bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Comparison of the Vorticity Dynamics Governing the Oceanic Bomb Cyclone of 4–5 January 1989 and the Super Derecho of 8 May 2009
Authors: Galarneau Jr. Thomas J. , Weisman Morris L. 
Published: August 2020

Abstract
Convection-allowing simulations of two warm seclusion cyclones are used to elucidate the vorticity dynamics that contribute to intensification of these systems. The rapidly intensifying oceanic “bomb” cyclone on 4–5 January 1989 and the super derecho on 8 May 2009 are the subject of this study. While these systems occupy different spatial scales, they both acquire characteristics of a warm seclusion cyclone. The aim of this study is to compare the basic structure and determine the dynamics driving increases in system-scale vertical vorticity during the intensification of these systems. Results from a vorticity budget show that system-scale stretching and the lateral transport of vertical vorticity to the cyclone center contribute to increases of system-scale low-level vertical vorticity during the intensification of the oceanic cyclone. The intercomparison of the oceanic cyclone and the super derecho shows that the relative contributions to increases in system-scale vertical vorticity by stretching and tilting as a function of height differ among the two cases. However, the lateral transport of vertical vorticity to the cyclone center is a key contributor to increases in low-level system-scale vertical vorticity for both cases. We hypothesize that this process may be common among a wide array of intense cyclonic systems across scales ranging from warm seclusion extratropical cyclones to some mesoscale convective systems.
The Climatology of Lower Tropospheric Temperature Inversions in China from Radiosonde Measurements: Roles of Black Carbon, Local Meteorology, and Large-Scale Subsidence
Authors: Guo Jianping , Chen Xinyan , Su Tianning , Liu Lin , Zheng Youtong , Chen Dandan , Li Jian , Xu Hui , Lv Yanmin , He Bingfang , Li Yuan , Hu Xiao-Ming , Ding Aijun , Zhai Panmao 
Published: August 2020

AbstractThe variability of the lower tropospheric temperature inversion (TI) across China remains poorly understood. Using seven years’ worth of high-resolution radiosonde measurements at 120 sites, we compile the climatology of lower tropospheric TI in terms of frequency, intensity, and depth during the period from 2011 to 2017. The TI generally exhibits strong seasonal and geographic dependencies. Particularly, the TI frequency is found to be high in winter and low in summer, likely due to the strong aerosol radiative effect in winter. The frequency of the surface-based inversion (SBI) exhibits a “west low, east high” pattern at 0800 Beijing time (BJT), which then switches to “west high, east low” at 2000 BJT. Both the summertime SBI and elevated inversion (EI) reach a peak at 0800 BJT and a trough at 1400 BJT. Interestingly, the maximum wintertime EI frequency occurs over Southeast China (SEC) rather than over the North China Plain (NCP), likely attributable to the combination of the heating effect of black carbon (BC) originating from the NCP, along with the strong subsidence and trade inversion in SEC. Correlation analyses between local meteorology and TI indicate that larger lower tropospheric stability (LTS) favors more frequent and stronger TIs, whereas the stronger EI under smaller LTS conditions (unstable atmosphere) is more associated with subsidence rather than BC. Overall, the spatial pattern of the lower tropospheric TI and its variability in China are mainly controlled by three factors: local meteorology, large-scale subsidence, and BC-induced heating. These findings help shed some light on the magnitude, spatial distribution, and underlying mechanisms of the lower tropospheric TI variation in China.
Contributions of Different Combinations of the IPO and AMO to the Concurrent Variations of Summer East Asian Jets
Authors: Xiao Xiucheng , Huang Danqing , Yang Ben , Zhu Jian , Yan Peiwen , Zhang Yaocun 
Published: August 2020

