Extreme Cold Events Research Articles

Climate extremes drive the phenology of a dominant species in meadow steppe under gradual warming

Plant phenology in terrestrial ecosystems, especially in the Northern Hemisphere, is expected to change owing to the projected increasing frequency and intensity of climate extremes in the context of global warming. Although such changes under mean climate change have been extensively reported in the literature, little is known about the impacts of climate extremes. In this study, climatic changes and their effects on plant phenology were characterized using long-term climatic and phenological data from the start and end of the growing season (SOS and EOS, respectively) from 2005 to 2020 for Stipa baicalensis, a dominant species in a temperate meadow steppe. The results showed that the temperature, including the mean and minimum temperatures, and extreme warm indices significantly increased; however, annual precipitation, and the frequency of extreme cold and precipitation events decreased. The SOS of S. baicalensis was initially earlier and later, whereas the EOS trended to be delayed. However, the growing season (LOS) was slightly prolonged. Compared with the indices under mean temperature, the pre-season (before SOS or EOS) minimum temperature dominantly affected SOS and EOS, whereas the mean and extreme precipitation slightly affected them. Furthermore, the findings showed that plant phenology responded to extreme temperatures quicker and stronger than mean temperatures. This study provides insight into how key extreme climatic factors could affect plant phenophases and improve and refine the phenological model. This could also be useful in enhancing grassland ecosystem management and sustainable development.

An extreme cold event over East Asia during early January 2021 and its links to the deformation of stratospheric polar vortex during sudden stratospheric warming

AbstractIn early winter of 2020/2021, East Asia experienced two extreme cold events (ECEs), during which a number of national stations in China reached the standard of ECE or broke records. The underlying dynamical processes of these record‐breaking ECEs are investigated using Modern‐Era Retrospective Analysis for Research and Applications version 2 reanalysis dataset. Results show that these ECEs were closely related to the sudden stratospheric warming (SSW) event. During 29 December, 2020–1 January, 2021 (the first ECE), the tropospheric polar vortex migrated to mid‐latitude East Asia and more planetary wave propagated into the stratosphere. Then, the stratospheric polar vortex weakened and extended to mid‐latitude East Asia from 2 January. And, a SSW event occurred on 5 January. The easterly zonal wind accompanied by the deformation of stratospheric polar vortex over East Asia tended to strengthen the East Asian trough via reflecting the planetary wave from the stratosphere to troposphere. Simultaneously, the southward shifting of the Ural ridge resulted in the extremely strong East Asian trough migrating southward, which led to the strengthening and southward migration of near‐surface anticyclonic circulation. Then, another ECE broke out during 6–7 January (the second ECE). Therefore, the ECE in early January was jointly caused by the combined effects of deformation of stratospheric polar vortex during SSW event and the southward shifting of Ural ridge. Further analysis suggested that about 8% of the total ECEs during 1980/1981–2019/2020 were related to the extension of stratospheric polar vortex to East Asia.

Assessing thermal resilience of an assisted living facility during heat waves and cold snaps with power outages

Extreme hot and cold weather events are becoming more frequent, intense, and longer due to climate change. When these events occur coincidentally with power outages, the resulting extreme indoor temperatures pose a severe health hazard for occupants. This study conducted a holistic modeling and analysis of an assisted living facility, where senior residents live, to assess its thermal resilience performance under a six-day heat wave in 2015 and a three-day cold snap in 2021 with power outages. Impacts of 13 energy efficiency measures on thermal resilience and backup power capacity of the facility were evaluated. Three thermal resilience metrics: the SET (standard effective temperature) degree-hours, the Heat Index, and the Hours of Safety, were used and calculated from the EnergyPlus simulation models. Major findings are: (1) the facility would suffer from extreme temperatures during the cold and hot events without a power supply, not meeting the passive survivability requirements; (2) most passive envelope measures improve thermal resilience for both hot and cold events, but making the building envelope airtight results in conflicting performance between the hot and cold events; (3) natural ventilation is an effective measure to mitigate summer indoor overheating; and (4) the energy efficiency package can reduce backup power capacity by 19% for the three-day cold snap. It is recommended that building technologies and design strategies be evaluated to consider co-benefits of energy use, thermal resilience, and backup power needs through building energy codes or policies for existing and new buildings, which are transitioning for decarbonization and climate resilience.

