Northeast China Cold Vortex Research Articles

Climatology of Northeast China cold vortices during the warm season: A comparison of ERA5 and MERRA‐2 reanalyses

AbstractThe Northeast China cold vortex (NCCV) is an important type of synoptic scale system, which often induces local torrential rainfall events, strong winds, and lightning during warm seasons (May–September). By using an automatic identification method that involves a three‐step algorithm, NCCVs during warm seasons of 1980–2018 were identified based on ERA5 and MERRA‐2, the latest generation of reanalysis. Employing this recognition result and intensive surface observations, climatology of the NCCV was analysed. With respect to average climatic characteristics, the results indicate that the NCCV is most frequently located from the east of the Yablonov Mountains to the west of the Xiao Hinggan Mountains. The average rain belt and cold tongues resulting from NCCVs both mainly fall within Northeast China, Japan, Southeast Russia, and the Korean Peninsula, causing precipitation and temperature anomalies there, especially in Northeast China. Regarding interannual variation, the number of NCCV‐occurrence hours varies at a cycle of about 3 years, and has increased in the last 10 years compared to 1999–2008. The intensity of the NCCV also fluctuates in a cycle of approximately 3 years and shows a weakening trend, particularly from July to September. As for life characteristics, NCCVs usually form at the border area between China, Mongolia, and Russia, then develop and move eastwards, and finally disappear in areas of Heilongjiang in China, southeastern Russia, and the Okhotsk Sea. The NCCV moves in complex paths; among all 55 types of routes that occurred in warm seasons of 1980–2018, the most favoured paths are east, southeast, northeast, southeast‐to‐northeast, and circular. The above results based on the up‐to‐date reanalysis datasets with high resolutions are updates and supplements to previous studies, further improving our understanding of the NCCV in aspects of its cooling effects, weakening trends, and crucially, paths of movement and their occurrence frequency.

Study on Diagnosis Weather Process and Flight Impact of Heavy Snowfall in Northeast China “11/2021”

Based on ERA5 reanalysis data, the characteristics of weather situation, water vapor condition, dynamic uplift condition, energy condition, ice accumulation environment and flight effect of aircraft in the heavy snowfall process in northeast China from November 5 to 12, 2021 are analyzed. The results show that the heavy snowfall process in Northeast China is caused by the combination of Northeast China Cold Vortex, trough, low level frontal cyclone and cold front. Through the analysis of the physical field, it is found that the sufficient water vapor transport is from the south and the southeast, the convergence rising in the lower layer, divergence “pumping” in the upper layer, air flow rising in the vertical plane and a large amount of convection effective potential energy are all contributing to the heavy snowfall. The impact of heavy snowfall on flight mainly includes low visibility and ice accumulation. Water vapor flux, water vapor flux divergence, vertical velocity, potential temperature and convective effective potential energy can all be used as the judging indexes of heavy snowfall forecast.

Northeast China Cold Vortex Observed by FY‐3 MWTS‐2 and MetOp AMSU‐A

AbstractThe northeast China cold vortex (NCCV) refers to a closed low‐pressure system over northeast China extending from China‐Siberia to the northwest Pacific coast region. It is cut off from the westerly jet belt in the middle and upper troposphere, has a cold core, lasts several days, and could bring heavy rain events in late spring and summer that are of great challenge to weather forecasters. This study investigates the possibility of observing temperature structures of NCCVs by two microwave temperature sounders, that is, the Microwave Temperature Sounder‐2 (MWTS‐2) and the Advanced Microwave Sounding Unit‐A (AMSU‐A) onboard the two polar‐orbiting operational environmental satellites (POES) Fenyun‐3 satellite FY‐3D and Meteorological Operational satellite MetOp‐B, respectively. The MWTS‐2 and AMSU‐A together provide 3D atmospheric temperatures in the middle and upper troposphere, as well as the lower stratosphere four times daily. Both limb‐corrected direct observations of brightness temperature and retrievals of atmospheric temperature within NCCVs are characterized by cold and warm cores below and above the tropopause, respectively, comparing favorably with the European Centre for Medium‐Range Weather Forecasts ERA5 reanalysis. Compared with the ERA5 reanalysis in June 2019, the MWTS‐2 retrieved atmospheric temperatures have no scan‐dependent biases, the biases are smaller than ±0.2K, and root‐mean‐square errors (RMSEs) are smaller than and 2.0K at all altitudes. This study suggests the possibility of using multiple POES microwave‐temperature‐sounding observations for near‐real‐time monitoring of NCCVs' 3D temperature structures.