ABSTRACTHuang et al. recently reported that opposite phases of the interdecadal Pacific oscillation (IPO) and the Atlantic multidecadal oscillation (AMO) can affect the shift of the East Asian polar front jet (EAPJ) and the East Asian subtropical jet (EASJ) in the boreal winter. To give a full image of the relationship among the IPO, AMO, and concurrent variation of jets throughout the whole year, this study investigates the changes in summer jets response to the combinations of the IPO and AMO, and mostly focuses on the quantitative analysis in the role of the IPO and AMO. Both of the diagnostic analysis and atmospheric model simulations confirm that combinations of the negative phase of the IPO (“−IPO”) and the positive phase of the AMO (“+AMO”) can significantly enhance the EAPJ and reduce the EASJ in the summer, via the meridional temperature gradient and the Eady growth rate, and vice versa in the “+IPO −AMO” combination. The reanalysis data show that this relationship is particularly evident between the periods of 1999–2014 and 1979–98. Based on the simulations, the multilinear regression has indicated that −IPO plays a more important role than +AMO, particularly for the reduced EASJ. We have further revealed two pathways of the stationary Rossby wave activity anomaly, eastward from the North Atlantic to East Asia along 60°N and westward from the North Pacific to East Asia along 40°N. The two activities are associated with anomalous anticyclone along the active regions between EAPJ and EASJ, and therefore affect the jet variations.
Analysis of Record-High Temperature over Southeast Coastal China in Winter 2018/19: The Combined Effect of Mid- to High-Latitude Circulation Systems and SST Forcing over the North Atlantic and Tropical Western Pacific
Authors: Jian Yuntao , Lin Xiaoxia , Zhou Wen , Jian Maoqiu , Leung Marco Y. T. , Cheung Paxson K. Y. 
Published: August 2020

AbstractIn winter 2018/19, southeastern coastal China experienced extreme warm temperatures that were due to a weak East Asian winter monsoon. On the basis of observations from 10 meteorological stations and reanalysis data, the large-scale circulation patterns associated with this extreme warm winter and the possible driving mechanism of its related sea surface temperature (SST) anomalies are investigated in this study. During this winter, many places in this region reached their highest winter mean temperature record and had more extreme warm days and fewer extreme cold days relative to climatology. According to the circulation patterns during winter 2018/19, several large-scale circulation conditions associated mainly with the weak East Asian winter monsoon are identified: the eastward shift of the Siberian high and a shallower East Asian trough, which is related to the low blocking frequency over the Aleutian region, are both unfavorable for cold-air intrusion southward. Meanwhile, strong low-level southerly wind anomalies over southeastern China are related mainly to the 2018/19 El Niño event. Furthermore, the possible role of SST anomalies over the North Atlantic and tropical western Pacific Oceans is examined by using an atmospheric general circulation model, suggesting that both the “tripole pattern” of North Atlantic SST and tropical western Pacific SST anomalies in winter 2018/19 played a role in influencing the East Asian trough. The combined effect of all of these factors seems to be responsible for this extreme warm winter over southeastern coastal China.
Improved Detection of Interannual Cloud Variability over the Southern Hemisphere Using Legacy Satellites
Authors: Liu Shay , Staten Paul W. , Kahn Brian H. 
Published: August 2020

AbstractShifts in deep tropical convection and midlatitude jet streams both manifest themselves in high cloud anomalies. Such anomalies may play a significant role in local to global climate processes. This work investigates how high cloud properties covary with two primary interannual modes of variability in the Southern Hemisphere (SH): El Niño–Southern Oscillation (ENSO) and the southern annular mode (SAM). In contrast to several recent studies that utilize the latest remote sensing datasets (e.g., CloudSat), we employ a novel combination of imager and sounder data from legacy satellite instruments. Using these legacy data, we confirm the poleward shift of high cloud fields in the SH midlatitudes with SAM seen in other recent studies and characterize the opposing impacts of SAM and ENSO on the South Pacific convergence zone and Southern Hemisphere storm tracks. Furthermore, we demonstrate that the standard deviation of brightness temperature data from the window channel acts as a surrogate for high cloud fraction in the tropics and midlatitudes. Our results reconcile apparent differences in recent studies and suggest that brightness temperature standard deviations are climate relevant, in addition to being largely insensitive to instrument calibration.
Is the North Pacific Victoria Mode a Predictor of Winter Rainfall over South China?
Authors: Zou Qian , Ding Ruiqiang , Li Jianping , Tseng Yu-heng , Hou Zhaolu , Wen Tao , Ji Kai 
Published: August 2020

