Atmosphere-Ocean最新文献

{"title":"Measurement of Snow Physical Properties and Stable Isotope Variations in the Canadian Sub-Arctic and Arctic Snowpack","authors":"Simon Levasseur, K. Brown, A. Langlois, D. McLennan","doi":"10.1080/07055900.2021.1962240","DOIUrl":"https://doi.org/10.1080/07055900.2021.1962240","url":null,"abstract":"ABSTRACT In northern Canada, the annual peak in river discharge is dominated by the seasonal input of snowmelt. As such, climatic changes that alter snowmelt properties and timing will have cascading impacts on the hydrological system as the Arctic warms. Geochemical tracers provide a tool to characterize the various processes governing the seasonal evolution of the snowpack; however, a lack of snow observations from a variety of Arctic landscapes limits the broad applicability of such tracers and further impedes our understanding of the various processes governing snowpack evolution and its ultimate contribution to the spring discharge peak. This study aims to gain a better understanding of the spatial distribution and the temporal evolution of the natural stable isotope signatures of snow from two distinct ecoregions: open tundra and taiga. More specifically, we describe the geophysical and stable isotope properties of the snow cover at Wekweètì (Northwest Territories), a high sub-Arctic taiga site, and within the Greiner Lake Watershed, near Cambridge Bay (Nunavut), an open Arctic tundra site. Results illustrate a link between snowpack formation and stable isotope distributions at both study sites. Stable oxygen isotope ratios of snow (δ 18O-H2O) show a wide range from −41‰ to −17‰ across all snow depth classes; however, heavy isotope enrichment is clearly visible in the bottom snow layers at both sites. Vapour flux from the ground under a strong temperature gradient is considered to be the main driver for this enrichment due to kinetic metamorphism, which is more prominent at the open tundra site. The stable isotope signatures of the bottom hoar layers during winter were found to be similar to river water values sampled during spring and summer, highlighting the need for more in-depth hydrological cycle assessment.","PeriodicalId":55434,"journal":{"name":"Atmosphere-Ocean","volume":"59 1","pages":"137 - 151"},"PeriodicalIF":1.2,"publicationDate":"2021-05-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42922890","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Spatial and Temporal Variability of Oceanic Oxygen Changes and Underlying Trends","authors":"L. Stramma, S. Schmidtko","doi":"10.1080/07055900.2021.1905601","DOIUrl":"https://doi.org/10.1080/07055900.2021.1905601","url":null,"abstract":"ABSTRACT A recent analysis of observed oxygen changes shows a 2% decline in marine oxygen during the 50 years since 1960. However, these oxygen changes vary on time scales related to climate modes and by regions, including areas of increasing oxygen. Hence, any local oxygen change is related to various subsets of these drivers for the different regions and time scales. Here we provide an overview of drivers presently known for the different regions in the upper and deep ocean and the regional influence of climate modes, focussing on decadal and longer time scales for open ocean regions. We identify and compile regions where changes in solubility, stratification, decadal to multidecadal variability, source waters (either increases or decreases), overturning circulation or circulation-driven changes, and biological or nutrient stimulation have been shown to play a role in oxygen changes. The superposition and interaction of drivers and processes makes the decomposition of the impact on oxygen distribution difficult. Nevertheless, the description of the different drivers identified will help in better understanding the oxygen changes observed and lead to better verification of numerical models of future ocean oxygen levels.","PeriodicalId":55434,"journal":{"name":"Atmosphere-Ocean","volume":"59 1","pages":"122 - 132"},"PeriodicalIF":1.2,"publicationDate":"2021-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/07055900.2021.1905601","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42277775","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Correction","authors":"G. Han, Zhimin Ma, A. Slangen","doi":"10.1080/07055900.2021.1911512","DOIUrl":"https://doi.org/10.1080/07055900.2021.1911512","url":null,"abstract":"In this article, we presented three local sea level rise (SLR) scenarios at selected Canadian tide-gauge stations for the twenty-first century (Low, Intermediate, and High). The focus of this article is on the Intermediate and High scenarios. We have found an error in a script doing the calculation for the Low scenario. This error does not affect our conclusions in this paper, but it is necessary to correct resulting sea level projections for the Low scenario.","PeriodicalId":55434,"journal":{"name":"Atmosphere-Ocean","volume":"59 1","pages":"133 - 135"},"PeriodicalIF":1.2,"publicationDate":"2021-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/07055900.2021.1911512","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41483347","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Canadian