Short-term impact of an extreme weather event on the threatened Dupont’s LarkChersophilus duponti

SummaryThe frequency and intensity of extreme weather events represent a threat for biological diversity and are expected to increase in many regions over the following decades due to climate change. Our current knowledge about the impact of extreme weather events on the population dynamics of bird species is very limited. Here, we evaluated the impact of an extreme winter snowstorm on the abundance of 14 populations of the threatened Dupont’s LarkChersophilus duponti, a resident bird whose European population is restricted to Spain. We found a drastic and significant population decline in the next reproductive season following the extreme weather event. During the control period (2017–2020) the species suffered an overall annual decline of 19.4% (±5.0, SE). However, the overall annual decline after the storm was 67.6% (±9.4, period 2019–2021), with a mean decline of 66.5% (±15.9) for seven populations monitored both the year before and the year after the snowstorm (period 2020–2021). The snow covered the ground for over 10 days in central and eastern Spain, which together with a subsequent extreme cold wave could have reduced the species ability to find food resources and properly thermoregulate, forcing the species to move to unknown areas. Indeed a few days after the storm, several individuals were reported in areas typically avoided. Such displacements may increase the mortality risk for dispersing individuals, besides the direct effects of the extreme cold event, such as thermal challenges to energy balance or a reduced immune function. We discuss the potential role that extreme weather events may have on the population dynamics and conservation of the species.

Planning for winter peaking power systems in the United States

Most regions in the United States experience peak electricity demand during the summer months. Several regions, however, are dual peaking with distinct summer and winter peaks of roughly equal magnitude. Deep decarbonization of our energy system could lead to greater instances of dual or winter peaking power systems across the country. This seasonal shift has important implications for grid operations. Furthermore, the compounding impacts of decarbonization strategies and climate change could introduce new challenges in ensuring sufficient generator availability during peak demand. This paper provides policy recommendations to plan for a shift to dual or winter peaking power systems. We first analyze the seasonal peak demand trends between 2016 and 2021 at the regional and subregional levels. We provide key examples of how regulators and system operators plan for winter resource adequacy, focusing on the measures undertaken by different stakeholders, post-Winter Storm Uri. We then detail challenges posed by the multilevel regulation framework in planning for winter peaking power systems for both extreme cold events and a gradual shift due to electrification. Finally, we provide our policy recommendations for utilities and regulators on how they can robustly meet the challenges of winter peaking systems.

The key atmospheric drivers linking regional Arctic amplification with East Asian cold extremes

Across the winters of 1999–2011, both the frequency of extreme cold events in East Asia and the Arctic Amplification showed an upward trend. Here we constructed regional AA index in the winters of 1979–2019, and examine the atmospheric driver that linked with strong AA scenarios and cold extreme in EA. Results show that the local atmospheric blocking are key drivers for regional AA occurrence on the intraseasonal timescale. Ural-Siberia blocking, which is tightly linked to the warming over Barents-Kara Seas (BK), is the primary atmospheric mode when regional AA corresponds with extreme East Asian cold days. However, when there is no warming over BK during the associated cold days in EA, the warming over western hemisphere become prominent, accompanied by the negative phase of the North Atlantic Oscillation (NAO−) and blocking dipole system located at mid-Siberian and East Asian continent. Under this circulation configuration, not only does EA exhibits extremely cooling, but also northeastern North America experiences significant cold anomalies. Furthermore, precursor signals at 2–10 days are found between NAO− and each regional AA event when the days of BK warming are excluded. Our results highlight the importance of atmospheric circulation on linking the warming of different Arctic sectors and cold extremes in the mid-latitude continent, and point out the independent role of NAO− and BKS warming on regional AA.