AbstractThis study investigates the connection between the North Pacific Victoria mode (VM) during the boreal spring [February–April (FMA)] and the following boreal winter [January–March (JFM)] rainfall over South China (SC). The VM is defined as the second empirical orthogonal function mode (EOF2) of sea surface temperature (SST) anomalies (SSTAs) in the North Pacific poleward of 20°N. It is found that the boreal spring VM has a significant positive correlation with the following winter rainfall over SC. Analyses indicate that a strong positive VM during spring can induce El Niño during the following winter via an air–sea interaction, resulting in the generation of an anomalous anticyclone over the western North Pacific (WNPAC). The anomalous southwesterlies along the southeast coast of East Asia associated with the WNPAC favor an abundant supply of water vapor and anomalous ascending motion over SC. As a result, winter rainfall over SC increases. A linear regression model based on the VM shows that the VM can act as an effective predictor of winter rainfall over SC about 1 year in advance. It also has a higher prediction skill than ENSO in predicting winter rainfall over SC.
Response of the Asian Summer Monsoon Precipitation to Global Warming in a High-Resolution Global Nonhydrostatic Model
Authors: Takahashi Hiroshi G. , Kamizawa Nozomi , Nasuno Tomoe , Yamada Youhei , Kodama and Chihiro , Sugimoto Shiori , Satoh Masaki 
Published: August 2020

AbstractThis study examined the responses of Asian monsoon precipitation to global warming on the regional scale, focusing on monsoon westerlies and monsoon trough. This is because the Asian monsoon precipitation is closely associated with tropical disturbances. To reproduce convective precipitation and tropical disturbances, this study used outputs of a high-resolution climate simulation. Two sets of approximately 30-yr simulations under present-day (control) and warmer climate conditions (global warming) were conducted by the 14-km Nonhydrostatic Icosahedral Atmospheric Model (NICAM) with explicitly calculated convection. For understanding the spatial pattern of future precipitation changes, a further set of a 5-yr simulation [sea surface temperature (SST) + 4 K] was also conducted. Overall, the Asian summer monsoon was well simulated by the model. Precipitation increased as a result of global warming along the monsoon trough, which was zonally elongated across northern India, the Indochina Peninsula, and the western North Pacific Ocean. This increased precipitation was likely due to an increase in precipitable water. The spatial pattern of the increased precipitation was associated with enhanced cyclonic circulations over a large area along the monsoon trough, although it was difficult to determine whether the large-scale monsoon westerly was enhanced. This enhancement can be explained by future changes in tropical disturbance activity, including weak tropical cyclones. However, over part of South Asia, circulation changes may not contribute to the increased precipitation, suggesting regional characteristics. The regional increase in precipitation along the monsoon trough was mostly explained by the uniform increase in SST, whereas SST spatial patterns are important over some regions.
Origins of East Asian Summer Monsoon Seasonality
Authors: Chiang J. C. H. , Kong W. , Wu C. H. , Battisti D. S. 
Published: August 2020

AbstractThe East Asian summer monsoon is unique among summer monsoon systems in its complex seasonality, exhibiting distinct intraseasonal stages. Previous studies have alluded to the downstream influence of the westerlies flowing around the Tibetan Plateau as key to its existence. We explore this hypothesis using an atmospheric general circulation model that simulates the intraseasonal stages with fidelity. Without a Tibetan Plateau, East Asia exhibits only one primary convective stage typical of other monsoons. As the plateau is introduced, the distinct rainfall stages—spring, pre-mei-yu, mei-yu, and midsummer—emerge, and rainfall becomes more intense overall. This emergence coincides with a pronounced modulation of the westerlies around the plateau and extratropical northerlies penetrating northeastern China. The northerlies meridionally constrain the moist southerly flow originating from the tropics, leading to a band of lower-tropospheric convergence and humidity front that produces the rainband. The northward migration of the westerlies away from the northern edge of the plateau leads to a weakening of the extratropical northerlies, which, coupled with stronger monsoonal southerlies, leads to the northward migration of the rainband. When the peak westerlies migrate north of the plateau during the midsummer stage, the extratropical northerlies disappear, leaving only the monsoon low-level circulation that penetrates northeastern China; the rainband disappears, leaving isolated convective rainfall over northeastern China. In short, East Asian rainfall seasonality results from the interaction of two seasonally evolving circulations—the monsoonal southerlies that strengthen and extend northward, and the midlatitude northerlies that weaken and eventually disappear—as summer progresses.
Comparing Methods to Constrain Future European Climate Projections Using a Consistent Framework
Authors: Brunner Lukas , McSweeney Carol , Ballinger Andrew P. , Befort Daniel J. , Benassi Marianna , Booth Ben , Coppola Erika , de Vries Hylke , Harris Glen , Hegerl Gabriele C. , Knutti Reto , Lenderink Geert , Lowe Jason , Nogherotto Rita , O’Reilly Chris , Qasmi Saïd , Ribes Aurélien , Stocchi Paolo , Undorf Sabine 
Published: August 2020

