Cold Surge Events Research Articles

Climatic interactions between cold surges in the South China Sea and North Pacific extratropical cyclones

AbstractCold surge events in the South China Sea (over 110–117.5° E longitude at 15° N latitude) from 1979 to 2019 are divided into four types depending on their correlation with North Pacific extratropical cyclones (ECs). Climatologic relationships between the two phenomena reveal that 92% (39%) of all cold surges are accompanied by ECs (explosive extratropical cyclones, abbreviated as EC‐E), while 31% of ECs are accompanied by cold surges. The occurrence and development of ECs favour eruptions of cold air from higher latitudes, which in turn produce conditions conducive to cold surges. In the North Pacific, ECs travel in a northeastward direction, ultimately contributing to the Aleutian low. Meanwhile, the westerly jet is observed to strengthen following cold surge events. Both actions drive further EC activity, which in turn facilitates subsequent cold surges. Therefore, when ECs occur before and after cold surges, the cold surge event itself tends to be relatively strong and long lived. The transmission of energy by ECs is a primary link between the high and middle latitudes and contributes to the impact of cold surges on low latitudes. This study also explores the respective influences of the Siberia High and Aleutian Low on cold surges. The majority of cold surges that do not involve ECs occur in the context of the weaker Siberia High and Aleutian Low. Cold surges accompanied with ECs can be even stronger and longer lasting when the Siberia High and Aleutian Low strengthen.

Planetary Boundary Layer Flow over Complex Terrain during a Cold Surge Event: A Case Study

Planetary boundary layer (PBL) flow over complex terrain during a cold surge event was investigated using 3-hourly radiosonde measurements in upwind, near ridge, and downwind locations of mountains in the northeastern part of Republic of Korea and using a high-resolution (333-m) numerical simulation. A cold surge occurred on 23 January 2018 and lasted for 4 days. We analyzed onset day of the cold surge when air temperature dropped rapidly. Analysis of the radiosonde data shows that the PBL was characterized by an adiabatic layer with strong capping inversion in early morning and evening as well as during daytime in the upwind and near-ridge sites. The PBL flow at the near-ridge site was strongest among three sites except at 0600 local standard time (LST) when the PBL flow in the lee was strongest. We performed high-resolution (333-m) numerical simulations using the Weather Research and Forecasting (WRF) model. The adiabatic PBL in the upwind site at 0600 LST was simulated, although its depth was underestimated. The model reproduced the strong low-level wind at 0600 LST and large wind shear during the daytime in the lee, but it did not capture the exact timing of the large wind shear. The model showed overall good performance in simulating the vertical profile of the virtual potential temperature and wind below 2 km above ground level at the three sites, with a high index of agreement (IOA) except for the wind at 1200 and 1500 LST in the lee. To examine the cause for the different behavior of PBL flow in the lee of mountains between 0600 LST and the daytime, we calculated the Froude number for PBL flow using radiosonde measurements based on reduced gravity shallow water (RGSW) theory. At 0600 LST, the upwind Froude number F0 was close to 1, while during the daytime, it was much lower than 1. The observed lee flow behavior was consistent with the flow regime change of a single layer over an obstacle with changing F0; the flow with a propagating lee jump changes into that with a stationary lee jump with decreasing F0. Numerical simulation shows that the steepening of streamlines of lee-wave field leads to a jump-like structure in the lee of mountains during the daytime.

Impact of the cold surge event in January 2021 on the power system of China

During 6–10 January 2021, a recorded strong cold surge took place in China, with over 800 observational stations reaching their historical extremes. Unlike previous studies that focused on the response of either the power load or generation separately, this study quantitatively revealed the impacts on the balance between the demand and supply sides of the grid. On the demand side, the sensitivity of power load was found to increase substantially higher in southern China (0.533 GW °C−1) than in the northern region (0.139 GW °C−1) due to the limited municipal heating system. On the supply side, the hourly wind power generation dropped from the highest of 110 GW on 6 January to the lowest of 54 GW on 9 January due to the reduction in wind speed. In addition, a reduction in solar power generation was observed during 8–10 January. Thus, the balance of the power system was influenced by this cold event. As an effective adaptation measure, results further showed that early warning by three weeks ahead can be obtained by an operational climate model. The sensitivity of China's power system to such cold surge events may increase remarkably due to the expected increase in the proportion of wind and solar power generation in future new-type power systems. Thus, close cooperation between climate scientists and power engineers is needed to build the resilience of the power system to the cold extremes.

