Abstract In this study, the interdecadal variations of extreme precipitation in May over southwestern Xinjiang (SWX) and related mechanisms were investigated. The extreme precipitation in May over SWX exhibited a decadal shift in the 1990s (negative phase during 1970–86 and positive phase during 2003–18). The decadal shift corresponded to strengthened moist airflow from the Indian Ocean and an anomalous cyclone over SWX during 2003–18. It is found that the interdecadal change of the wave trains in Eurasia might account for the differences in atmospheric circulation between the above two periods. Further analyses reveal that spring snow cover over Eurasia is closely linked to extreme precipitation over SWX during 2003–18. Increased snow cover in western Europe (WE) from February to March is accompanied by more snowmelt. This resulted in less local snow cover and lower albedo, leading to warm temperatures over WE in May. The changes in temperatures increase the local 1000–500-hPa thickness over WE. These factors provide favorable conditions for the enhancement of the Eurasian wave trains, which significantly influence extreme precipitation over SWX. On the other hand, corresponding to decreased albedo caused by the reduction of snow cover in northern Eurasia (NE) in May, anomalous surface warming occurs over NE. The anomalous warming results in positive geopotential height anomalies that intensify the meridional geopotential height gradient over Eurasia and cause an acceleration of the westerly jet in May. Anomalous upper-level divergence in SWX induced by the enhanced westerly jet provides a favorable dynamical condition for increased extreme precipitation.
{"title":"Increased Extreme Precipitation in May over Southwestern Xinjiang in Relation to Eurasian Snow Cover in Recent Years","authors":"Ping Chen, Junqiang Yao, Weiyi Mao, Liyun Ma, Jing Chen, Tuoliewubieke Dilinuer, Shujuan Li","doi":"10.1175/jcli-d-23-0208.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0208.1","url":null,"abstract":"Abstract In this study, the interdecadal variations of extreme precipitation in May over southwestern Xinjiang (SWX) and related mechanisms were investigated. The extreme precipitation in May over SWX exhibited a decadal shift in the 1990s (negative phase during 1970–86 and positive phase during 2003–18). The decadal shift corresponded to strengthened moist airflow from the Indian Ocean and an anomalous cyclone over SWX during 2003–18. It is found that the interdecadal change of the wave trains in Eurasia might account for the differences in atmospheric circulation between the above two periods. Further analyses reveal that spring snow cover over Eurasia is closely linked to extreme precipitation over SWX during 2003–18. Increased snow cover in western Europe (WE) from February to March is accompanied by more snowmelt. This resulted in less local snow cover and lower albedo, leading to warm temperatures over WE in May. The changes in temperatures increase the local 1000–500-hPa thickness over WE. These factors provide favorable conditions for the enhancement of the Eurasian wave trains, which significantly influence extreme precipitation over SWX. On the other hand, corresponding to decreased albedo caused by the reduction of snow cover in northern Eurasia (NE) in May, anomalous surface warming occurs over NE. The anomalous warming results in positive geopotential height anomalies that intensify the meridional geopotential height gradient over Eurasia and cause an acceleration of the westerly jet in May. Anomalous upper-level divergence in SWX induced by the enhanced westerly jet provides a favorable dynamical condition for increased extreme precipitation.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":"1 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2024-03-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140202432","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-03-22DOI: 10.1175/jcli-d-22-0850.1
Jiao Li, Yang Zhao, Deliang Chen, Ping Zhao, Chi Zhang, Yinjun Wang
Abstract Two distinct categories of weather patterns, denoted as Type 1 and Type 2, which show higher-than-expected frequency of summer heavy rainfall days (HRDs) over North China (NC), are selected from nine weather patterns categorized by the self-organizing map algorithm during 1979–2019. The respective HRDs over NC exhibit dissimilar characteristics, with Type 1 showing a northern distribution and Type 2 a southern distribution. The quantitative disparities in terms of moisture content and vertical motion are discussed in reactions to the synoptic-scale patterns associated with HRDs. The outcomes of a 20-day backward tracking, using the so-called Water Accounting Model-2layers, reveal noteworthy contrasts in moisture sources. Type 1 predominantly receives moisture from the western North Pacific, while Type 2 relies more on contributions from the Arabian Sea, Bay of Bengal, and Eurasia. However, the major moisture sources with grid cells contributing more than 0.01 mm show a consistent cumulative contribution of 77% for Type 1 and 80% for Type 2. The finding suggests that the discrepancy between the two types cannot be solely attributed to moisture supply. Further examination of the transverse and shearwise Q-vector components provides insights into how these distinct weather patterns influence HRDs by the alteration of vertical motion. In Type 1, an upper-level jet entrance induces a thermally direct secondary circulation that enhances vertical motion, while a baroclinic trough plays a dominant role in generating vertical motion in Type 2. Moreover, these unique configurations for each type of weather pattern are not only pre-existing but also intensified during HRDs.