Possible Causes of Extremely Warm Early Summer in North China During Cold and Warm Periods

The abnormal characteristics of extremely warm early summer (EWES) in North China under different decadal backgrounds were contrastively analyzed. Their relationships with upper- and lower-level atmospheric circulation and global sea surface temperature anomalies (SSTAs) are also discussed. Results show that temperature anomalies of EWES in North China are overall higher than normal in both cold (1961–1993) and warm (1994–2019) periods, but the anomalies of the latter are much higher than that of the former. EWES in North China is directly related to the circulation lying between 40° and 50°N in the middle troposphere, which leads to positive temperature anomalies occurring from the bottom to the upper level of the troposphere together with a high anomaly trend tilting northward. The persistent and strong Eurasian continental high (ECH) and weak Northeast China cold vortex (NECV) activity, together with the strong western Pacific subtropical high (WPSH) are major factors that directly lead to EWES in North China. ECH and WPSH are stronger and larger, and NECV are weaker and more northward in the warm period than in the cold period. In addition, the positive SSTAs in the tropical Indian Ocean and the Kuroshio area are favorable for the stronger and larger ECH and WPSH as well as the weaker and more northward NECV, causing strong anticyclonic and downward circulation system controlling North China, resulting in the extremely warm temperatures there. The joint impact of the positive tropical Indian Ocean SSTAs and the Kuroshio region SSTAs is more significant during warm than cold periods, resulting in much stronger EWES in North China during warm periods.

Deep Learning-Based Radar Composite Reflectivity Factor Estimations from Fengyun-4A Geostationary Satellite Observations

Ground-based weather radar data plays an essential role in monitoring severe convective weather. The detection of such weather systems in time is critical for saving people’s lives and property. However, the limited spatial coverage of radars over the ocean and mountainous regions greatly limits their effective application. In this study, we propose a novel framework of a deep learning-based model to retrieve the radar composite reflectivity factor (RCRF) maps from the Fengyun-4A new-generation geostationary satellite data. The suggested framework consists of three main processes, i.e., satellite and radar data preprocessing, the deep learning-based regression model for retrieving the RCRF maps, as well as the testing and validation of the model. In addition, three typical cases are also analyzed and studied, including a cluster of rapidly developing convective cells, a Northeast China cold vortex, and the Super Typhoon Haishen. Compared with the high-quality precipitation rate products from the integrated Multi-satellite Retrievals for Global Precipitation Measurement, it is found that the retrieved RCRF maps are in good agreement with the precipitation pattern. The statistical results show that retrieved RCRF maps have an R-square of 0.88-0.96, a mean absolute error of 0.3-0.6 dBZ, and a root-mean-square error of 1.2-2.4 dBZ.

A feasible approach to improve forecast skill of summer precipitation in northeast China by statistical regression of the northeast China cold vortex in the multimodel ensemble

AbstractHindcasts during 1991–2010 are analysed to investigate the forecast skills for summer precipitation in northeast China (NEC) and circulations in northeast Asia with a leading time of 1‐month in three operational climate models and their equally weighted mean. It is found that the precipitation prediction ability of all the models and their combinations are much low in NEC. However, both the single model and their averages can well reproduce the basic summer circulation characteristics over Northeast Asia, especially the northeast China cold vortex (NECV) that directly affects precipitation in NEC. Observed precipitation is significantly correlated with the forecasted vorticities in each model and their combinations, particularly in the ensemble mean of the models (MME). Furthermore, the interannual variability of the NECV in MME agrees well with the observations. Linear regression between the simulated NECV and the precipitation in NEC is established for each model and their averages. The root‐mean‐square errors (RMSEs) of precipitation forecast from the regression of NECV are much lower than the direct outputs in above models, while the correlation coefficients (CCs) are much higher. The CC between observation and forecasts by the regression method based on the NECV in MME is the highest (0.5), closest to the value of 0.58 in observation, and the RMSE is the smallest (0.54), decreased by 13% compared with MME direct outputs. The cross‐validation during the 20 years can provide better prediction skills with a CC of 0.37, higher than that for the single‐model outputs, the averages of random two models and the MME. Independent forecasts also provide higher prediction skills than the official forecast of China Meteorological Administration in 4 years during 2013–2018, especially the extreme flood summer of 2013. The results indicate it might be a feasible approach to improve the prediction skill of summer precipitation in NEC.