Impacts of social distancing, rapid antigen test and vaccination on the Omicron outbreak during large temperature variations in Hong Kong: A modelling study

BackgroundThe impacts of non-pharmaceutical interventions (NPIs) and vaccine boosters on the transmission of the largest outbreak of COVID-19 (the fifth wave) in Hong Kong have not been reported. The outbreak, dominated by the Omicron BA.2 subvariant, began to spread substantially after the Spring Festival in February, 2022, when the temperature varied greatly (e.g. a cold surge event). Tightening social distancing measures did not succeed in containing the outbreak until later with the use of rapid antigen tests (RAT) and increased vaccination rates. Temperature has been previously found to have significant impact on the transmissibility. Understanding how the public health interventions influence the number of infections in this outbreak provide important insights on prevention and control of COVID-19 during different seasons. MethodsWe developed a transmission model incorporating stratified immunity with vaccine-induced antibody responses and the daily changes in population mobility, vaccination and weather factors (i.e. temperature and relative humidity). We fitted the model to the daily reported cases detected by either PCR or RAT between 1 February and 31 March using Bayesian statistics, and quantified the effects of individual NPIs, vaccination and weather factors on transmission dynamics. ResultsModel predicted that, with the vaccine uptake, social distancing reduced the cumulative incidence (CI) from 58.2% to 44.5% on average. The use of RAT further reduced the CI to 39.0%. Without vaccine boosters in these two months, the CI increased to 49.1%. While public health interventions are important in reducing the total infections, the outbreak was temporarily driven by the cold surge. If the coldest two days (8.5 °C and 8.8 °C) in February were replaced by the average temperature in that month (15.2 °C), the CI would reduce from 39.0% to 28.2%. ConclusionPreventing and preparing for the transmission of COVID-19 considering the change in temperature appears to be a cost-effective preventive strategy to lead people to return to normal life.

Simulation of the Boreal Winter East Asian Cold Surge by IAP AGCM4.1

In this study, we evaluate the performances of the Institute of Atmospheric Physics atmospheric general circulation model (IAP AGCM version4.1) and atmospheric component of Chinese Academy of Science Earth System Model, version 1 (CAS-ESM1) in the simulation of the cold surge (CS) events in East Asia. In general, the model can capture the main features of anomalous precipitation and circulation associated with the cold surge days. Compared with climatological means of boreal winter, on CS days, the precipitation increases in the southern part of the South China Sea (SCS), while decreases in the subtropical regions near the southern China. In addition, the climatological northeasterly wind over the SCS region strengthens on CS days. In the first day composites of CS events, it shows a dipole pattern in middle latitude over East Asia, with a positive (negative) sea level pressure (SLP) anomaly in the west (east). Based on the anomalous SLP signs in the two centers of the dipole pattern, the CS days can be further classified into two types: positive-west–negative-east-type and positive-west–positive-east-type. All these features can be reasonably reproduced by IAP AGCM4.1. Although in most CS days there is positive SLP anomaly in the East China, some negative events were investigated in this study. In these negative events the northerly anomaly in SCS is associated with an anticyclonic circulation anomaly around the eastern part of the Tibetan Plateau, rather than descending from the mid-to-high latitude cold air outbreaks. The feature can also be captured by the model.

