Processes shaping the spatial pattern and seasonality of the surface air temperature response to anthropogenic forcing     

Fangxing Tian  Buwen Dong  Jon Robson  Rowan Sutton  Laura Wilcox 《Climate Dynamics》2020,54(9):3959-3975

In the period 1960–2010, the land surface air temperature (SAT) warmed more rapidly over some regions relative to the global mean. Using a set of time-slice experiments, we highlight how different physical processes shape the regional pattern of SAT warming. The results indicate an essential role of anthropogenic forcing in regional SAT changes from the 1970s to 2000s, and show that both surface–atmosphere interactions and large-scale atmospheric circulation changes can shape regional responses to forcing. Single forcing experiments show that an increase in greenhouse gases can lead to regional changes in land surface warming in winter (DJF) due to snow-albedo feedbacks, and in summer (JJA) due to soil-moisture and cloud feedbacks. Changes in anthropogenic aerosol and precursor (AA) emissions induce large spatial variations in SAT, characterized by warming over western Europe, Eurasia, and Alaska. In western Europe, SAT warming is stronger in JJA than in DJF due to substantial increases in clear sky shortwave radiation over Europe, associated with decreases in local AA emissions since the 1980s. In Alaska, the amplified SAT warming in DJF is due to increased downward longwave radiation, which is related to increased water vapor and cloud cover. In this case, although the model was able to capture the regional pattern of SAT change, and the associated local processes, it did not simulate all processes and anomalies correctly. For the Alaskan warming, the model is seen to achieve the correct regional response in the context of a wider North Pacific anomaly that is not consistent with observations. This demonstrates the importance of model evaluation that goes beyond the target variable in detection and attribution studies.  相似文献   

Decadal predictions of the cooling and freshening of the North Atlantic in the 1960s and the role of ocean circulation     

Jon Robson  Rowan Sutton  Doug Smith 《Climate Dynamics》2014,42(9-10):2353-2365

In the 1960s North Atlantic sea surface temperatures (SST) cooled rapidly. The magnitude of the cooling was largest in the North Atlantic subpolar gyre (SPG), and was coincident with a rapid freshening of the SPG. Here we analyze hindcasts of the 1960s North Atlantic cooling made with the UK Met Office’s decadal prediction system (DePreSys), which is initialised using observations. It is shown that DePreSys captures—with a lead time of several years—the observed cooling and freshening of the North Atlantic SPG. DePreSys also captures changes in SST over the wider North Atlantic and surface climate impacts over the wider region, such as changes in atmospheric circulation in winter and sea ice extent. We show that initialisation of an anomalously weak Atlantic Meridional Overturning Circulation (AMOC), and hence weak northward heat transport, is crucial for DePreSys to predict the magnitude of the observed cooling. Such an anomalously weak AMOC is not captured when ocean observations are not assimilated (i.e. it is not a forced response in this model). The freshening of the SPG is also dominated by ocean salt transport changes in DePreSys; in particular, the simulation of advective freshwater anomalies analogous to the Great Salinity Anomaly were key. Therefore, DePreSys suggests that ocean dynamics played an important role in the cooling of the North Atlantic in the 1960s, and that this event was predictable.  相似文献   

Racing climate change: Collaboration and conflict in California's global climate change policy arena     

Jonathan London  Alex Karner  Julie Sze  Dana Rowan  Gerardo Gambirazzio  Deb Niemeier 《Global Environmental Change》2013,23(4):791-799

Media accounts routinely refer to California's Assembly Bill 32 (AB 32), the Global Warming Solutions Act of 2006, as “landmark” climate change legislation. On its surface, this label is an accurate reflection of the state's forward-thinking stance across many environmental issues including pesticides, toxic substances, solid waste, and air quality. For all its promise, however, AB 32 can also be considered a low point in the landscape of conflict between state environmental regulators and California's environmental justice movement. While the legislation included several provisions to address the procedural and distributive dimensions of environmental justice, the implementation of AB 32 has been marked by heated conflict. The most intense conflicts over AB 32 revolve around the primacy of market mechanisms such as “cap and trade.” This article examines the drivers and the manifestations of these dynamics of collaboration and conflict between environmental justice advocates and state regulators, and pays particular attention to the scalar and racialized quality of the neoliberal discourse. The contentiousness of climate change politics in California offers scholars and practitioners around the world a cautionary tale of how the best intentions for integrating environmental justice principles into climate change policy do not necessarily translate into implementation and how underlying racialized fractures can upend collaboration between state and social movement actors.  相似文献   

Sediment fingerprinting as an environmental forensics tool explaining cyanobacteria blooms in lakes   总被引：1，自引：0，他引：1  

