Three hundred years of snowpack variability in southwestern British Columbia reconstructed from tree-rings     

Bryan J. Mood  Bethany Coulthard  Dan J. Smith 《水文研究》2020,34(25):5123-5133

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Oligomerization of levoglucosan by Fenton chemistry in proxies of biomass burning aerosols     

Bryan J. Holmes  Giuseppe A. Petrucci 《Journal of Atmospheric Chemistry》2007,58(2):151-166

Reactions of levoglucosan with produced from Fenton chemistry were studied in solution serving as a proxy for biomass burning aerosols. Two modes of oligomerization (≤2000 u) were observed for reaction times between 1 and 7 days using matrix-assisted laser desorption time-of-flight mass spectrometry (MALDI-TOF-MS) and laser desorption ionization time-of-flight mass spectrometry (LDI-TOF-MS). Single-mass unit continuum mass distributions with dominant −2 u patterns were measured and superimposed by a +176/+162 u oligomer series. This latter oligomer pattern was attributed to a Criegee rearrangement (+14 u) of levoglucosan, initiated by , forming a lactone (176 u). The acid-catalyzed reaction of any ROH from levoglucosan (+162 u) forms an ester through transesterification of the lactone functionality, whereupon propagation forms polyesters. Proposed products and chemical mechanisms are suggested as sources and precursors of humic-like substances (HULIS), which are known to possess a large saccharic component and are possibly formed from biomass burning aerosols (Andreae, Global Biomass Burning, MIT Press, Cambridge, Massachusetts, 3–21, 1991).  相似文献   

Analytical and Numerical Investigation of Two-Dimensional Katabatic Flow Resulting from Local Surface Cooling     

Alan Shapiro  Bryan Burkholder  Evgeni Fedorovich 《Boundary-Layer Meteorology》2012,145(1):249-272

The analysis of katabatic flows is often complicated by heterogeneity in surface characteristics. This study focuses on an idealized type of katabatic flow driven by a simple form of inhomogeneous surface forcing: a buoyancy or buoyancy flux that varies down the slope as a top-hat profile (cold strip). We consider the two-dimensional Boussinesq system of governing flow equations with the slope angle, Brunt–Väisälä frequency, and coefficients of eddy viscosity and diffusivity treated as constants. The steady-state problem is solved analytically in a linearized boundary-layer framework. Key flow structures are a primary katabatic jet (essentially the classical one-dimensional Prandtl jet), a rotor-like feature straddling the upslope end of the strip, and two nearly horizontal jets: an inward jet of environmental air feeding into the primary jet on the upslope end of the strip and an outward jet resulting from the intrusion of the primary katabatic jet into the environment on the downslope end of the strip. Next, the corresponding nonlinear initial value problem is solved numerically until a steady state is reached at low levels. The main features of the linear solution are seen in the numerical results, but with some notable differences: (i) the primary jet in the numerical simulation requires a longer distance to attain a one-dimensional boundary-layer structure and extends further downslope off the strip before intruding into the environment; (ii) the numerically simulated outward environmental jet is narrower and more intense than the inward jet, and has a pronounced wave-like structure.  相似文献   

East African food security as influenced by future climate change and land use change at local to regional scales   总被引：3，自引：0，他引：3  

Nathan Moore  Gopal Alagarswamy  Bryan Pijanowski  Philip Thornton  Brent Lofgren  Jennifer Olson  Jeffrey Andresen  Pius Yanda  Jiaguo Qi 《Climatic change》2012,110(3-4):823-844

Climate change impacts food production systems, particularly in locations with large, vulnerable populations. Elevated greenhouse gases (GHG), as well as land cover/land use change (LCLUC), can influence regional climate dynamics. Biophysical factors such as topography, soil type, and seasonal rainfall can strongly affect crop yields. We used a regional climate model derived from the Regional Atmospheric Modeling System (RAMS) to compare the effects of projected future GHG and future LCLUC on spatial variability of crop yields in East Africa. Crop yields were estimated with a process-based simulation model. The results suggest that: (1) GHG-influenced and LCLUC-influenced yield changes are highly heterogeneous across this region; (2) LCLUC effects are significant drivers of yield change; and (3) high spatial variability in yield is indicated for several key agricultural sub-regions of East Africa. Food production risk when considered at the household scale is largely dependent on the occurrence of extremes, so mean yield in some cases may be an incomplete predictor of risk. The broad range of projected crop yields reflects enormous variability in key parameters that underlie regional food security; hence, donor institutions’ strategies and investments might benefit from considering the spatial distribution around mean impacts for a given region. Ultimately, global assessments of food security risk would benefit from including regional and local assessments of climate impacts on food production. This may be less of a consideration in other regions. This study supports the concept that LCLUC is a first-order factor in assessing food production risk.  相似文献   