Projected changes and uncertainty in cold surges over northern China using the CMIP6 weighted multi-model ensemble

Cold surge (CS) events are the most serious extreme cold events in winter in China, causing large economic losses and casualties. The occurrence of CS events has slightly increased since the 1990s. However, the possible future changes in these events remain unclear, and quantifying robust projected changes in CS events is important for developing adaptation and policy planning. Here, we project the occurrence of CS events and strong CS (SCS) events using the weighted multi-model ensemble (MME) of the Coupled Model Intercomparison Project 6 (CMIP6) through the application of the rank-based weighting (RBW) approach under three shared socioeconomic pathway (SSP126, SSP245, and SSP585) scenarios. The corresponding weights of each model were obtained depending on the comprehensive historical performance from three aspects: climatology, spatial variation, and interannual variability. The results show that the RBW approach can reduce the relative bias by approximately 50% compared to the unweighted MME. The occurrence of CS and SCS events shows a decreasing trend during 2015–2099 over northern China under the three SSP scenarios. There are also robust change projections during the long-term (2080–2099) and 2015–2099 periods under SSP245 and SSP585, especially in the NEC region, which exhibits a signal-to-noise ratio (SNR) that is >1. However, the occurrence of SCS events shows slight increases of 1.18% and 3.55% over northern China (notably western and eastern Northwest China) during the near-term (2020–2039) under SSP126 and SSP245, respectively. Obvious reductions in projected uncertainty are widespread throughout northern China after applying the RBW approach compared to the unweighted MME, which mainly depends on the scenario, region, and term variation. Then, a robust decreased frequency may contribute to projected changes in large-scale atmospheric circulation (a more positive AO and weaker SH and EAT) under SSP585. Our results emphasize that the weighted MME can be taken into account when projecting future extreme climate change in some areas to enhance reliability.

A new approach to cold surge classification in East Asia

Evidence showing a strengthening of intense cold surge event (CSE) in East Asia, e.g. CSE of Jan 2016 and Jan–Feb 2008, is focusing attention towards the science of CSE onset prediction. Predicting the onset of such strong CSEs remains elusive as the extent of these surges varies over spatial and temporal scales. Changes in radiative cooling over Siberia in winter as potentially affected by changes in the Arctic are further expected to influence CSE occurrences in East Asia. Moreover, unprecedented and long lasting CSEs in East Asia have a very distinct Jet Stream pattern via their shifts from the climatological mean, influencing the lower troposphere. Here, using modelling framework we propose a new relationship between Jet Stream and Aleutian Low for identifying and characterizing atmospheric process that leads to CSEs in East Asia. Our results reveal new insight into the mechanisms of CSEs occurrences, the absence of which may lead to major constraints on reducing CSE onset prediction error.

Composite Life Cycle of West Pacific Jet-Superposition Events and the Large-Scale Environmental Response over Western North America

AbstractVertical alignment of the polar and subtropical jet streams in the west Pacific basin occurs most often during the boreal cold season. Recent work has revealed that the large-scale environment conducive to producing such superpositions involves interaction between East Asian winter monsoon cold-surge events, lower-latitude convection, and internal jet dynamics. The evolution of the large-scale environments associated with these events post-superposition as well as the significance of that evolution on aspects of the wintertime Northern Hemisphere general circulation is examined through construction of a 44-case composite. The post-superposition west Pacific jet extends eastward associated with an anomalous positive–negative geopotential height couplet straddling the jet’s exit region. This jet extension results in ridge building over Alaska and northwestern Canada. The large-scale evolutions associated with the composite post-superposition environment occur consistently among the majority of cases considered within this analysis. The positive–negative geopotential height anomaly couplet, enhanced jet entrance circulation, low-latitude convection, and internal jet dynamics present in the pre-superposition environment weaken post-superposition. As a result, the characteristic vertical PV “wall” associated with the composite vertically superposed jet weakens. Last, investigation of the value of using the two most dominant modes of west Pacific jet variability in observing the evolution of the superposed west Pacific jet post-superposition reveals that, while the extension of the jet is exhibited, significant variability exists when analyzing each of the 44 cases of interest individually.