{"title":"The Quantitative Role of Moisture and Vertical Motion in Shaping Summer Heavy Rainfall over North China under Two Distinct Large-Scale Weather Patterns","authors":"Jiao Li, Yang Zhao, Deliang Chen, Ping Zhao, Chi Zhang, Yinjun Wang","doi":"10.1175/jcli-d-22-0850.1","DOIUrl":"https://doi.org/10.1175/jcli-d-22-0850.1","url":null,"abstract":"Abstract Two distinct categories of weather patterns, denoted as Type 1 and Type 2, which show higher-than-expected frequency of summer heavy rainfall days (HRDs) over North China (NC), are selected from nine weather patterns categorized by the self-organizing map algorithm during 1979–2019. The respective HRDs over NC exhibit dissimilar characteristics, with Type 1 showing a northern distribution and Type 2 a southern distribution. The quantitative disparities in terms of moisture content and vertical motion are discussed in reactions to the synoptic-scale patterns associated with HRDs. The outcomes of a 20-day backward tracking, using the so-called Water Accounting Model-2layers, reveal noteworthy contrasts in moisture sources. Type 1 predominantly receives moisture from the western North Pacific, while Type 2 relies more on contributions from the Arabian Sea, Bay of Bengal, and Eurasia. However, the major moisture sources with grid cells contributing more than 0.01 mm show a consistent cumulative contribution of 77% for Type 1 and 80% for Type 2. The finding suggests that the discrepancy between the two types cannot be solely attributed to moisture supply. Further examination of the transverse and shearwise Q-vector components provides insights into how these distinct weather patterns influence HRDs by the alteration of vertical motion. In Type 1, an upper-level jet entrance induces a thermally direct secondary circulation that enhances vertical motion, while a baroclinic trough plays a dominant role in generating vertical motion in Type 2. Moreover, these unique configurations for each type of weather pattern are not only pre-existing but also intensified during HRDs.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":"40 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2024-03-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140202265","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-03-21DOI: 10.1175/jcli-d-23-0501.1
Alex J. Cannon, Dae-Il Jeong, Ka-Hing Yau
Abstract Global warming is expected to lead to increases in atmospheric moisture and intensify sub-hourly to hourly rainfall extremes. However, signal-to-noise ratios are low, especially at the local scale, making detection of changes in the observational record difficult. For Canada, previous studies based on short data records from 1965-2005 did not show conclusive evidence of increases in short-duration extreme rainfall. This study updates single-site and regional trend analyses of 5 minute to 24 hour annual maximum rainfall in Canada using data from 1950-2021. Estimates of temporal trends are extended to also consider the association between rainfall intensity and dew point temperature, a measure of moisture availability. With longer records, evidence for increases in extreme rainfall at individual sites is stronger. Field significant increasing trends are found for the majority of durations, whereas before results were mixed and typically not statistically significant. Intensification is even more pronounced in single-site scaling of rainfall intensity with summer mean dew point temperature. Field significant positive scaling rates are detected for all durations. When data are pooled in space – irrespective of choice of regionalization – the results are even more clear. Notably, the strongest and most spatially homogeneous intensification of short-duration extreme rainfall is detected in sub-hourly to 2 hour durations. When data are pooled across Canadian climate regions, field significant positive scaling is found in 72.7% to 81.8% of regions for 5 minute to 2 hour durations, with median scaling rates ranging from 5.3 to 9.4% °C−1. For durations ≥ 6 hours, this falls to 27.3% to 53% of regions, with scaling rates less than 4% °C−1.