J.S. Rowan  S. Black 《Applied geography (Sevenoaks, England)》2012,32(2):832-843

Cyanobacteria (blue-green algae) blooms in water bodies present serious public health issues with attendant economic and ecological impacts. Llyn Tegid (Lake Bala) is an important conservation and amenity asset within Snowdonia National Park, Wales which since the mid-1990s has experienced multiple toxic cyanobacteria blooms threatening the ecology and tourism-dependent local economy. Multiple working hypotheses explain the emergence of this problem, including climate change, land management linked to increased nutrient flux, hydromorphological alterations or changing trophic structure - any of which may operate individually or cumulatively to impair lake function. This paper reports the findings of a sediment fingerprinting study using dated lake cores to explore the linkages between catchment and lake management practices and the emergence of the algal blooms problem. Since 1900 AD lake bed sedimentation rates have varied from 0.06 to 1.07 g cm⁻² yr⁻¹, with a pronounced acceleration since the early 1980s. Geochemical analysis revealed increases in the concentrations of total phosphorus (TP), calcium and heavy metals such as zinc and lead consistent with eutrophication and a rising pollution burden, particularly since the late 1970s. An uncertainty-inclusive sediment fingerprinting approach was used to apportion the relative fluxes from the major catchment land cover types of improved pasture, rough grazing, forestry and channel banks. This showed improved pasture and channel banks are the dominant diffuse sources of sediment in the catchment, though forestry sources were important historically. Conversion of rough grazing to improved grassland, coupled with intensified land management and year-round livestock grazing, is concluded to provide the principal source of rising TP levels. Lake Habitat Survey and particle size analysis of lake cores demonstrate the hydromorphological impact of the River Dee Regulation Scheme, which controls water level and periodically diverts flow into Llyn Tegid from the adjacent Afon Tryweryn catchment. This hydromorphological impact has also been most pronounced since the late 1970s. It is concluded that an integrated approach combining land management to reduce agricultural runoff allied to improved water level regulation enabling recovery of littoral macrophytes offers the greatest chance halting the on-going cyanobacteria issue in Llyn Tegid.  相似文献   

The influence of oceanic conditions on the hot European summer of 2003     

Emily Black  Rowan Sutton 《Climate Dynamics》2007,28(1):53-66

The summer of 2003 was the hottest on record throughout much of Europe. Understanding how the event developed and the factors that contributed to it may help us improve seasonal forecasting models and assess the risk of such events in the future. This study uses atmosphere-only model integrations and observed data to investigate the potential predictability of the climate anomalies, and in particular the impact that the warming in the Indian Ocean and Mediterranean Sea had on the development of the temperature anomalies. The model results suggest that the temperature anomalies were potentially predictable and that both Indian Ocean and Mediterranean sea surface temperature anomalies contributed to the development of the observed warm and dry anomalies over Europe. Furthermore, it was found that, in the model, the Mediterranean anomalies contributed most strongly to the warming in June and July and the Indian Ocean anomalies enabled the positive temperature anomalies to persist into August. Previously published work has described the role of the Indian monsoon in modulating the seasonal cycle in rainfall over Europe. Comparison with this work suggests a mechanism by which warming in the Indian Ocean may have contributed to the persistence of the temperature and precipitation anomalies into August.  相似文献   

Sediment focusing and210Pb dating: a new approach     

D. J. Rowan  R. J. Cornett  K. King  B. Risto 《Journal of Paleolimnology》1995,13(2):107-118

In this paper we test the utility of the mud deposition boundary depth (mud DBD) theory (Rowanet al. 1992) as a means of maximizing sampling efficiency in paleolimnological investigations, particularly those that apply to²¹⁰Pb dating. The mud DBD is defined by the relationship between near bottom wave velocity and particle threshold velocity, with wave and particle threshold theory simplified to terms of exposure and depth. Mud DBD theory can be used to define the depositional zone in lakes, and within the depositional zone defined by the mud DBD: 1) there is a high probability of obtaining a representative core, 2) variation in mass sediment accumulation rate (MSAR) is not correlated with water depth, and 3) variation in MSAR is considerably reduced from the whole lake average. This suggests that mud DBD theory can account for the effects of sediment focusing, and that the mud DBD defined depositional zone is the zone to which fine-grained sediments are focused. Finally, we have shown that to optimize sampling effort, 5 to 10 cores within the depositional zone are necessary for a reasonably precise estimate of the mean mass sediment accumulation rate. In addition, the use of mud DBD theory prior to sampling can dramatically reduce the cost associated with analyzing large numbers of cores for²¹⁰Pb.This is the fifth of a series of papers to be published by this journal following the 20 ^th anniversary of the first application of²¹⁰Pb dating of take sediments. Dr P. G. Appleby is guest editing this series.  相似文献   

Compositional analysis of catch curve data, with an application to Sebastes maliger     

Schnute  Jon T.; Haigh  Rowan 《ICES Journal of Marine Science》2007,64(2):218-233

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Tritium across the hydrologic systems of southern Ontario,Canada: implications for groundwater age dating in the Great Lakes Basin     

Priebe  E. H.  Hamilton  S. M.  Lemieux  A.  Rowan  D. J.  Clark  I. D. 《Hydrogeology Journal》2023,31(3):641-659