The Characteristics of Northeast China Cold Vortex With Different Active Paths in June and Their Relationship With Precipitation and Pre-SST

In this study, a K-means clustering (KMC) method was used to identify the paths of the Northeast China (NEC) Cold Vortex (NCCV). The NCCV was divided into four types according to the identified active paths: (1) Eastward movement type (EM); (2) Southeastward long-distance movement type (SLM); (3) Eastward short-distance movement type (ESM); and (4) Southward short-distance movement type (SSM). The characteristics of the four types of the NCCV, along with their impacts on the precipitation during early summer in NEC, were studied. The results showed that the KMC method can effectively divide the NCCV events into four different types. The maintaining days of these four types of the NCCV were found to have obvious interannual and interdecadal variation features. For example, the maintaining days of the EM and ESM types were mainly characterized by interannual variability, while the SLM and SSM types have the obvious 10–13a interdecadal variation along with interannual variability. In terms of the spatial distributions and impacts on precipitation, the EM type was found to appear in the majority of the areas located in NEC, the SLM type mainly occurred in the northwestern region of NEC and the highest rain center was located in the south-central portion, while the ESM type and SSM type were observed precipitation only appear in a small portion of the northeastern region. In addition, it is also observed the distribution of the sea-surface temperature (SST) anomalies had close relationship with the formation of these four types of the NCCV. The tripole distributions of the SST anomalies in the Atlantic Ocean corresponded to the EM type of the NCCV, the positive anomalies of SST in the eastern equatorial Pacific Ocean and negative anomalies in the western equatorial Pacific corresponded to the SLM type, the positive SSTs in the Northwest Pacific correspond to the ESM type, while negative anomalies SST in the western equatorial Pacific Ocean corresponded to the SSM type of the NCCV.

Classification of Northeast China Cold Vortex Activity Paths in Early Summer Based on K-means Clustering and Their Climate Impact

The classification of the Northeast China Cold Vortex (NCCV) activity paths is an important way to analyze its characteristics in detail. Based on the daily precipitation data of the northeastern China (NEC) region, and the atmospheric circulation field and temperature field data of ERA-Interim for every six hours, the NCCV processes during the early summer (June) seasons from 1979 to 2018 were objectively identified. Then, the NCCV processes were classified using a machine learning method (k-means) according to the characteristic parameters of the activity path information. The rationality of the classification results was verified from two aspects, as follows: (1) the atmospheric circulation configuration of the NCCV on various paths; and (2) its influences on the climate conditions in the NEC. The obtained results showed that the activity paths of the NCCV could be divided into four types according to such characteristics as the generation origin, movement direction, and movement velocity of the NCCV. These included the generation-eastward movement type in the east of the Mongolia Plateau (eastward movement type or type A); generation-southeast long-distance movement type in the upstream of the Lena River (southeast long-distance movement type or type B); generation-eastward less-movement type near Lake Baikal (eastward less-movement type or type C); and the generation-southward less-movement type in eastern Siberia (southward less-movement type or type D). There were obvious differences observed in the atmospheric circulation configuration and the climate impact of the NCCV on the four above-mentioned types of paths, which indicated that the classification results were reasonable.

2018: The Hottest Summer in China and Possible Causes

In 2018, China experienced the hottest summer since 1961. The maximum, mean, and minimum temperatures all reached the highest. Air temperatures in most regions were much higher than normal; in northern China especially, the temperature anomalies were above double of the standard deviations. Consistent variations of temperature anomalies appeared in the national mean and in northern China on different timescales from intraseasonal to annual, indicating that the above normal temperature in northern China contributed significantly to the record-breaking hot summer of entire China. Relationships among the high temperature in summer 2018, the tropospheric circulation, and the global sea surface temperatures (SSTs) are further analyzed. It is found that the intensified and more northward western Pacific subtropical high (WPSH), weakened Northeast China cold vortex (NECV), and positive geopotential height anomaly from northern China to the Sea of Japan resulted in the abnormally high temperature in summer 2018. From late July to mid August, the WPSH was stronger than normal, with its ridge line jumping to north of 40°N; meanwhile, the NECV was much weaker and more northward than normal; both of the two systems led to the persistent high temperature in northern China during this period. In addition, the SSTs in Kuroshio and its extension area (K–KE) in summer 2018 were also the highest since 1961 and the greatest positive SST anomaly in K–KE was favorable for the above normal geopotential height over North China–Northeast China–Japan at 500 hPa, giving rise to the exceptionally high temperature in northern China.