{"title":"Updated Observations Provide Stronger Evidence for Increases in Sub-hourly to Hourly Extreme Rainfall in Canada","authors":"Alex J. Cannon, Dae-Il Jeong, Ka-Hing Yau","doi":"10.1175/jcli-d-23-0501.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0501.1","url":null,"abstract":"Abstract Global warming is expected to lead to increases in atmospheric moisture and intensify sub-hourly to hourly rainfall extremes. However, signal-to-noise ratios are low, especially at the local scale, making detection of changes in the observational record difficult. For Canada, previous studies based on short data records from 1965-2005 did not show conclusive evidence of increases in short-duration extreme rainfall. This study updates single-site and regional trend analyses of 5 minute to 24 hour annual maximum rainfall in Canada using data from 1950-2021. Estimates of temporal trends are extended to also consider the association between rainfall intensity and dew point temperature, a measure of moisture availability. With longer records, evidence for increases in extreme rainfall at individual sites is stronger. Field significant increasing trends are found for the majority of durations, whereas before results were mixed and typically not statistically significant. Intensification is even more pronounced in single-site scaling of rainfall intensity with summer mean dew point temperature. Field significant positive scaling rates are detected for all durations. When data are pooled in space – irrespective of choice of regionalization – the results are even more clear. Notably, the strongest and most spatially homogeneous intensification of short-duration extreme rainfall is detected in sub-hourly to 2 hour durations. When data are pooled across Canadian climate regions, field significant positive scaling is found in 72.7% to 81.8% of regions for 5 minute to 2 hour durations, with median scaling rates ranging from 5.3 to 9.4% °C−1. For durations ≥ 6 hours, this falls to 27.3% to 53% of regions, with scaling rates less than 4% °C−1.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":"10 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2024-03-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140205607","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-03-20DOI: 10.1175/jcli-d-23-0547.1
Michael Morris, Paul J. Kushner, G.W.K. Moore, Oya Mercan
Abstract The effect of anthropogenic climate change on extreme near-surface wind speeds is uncertain. Observed trends are weak and difficult to disentangle from internal variability, and model projections disagree on the sign and magnitude of trends. Standard coarse-resolution climate models represent fine structures of relevant physical phenomena such as extratropical cyclones (ETCs), upper-level jet streaks, surface energy fluxes, and land surface variability less skillfully than their high-resolution counterparts. Here we use simulations with the NCAR Community Earth System Model with both uniform (110 km) resolution and the variable resolution configuration (VR-CESM-SONT, 110 km to 7 km), to study the effect of refined spatial resolution on projections of extreme strong and weak wind speeds in the Great Lakes region under end-of-century RCP8.5 forcing. The variable-resolution configuration projects strengthening of strong-wind events in the refined region with the opposite occurring in the uniform-resolution simulation. The two configurations provide consistent changes to synoptic scale circulations associated with high-wind events. However, only the variable resolution configuration projects weaker static stability, enhanced turbulent vertical mixing, and consequentially enhanced surface wind speeds, because boundary layer dynamics are better captured in the refined region. Both models project increased frequency of extreme weak winds, though only VR-CESM-SONT resolves the cold-season inversions and summertime high temperatures associated with stagnant wind events. The identifiable mechanism of the changes to strong winds in VR-CESM-SONT provides confidence in its projections and demonstrates the value of enhanced spatial resolution for the study of extreme winds under climate change.
