with large-scale surface air temperature during boreal winter. A total number of 134 LSTR events with zonal extent exceeding 90° of longitude on the peak day are identified. Using self-organizing map (SOM), the LSTRs are classified into five clusters that are characterized by different spatial distributions and orientations. The leading two clusters are closely associated with extensive and persistent cold events over different places. Considering the first cluster, LSTRs extend from the Ural Mountains to Northeast Asia and are favorable for the amplification and southeastward extension of the Siberian high. Therefore, this cluster is closely associated with the occurrence of extensive and persistent cold events in china. In comparison with the first cluster, the LSTRs of second group are situated to the west, with starting points from the Kola Peninsula, and cause extensive and persistent cold events over Eastern Europe, central Asia, and central Siberia. The results suggest that the vertical coupling between LSTRs and the corresponding anomalous sea level pressure is crucial for the persistent cold temperature events associated with the leading two SOM clusters.

Sand and dust storms (SDSs) are particularly concerning natural disasters in East Asia. At present, there is still a lack of comprehensive knowledge of the characteristics of the cross-border SDSs between Mongolia and Northern China and the associated weather systems. This study identifies and documents the spring cross-border SDSs between Mongolia and Northern China based on the MODIS AOD map and Himawari-8/9 dust RGB images and analyzes the corresponding weather system types. A total of 76 spring cross-border SDSs were identified during 2000–2023, accounting for 55.1% of the total SDSs in both countries. The vast majority of the cross-border SDSs (86.8%) were related to Mongolian cyclones (MCs). Among them, 53.9% of the cross-border SDSs were mainly driven by Mongolian cyclones alone, and 32.9% were driven by the combination of MCs and cold highs (MC-CH type). Significant differences in the horizontal distribution of the SDSs were observed for different weather types. MCs alone trigger SDSs in the southern halves of the MCs, so the horizontal extent of the SDSs is consistent with that of MCs but larger than that associated with cold fronts. For the MC-CH type, strong winds in the southern flanks of MCs and their rear cold highs jointly drive a large-scale zonally extensive SDS belt. In recent years, particularly in 2021 and 2023, the strong cross-border SDSs have been dominated by the MC–CH type. This study provides a reference for the forecasting and early identification of cross-border SDS disasters. [ABSTRACT FROM AUTHOR]

Rainstorms always occur in the southeast and northeast quadrants of the Northeast China Cold Vortex (NCCV), resulting in significant flooding. This study investigated water vapor and trigger mechanisms for rainstorms within these two regions of an NCCV event during 11–14 June 2022 in terms of Lagrangian backward tracking, stratification stability, and upward motion using the ERA5 reanalysis. In the mid-troposphere, a quasi-stationary "ridge-NCCV-ridge" pattern resided over northeastern China, with an "anticyclonic-cyclonic-anticyclonic" airflow in the lower troposphere. As a result, water vapor originated from the Yellow Sea and was transported in an "L" shape toward both two regions. The southeast region was influenced by southwesterly and northwesterly airflows, resulting in the convergence of moist air from the Yangtze River and Lake Baikal and significant vertical shear of positive vorticity advection. This dynamic created deep and pronounced upward currents in the southeast of the NCCV, leading to the development of intensive and extensive rainstorms in situ. In contrast, the northeast region of the NCCV was dominated by southerly airflow. The moist air converged against the lee side of the Great Khingan Mountains and generated shallow, unstable stratification. The upward motion in this area was relatively weaker and thus induced regional rainstorms. [ABSTRACT FROM AUTHOR]