In Situ Snow Cover Trends for 1955–2017 Including an Assessment of the Impact of Automation","authors":"R. Brown, C. Smith, C. Derksen, L. Mudryk","doi":"10.1080/07055900.2021.1911781","DOIUrl":"https://doi.org/10.1080/07055900.2021.1911781","url":null,"abstract":"ABSTRACT Snow cover trends for Canada over the 1955–2017 period for the daily snow depth–observing network of Environment and Climate Change Canada (ECCC) are presented based on an updated quality-controlled historical daily in situ snow depth dataset. The period since approximately 1995 is characterized by a rapid decline in manual observations (loss of over 800 manual observing sites between 1995 and 2017) and an increasing number of automated stations equipped with sonic snow depth sensors. In 2017 these accounted for approximately 45% of the network and more than 80% of the snow depth–observing network north of latitude 55°N. Automated stations are characterized by more frequent missing and anomalous data than manual ruler observations, particularly at Arctic sites. A comparison of closely located automated sonic and manual ruler observations showed similar numbers of days with snow cover but the sonic sensors detected significantly lower snow depths. For time series analysis of annual snow cover variables, the systematic difference between ruler and sonic snow depth can be removed using a common 2003–2016 reference period to compute snow cover anomalies. The updated trend results are broadly similar to previously published assessments showing long-term decreases in annual snow cover duration (SCD) and snow depth over most of Canada, with the largest decreases observed in spring snow cover and seasonal maximum snow depth (SDmax). Significant declines in SCD and SDmax of −1.7 (±1.1) days decade-1 and −1.8 cm (±0.8) cm decade−1 were observed in the Canada–averaged series over the 1955–2017 period. These trends mainly reflect snow cover conditions over southern Canada where the observing network is concentrated and where there are significant negative correlations between snow cover and winter air temperature. Declining numbers of stations reporting snow depth, issues with sonic sensor data quality, and systematic differences between ruler and sonic sensor measurements are major challenges for continued climate monitoring with the current ECCC snow depth–observing network.","PeriodicalId":55434,"journal":{"name":"Atmosphere-Ocean","volume":"59 1","pages":"77 - 92"},"PeriodicalIF":1.2,"publicationDate":"2021-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/07055900.2021.1911781","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45498957","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Linkage Between the Intraseasonal Oscillation of Atmospheric Heat Sources Over the Tibetan Plateau and Amplified Precipitation to the South of MLYR","authors":"Shanshan Zhong, Shuhui Li, Xinchang Zhang","doi":"10.1080/07055900.2021.1915742","DOIUrl":"https://doi.org/10.1080/07055900.2021.1915742","url":null,"abstract":"ABSTRACT Based on the daily Japanese 55-year Reanalysis (JRA-55) from 1979 to 2015, this study shows that atmospheric heat sources over the Tibetan Plateau (TP) and its surrounding areas (TPSR) in summer have a significant 10- to 30-day intraseasonal oscillation (ISO). The linkage of the ISO with the amplified precipitation to the south of the middle and lower reaches of the Yangtze River (MLYR) is also investigated. The results show that when anomalous positive heat sources over the TPSR strengthen, an anomalous thermal low pressure develops, leading to anomalous positive vorticity over the TPSR. Meanwhile, a mid-high latitude wavetrain with alternating positive and negative vorticity anomaly centres over the Eurasian continent propagates eastward across the TP. The anomalous positive vorticity over the northeastern TP is enhanced when combined with a deep positive vorticity anomaly over the TPSR. The wave-activity flux in the eastern TPSR turns southward or southeastward, with a positive vorticity anomaly propagating to the southeast of China. As a result, positive vorticity advection to the south of the MLYR increases with height and is conducive to convergence, upward motion, and increased precipitation. The situation is the reverse when negative anomalous heat sources develop over the TPSR. Therefore, the 10- to 30-day ISO of the atmospheric heat source over the TPSR in summer could contribute to the amplification of the intraseasonal precipitation anomalies to the south of the MLYR by regulating the range and intensity of the anomalous vorticity of the Eurasian wavetrain.","PeriodicalId":55434,"journal":{"name":"Atmosphere-Ocean","volume":"59 1","pages":"107 - 121"},"PeriodicalIF":1.2,"publicationDate":"2021-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/07055900.2021.1915742","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41912571","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Not Cool: On the Loss of Cold Weather in the