{"title":"Resolution-Dependence of Extreme Wind Speed Projections in the Great Lakes Region","authors":"Michael Morris, Paul J. Kushner, G.W.K. Moore, Oya Mercan","doi":"10.1175/jcli-d-23-0547.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0547.1","url":null,"abstract":"Abstract The effect of anthropogenic climate change on extreme near-surface wind speeds is uncertain. Observed trends are weak and difficult to disentangle from internal variability, and model projections disagree on the sign and magnitude of trends. Standard coarse-resolution climate models represent fine structures of relevant physical phenomena such as extratropical cyclones (ETCs), upper-level jet streaks, surface energy fluxes, and land surface variability less skillfully than their high-resolution counterparts. Here we use simulations with the NCAR Community Earth System Model with both uniform (110 km) resolution and the variable resolution configuration (VR-CESM-SONT, 110 km to 7 km), to study the effect of refined spatial resolution on projections of extreme strong and weak wind speeds in the Great Lakes region under end-of-century RCP8.5 forcing. The variable-resolution configuration projects strengthening of strong-wind events in the refined region with the opposite occurring in the uniform-resolution simulation. The two configurations provide consistent changes to synoptic scale circulations associated with high-wind events. However, only the variable resolution configuration projects weaker static stability, enhanced turbulent vertical mixing, and consequentially enhanced surface wind speeds, because boundary layer dynamics are better captured in the refined region. Both models project increased frequency of extreme weak winds, though only VR-CESM-SONT resolves the cold-season inversions and summertime high temperatures associated with stagnant wind events. The identifiable mechanism of the changes to strong winds in VR-CESM-SONT provides confidence in its projections and demonstrates the value of enhanced spatial resolution for the study of extreme winds under climate change.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":"179 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2024-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140202334","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-03-20DOI: 10.1175/jcli-d-23-0392.1
Chao Zhang, Shuanglin Li, Zhe Han
Abstract Among 9 La Niña events since 1980, there are 7 double-peaked La Niña events which typically persist for two years and peak twice in the two consecutive boreal winters. In the study, the individual impacts of the first and second peak episodes of such La Niña on the Antarctic sea ice in austral spring (September to November) were compared. The results suggest a difference. The first episode induces a tripolar distribution of sea ice concentration (SIC) with negative anomaly in the Bellingshausen Sea sandwiched with positive anomalies in the Ross Sea and the northeastern Weddell Sea. The second causes a SIC reduction in most parts of the Southern Ocean except for the eastern Ross-western Amundsen Seas where an increase is observed. Mechanistically, the first episode forces one single Rossby wave train propagating southeastward, causing a strong cyclone anomaly over the eastern Ross-Amundsen-Bellingshausen Seas along with a weak anticyclone over the Weddell Sea. In comparison, the second La Niña excites two branches of Rossby wave trains emanating from the southeastern tropical Indian Ocean and the central equatorial Pacific, respectively, which induce three anomalous anticyclones and two anomalous cyclones over the Southern Ocean. These different atmospheric circulation anomalies shape their different sea ice distributions between the two La Niña episodes through both dynamic and thermodynamic processes. The modeling results from CAM5 verify these differences.
摘要 在 1980 年以来的 9 次拉尼娜现象中，有 7 次是双峰拉尼娜现象，通常持续两年，并在连续两个北方冬季达到两次峰值。研究比较了这种拉尼娜现象的第一次和第二次峰值对南极海冰在澳大利亚春季（9 月至 11 月）的影响。结果表明两者存在差异。第一次拉尼娜现象导致海冰浓度（SIC）呈三极分布，贝林斯豪森海出现负异常，罗斯海和威德尔海东北部出现正异常。第二次异常导致南大洋大部分地区的 SIC 值下降，只有罗斯海东部-阿蒙森海西部的 SIC 值上升。从机理上讲，第一次拉尼娜现象迫使一个单一的罗斯比波列向东南传播，在罗斯-阿蒙森-贝林斯豪森海东部造成强气旋异常，同时在威德尔海造成弱反气旋。相比之下，第二次拉尼娜现象激发了分别来自热带印度洋东南部和赤道太平洋中部的两支罗斯比波列，在南大洋上空引发了三个异常反气旋和两个异常气旋。这些不同的大气环流异常通过动力学和热力学过程在两次拉尼娜现象之间形成了不同的海冰分布。CAM5 的建模结果验证了这些差异。
{"title":"A comparison of the impacts of two consecutive double-peaked La Niña events on Antarctic sea ice in austral spring","authors":"Chao Zhang, Shuanglin Li, Zhe Han","doi":"10.1175/jcli-d-23-0392.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0392.1","url":null,"abstract":"Abstract Among 9 La Niña events since 1980, there are 7 double-peaked La Niña events which typically persist for two years and peak twice in the two consecutive boreal winters. In the study, the individual impacts of the first and second peak episodes of such La Niña on the Antarctic sea ice in austral spring (September to November) were compared. The results suggest a difference. The first episode induces a tripolar distribution of sea ice concentration (SIC) with negative anomaly in the Bellingshausen Sea sandwiched with positive anomalies in the Ross Sea and the northeastern Weddell Sea. The second causes a SIC reduction in most parts of the Southern Ocean except for the eastern Ross-western Amundsen Seas where an increase is observed. Mechanistically, the first episode forces one single Rossby wave train propagating southeastward, causing a strong cyclone anomaly over the eastern Ross-Amundsen-Bellingshausen Seas along with a weak anticyclone over the Weddell Sea. In comparison, the second La Niña excites two branches of Rossby wave trains emanating from the southeastern tropical Indian Ocean and the central equatorial Pacific, respectively, which induce three anomalous anticyclones and two anomalous cyclones over the Southern Ocean. These different atmospheric circulation anomalies shape their different sea ice distributions between the two La Niña episodes through both dynamic and thermodynamic processes. The modeling results from CAM5 verify these differences.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":"111 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2024-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140167211","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-03-19DOI: 10.1175/jcli-d-23-0387.1