Based on daily data from the Japanese 55-year Reanalysis (JRA-55) covering the winters (NDJFM) from 1958 to 2018, this study examines the growth and decay mechanisms of the baroclinic wave packet (BWP) inferred from regression analysis over the North Pacific. Day-to-day kinetic energy (KE) and available potential energy (APE) budget analysis suggest that BWP is driven mainly by baroclinic energy conversion (CPB), barotropic energy conversion (CKB), and the nonlinear term (CKE). CPB acts as a predominant APE source for BWP. Part of CPB acts to overcome the APE loss caused by transient eddy flux and most of it acts as a dominant KE source to drive BWP throughout its lifespan. CKB acts as a KE source before day −1, and as a major KE sink to damp BWP afterward, in which the north–south gradient of the climatological meridional flow plays a key role. Similarly, CKE acts as a KE source before day 0 and as a major KE sink afterward. The damping effect of CKE comes mainly from the scale interaction through the advection of high-frequency meridional momentum by the low-frequency zonal flow. It turns out that the vertical geopotential flux divergence also plays an active role in the dynamical coupling of different vertical BWP parts. There is persistent geopotential flux transfer from the middle-tropospheric layer into the lower- and upper-tropospheric layers, which serves as a major KE source to drive the BWP anomalies for the two layers and a major KE sink for the middle-tropospheric layer where the baroclinic energy conversion is the strongest. Significance Statement: Previous studies indicate that baroclinic waves tend to organize into wave packets and are driven by the baroclinic instability. This study finds that the baroclinic waves decay mainly through the barotropic energy conversion and nonlinear processes. The results also indicate that the vertical geopotential flux divergence plays an active role in the dynamical coupling of the BWP anomalies in different layers of the troposphere. It is therefore very important to improve the representations of the climatological-mean flow, wave–mean flow interaction, and wave–wave interaction between high- and low-frequency waves in the midlatitudes, as well as the process of vertical transfer of the geopotential flux in numerical models for a better prediction of weather and climate variability in the extratropic regions. [ABSTRACT FROM AUTHOR]

Dust storms are common in Mongolia and northern China, this is a serious threat to the ecological security and socioeconomic development of both countries and the surrounding areas. However, a complete quantitative study of the source area, affected area, and moving path of dust storm events (DSEs) in Mongolia and China is still lacking. In this study, we monitored and analyzed the spatiotemporal characteristics of the source area and affected areas of DSEs in Mongolia and China using the high-spatiotemporal-resolution images taken by the Himawari-8 satellite from March to June 2016–2020. In addition, we calculated the moving path of dusty weather using the HYSPLIT model. The results show that (1) temporality, a total of 605 DSEs occurred in the study area, with most of them occurring in April (232 DSEs), followed by May (173 DSEs). Spatially, the dust storm sources were concentrated in the arid inland areas such as the Taklimakan Desert (TK, 138 DSEs) and Badain Jaran Desert (BJ, 87 DSEs) in the western, and the Mongolian Gobi Desert (GD, 69 DSEs) in the central parts of the study area. (2) From the affected areas of the DSEs, about 60% of the DSEs in Mongolia started locally and then affected downwind China, as approximately 55% of the DSEs in the Inner Mongolia Desert Steppe and Hunshandake Sandy Land came from Mongolia. However, the DSEs in the TK located in the Tarim Basin of northwest China affected the entire study area, with only 31.3% belonging to the local dust. (3) From the moving path of the dusty weather, the dusty weather at the three meteorological stations (Dalanzadgad, Erlian, and Beijing), all located on the main transmission path of DSEs, was mainly transported from the windward area in the northwest, accounting for about 65.5% of the total path. This study provides a reliable scientific basis for disaster prevention and control, and has practical significance for protecting and improving human settlements. [ABSTRACT FROM AUTHOR]