Alternate modulations of ENSO and the Arctic Oscillation on winter extreme cold events in China

Station observations and global reanalysis datasets were applied to investigate the dominant modes of winter cold days (CDs) in China and their relationships with the Arctic Oscillation (AO) and El Niño–Southern Oscillation (ENSO). The dominant modes of the CDs exhibited an interdecadal shift around the 1980s. The first mode reflected a nearly coherent interannual variability with a maximum center over central-northeastern China during 1961–1985 (P1), whereas the maximum center shifted to central-southwestern China during 1993–2017 (P2). The second mode represented a north-south dipole variation, with maximum variations over southern China in the P1 but northeastern China in the P2. The first mode was significantly related to the AO in the P1 and ENSO in the P2, whereas the second mode was closely linked to ENSO in the P1 and the AO in the P2. During the P1, an anomalous quasi-barotropic cyclone over northern East Asia was induced by a negative AO, deepening the East Asian trough along the East Asian coast, which was favorable for the occurrence of CDs over central-northeastern China (i.e., the first mode). The El Niño excited an anomalous anticyclonic circulation over the Northwest Pacific, impeding cold air along the coast of southern China, which seemed to produce a pattern of the second mode. During the P2, the AO was weaker (smaller magnitude), and the AO-related anomalous cyclone shifted northwestward compared to that in the P1, limiting its effect to northeastern China and inducing a north-south dipole pattern. On the other hand, ENSO-related anomalous circulation shifted southwestward compared to the P1, modulating CDs over central-southwestern China and producing an anomalous pattern of CDs similar to the first mode.

On the Successiveness of the Two Extreme Cold Events in China during the 2020/21 Winter According to Cold Air Trajectories

Two extreme cold air events successively hit China during 28–31 December 2020 (the late 2020 event) and during 6–8 January 2021 (the early 2021 event), which caused great losses. These two events have received extensive attention in relation to synoptic weather systems and remote forcing. Although it has been noted that a near-surface cool condition can greatly impact tropospheric circulation, its role in the successiveness of two such extreme cold waves remains unclear. This study focused on cold air pathways from the Lagrangian perspective, and explored the potential influence of cold air over the key region in terms of connecting the two cold events using a piecewise potential vorticity inversion. With the obtained results, three cold air sources with three corresponding air routes were identified in the two cold events. The northern pathway dominated the late 2020 event, in which the cold air intruded from the eastern Laptev Sea and moved southward to China. In contrast, the early 2021 event was mainly associated with the northwestern pathway in which the cold air came from the Ural Mountains and moved clockwise. Notably, cold air traveling along the western route from western Lake Balkhash arrived at the north of the Tianshan Mountains earlier and amplified the positive height anomaly in situ. Moreover, such an enhanced positive height anomaly moved the direction of the cold air from the northern and northwestern routes southward and thus played a key role in the successiveness of the two extreme cold events.

Cascading disasters and mental health inequities: Winter Storm Uri, COVID-19 and post-traumatic stress in Texas

Previous research on health effects of extreme weather has emphasized heat events even though cold-attributable mortality exceeds heat-attributable mortality worldwide. Little is known about the mental health effects of cold weather events, which often cascade to produce secondary impacts like power outages, leaving a knowledge gap in context of a changing climate. We address that gap by taking a novel “cascading disaster health inequities” approach to examine winter storm-associated post-traumatic stress (PTS) using survey data (n = 790) collected in eight Texas metro areas following Winter Storm Uri in 2021, which occurred against the backdrop of COVID-19. The incidence of storm-related PTS was 18%. Being Black (odds ratio [OR]: 6.6), Hispanic (OR: 3.5), or of another non-White race (OR: 4.2) was associated with greater odds of PTS compared to being White, which indicates substantial racial/ethnic inequities in mental health impacts (all p < 0.05). Having a disability also increased odds of PTS (OR: 4.4) (p < 0.05). Having piped water outages (OR: 1.9) and being highly impacted by COVID-19 (OR: 3.3) increased odds of PTS (both p < 0.05). When modelling how COVID-19 and outages cascaded, we compared householders to those with no outages and low COVID-19 impacts. PTS was more likely (p < 0.05) if householders had a water or power outage and high COVID-19 impacts (OR: 4.4) and if they had water and power outages and high COVID-19 impacts (OR: 7.7). Findings provide novel evidence of racial/ethnic inequities and cascading effects with regard to extreme cold events amid the COVID-19 pandemic.