AbstractPolitical decisions, adaptation planning, and impact assessments need reliable estimates of future climate change and related uncertainties. To provide these estimates, different approaches to constrain, filter, or weight climate model projections into probabilistic distributions have been proposed. However, an assessment of multiple such methods to, for example, expose cases of agreement or disagreement, is often hindered by a lack of coordination, with methods focusing on a variety of variables, time periods, regions, or model pools. Here, a consistent framework is developed to allow a quantitative comparison of eight different methods; focus is given to summer temperature and precipitation change in three spatial regimes in Europe in 2041–60 relative to 1995–2014. The analysis draws on projections from several large ensembles, the CMIP5 multimodel ensemble, and perturbed physics ensembles, all using the high-emission scenario RCP8.5. The methods’ key features are summarized, assumptions are discussed, and resulting constrained distributions are presented. Method agreement is found to be dependent on the investigated region but is generally higher for median changes than for the uncertainty ranges. This study, therefore, highlights the importance of providing clear context about how different methods affect the assessed uncertainty—in particular, the upper and lower percentiles that are of interest to risk-averse stakeholders. The comparison also exposes cases in which diverse lines of evidence lead to diverging constraints; additional work is needed to understand how the underlying differences between methods lead to such disagreements and to provide clear guidance to users.
Severe Cold Winter in North America Linked to Bering Sea Ice Loss
Authors: Iida Mizuki , Sugimoto Shusaku , Suga Toshio 
Published: August 2020

AbstractNorth America experienced an intense cold wave with record low temperatures during the winter of 2017/18, at the time reaching the smallest rank of sea ice area (SIA) in the Bering Sea over the past four decades. Using observations, ocean reanalysis, and atmospheric reanalysis data for 39 winters (1979/80–2017/18), both the Bering SIA loss and cold winters in North America are linked robustly via sea level pressure variations over Alaska detected as a dominant mode, the Alaska Oscillation (ALO). The ALO differs from previously identified atmospheric teleconnection and climate patterns. In the positive ALO, the equatorward cold airflow through the Bering Strait increases, resulting in surface air cooling over the Bering Sea and an increase in Bering SIA, as well as surface warming (about 4 K for the winter mean) for North America in response to a decrease of equatorward cold airflow, and vice versa for negative phase. The northerly winds with the cold air over the Bering Sea result in substantial heat release from ocean to atmosphere over open water just south of the region covered by sea ice. Heating over the southern part of Bering Sea acts as a positive feedback for the positive ALO and its related large-scale atmospheric circulation in a linear baroclinic model experiment. Bering SIA shows no decreasing trend, but has remained small since 2015. CMIP6 climate models of the SSP5–8.5 scenario project a decrease of Bering SIA in the future climate. To explain severe cold winters in North America under global warming, it is necessary to get an understanding of climate systems with little or no sea ice.
How Well Do CMIP6 Historical Runs Match Observed Northeast U.S. Precipitation and Extreme Precipitation–Related Circulation?
Authors: Agel Laurie , Barlow Mathew 
Published: August 2020