Application study of monthly precipitation forecast in Northeast China based on the cold vortex persistence activity index

This paper introduces three quantitative indicators to conduct research for characterizing Northeast China cold vortex persistence activity: cold vortex persistence, generalized “cold vortex,” and cold vortex precipitation. As discussed in the first part of paper, a hindcast is performed by multiple regressions using Northeast China precipitation from 2012 to 2014 combination with the previous winter 144 air-sea system factors. The results show that the mentioned three cold vortex index series can reflect the spatial and temporal distributions of observational precipitation in 2012–2014 and obtain results. The cold vortex factors are then added to the Forecast System on Dynamical and Analogy Skills (FODAS) to carry out dynamic statistical hindcast of precipitation in Northeast China from 2003 to 2012. Based on the characteristics and significance of each index, precipitation hindcast is carried out for Northeast China in May, June, July, August, May–June, and July–August. It turns out that the Northeast Cold Vortex Index Series, as defined in this paper, can make positive corrections to the FODAS forecast system, and most of the index correction results are higher than the system’s own correction value. This study provides quantitative index products and supplies a solid technical foundation and support for monthly precipitation forecast in Northeast China.

Climate characteristics of abnormal double-blocking activities over the Ural Mountains and Sea of Okhotsk

By using NCEP–NCAR daily reanalysis data for June–August of 1948–2009, the synoptic situation of the double-blocking high pressure process over the Ural Mountains–Sea of Okhotsk region was identified objectively, and the climatic characteristics and dynamic mechanism during the double blockings were also investigated. The results suggest that the Urals–Okhotsk double-blocking high experienced obviously an abrupt change around 1977. After the change, the occurrence frequency and number of sustained days of the blocking high reduced significantly. Moreover, the zonal spacing between the Urals blocking and the Okhotsk blocking also decreased, while their meridional locations did not change much. The double blockings became strengthened in general, and the blocking high over the Sea of Okhotsk extended northward evidently. However, during the process without double-blocking activities, the intensity and location of the double-blocking high showed no noticeable variation before and after the abrupt change. In addition, dynamic diagnosis shows that after the abrupt change, the energy of the double-blocking high mainly propagated vertically from low to high levels, and transferred horizontally from low to high latitudes; whereas, previously, before the abrupt change, this occurred from high to low latitudes. Meanwhile, the development of a low pressure system was fueled between the double blockings, which meant that the double-blocking activity was beneficial to the maintenance and development of the Northeast China cold vortex. In short, diagnosis of the wave energy has provided us with a better explanation of the life cycle characteristics of this double-blocking phenomenon before and after 1977.

Mechanisms for the formation of Northeast China cold vortex and its activities and impacts: An overview

In the mid 20th century, great efforts were made to investigate the formation process of high-latitude cold vortex, which is regarded as a major weather system in the atmospheric circulation. In the late 1970s, Chinese researchers noticed that the Northeast China cold vortex (NECV) is an active and frequently occurring weather system over Northeast Asia, which is generated under specific conditions of topography and land–sea thermal contrast on the local and regional scales. Thereby, the NECV study was broadened to include synoptic situations, mesoscale and dynamic features, the heavy rain process, etc. Since the 21st century, in the context of the global warming, more attention has been paid to studies of the mechanisms that cause the NECV variations during spring and early summer as well as the climatic impacts of the NECV system. Note that the NECV activity, frequent or not, not only affects local temperature and precipitation anomalies, but also regulates the amount of precipitation over northern China, the Huai River basin, and the middle and lower reaches of Yangtze River. The NECV influence can even reach the Guangdong–Guangxi region. However, compared to the achievements for the blocking system study, theoretical studies with regard to the NECV system are still insufficient. Research activities regarding the mechanisms for the NECV formation, particularly theoretical studies using linear or weak nonlinear methods need to be strengthened in the future. Meanwhile, great efforts should be made to deepen our understanding of the relations of the NECV system to the oceanic thermal forcing, the low-frequency atmospheric variations over mid–high latitudes, and the global warming.

Cold vortex events over Northeast China associated with the Yakutsk-Okhotsk blocking

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.

Objective identification research on cold vortex and mid-summer rainy periods in Northeast China**Project supported by the National Natural Science Foundation of China (Grant Nos. 41205040 and 41375078), the State Key Development Program for Basic Research, China (Grant No. 2012CB955203), and the Special Scientific Research Project for Public Interest (Grant No. GYHY201306021).