In this study, the northern Asian summer onset (NASO) is investigated in terms of its key features, thermodynamic driving factors, and its associations with the rainfall pattern in eastern China on the basis of the U.S. National Centers for Environmental Prediction and the U.S. National Center for Atmospheric Research reanalysis data, the snow cover extent data archived by the National Oceanic and Atmospheric Administration's National Centers for Environmental Information, and the precipitation data of observational stations in China. We define the NASO as the critical time when seasonal surface warming in northern Asia accelerates prior to this time and then stabilizes after this time. The climatological NASO occurs in the second pentad of June, across which systematic changes occur in the near surface warming in northern Asia. The heat budget analysis demonstrates from the climatic perspective that the snowmelt process in northern Asia plays a crucial role in the NASO. The positive feedback between surface warming and snowmelt facilitates an intense surface warming associated with the NASO. It is revealed that large‐scale wave patterns in the sea‐level pressure field contribute to early and late advents of NASOs. In association with the wave patterns, the horizontal linear advection term and adiabatic term are the primary thermodynamic drivers to the early and late NASOs. From late May to early July, the circulation anomalies from northern Asia to the subtropical western Pacific are significantly different between the early and late NASO years. Accordingly, in the rainy period, the seasonal evolution of rainfall pattern in eastern China also shows a considerable difference in these two NASO years. [ABSTRACT FROM AUTHOR]

The purpose of this study is the selection of an appropriate coupled general circulation model (CGCM) for seasonal weather prediction of winter temperatures in two cities of Pakistan: Islamabad and Lahore. The data used in the study comprises 32 years (1969–2000) of real‐time observations from the Pakistan Meteorological Department (PMD) and simulation data from CGCMs, including the European Centre for Medium Range Weather Forecasts (ECMWF) and the UK Met Office (UKMO). This study attempts to establish accurate average seasonal weather predictions using a single‐model Ensemble Prediction System (EPS). Accurate seasonal prediction is important for developing an early warning system. The probabilistic forecast is calculated for the lower tercile (i.e. [0, 0.33]) keeping in view the trend of winter temperature for both cities. The initial conditions (ICs) obtained from the CGCMs have been alternatively processed for better results. The probabilistic forecast obtained from the EPS has been further verified against PMD observations and European Reanalysis Data (ERA‐40) using two different measures of probabilistic skill: the Brier Skill Score (BSS) and the Relative Operating Characteristic Skill Score (ROCSS). The ECMWF and UKMO models were used for both of the cities under study. The results demonstrate that the ECMWF model is more suitable for Islamabad, whereas the UKMO model is more suitable for Lahore. The results from these models might be generalised for other areas at the same latitudes with similar topographic and climatic conditions. [ABSTRACT FROM AUTHOR]

ABSTRACT Northeast China cold vortex ( NCCV) circulation associated with a blocking-type circulation over the Yakutsk/Okhotsk ( YO) region brings persistent cool weather over Northeast China from May to mid-June and often causes a considerable reduction of local crop production. This study investigated the dynamic features of the YO-NCCV event on intraseasonal time scale and its relation with climate background circulation through analyzing two typical cases of YO-NCCV events. The first event (E1, from 25 May to 4 June, 2008) selected in this study was a long-lived (12 days) case, while the second event (E2, 16-18 May, 1972) was a short-lived one (only 3 days). Though two typical YO-NCCV events both developed from the southeastward movement of the polar high potential vorticity ( PV) air, they showed different life cycle features. In the E1, the formation of the NCCV circulation was associated with the poleward intrusion of two low- PV tongues over the Kamchatka Peninsula and the Ural Mountains. The low-frequency Rossby waves propagating from the Scandinavia Peninsula along the westerly to Northeast China mainly contributed to the maintenance of the NCCV circulation. In contrast, for the E2, the low- PV tongue over the Ural Mountains was absent and the PV field over Eurasian continent exhibited a synoptic wave feature. The transient eddy feedback forcing ( TEFF) anomalies contributed greatly to the formation and development of the YO-NCCV circulation. From the climatic view, the circulation anomalies associated with the E1 may be regarded as an intensive development of the climatological mean eddy field on the intraseasonal time scale. Results also show that the YO-NCCV event, among the four main types of NCCV event, was most closely related to the negative phase of western Pacific (WP) pattern. [ABSTRACT FROM AUTHOR]