Zizhen Dong, Lin Wang, Ruowen Yang, Jie Cao
Abstract This study investigates the propagation and maintenance mechanisms of the dominant intraseasonal oscillation over the western North Pacific in boreal winter, the quasi-biweekly oscillation (QBWO). The wintertime QBWO over the western North Pacific is characterized by the westward-northwestward movement from the tropical western Pacific to the western North Pacific and resembles the n = 1 equatorial Rossby wave. Its westward migration is primarily driven by the seasonal-mean zonal winds that advect vorticity anomalies in the lower-middle troposphere and moisture anomalies in the lower troposphere. Its northward movement is preconditioned by the vorticity dynamics of the beta effect, the low-level vertical moisture variation, and the local air-sea interaction. The latter involves the atmospheric forcing on the underlying ocean by changing the surface heat flux fluctuations and the sea surface temperature feedback on the low-level atmospheric instability. Its maintenance is primarily through atmospheric external energy sources from diabatic heating, which first generates eddy available potential energy and then converts it to eddy kinetic energy.
摘要 本研究探讨了北太平洋西部冬季主导季内振荡--准双周振荡（QBWO）的传播和维持机制。北太平洋西部冬季 QBWO 的特点是从热带西太平洋向西北偏西移动到北太平洋西部，类似于 n = 1 的赤道罗斯比波。它的西移主要受季节平均带风的驱动，季节平均带风将对流层中下部的涡度异常和对流层下部的湿度异常平移到对流层中下部。其北移的先决条件是贝塔效应的涡度动态、低层垂直水汽变化以及当地的海气相互作用。后者包括通过改变海面热通量波动和海面温度对低层大气不稳定性的反馈而对下层海洋产生的大气强迫。其维持主要是通过大气外部能量来源的二重加热，首先产生涡旋可用势能，然后将其转化为涡旋动能。
{"title":"Propagation and Maintenance of the Quasi-Biweekly Oscillation over the Western North Pacific in Boreal Winter","authors":"Zizhen Dong, Lin Wang, Ruowen Yang, Jie Cao","doi":"10.1175/jcli-d-23-0387.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0387.1","url":null,"abstract":"Abstract This study investigates the propagation and maintenance mechanisms of the dominant intraseasonal oscillation over the western North Pacific in boreal winter, the quasi-biweekly oscillation (QBWO). The wintertime QBWO over the western North Pacific is characterized by the westward-northwestward movement from the tropical western Pacific to the western North Pacific and resembles the n = 1 equatorial Rossby wave. Its westward migration is primarily driven by the seasonal-mean zonal winds that advect vorticity anomalies in the lower-middle troposphere and moisture anomalies in the lower troposphere. Its northward movement is preconditioned by the vorticity dynamics of the beta effect, the low-level vertical moisture variation, and the local air-sea interaction. The latter involves the atmospheric forcing on the underlying ocean by changing the surface heat flux fluctuations and the sea surface temperature feedback on the low-level atmospheric instability. Its maintenance is primarily through atmospheric external energy sources from diabatic heating, which first generates eddy available potential energy and then converts it to eddy kinetic energy.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":"19 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2024-03-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140167345","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-03-19DOI: 10.1175/jcli-d-23-0569.1
Emily J. Becker, Michael K. Tippett
Abstract The effect of the El Niño/Southern Oscillation (ENSO) teleconnection and climate change trends on observed North American wintertime daily 2-m temperature is investigated for 1960–2022 with a quantile regression model, which represents the variability of the full distribution of daily temperature, including extremes and changes in spread. Climate change trends are included as a predictor in the regression model to avoid the potentially confounding effect on ENSO teleconnections. Based on prior evidence of asymmetric impacts from El Niño and La Niña, the ENSO response is taken to be piecewise linear, and the regression model contains separate predictors for warm and cool ENSO. The relationship between these predictors and shifts in median, interquartile range, skewness, and kurtosis of daily 2-m temperature are summarized through Legendre polynomials. Warm ENSO conditions result in significant warming shifts in the median and contraction of the interquartile range in central-northern North America, while no opposite effect is found for cool ENSO conditions in this region. In the southern U.S., cool ENSO conditions produce a warming shift in the median, while warm ENSO has little impact on the median, but contracts the interquartile range. Climate change trends are present as a near-uniform warming in the median and across quantiles and have no discernable impact on interquartile range or higher-order moments. Trends and ENSO together explain a substantial fraction of the interannual variability of daily temperature distribution shifts across much of North America and, to a lesser extent, changes of the interquartile range.