Drivers of extreme wind events in Mexico for windpower applications

AbstractIn this study, we use a k‐mean clustering approach to investigate the weather patterns responsible for extreme wind speed events throughout Mexico using 40 years of the ERA‐5 atmospheric reanalysis. Generally, we find a large geographical split between the weather patterns that generate the strongest winds across the country. The highest wind power production periods therefore occur at different times in different regions across the country. In the South, these are associated with cold surge events, where an anticyclone is present in the Gulf of Mexico resulting in a strong Northerly flow across the Isthmus of Tehuantepec. In the North‐East, Easterly trade winds are responsible for the strongest wind events, whereas in the North‐West, it is the proximity of the North Pacific High. However, the weakest winds and lowest power production periods occur at the same times for all stations with the exception of Baja California Sur, meaning that low wind power production may be unavoidable at these times. The El Niño Southern Oscillation is found to influence wind speeds at some locations across Mexico at sub‐seasonal time‐scales. We report that statistically stronger wind speeds are observed during the Summer during El Niño months than during La Niña months for both sites in Chiapas and Oaxaca.

Influence of Siberian Blocking on Long-Lived Cold Surges over the South China Sea

AbstractCold surges occur frequently over the South China Sea (SCS) in winter, and most of them last only a few days. However, some cold surge events can persist longer, for instance, more than 5 days. This study focuses on these long-lived cold surge events and investigates the associated extratropical circulation anomalies. The results indicate that long-lived cold surges, characterized as strong northerlies over the SCS, can be triggered by a successive high anomaly center over East Asia. Accompanying this is an anomalously extensive and quasi-stationary anticyclone over Siberia in the midtroposphere, hinting at a more frequent occurrence of Siberian blocking. Further analyses reveal that the blocking frequency is indeed significantly high over 90°–150°E from day −4 to day +2 relative to the onset of long-lived cold surge events. Furthermore, there exist significant correlations between the leading occurrence of Siberian blocking and the sea level pressure (SLP) anomalies over East Asia, which are directly related to long-lived cold surges. The intensification of the high SLP anomaly over East Asia is found to mainly result from cold advection induced by the anomalous northerly winds along the southeastern edge of the Siberian blocking.

Sea-land breeze diurnal component and its interaction with a cold front on the coast of Sisal, Yucatan: A case study

The breeze phenomenon is of great importance in coasts around the world owing to both its impact on local atmospheric dynamics and its influence on coastal processes. The northwest of the Yucatan Peninsula (YP) is characterized by the presence of intense sea breezes and Cold Surge (CS) events (locally known as Nortes). Field observations suggest that nearshore hydrodynamics and beach evolution in the study area are strongly controlled by waves generated during sea breeze events. In this paper, the diurnal wind component associated with the breeze phenomenon and its variability due to the presence of a CS event are investigated utilizing the Weather Research and Forecasting (WRF) model. The WRF model is implemented in three nested domains with a maximum resolution of 3.6-km. The numerical model was validated with observations at 20 stations located across the YP, adequately reproducing wind speed and direction at Sisal, Yuc. coast, with a correlation coefficient of 0.56 and a circular correlation coefficient of 0.83, respectively. Diurnal wind components were least-squares fitted to a sinusoidal signal, and the resulting parameters were used to obtain an elliptical hodograph related to the breeze phenomenon. Numerical results suggest that sea breezes, with wind intensities higher than 10 ms−1, extend more than 100 km offshore in the northern YP. Although breeze events are caused by differential heating at a small spatial scale, particularly in the Gulf of Mexico, this diurnal signal exceeds the local spatial scale. Furthermore, the interaction between the sea breeze and the mean wind associated to the trade winds generates a line of convergence that crosses the YP. Model results allow us to identify that the mechanisms responsible of such large amplitude of the diurnal signal in this area are: (i) the thermal gradient, (ii) the relatively small value of the Coriolis force, (iii) the orography, (iv) the friction, and (v) the peninsula's geometry. The numerical results revealed that during the interaction between local breezes and a CS event, the diurnal signal remains, except for the initial day of the event. However, further research is needed to generalize the current results for other CS events with different intensity and displacement characteristics.