Modern, ambient tritium concentrations in precipitation are lower and more temporally consistent now that they have recovered from the historic thermonuclear bomb peak of the mid-1960s. With the bomb peak no longer the overriding influence on atmospheric tritium concentrations, anthropogenic point sources, such as nuclear-generating stations (NGS), have the largest influence, though the extent and temporal variability of this influence remains uncharacterized. The lack of precipitation monitoring locations means that spatial trends in tritium concentrations in precipitation are unknown. To address this data gap, tritium concentrations in shallow modern groundwater are interpolated throughout southern Ontario (Canada), at the center of the Great Lakes Basin, and the interpolation is tested as a precipitation proxy with a statistical comparison that shows good agreement between the shallow groundwater and precipitation datasets. The shallow groundwater tritium interpolation is used to delineate the extent of NGS influence as representing 66% of the study area. Recharge timings in the subcropping bedrock aquifers of the study area are interpreted qualitatively in areas outside of NGS influence to be primarily a mix of pre-bomb and modern recharge, with no indication of peak recharge levels remaining. The influence of drift thickness on the proportion of tritium-dead versus tritium-live samples is observed spatially and confirmed by comparing data distributions. The oldest waters (pre-1953) tend to occur in subcropping bedrock aquifers underlying the thickest sediment packages.

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Last glacial aggradation and postglacial sediment production from the non-glacial Waipaoa and Waimata catchments, Hikurangi Margin, North Island, New Zealand   总被引：1，自引：0，他引：1  

Michael Marden  Colin Mazengarb  Alan Palmer  Kelvin Berryman  Donna Rowan 《Geomorphology》2008,99(1-4):404-419

The sediment flux generated by postglacial channel incision has been calculated for the 2150 km², non-glacial, Waipaoa catchment located on the tectonically active Hikurangi Margin, eastern North Island, New Zealand. Sediment production both at a sub-catchment scale and for the Waipaoa catchment as a whole was calculated by first using the tensioned spline method within ARC MAP to create an approximation of the aggradational Waipaoa-1 surface (contemporaneous with the Last Glacial Maximum), and second using grid calculator functions in the GIS to subtract the modern day surface from the Waipaoa-1 surface. The Waipaoa-1 surface was mapped using stereo aerial photography, and global positioning technology fixed the position of individual terrace remnants in the landscape. The recent discovery of Kawakawa Tephra within Waipaoa-1 aggradation gravels in this catchment demonstrates that aggradation was coincidental with or began before the deposition of this 22 600 ¹⁴C-year-old tephra and, using the stratigraphic relationship of Rerewhakaaitu Tephra, the end of aggradation is dated at ca 15 000 ¹⁴C years (ca 18 000 cal. years BP). The construction of the Waipaoa-1 terrace is considered to be synchronous and broadly correlated with aggradation elsewhere in the North Island and northern South Island, indicating that aggradation ended at the same time over a wide area. Subsequent downcutting, a manifestation of base-level lowering following a switch to postglacial incision at the end of glacial-age aggradation, points to a significant Southern Hemisphere climatic warming occurring soon after ca 15 000 ¹⁴C years (ca 18 000 cal. years BP) during the Older Dryas interval. Elevation differences between the Waipaoa-1 (c.15 ka) terrace and the level of maximum channel incision (i.e. before aggradation since the turn of the 20th century) suggest about 50% of the topographic relief within headwater reaches of the Waipaoa catchment has been formed in postglacial times. The postglacial sediment flux generated by channel incision from Waipaoa catchment is of the order of 9.5 km³, of which ~ 6.6 km³ is stored within the confines of the Poverty Bay floodplain. Thus, although the postglacial period represented a time of high terrigenous sediment generation and delivery, only ~ 30% of the sediment generated by channel incision from Waipaoa catchment probably reached the marine shelf and slope of the Hikurangi Margin during this time. The smaller adjacent Waimata catchment probably contributed an additional 2.6 km³ to the same depocentre to give a total postglacial sediment contribution to the shelf and beyond of ~ 5.5 km³. Sediment generated by postglacial channel incision represents only ~ 25% of the total sediment yield from this landscape with ~ 75% of the estimated volume of the postglacial storage offshore probably derived from hillslope erosion processes following base-level fall at times when sediment yield from these catchments exceeded storage.  相似文献   

Fragmentation in molecular clouds and its connection to the IMF     

Rowan J. Smith  Paul C. Clark  Ian A. Bonnell 《Monthly notices of the Royal Astronomical Society》2009,396(2):830-841

We present an analysis of star-forming gas cores in a smooth particle hydrodynamics simulation of a giant molecular cloud. We identify cores using their deep potential wells. This yields a smoother distribution with clearer boundaries than density. Additionally, this gives an indication of future collapse, as bound potential cores (p-cores) represent the earliest stages of fragmentation in molecular clouds. We find that the mass function of the p-cores resembles the stellar initial mass function and the observed clump mass function, although p-core masses  (∼0.7 M_⊙)  are smaller than typical density clumps. The bound p-cores are generally subsonic, have internal substructure and are only quasi-spherical. We see no evidence of massive bound cores supported by turbulence. We trace the evolution of the p-cores forward in time, and investigate the connection between the original p-core mass and the stellar mass that formed from it. We find that there is a poor correlation, with considerable scatter suggesting accretion on to the core is dependent on more factors than just the initial core mass. During the accretion process the p-cores accrete from beyond the region first bound, highlighting the importance of the core environment to its subsequent evolution.  相似文献