Recent Wyoming temperature trends,their drivers,and impacts in a 14,000-year context     

Bryan?ShumanEmail author 《Climatic change》2012,112(2):429-447

Wyoming provides more fossil fuels to the remainder of the United States than any other state or country, and its citizens remain skeptical of anthropogenic influences on their climate. However, much of the state including Yellowstone National Park and the headwaters of several major river systems, may have already been affected by rising temperatures. This paper examines the historic climate record from Wyoming in the context of ∼14,000-year temperature reconstructions based on fossil pollen data. The analysis shows that 24 of 30 U.S. Historical Climatology Network records from the state show an increase in the frequency of unusually warm years since 1978. Statewide temperatures have included 15 years (50%) from 1978 to 2007 that were greater than 1σ above the mean annual temperature for 1895–1978. The frequent warm years coincide with a reduction in the frequency of extremely low (<−20°C) January temperatures, and are not well explained by factors such as solar irradiance and the Pacific Decadal Oscillation. Linear regressions require inclusion of atmospheric greenhouse gas concentrations to explain the multi-decadal temperature trends. The observed warming is large in Yellowstone National Park where 21 years (70%) from 1978 to 2007 were greater than 1σ above the 1895–1978 mean; the deviation from the mean (>1°C) is greater than any time in the past 6,000 years. Recent temperatures have become as high as those experienced from 11,000 to 6,000 years ago when summer insolation was >6% higher than today and when regional ecosystems experienced frequent severe disturbances.  相似文献   

Impact of ocean model resolution on CCSM climate simulations   总被引：1，自引：1，他引：0  

Ben P. Kirtman  Cecilia Bitz  Frank Bryan  William Collins  John Dennis  Nathan Hearn  James L. Kinter III  Richard Loft  Clement Rousset  Leo Siqueira  Cristiana Stan  Robert Tomas  Mariana Vertenstein 《Climate Dynamics》2012,39(6):1303-1328

The current literature provides compelling evidence suggesting that an eddy-resolving (as opposed to eddy-permitting or eddy-parameterized) ocean component model will significantly impact the simulation of the large-scale climate, although this has not been fully tested to date in multi-decadal global coupled climate simulations. The purpose of this paper is to examine how resolved ocean fronts and eddies impact the simulation of large-scale climate. The model used for this study is the NCAR Community Climate System Model version 3.5 (CCSM3.5)—the forerunner to CCSM4. Two experiments are reported here. The control experiment is a 155-year present-day climate simulation using a 0.5° atmosphere component (zonal resolution 0.625 meridional resolution 0.5°; land surface component at the same resolution) coupled to ocean and sea-ice components with zonal resolution of 1.2° and meridional resolution varying from 0.27° at the equator to 0.54° in the mid-latitudes. The second simulation uses the same atmospheric and land-surface models coupled to eddy-resolving 0.1° ocean and sea-ice component models. The simulations are compared in terms of how the representation of smaller scale features in the time mean ocean circulation and ocean eddies impact the mean and variable climate. In terms of the global mean surface temperature, the enhanced ocean resolution leads to a ubiquitous surface warming with a global mean surface temperature increase of about 0.2?°C relative to the control. The warming is largest in the Arctic and regions of strong ocean fronts and ocean eddy activity (i.e., Southern Ocean, western boundary currents). The Arctic warming is associated with significant losses of sea-ice in the high-resolution simulation. The sea surface temperature gradients in the North Atlantic, in particular, are better resolved in the high-resolution model leading to significantly sharper temperature gradients and associated large-scale shifts in the rainfall. In the extra-tropics, the interannual temperature variability is increased with the resolved eddies, and a notable increases in the amplitude of the El Ni?o and the Southern Oscillation is also detected. Changes in global temperature anomaly teleconnections and local air-sea feedbacks are also documented and show large changes in ocean–atmosphere coupling. In particular, local air-sea feedbacks are significantly modified by the increased ocean resolution. In the high-resolution simulation in the extra-tropics there is compelling evidence of stronger forcing of the atmosphere by SST variability arising from ocean dynamics. This coupling is very weak or absent in the low-resolution model.  相似文献   