Interdecadal Variation of Winter Cold Surge Path in East Asia and Its Relationship with Arctic Sea Ice

AbstractThe paths of winter cold surge (CS) events in East Asia (EA) from 1979 to 2017 are tracked by the Flexible Particle (FLEXPART) model using ERA-Interim daily datasets, and the probability density distribution of the paths is calculated by the kernel density estimation (KDE) method. The results showed that the paths of CSs are significantly correlated with the intensity of the CSs, which shows an interdecadal transition from weak to strong around 1995. CS paths can be classified into two types, namely, the western path type and the northern path type, which were more likely to occur before and after 1995, respectively. Before 1995, the cold air mainly originated from Europe and moved from west to east, and the synoptic features were associated with the zonal wave train. After 1995, cold air accumulated over western Siberia and then invaded EA along the northern path, and the synoptic features were mainly associated with the blocking structure. The geopotential height (GPH) anomalies over the Arctic were abnormally strong. This paper further analyzes the relationship between CSs and winter sea ice concentration (SIC) in the Arctic. The results show that the intensity of CSs is negatively correlated with the Barents SIC (BSIC). When the BSIC declines, the upward wave flux over the Barents Sea is enhanced and expanded to the midlatitude region. GPH anomalies over the Arctic are positive and form a negative AO-like pattern, which is conducive to the formation of the northern path CS. Furthermore, the observed results are supported by numerical experiments with the NCAR Community Atmosphere Model, version 5.3 (CAM5.3).

Variability in Onshore Sediment Transport on a Natural Beach during a Central American Cold Surge Event

Briggs, T.R.; Figlus, J.; Torres-Freyermuth, A.; Puleo, J.A.; Warren, W., and Alrushaid, T., 2020. Variability in onshore sediment transport on a natural beach during a Central American cold surge event. Journal of Coastal Research, 36(3), 487–497. Coconut Creek (Florida), ISSN 0749-0208.Beaches facing the Gulf of Mexico along the northern part of the Yucatan Peninsula experience frequent Central American cold surge events, or northerly storms locally called “Nortes,” which interrupt the usual daily patterns of sea- and land-breeze–dominated nearshore dynamics. These perturbations of prevailing hydrodynamic forcing conditions also affect sediment distribution and transport parameters in the surf and swash zone, which are critical elements in understanding and modeling complex morphodynamic processes during storm events. However, detailed measurements of sediment characteristics throughout the water column during a storm event are scarce. This study presents field measurements of bottom and suspended sediment transported in the onshore direction during a 24-hour storm event impacting the Yucatan Peninsula. Sediment load data within the water column collected in 3 hour intervals via vertical arrays of streamer traps, deployed at two cross-shore locations in the inner surf zone, are compared with sediment data from collocated bottom grab samples. Time series of grain size distributions, sediment statistics, and respective vertical variations throughout the water column are related to measured bed-level changes to verify applicability of simple erosion and accretion predictors. Results indicate that bottom sediment and sediment distributions throughout the water column deviate substantially due to storms, highlighting the complexity and difficulty of assessing sediment transport and morphodynamic processes with a single-parameter sediment characteristic. Calculated total onshore transport rates during the Norte were on average one order of magnitude higher than during nonstorm conditions.