The present study identified the large-scale tilted ridge and trough (LSTR and LSTT, respectively) axes of the midtropospheric circulation over mid- and high-latitude regions using an objective identification technique that has not previously been applied. In this method, the identification procedure classified contours of 500-hPa height (Z500) fields into three types: the circumpolar wavy contour, the circumpolar contour containing the meridionally overturned (or wave breaking) part, and the locally closed contour. The ridge and trough points were defined on these three types of contours and, subsequently, the ridge or trough axes were identified after connecting successively the nearest ridge or trough points of the neighboring contours under a minimum distance constraint. The performance of the identification method was tested in the daily Z500 fields during 15 November 2011-15 March 2012. The hit rate, false-alarm ratio, and threat score of the method in test reveal that it performs well with a reasonably good skill. An examination of the wave-breaking features during the same period also suggests that the method performs well in the identification of LSTRs and LSTTs for the meridionally overturned parts of the Z500 contours. This objective technique was also applied to an extensive and persistent cold event over East Asia. Results show that the horizontal extent of the Siberian high corresponds well with the zonal extents of the identified LSTR and LSTT. The identification method in the present study might be useful for identifying the key circulation systems associated with extensive and persistent cold air outbreaks during winter. [ABSTRACT FROM AUTHOR]

A deep and cold vortex circulation often occurs over northeast China. Known as the northeast China cold vortex (NCCV), the phenomenon is most active from May to mid-June and can lead to extremely cold local temperatures. This study used rotated principle component analysis to categorize NCCV events into four types, which were characterized by ridges (or blocks) over the following regions: Lake Baikal (BKL), the Yenisei River valley (YNS), the Ural Mountains (UR), and the Yakutsk-Okhotsk region (YO). On the intraseasonal time scale, it was found that BKL- and YNS-type NCCVs formed when the wave train height anomalies originating from the North Atlantic and Europe propagated to East Asia. In contrast, YO- and UR-type NCCVs formed in conjunction with the development of a meridional dipole pattern over northeast Asia. The existence of a blocking-type circulation over the Yakutsk-Okhotsk region favored maintenance of the NCCV circulation for the long-lived (more than 5 days) NCCV events of the four types. The typical circulation over northeast Asia for the long-lived NCCV event was closely associated with wave breaking, whereas the short-lived (3-5 days) event showed only wave propagation. The YNS-type NCCV caused cold surface air temperatures (SAT) not only over northeast China, but also over central and south China, whereas the other three types led only to regional cold SAT anomalies over northeast China. All four types of NCCVs caused a precipitation increase over northeast China, and this effect was broader for the UR- and YO-type NCCVs than that for BKL- and YNS-type NCCVs. [ABSTRACT FROM AUTHOR]

The rationale of this study is to highlight the significance of relationships of dengue transmission with climate and societal factors for four major cities in Pakistan (i.e., Islamabad, Rawalpindi, Lahore, and Karachi). These cities have been observed to report higher numbers of dengue cases in the last few years, with the highest number of cases reported during 2011. With careful consideration, the relationships of dengue transmission with climate factors, human population density, and traveling in the study areas have been taken into account. Regression model and generalized linear mixed model (GLM) with Markov chain Monte Carlo (MCMC) algorithm are computed to determine the relationships and random effects of different social (human population density, traveling) and climate (minimum-maximum temperatures, and rainfall) factors on dengue transmission. Neural network (NN) with multilayer perceptron algorithm is used to analyze the normalized importance of different covariates relative to dengue transmission. The results show that minimum temperature and rainfall, together with societal factors, significantly affecting the transmission of dengue in the study areas. The magnitude of these relationships is also shown by the results of the neural network. GLM also shows the significant random effects of minimum temperature, rainfall, human population density, and traveling on dengue transmission during the studied years (2009–2018). [ABSTRACT FROM AUTHOR]