{"title":"Impact of ENSO and trends on the distribution of North American wintertime daily temperature","authors":"Emily J. Becker, Michael K. Tippett","doi":"10.1175/jcli-d-23-0569.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0569.1","url":null,"abstract":"Abstract The effect of the El Niño/Southern Oscillation (ENSO) teleconnection and climate change trends on observed North American wintertime daily 2-m temperature is investigated for 1960–2022 with a quantile regression model, which represents the variability of the full distribution of daily temperature, including extremes and changes in spread. Climate change trends are included as a predictor in the regression model to avoid the potentially confounding effect on ENSO teleconnections. Based on prior evidence of asymmetric impacts from El Niño and La Niña, the ENSO response is taken to be piecewise linear, and the regression model contains separate predictors for warm and cool ENSO. The relationship between these predictors and shifts in median, interquartile range, skewness, and kurtosis of daily 2-m temperature are summarized through Legendre polynomials. Warm ENSO conditions result in significant warming shifts in the median and contraction of the interquartile range in central-northern North America, while no opposite effect is found for cool ENSO conditions in this region. In the southern U.S., cool ENSO conditions produce a warming shift in the median, while warm ENSO has little impact on the median, but contracts the interquartile range. Climate change trends are present as a near-uniform warming in the median and across quantiles and have no discernable impact on interquartile range or higher-order moments. Trends and ENSO together explain a substantial fraction of the interannual variability of daily temperature distribution shifts across much of North America and, to a lesser extent, changes of the interquartile range.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":"163 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2024-03-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140167684","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-03-18DOI: 10.1175/jcli-d-23-0391.1
Hanii Takahashi, Catherine M. Naud, Derek J. Posselt, George A. Duffy
Abstract Extratropical cyclones (ETCs) produce most of the winter precipitation at midlatitudes and are often associated with the most extreme winter weather events. For climate models to accurately predict the occurrence and severity of these extreme events in a changing climate, they need to accurately represent moist processes in general and ice processes in particular. To provide an observational constraint for model evaluation, because cloud cover and precipitation are prevalent in warm-frontal regions, a compositing method is applied to ice retrievals from satellite observations to explore the ice distribution across warm fronts in both hemispheres. Ice water path (IWP) and its variability are compared between Northern Hemisphere (NH) and Southern Hemisphere (SH) warm fronts for different ETC-wide characteristics, as well as for different ETC origination regions. Results reveal that warm-frontal IWP and its variability tend to be higher in the NH than the SH, even when controlling for the ETC strength and environmental precipitable water (PW). IWP differences between NH and SH are found to be primarily related to where the cyclones originate. As the intertropical convergence zone is shifted north, ETCs that originate close to the northern tropics have more PW than those that originate close to the southern tropics. This, in turn, seems to lead to larger IWP in NH frontal clouds than in the SH frontal clouds at a later time. This highlights the importance, for ice amounts generated in warm-frontal regions, of the environmental conditions that an ETC encounters during its genesis phase. Significance Statement Extratropical cyclones (ETCs) are responsible for most of the winter precipitation in the midlatitudes and are often associated with severe winter weather events. In order for climate models to accurately predict these extreme events in a changing climate, they need to correctly represent moist processes, especially those involving ice. To evaluate and improve these models, we apply a compositing method to satellite observations of ice profiles in warm-frontal regions, which are known for having high cloud cover and precipitation. This helps us understand the distribution of ice across warm fronts in both the Northern Hemisphere (NH) and the Southern Hemisphere (SH). We compare the ice water path (IWP) and its variability between NH and SH warm fronts, considering different characteristics of ETCs and their formation regions. Our findings show that NH warm fronts generally contain more ice, and the amount varies a lot more across warm fronts than for SH warm fronts. This is true even when accounting for the strength of the cyclones and the moisture available to them. These differences in IWP between NH and SH are found to be primarily related to the locations where the cyclones originate. As the intertropical convergence zone (ITCZ) is shifted northward, ETCs originating closer to the northern tropics tend to have more moisture available