Extreme Temperature Change of the Last 110 Years in Changchun, Northeast China

In China and East Asia, the long-term continuous observational data at daily resolution are insufficient, and thus there is a lack of good understanding of the extreme climate variation over the last 100 years plus. In this study, the extreme temperature indices defined by ETCCDI (Expert Team on Climate Change Detection and Indices) and local meteorological administrations were analyzed for Changchun City, Northeast China, by using the daily maximum temperature (Tmax) and daily minimum temperature (Tmin) over 1909−2018. The results showed that extreme cold events, such as cold days, cold nights, frost days, icing days, and low temperature days, decreased significantly at rates of −0.41 d (10 yr)−1, −1.45 d (10 yr)−1, −2.28 d (10 yr)−1, −1.16 d (10 yr)−1 and −1.90 d (10 yr)−1, respectively. Warm nights increased significantly at a rate of 1.71 d (10 yr)−1, but warm days decreased slightly and the number of high temperature days decreased at a rate of −0.20 d (10 yr)−1. The frequency of cold surge events increased significantly at a rate of 0.25 d (10 yr)−1, occurring mainly from the mid-1950s to late-1980s. The average Tmax, average Tmin and extreme Tmin increased at rates of 0.09°C (10 yr)−1, 0.36°C (10 yr)−1 and 0.54°C (10 yr)−1, respectively; and extreme Tmax decreased significantly at a rate of −0.17°C (10 yr)−1. In 1909−2018, 1951−2018 and 1979−2018, the indices related to cold events decreased, while the trends of the indices related to warm events were different for different periods.

Seasonal Dependence of Cold Surges and their Interaction with the Madden–Julian Oscillation over Southeast Asia

AbstractNortheasterly cold surges strongly influence the rainfall patterns over the Malay Peninsula during the northeast monsoon season. This study looks at the changes in the cold surges and Madden–Julian oscillation (MJO) characteristics through the northeast monsoon season and their interaction. Nearly 75% of the cold surge events tend to cross the equator around the Java Sea area (100°–110°E) in February–March with drier conditions prevailing over the Malay Peninsula and increased rainfall over Java. Both the cold surges and the MJO undergo seasonal variations with well-defined regional features. Wavelet analysis shows that MJO amplitude and high-frequency rainfall variations over Southeast Asia peak in November–December. MJO amplitude is suppressed during February and March. This is linked to the high-frequency surges of meridional winds that are prominent during the early part of the season, but February–March is dominated by low-frequency (~20–90 days) cross-equatorial monsoon flow. These prolonged periods of strong meridional flow at the equator interact with the MJO both dynamically and thermodynamically and act as a barrier for convection from propagating from the Indian Ocean to the Maritime Continent (MC). These interactions may have implications for weather and seasonal forecasting over the region. An evaluation of the properties of cold surges and their interaction with the seasonal cycle in the Met Office Unified Model is performed. The atmosphere–ocean coupled model performs better in representing the pattern of influence of the cold surges despite the biases in intensity and spatial distribution of rainfall extremes. These diagnostics are presented with the aim of developing a set of model evaluation metrics for global and regional models.

Spatiotemporal Storm Impact on the Northern Yucatan Coast during Hurricanes and Central American Cold Surge Events

We investigate the storm impact associated with historical events in the northern Yucatan Peninsula. The study area is prone to coastal flooding due to both its geographical location and low-lying areas. Extreme events associated with tropical cyclones and Central American cold surge (CACS; locally known as Nortes) are ubiquitous in this region, and coastal development in the study area has exacerbated the erosion of the sand beach-dune system. This study aims to assess the impact on the northern coast of Yucatan associated with different types of storms and to investigate the role of the dune in its spatial variability. Nearshore hydrodynamics, associated with hurricanes (Gilbert: 14 September 1988; Isidore: 22 September 2002) and energetic Nortes (Norte A: 12 March 1993; Norte B: 25 December 2004), were computed using a numerical model. The beach and dune characteristics were extracted from a LIDAR flight with a spatial resolution of 1 m conducted in 2011. Furthermore, the extreme water levels and the spatiotemporal variability of the storm-impact regime (swash, collision, overwash, or inundation), along a 41.5 km stretch of coast, were derived using both runup parametrizations and the modeling results. On the one hand, the predominant storm impact regimes for Hurricanes Gilbert and Isidore were inundation and overwash, respectively. The flood that propagated from east to west in the northern Yucatan was due to westerly-directed hurricane tracks. On the other hand, for the Norte events, the predominant impact regimes were collision and overwash for Nortes A and B, respectively. This difference in the impact regime between Norte events can be ascribed to tidal differences. Moreover, during the passages of Nortes A and B, the flood was propagated from west to east in the northern Yucatan, consistent with cold-front paths. The results suggest that the western part of the study area presented a stronger impact regime due to the dune degradation caused by coastal infrastructure and settlements established in those areas. This work highlights the important role of sand dunes in providing natural coastal protection during Norte events.