Realistic ocean initial condition for stimulating the successful prediction of extreme cold events in the 2020/2021 winter

In the first half of winter 2020/2021, several unprecedented cold events occurred in most parts of China and caused record-breaking low temperatures in many cities. However, seasonal predictions related to the onset and evolution of extreme cold events are still challenging. In this study, we first evaluated the short-term climate prediction skills in winter of the CAS-ESM-c global coupled model and revealed the key dynamic processes of the onset and development of 2020/2021 extreme cold events based on the ensemble forecasts starting on October 1st, 2020. Under the background provided by the synergistic effect of the warm Arctic and the cold tropical Pacific (La Niña), the model captured the abnormal meridional atmospheric pattern well, including the intensification of the Ural Blocking High and the negative phase of the Arctic Oscillation, forecasted the negative geopotential height anomalies over the Eastern Asian region, and finally, successfully predicted the outbreak of cold waves in December 2020 two months in advance. Moreover, the dominant differences in the initial ocean fields between the best and the worst forecast members were further compared to isolate the triggering factor for predicting cold events by CAS-ESM-c. The initial warm sea surface temperature over the Barents Sea can gradually form a meridional pattern between the warm Arctic and the cold Asian continent, which could lead to a reduction in the large-scale meridional temperature gradient at mid-high latitudes and weaken the atmospheric baroclinicity with more conducive to the southward outbreak of cold waves, highlighting that realistic Arctic ocean conditions in autumn can be reasonably assimilated into coupled models to stimulate the successful prediction of extreme cold events in the 2020/2021 winter.

Cold waves in Terai region of Nepal and farmer’s perception of the effect of fog events and cold waves on agriculture

Cold waves are considered one of the important extreme weather events affecting winter crop production in the Indo-Gangetic Plain (IGP). In spite of media coverage of extreme cold events in the Terai area of Nepal (Nepal section of IGP) in recent years, few studies on this topic were found. This study investigates cold waves and their impact on agriculture during winter in the Terai region of Nepal. Historical daily maximum and minimum temperature data from six stations in the Terai (Dhangadhi, Nepalgunj, Bhairahawa, Simara, Janakpur, and Biratnagar) during 1971–2015 were analyzed to study the occurrence of cold days, cold nights, extreme cold days, extreme cold nights, cold wave days, and extreme cold wave days in the Terai. The average number of cold days per annum ranges from 15.6 to 17.9 days and the extreme cold days per annum ranges from 3.2 to 3.6 days in the Terai. Except for Nepalgunj, all the Terai stations show statistically significant increasing trends in the frequency of cold days and extreme cold days over the last four decades. Similarly, the average number of cold wave days varies from 9.2 to 13.8 per annum and the average number of extreme cold wave days varies from 1.4 to 3.8 days in the Terai region of Nepal. By comparing the co-occurrence of foggy days and cold and extreme cold wave days at Biratnagar, Simara, Bhairahawa, and Nepalgunj airport, it is also observed that most of the cold and extreme cold wave days are also foggy days. The perception of farmers regarding the effect of fog and cold wave events was explored through focus group discussions at Dhanusha and Sunsari districts of Nepal and found that the fog and cold events have significantly affected their winter crops, livestock, and their day-to-day life.

A Comparative Analysis of Changes in Temperature and Precipitation Extremes since 1960 between China and Greece