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Pub Date : 2024-03-18DOI: 10.1175/jcli-d-23-0346.1
Yeon-Woo Choi, Muhammad Khalifa, Elfatih A. B. Eltahir
Abstract Here, we introduce the concept of “outdoor days” to describe how climate change can affect quality of life for different communities and individuals. An outdoor day is characterized by moderate temperature, neither too cold nor too hot, allowing most people to enjoy outdoor activities. The number of “outdoor days” is a non-linear function of the daily surface air temperature. If the latter falls within a specific range describing assumed thermal comfort conditions, then we assign that day as an “outdoor day”. Using this function, we describe climate change impacts on temperature differently compared to other studies which often describe these impacts in terms of the linear averaging of daily surface air temperature. The introduction of this new concept offers another way for communicating how climate change may impact the quality of life for individuals who usually plan their outdoor activities based on how local weather conditions compare to their preferred levels of thermal comfort. Based on our analysis of regional variations in “outdoor days”, we present observational and modeling evidence of a north-south disparity in climate change impacts. Under highemission scenarios, CMIP5 and CMIP6 models project fewer “outdoor days” for people living in developing countries, primarily located in low-latitude regions. Meanwhile, developed countries in middle- and high-latitude regions could gain more “outdoor days”, redistributed across seasons.
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Abstract Climate model simulations tend to drift away from the real world because of model errors induced by an incomplete understanding and implementation of dynamics and physics. Parameter estimation uses the data assimilation methods to optimize model parameters, which minimizes model errors by incorporating observations into the model through state-parameter covariance. However, traditional parameter estimation schemes that simultaneously estimate multiple parameters using observations could fail to reduce model errors because of the low signal-to-noise ratio in the covariance. Here, based on the saturation time scales of model sensitivity that depend on different parameters and model components, we design a new multicycle parameter estimation scheme, where each cycle is determined by the saturation time scale of sensitivity of the model state associated with observations in each climate system component. The new scheme is evaluated using two low-order models. The results show that due to high signal-to-noise ratios sustained during the parameter estimation process, the new scheme consistently reduces model errors as the number of estimated parameters increases. The new scheme may improve comprehensive coupled climate models by optimizing multiple parameters with multisource observations, thereby addressing the multiscale nature of component motions in the Earth system.
{"title":"Multicycle Parameter Estimations in Coupled Earth System Models Based on Multiscale Sensitivity Responses in the Context of Low-Order Models","authors":"Haoyu Yang, Shaoqing Zhang, Jinzhuo Cai, Dong Wang, Xiong Deng, Yang Gao","doi":"10.1175/jcli-d-23-0615.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0615.1","url":null,"abstract":"Abstract Climate model simulations tend to drift away from the real world because of model errors induced by an incomplete understanding and implementation of dynamics and physics. Parameter estimation uses the data assimilation methods to optimize model parameters, which minimizes model errors by incorporating observations into the model through state-parameter covariance. However, traditional parameter estimation schemes that simultaneously estimate multiple parameters using observations could fail to reduce model errors because of the low signal-to-noise ratio in the covariance. Here, based on the saturation time scales of model sensitivity that depend on different parameters and model components, we design a new multicycle parameter estimation scheme, where each cycle is determined by the saturation time scale of sensitivity of the model state associated with observations in each climate system component. The new scheme is evaluated using two low-order models. The results show that due to high signal-to-noise ratios sustained during the parameter estimation process, the new scheme consistently reduces model errors as the number of estimated parameters increases. The new scheme may improve comprehensive coupled climate models by optimizing multiple parameters with multisource observations, thereby addressing the multiscale nature of component motions in the Earth system.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":"25 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2024-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140146400","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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