Two Distinct Types of Extratropical Circulation Anomalies Associated with Cold Surges over the South China Sea

Abstract This study investigated the extratropical circulation anomalies responsible for cold surges over the South China Sea in winter. The surge events were identified by the intensity of northerly winds over 110°–117.5°E along 15°N at 925 hPa. Two distinct patterns of sea level pressure (SLP) anomalies in East Asia were found to have a crucial role in inducing cold surges over the South China Sea. Accordingly, the cold surge events were classified into two types. The first type of cold surge is characterized by a pair of SLP anomalies with positive and negative ones centered over China and Japan, respectively, whereas the second type of cold surge is characterized by widespread and persistent positive SLP anomalies over East Asia. Furthermore, the first type of cold surge is accompanied by a deepened East Asian trough and precursory Rossby wave trains across the Eurasian continent in the mid- and upper troposphere, but the latter is not. Prior to both types of the cold surges, the Siberian high is significantly intensified. However, diagnosis of the SLP tendency indicates that the intensification is related to different physical processes. In the first type of cold surge, the Rossby wave trains favor negative vorticity advection and cold advection, inducing intensification of the Siberian high. By contrast, in the second type of cold surge, vorticity advection can be ignored due to the lack of Rossby wave trains, and only the lower-tropospheric cold advection induced by anomalous northerly winds, resulting from the anomalous Siberian high, contributes to the further intensification of the Siberian high.

Spatial-temporal variations in cold surge events in northern China during the period 1960–2016

Among the most devastating extreme weather events, cold surge (CS) events frequently impact northern China. It has been reported that extreme weather events will increase in the global warming context. However, the direct evidence of this hypothesis is limited. Here, we investigated the changes in frequency, number, duration, and temperature of CS events in northern China using the daily minimum temperature dataset of 331 stations from 1960 to 2016. The results indicate that the annual CS events in terms of frequency and number decreased, and the duration shortened as the starting date was later and the ending date earlier. Meanwhile, the annual CS temperature increased. In addition, spatial trends in the CS events in terms of frequency, number, and duration decreased while the CS temperature increased in most regions of northern China. We interpreted these variations as a response to global warming. However, the extreme CS events in terms of frequency, number and the earliest starting date and the latest ending date showed little change though the extreme CS temperature increased, implying climate warming had not limited extreme CS events. The adverse effect of CS events on agriculture and human health remain concerning.

Relationship between East Asian Cold Surges and Synoptic Patterns: A New Coupling Framework

Strong cold surge events (CSEs) are some of the most distinct winter weather events in East Asia, impacting natural ecosystems and over 100 million individuals. The impact of such extreme CSEs as driven by synoptic systems is direct and immediate. Changes in large-scale synoptic patterns as potentially affected by changes in the Arctic are further expected to influence CSE occurrences in East Asia. Defying a straightforward analysis, semi-permanent atmospheric systems such as the Siberian High (SH), influencing large-scale synoptic patterns, make the atmospheric circulation highly variable and assessment of CSE onset difficult. Rather varied region-specific metrics are currently adopted for predicting CSE occurrence locally but the fundamental understanding of the onset of CSEs continues to be a major challenge. Based on an analysis of monthly synoptic patterns for three unusual CSEs in East Asia and further extended for eight strong to extreme CSEs, we propose a new coupling framework for an improved understanding and interpretation of the atmosphere dynamics driving CSE onset. The coupling framework involves linkages between the Siberian High, Aleutian Low, and Jet Stream. We also present the first meteorological scale for categorizing the intensity of such unusual CSEs.

Cold Air Mass Analysis of the Record-Breaking Cold Surge Event over East Asia in January 2016

Cold Air Mass Analysis of the Record-Breaking Cold Surge Event over East Asia in January 2016