The temporal and spatial variations of 26 extreme temperature and precipitation indices for China and Greece were comparatively analysed. Also, their association with atmospheric circulation types was evaluated using multiple linear regression. The calculation of the extreme indices was based on homogenized daily temperature and precipitation time series from 1960 to 2010 for Greece and 2021 for China. Extreme precipitation, intensity, and short-term heavy precipitation increased, while persistent heavy precipitation has decreased since 1960 in China. Short-term heavy precipitation has also shown an increasing trend in Greece, though total precipitation and persistent heavy precipitation decreased there between 1960 and 2010. Extreme cold events have tended to decrease, and extreme warm events have increased in both countries, a fact that can be attributed to global warming. For comparison, climatic warming in China was mainly seen in the half year of winter, while the extreme indices relevant to cold seasons such as FD0 and ID0 presented a small trend in Greece. The observed changes in many climatic indices, including RX5day and WSDI in China and R20MM, RX5day, CDD, PRCPTOT and FD0 in Greece, could be partly explained by those of the main large-scale circulation types in the corresponding regions. The significant multiple correlation coefficients of the main circulation types were up to 0.53 for RX5day and 0.54 for WSDI in China, and 0.74 for PRCPTOT and 0.71 for R20MM in Greece. The relationships between climatic indices and circulation types were closer in Greece than in China, especially for the precipitation indices.

CORDEX-EA Phase 2 다중 지역기후모델 앙상블을 이용한 전지구 온난화 제한 목표(1.5, 2.0℃)하에서의 한반도 미래 기온 전망

This study presents a future projection of temperature over the Korean Peninsula (KP) under the global warming targets of 1.5℃ and 2.0℃ set in the 2015 Paris Agreement. For projection, simulation data from the multi-Regional Climate Model (RCM) ensemble in Coordinated Regional Climate Downscaling Experiment (CORDEX)-East Asia (EA) Phase 2 are used. Under the 2.0℃ (1.5℃) global warming condition, mean temperature over KP would increase 2.13℃ (1.51℃) compared to the present period (1985 ~ 2005 years). Extreme minimum and maximum temperature intensity indices (TNn and TXx) would also increase 2.61℃ (1.91℃) and 2.38℃ (1.58℃). In addition, changes in probabilities of extreme temperature events that occurs once in 20 years during the present period are investigated. Extreme cold events would occur once in 28.9 years (22.6 years) and warm events once in 5.9 years (7.2 years). Meanwhile, there are several noteworthy points about the future projection. The temperature over KP would increase more over the northern KP than the southern KP and this feature is more distinct in TNn. The uncertainties of the projection are higher for the 1.5℃ warming condition than the 2.0℃ warming condition and for extreme temperature versus mean temperature. The spatial pattern of change in extreme temperature frequency is different from that of intensity. In other words, a smaller increase in the frequency of extreme cold events is expected over the inland KP.

Morphological and physiological response of Chinese tallow (Triadica sebifera) to an extreme cold spell in subtropical, coastal forests of China

Acute and extreme weather events can cause considerable damage to the tissues of trees, including stem death and branch or leaf distortion, which may limit their survival and reproduction. In January 2016, a rare cold spell impacted the coastal forests of subtropical China. Using post-hoc assessments, we evaluated the morphological and physiological response of Chinese tallow (Triadica sebifera L.) to the extreme cold spell in two distinct ecoregions, one (Xiangshan, China) representing the cold spell impacted zone and the other (Taizhou, China) representing the non-affected zone. To determine if the extreme cold events impacted the vigor of Chinese tallow, we assessed differences in growth rate, leaf characteristics, and leaf gas exchange. As age may affect tree morphological and physiological response to stress, we grouped subject trees into three distinct cohorts, namely, seedlings (1–2 years old), young-aged (5–6 years old), and middle-aged (10–12 years old). Our results suggest that although tree height and diameter did not differ, leaf area expansion and leaf mass were reduced in the impacted zone. In seedling and young-aged trees, the cold spell significantly reduced leaf net photosynthetic (An), transpiration rates (Tr), stomatal conductance (Gs) and water use efficiency (WUE) while leaf intercellular CO2 concentration (Ci), vapor pressure deficit (Vpd), and intercellular CO2 pressure (Ci-Pa) increased. In contrast, the middle-aged group was less responsive to the cold spell. Across all cohorts, the event did not affect leaf temperature (Tleaf), but the activity of superoxide dismutase (SOD) and peroxidase (POD) decreased. We also detected increases of leaf malondialdehyde (MDA) and free proline (Pro) contents in young-aged and middle-aged groups. Hence, the extreme cold spell caused remarkable negative effects on the morphological and physiological traits of Chinese tallow. Redundancy analysis revealed that the cold spell also impacted the subsequent recovery process of damaged Chinese tallow by reducing the ability of leaf to utilize microenvironmental resources (radiation, air humidity, and CO2) for gas exchange. Results from this study are important to strengthen our understanding of Chinese tallow responding to extreme cold stress within its native range, also be helpful to predict the distributions of Chinese tallow in its invasive range where it has devastating impacts to coastal ecosystems in the southeast US.