Canadian Arctic","authors":"D. Blair, Amy Mann, Halah Mhanni, Safia Soussi, Matthew Loxley","doi":"10.1080/07055900.2021.1915238","DOIUrl":"https://doi.org/10.1080/07055900.2021.1915238","url":null,"abstract":"ABSTRACT Most studies of climate change in the Arctic report how much warmer the climate is getting. In this study we use 1950–2020 daily observed minimum temperatures at 34 weather stations in Canada’s north to examine how rapidly the region is losing annual occurrences of cold weather (−30°C or colder). Kendall–Theil trend analysis is used to assess the strength and significance of trends. Twenty-nine of the stations were found to have significant negative trends, with an average of 4.89 fewer annual cold days per decade; on average, the stations have lost over 40% of their cold days in recent decades. An ensemble of downscaled Coupled Model Intercomparison Project, phase 5 (CMIP5) models is used to show how the numbers of cold days are projected to change in the coming decades with the representative concentration pathway (RCP4.5 and RCP8.5) scenarios. Finally, we discuss the implications of the loss of cold weather in the Canadian Arctic and beyond.","PeriodicalId":55434,"journal":{"name":"Atmosphere-Ocean","volume":"59 1","pages":"93 - 106"},"PeriodicalIF":1.2,"publicationDate":"2021-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/07055900.2021.1915238","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43224530","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Projected Trends of Wintertime North American Surface Mean and Extreme Temperatures over the Next Half-century in Two Generations of Canadian Earth System Models","authors":"B. Yu, Guilong Li, Hai Lin, Shangfeng Chen","doi":"10.1080/07055900.2021.1879726","DOIUrl":"https://doi.org/10.1080/07055900.2021.1879726","url":null,"abstract":"ABSTRACT Based on two single-model initial-condition 50-member ensembles of climate simulations conducted with two generations of Canadian Earth System Models (CanESM2 and its successor CanESM5), we analyze the ensemble mean and spread of the projected trends of wintertime North American surface air temperature (SAT) and extreme indices of cold (TX10) and warm (TX90) days over the next half-century (2021–2070) and explore the contribution of internal climate variability to these trends. The ensemble mean of future climate simulations forced by the high-emissions scenario Representative Concentration Pathway 8.5 (RCP8.5) in CanESM2 and the Shared Socioeconomic Pathway 8.5 (SSP5-8.5) in CanESM5 reveals a poleward intensified warming, high risk of severe warm days over the west coast of North America and northern Canada, and a weakening belt of extreme cold days extending from Alaska to the northeastern United States. The warming trend is stronger in CanESM5 than in CanESM2, likely because of higher climate sensitivity and slightly higher CO2 emissions in CanESM5. Large ensemble spreads are apparent in the SAT trend and in the historical simulations and future projections of extreme temperatures, especially for the TX10 index. Individual realizations differ from the ensemble mean in both spatial pattern and magnitude of the projected trends. The signal-to-noise ratio reveals strong signals of the SAT and TX90 trends primarily over the west coast of North America and northern Canada, along with relatively strong signals of the TX10 trend over most of the central to eastern parts of North America in CanESM2 and western Canada and the southwestern and eastern United States in CanESM5. The components of the mean and extreme temperature trends generated by internal climate variability exhibit large-scale spatial coherences and are comparable to the externally anthropogenic-forced components of the trends, mostly in the central parts of North America. Overall, similar ensemble mean patterns of North American mean and extreme temperature trends are evident in the two models; CanESM5 tends to be less uncertain in projecting those trends than CanESM2.","PeriodicalId":55434,"journal":{"name":"Atmosphere-Ocean","volume":"59 1","pages":"53 - 75"},"PeriodicalIF":1.2,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/07055900.2021.1879726","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42255735","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Construction of the Apparent Moisture Sink Index for the Movement of the South Asian High and Associated Indicative Significance","authors":"Sidou Zhang, Shi-yin Liu, Tengfei Zhang","doi":"10.1080/07055900.2021.1877106","DOIUrl":"https://doi.org/10.1080/07055900.2021.1877106","url":null,"abstract":"ABSTRACT Previous studies indicate that the “spring flood” precipitation in northwestern Yunnan is closely related to the movement of the South Asian High (SAH) and the apparent moisture sink (Q 2) in the southeastern Tibetan Plateau (TP). In this study, using 38 years of ERA-Interim daily- and monthly-mean grid data along with 35 years of Gongshan daily precipitation data, the correlation between the movement of the SAH and Q 2 in the southeastern TP was analyzed. Then the Q 2 index (QI) of the SAH movement was constructed, and its impact on the activities of the SAH was analyzed. The results show that the QI affects the vertical transport of latent heat by interfering with the “chimney” effect, which in turn affects the atmospheric vertical motion in the southeastern TP and adjacent areas. This affects the upper 100 hPa wind field, resulting in changes in wind speed and direction in the upper air, the distribution of the geopotential height field, and the intensity and position of the SAH centre. The QI is positively and negatively correlated with the longitude and latitude of the SAH centre, respectively, and positively correlated with the intensity, implying a predictive effect on the movement trend and intensity evolution of the SAH.","PeriodicalId":55434,"journal":{"name":"Atmosphere-Ocean","volume":"59 1","pages":"15 - 28"},"PeriodicalIF":1.2,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/07055900.2021.1877106","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42826349","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Seasonality in the Vertical Structure of Long-Term Temperature Trends Over North America","authors":"N. Thomas, S. Nigam, V. Ravi","doi":"10.1080/07055900.2020.1855409","DOIUrl":"https://doi.org/10.1080/07055900.2020.1855409","url":null,"abstract":"ABSTRACT The surface warming of northern continents during the twentieth century is not uniform across seasons. Surface warming is particularly pronounced over northwestern Canada, where winter trends are much larger than summer ones. The upper-air temperature trends over the region are analyzed in three radiosonde datasets from 1958 to 2012 to assess their seasonal structure. The seasonal variation of upper-air trends can provide insights into the dynamical and thermodynamical processes generating these trends, including warming at the surface. The focus is not on the canonical structure of secular (i.e., long-term) trends—tropospheric warming and stratospheric cooling—but its seasonal variation. We find the boreal winter-minus-summer difference in trends over northwestern Canada to be positive and large in the lower troposphere (p ≳ 500 hPa) and lower stratosphere (50 hPa ≲ p ≲ 150 hPa); it is largest at the surface and smallest at the tropopause. The decreasing seasonality of the tropospheric trend with height supports the attribution of the notable seasonality of surface warming in this region to both land–surface–hydroclimate interactions and changes in winter circulation. In the lower stratosphere, a cooling trend is evident in all seasons, not unexpectedly, but a pronounced seasonality is again apparent, with the strongest cooling in summer. The near-zero trend tropopause region is a rare point of confluence for seasonal trends.","PeriodicalId":55434,"journal":{"name":"Atmosphere-Ocean","volume":"59 1","pages":"29 - 38"},"PeriodicalIF":1.2,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/07055900.2020.1855409","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41322239","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The Influence of Sudden Arctic Sea-Ice Thinning on North Atlantic Oscillation Events","authors":"G. Dai, M. Mu, Lei Wang","doi":"10.1080/07055900.2021.1875976","DOIUrl":"https://doi.org/10.1080/07055900.2021.1875976","url":null,"abstract":"ABSTRACT Utilizing the Community Atmosphere Model, version 4 (CAM4), the influence of sudden Arctic sea-ice thinning on North Atlantic Oscillation (NAO) events is investigated on a sub-seasonal time scale. First, the control simulation with CAM4 using prescribed daily boundary conditions produces realistic descriptions for the frequency and evolution of NAO events. Second, sensitivity experiments are then conducted to investigate the impact of sudden Arctic sea-ice thinning on NAO events. Numerical results show that the NAO has obvious responses to sudden sea-ice thinning over 10 days. Finally, the NAO responses to sudden sea-ice thinning are related to the positions of the NAO event. Further diagnostic analysis reveals that when the poleward centre of a positive NAO event is located west (east) of Greenland, cold (warm) advection would be induced because of the sudden sea-ice thinning along with the northward (southward) wind. This cooling (warming) causes the air to contract (expand) and further results in a decrease (increase) in the geopotential height and sea level pressure fields, which corresponds to a positive NAO (negative NAO) response. The results of this investigation show that the response of atmospheric circulation to boundary conditions is determined by both boundary condition changes and the atmospheric circulation regime, which provides an understanding of the effect on an NAO event of sudden sea-ice thinning on a sub-seasonal time scale.","PeriodicalId":55434,"journal":{"name":"Atmosphere-Ocean","volume":"59 1","pages":"39 - 52"},"PeriodicalIF":1.2,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/07055900.2021.1875976","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43825362","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}