AbstractSixteen historical simulations (1950–2014) from phase 6 of the Coupled Model Intercomparison Project (CMIP6) are compared to Northeast U.S. observed precipitation and extreme precipitation–related synoptic circulation. A set of metrics based on the regional climate is used to assess how realistically the models simulate the observed distribution and seasonality of extreme precipitation, as well as the synoptic patterns associated with extreme precipitation. These patterns are determined byk-means typing of 500-hPa geopotential heights on extreme precipitation days (top 1% of days with precipitation). The metrics are formulated to evaluate the models’ extreme precipitation spatial variations, seasonal frequency, and intensity; and for circulation, the fit to observed patterns, pattern seasonality, and pattern location of extreme precipitation. Based on the metrics, the models vary considerably in their ability to simulate different aspects of regional precipitation, and a realistic simulation of the seasonality and distribution of precipitation does not necessarily correspond to a realistic simulation of the circulation patterns (reflecting the underlying dynamics of the precipitation), and vice versa. This highlights the importance of assessing both precipitation and its associated circulation. While the models vary in their ability to reproduce observed results, in general the higher-resolution models score higher in terms of the metrics. Most models produce more frequent precipitation than that for observations, but capture the seasonality of precipitation intensity well, and capture at least several of the key characteristics of extreme precipitation–related circulation. These results do not appear to reflect a substantial improvement over a similar analysis of selected CMIP5 models.
The Role of Tropical, Midlatitude, and Polar Cloud-Radiative Changes for the Midlatitude Circulation Response to Global Warming
Authors: Albern Nicole , Voigt Aiko , Thompson David W. J. , Pinto Joaquim G. 
Published: August 2020

AbstractPrevious studies showed that global cloud-radiative changes contribute half or more to the midlatitude atmospheric circulation response to global warming. Here, we investigate the relative importance of tropical, midlatitude, and polar cloud-radiative changes for the annual-mean, wintertime, and summertime circulation response across regions in AMIP-like simulations. To this end, we study global warming simulations from the ICON model run with the cloud-locking method and prescribed sea surface temperatures, which isolate the impact of changes in atmospheric cloud-radiative heating. Tropical cloud changes dominate the global cloud impact on the 850 hPa zonal wind, jet strength, and storm track responses across most seasons and regions. For the jet shift, a more diverse picture is found. In the annual mean and DJF, tropical and midlatitude cloud changes contribute substantially to the poleward jet shift in all regions. The poleward jet shift is further supported by polar cloud changes across the Northern Hemisphere but not in the Southern Hemisphere. In JJA, the impact of regional cloud changes on the jet position is small, consistent with an overall small jet shift during this season. The jet shift can be largely understood via the anomalous atmospheric cloud-radiative heating in the tropical and midlatitude upper troposphere. The circulation changes are broadly consistent with the influence of cloud-radiative changes on upper-tropospheric baroclinicity and thus the mean potential energy available for conversion into eddy kinetic energy. Our results help to explain the jet response to global warming and highlight the importance of tropical and midlatitude cloud-radiative changes for this response.
Trends and Variability in Airmass Frequencies: Indicators of a Changing Climate
Authors: Lee Cameron C. 
Published: August 2020

AbstractRecent international efforts at communicating climate change have begun using the notion of a climate indicator—a climate-related metric that can be used to track changes in the Earth system over time. Based upon a recently developed global-scale classification of daily air masses, this research examines the trends and variability in the frequencies of these air masses and then utilizes them to develop two nontraditional climate indicators: a warm/cool index (WCI) and a global extremes index (GEI). Results show that both indices trend significantly upward over the 40-yr period of record, indicating an increase in warm-based air masses (WCI) and extreme air masses (GEI). The two indices also exhibit a moderate (GEI) to strong (WCI) association with the global mean temperature record, multiple near-surface climate variables, and other existing climate indicators over that same time, showing promise as global indicators. Shorter-term variability in these indices also show a linear relationship between the WCI and changes in the Atlantic multidecadal oscillation and a nonlinear relationship between GEI and El Niño–Southern Oscillation. While many published climate indicators are based upon a single variable, and/or are regional in scope, the two indices presented herein are unique in that they are representative of the trends in the multivariate (and extreme, in the case of the GEI) weather conditions that are experienced near Earth’s surface, while also being global in scope.