Enhanced Intensity of the Interannual Variability of February Surface Air Temperature Over Mid‐ and High‐Latitude Asia Since the Late‐1990s

AbstractThis study investigates the interdecadal variation of the intensity of the interannual variability (IIV) of surface air temperature (SAT) over mid‐ and high‐latitude Asia (MHLA) in winter months (December–February) during 1980–2015 and the role of the Arctic sea‐ice. Results show only the IIV of February SAT is significantly enhanced around the late‐1990s, which partly results from enhanced IIV of the frequency of extreme warm and cold events (FEWE and FECE). The influence of the sea‐ice in the Barents Sea from December to February on the February SAT, FEWE and FECE over MHLA is remarkably enhanced around the late‐1990s. During 1998–2015, the sea‐ice anomalies contribute to the enhanced IIV of February SAT over MHLA by modulating the monthly and synoptic tripole patterns over northern Eurasia, the positive phase of which exhibits an anomalous low over Eurasia north of 60°N and anomalous highs over southern Europe and MHLA. On the monthly average, the increased sea‐ice induces Rossby waves and then a positive phase of the monthly tripole pattern, inducing weakened East Asian trough and Siberian high, enhanced westerlies over 50°–70°N, and resultant decreased blocking high frequency over Eurasia north of 60°N. These anomalies favor increased February SAT over MHLA. On synoptic timescales, the increased blocking over the north side of the Ural Mountains favors more (fewer) extreme positive (negative) phases of the synoptic tripole pattern and hence increased FEWE (decreased FECE) over MHLA, further strengthening the increased SAT. Numerical experiments basically confirm the mechanisms above.

Arctic and Pacific Ocean Conditions Were Favorable for Cold Extremes over Eurasia and North America during Winter 2020/21

Abstract A sequence of extreme cold events occurred across Eurasia and North America during winter 2020/21. Here, we explore the causes and associated mechanisms for the extremely cold temperatures using both observations and large-ensemble simulations. Experiments were conducted with observed ocean surface boundary conditions prescribed globally, and regionally to discern the specific influence of Arctic, tropical Pacific, and North Pacific drivers. Increased likelihood of daily cold extremes in mid-December to mid-January are found in Eurasian midlatitudes in response to reduced Arctic sea ice. Tropical sea surface temperature anomalies, more specifically the La Niña pattern, increased probability of extreme cold over high-latitude Eurasia in early January to early February. Both reduced Arctic sea ice and La Niña increased the probability of daily cold extremes over western North America in late January to late February. We conclude that a combination of reduced Arctic sea ice, La Niña, and a sudden stratospheric warming in January 2021 were factors in the February 2021 extreme cold wave that caused huge societal disruptions in Texas and the southern Great Plains. Although the magnitude of the simulated cold extremes are relatively small when compared with observed anomalies, the Arctic and Pacific Ocean surface conditions in winter 2020/21 increased the probability of cold days as cold or colder than observed by approximately 17%–43%.