Considering the differences between the Northeast China Cold Vortex (CV) and the Mid-Summer (MS) rainy period and their corresponding atmospheric circulations are comprehensively analyzed, and the objective identification methods of defining the annual beginning and ending dates of Northeast China CV and MS rainy periods are developed respectively. The annual beginning date of the CV (MS) rainy period is as follows. In a period from April to August, if daily regional mean precipitation ryi is larger than yearly regional mean precipitation R (or 2R) on a certain day, the station precipitation rs is larger than the station yearly mean precipitation 〈r〉 (or 2〈r〉) in at least 50% of stations in Northeast China, and this condition is satisfied in the following 2 (7) days, then this date is defined as the beginning date of the CV (MS) rainy period. While the definition of the ending date of the MS rainy period shows the opposite process to its beginning date. With this objective identification method, the multi-year average (1981–2010) beginning date of the CV rainy period is May 3, the beginning date of the MS rainy period is June 27, the ending day of the CV rainy period is defined as the day before the beginning date of the MS rainy period, and the ending date of the MS rainy period is August 29. Meanwhile, corresponding anomaly analysis at a 500-hPa geopotential height, 850-hPa wind, Omega and relative humidity fields all show that the definitions of the average beginning and ending dates of the CV and MS rainy periods have a certain circulation meaning. Furthermore, the daily evolution of the CV index, meridional and zonal wind index, etc. all show that these objectively defined beginning and ending dates of the CV and MS rainy periods have climate significance.

Different Types of Cold Vortex Circulations over Northeast China and Their Weather Impacts

Abstract 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.

Quadrant-Averaged Structure and Evolution Mechanisms of a Northeast Cold Vortex during Its Mature Stage

AbstractA Northeast China cold vortex (NCCV) that maintained from 0200 UTC 3 July to 0500 UTC 3 July 2013 and caused several heavy rainfall events was analyzed in detail to reveal its quadrant-averaged structure and main maintaining mechanisms during its mature stage. Results indicated the vortex's intensity, divergence, ascending motions, precipitable water (PW), and thermal structures were all characterized by significant unevenness, and their main pattern changed gradually during the mature stage. Mechanisms accounting for the maintenance of the NCCV were also characterized by remarkable unevenness. Within different quadrants, dominant factors for the vortex's evolution may have differed from each other significantly. The NCCV-averaged vorticity budget revealed that the vertical advection of vorticity, which is closely related to convective activities, was the most favorable factor for maintaining the NCCV, whereas the tilting effect, which is closely related to the vertical shear of the horizontal win...

Study on the Evolution of a Northeast China Cold Vortex during the Spring of 2010

Study on the Evolution of a Northeast China Cold Vortex during the Spring of 2010

The 2009 summer low temperature in northeast china and its association with prophase changes of the air-sea system

Under the background of global warming, summer (JJA) low temperature events in Northeast China had not occurred for about 15 yr since 1994, but one such event took place in 2009. By using the NCEP/NCAR reanalysis data, the 100-yr station temperature data at Harbin and Changchun, and the Hadley Center sea surface temperature (SST) data, this paper intends to reveal the cause, circulation background, and influencing factors of this event. Analysis of both horizontal and vertical circulations of a low-value system over Northeast China in summer 2009 during the low temperature event shows that anomalous activities of the Northeast China cold vortex (NECV) played the most direct role. A decadal cooling trend of — 0.8°C (10 yr)−1 over 1999–2008 at Changchun and Harbin was found, which is obviously out-of-phase with the linear warming trend (0.2°C (10 yr)−1) over 1961–2000 for Northeast China in response to the global warming. The previous winter North Pacific polar vortex (NPPV) area index, significantly positively related to the observed summer temperatures of Harbin and Changchun, was also in a significantly declining tendency. These provide favorable decadal backgrounds for the 2009 low temperature event. Different from the average anomaly field of 500-hPa height for summer 1994–2008 in Northeast China, in the summer of 2009, the Arctic Oscillation (AO) showed a strong negative phase distribution, and significant negative height anomalies dominated Northeast Asia, Aleutian Islands, and North Atlantic. Furthermore, the negative phase of North Pacific Oscillation (NPO) in the winter of 2008 was obviously strong, and it maintained in the spring of 2009. Meanwhile, the SSTA in the equatorial eastern-central Pacific Ocean in the winter of 2008 showed a La Nina phase, but the strength of the La Nina weakened obviously in the spring of 2009. The abnormally strong activities of NECV in June and July of 2009 were related to the disturbances of stationary waves that replaced the original ultra-long waves over the North Pacific region in April and May 2009. The singular value decomposition (SVD) and harmonic analysis results suggest that the anomalous phase of NPO is an important precursor for summer temperature variations over Northeast China, and also a stable planetary-scale component that can be extracted from the atmospheric circulation in addition to the chaotic components on the synoptic scale.

Circulation and Eddy Kinetic Energy Budget Analyses on the Evolution of a Northeast China Cold Vortex (NCCV) in May 2010

Circulation and Eddy Kinetic Energy Budget Analyses on the Evolution of a Northeast China Cold Vortex (NCCV) in May 2010