The combined impact of subtropical wave train and Polar−Eurasian teleconnection on the extreme cold event over North China in January 2021

The combined impact of subtropical wave train and Polar−Eurasian teleconnection on the extreme cold event over North China in January 2021

Interdecadal Change of Ural Blocking Highs and Its Atmospheric Cause in Winter during 1979–2018

The Ural blocking (UB) high is a weather system closely related to the cold air process during winter, which could trigger extreme cold events in East Asia. By retrieving five single blocking indexes, including accumulation frequency, central latitude, blocking intensity, mean duration and north rim, it is found that the UB in winter occurs more frequently, grows stronger, lasts longer and is located more northward after 2002, compared with 1985–2001. In order to describe the UB comprehensively, a new comprehensive blocking index (CBI) is developed based on the above five blocking indexes. The CBI can also reflect the interdecadal change of UB synthetically. Analysis on the corresponding atmospheric circulation shows that the relationship between the UB and atmospheric circulation, such as the polar vortex and jet, is closer in 2002–2018 than in 1985–2001. Compared with the atmospheric circulation in 1985–2001, the most prominent feature in 2002–2018 is that the intensity of the polar vortex is weaker at 100 hPa, and that the subtropical jet moves northward. Meanwhile, the East Asian trough downstream of the Urals deepens at 500 hPa and the Siberian high strengthens, indicating that the East Asia winter monsoon is stronger during 2002–2018. Further analysis on atmospheric waves and baroclinicity demonstrates that the meridional circulation of planetary waves strengthens, especially the 2-waves, which may increase the frequency of the UB and shift its location northward after 2002. Additionally, the baroclinicity (−∂T/∂y) in the mid-high latitudes is weakened during winter since 2002, which is also beneficial for the establishment of meridional circulation, causing a stronger intensity and longer duration of the UB.

Intra-Seasonal Features of Winter Extreme Cold Events in Northeast–North China and Synergistic Effects of Circulation Systems in Mid-High Latitude

Based on the daily minimum air temperature (Tmin) data from the China Meteorological Data Network and the NCEP/DOE reanalysis data, the intra-seasonal circulation characteristics and evolution of extreme cold events (ECEs) in Northeast–North China (NE-N) during the winter of 1979–2018 are explored, and the synergistic effects of key circulation systems in the mid-high latitude on ECEs are discussed. The results show that: (1) the winter daily Tmin in the NE-N region presents a significant low-frequency period of 10–30 d; during the cooling phases, a pair of cyclone–anticyclone in the lower troposphere moves southeastward, accompanying the intensifying Siberian High, and leads to the abnormal northerly; the developing wave trains in the middle troposphere result in enhancing and maintaining cold air; furthermore, the situation of the upper tropospheric jet weakening in the north and strengthening in the south is favorable for cold air to move southward and accumulate in the NE-N region. (2) There are two wave trains in the Eurasian at 200 hPa level. The north one moves southeastward through the Ural Mountains to the coast of East Asia, with the upstream wave activity flux dispersing to NE-N region, causing the northeast cold vortex to develop. The south one with relatively weak intensity disperses the wave flux northward, and enhances the cold vortex. (3) The key circulation systems of ECEs are the Siberian High, the Ural Mountain Blocking High, the Northeast Cold Vortex, and the East Asian Subtropical Jet. The Ural Mountains Blocking High leads four phases earlier than low temperature, and the rest of the systems are basically in phase with low temperature. The synergistic effect of circulation systems will lead to extended-range cold in the NE-N region.

Probabilistic Peak Demand Estimation Using Members of the Clayton Generalized Gamma Copula Family

Climate change impacts many aspects of life and requires innovative thinking on various issues. The electricity sector is affected in several ways, including changes in the production components and consumption patterns. One of the most important issues for Independent System Operators, a state-controlled organization responsible for ensuring the reliability, availability, and quality of electricity delivery in the country, is the response to climate change. This is reflected in the appropriate design of production units to cope with the increase in demand due to extreme heat and cold events and the development of models aimed at predicting the probability of such events. In our work, we address this challenge by proposing a novel probability model for peak demand as a function of wet temperature (henceforth simply temperature), which is a weighting of temperature and humidity. We study the relationship between peak demand and temperature using a new Archimedean copula family, shown to be effective for this purpose. This family, the Clayton generalized Gamma, is a multi-parameter copula function that comprises several members. Two new measures of fit, an economic measure and a conditional coverage measure, were introduced to select the most appropriate family member based on the empirical data of daily peak demand and minimum temperature in the winter. The Clayton Gamma copula showed the lowest cost measure and the best conditional coverage and was, therefore, proven to be the most appropriate member of the family.