Glaciation in the Andes during the Lateglacial and Holocene     

Donald T. Rodbell  Jacqueline A. Smith  Bryan G. Mark   《Quaternary Science Reviews》2009,28(21-22):2165-2212

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Holocene lake-level trends in the Rocky Mountains, U.S.A.     

Bryan Shuman  Anna K. Henderson  Steven M. Colman  Jeffery R. Stone  Sherilyn C. Fritz  Lora R. Stevens  Mitchell J. Power  Cathy Whitlock   《Quaternary Science Reviews》2009,28(19-20):1861-1879

The availability of water shapes life in the western United States, and much of the water in the region originates in the Rocky Mountains. Few studies, however, have explicitly examined the history of water levels in the Rocky Mountains during the Holocene. Here, we examine the past levels of three lakes near the Continental Divide in Montana and Colorado to reconstruct Holocene moisture trends. Using transects of sediment cores and sub-surface geophysical profiles from each lake, we find that mid-Holocene shorelines in the small lakes (4–110 ha) were as much as 10 m below the modern lake surfaces. Our results are consistent with existing evidence from other lakes and show that a wide range of settings in the region were much drier than today before 3000–2000 years ago. We also discuss evidence for millennial-scale moisture variation, including an abruptly-initiated and -terminated wet period in Colorado from 4400 to 3700 cal yr BP, and find only limited evidence for low-lake stands during the past millennium. The extent of low-water levels during the mid-Holocene, which were most severe and widespread ca 7000–4500 cal yr BP, is consistent with the extent of insolation-induced aridity in previously published regional climate model simulations. Like the simulations, the lake data provide no evidence for enhanced zonal flow during the mid-Holocene, which has been invoked to explain enhanced mid-continent aridity at the time. The data, including widespread evidence for large changes on orbital time scales and for more limited changes during the last millennium, confirm the ability of large boundary-condition changes to push western water supplies beyond the range of recent natural variability.  相似文献   

青藏高原东北部隆升：来自宁夏同心小洪沟剖面的证据   总被引：3，自引：0，他引：3  

林秀斌  陈汉林  Karl-Heinz Wyrwoll  程晓敢  王旭龙  付可昂  廖林  肖骏  Krapez Bryan 《地质学报》2009,83(4):455-467

青藏高原边界地区的研究,尤其是砾石研究,对探讨青藏高原的隆升过程及隆升机制具有重要意义。本文选取青藏高原东北部香山山前小洪沟剖面,对出露的新生界各层位的砾石进行统计。统计结果显示,该剖面寺口子组上段、红柳沟组下段、红柳沟组上段、第四系以及现今河床出露的砾石成分主要为砂岩和石英砂岩,这与香山地区岩性相符合;砾石主要呈次圆状和次棱角状;长短轴比主要为1至2之间,为近圆状;砾石主要集中在中砾和小砾类别;分选好至中等好。砾石粒径分布显示出向细粒成分偏的特征,主要呈尖峰正态分布。这些特征表明各层位砾石相似的搬运过程,为中距离山前河流冲积砾石。沉积分析表明该砾石与气候振荡无必然联系,为构造隆升的产物。砾石沉积年龄由邻区磁性地层定年结果来限定。砾石特征结合邻区沉积分析表明香山地区在寺口子组沉积时（始新世）沉积之前已具有相当大的高程;至清水营组沉积时（渐新世）,该山体被剥蚀剥蚀夷平;到红柳沟组沉积时（中新世早、中期）,香山经历了再次的隆升;至干河沟组沉积时（中新世晚期到上新世）,构造趋于稳定;到更新世时,再次出现隆升事件。始新世香山山体可能与晚白垩世至新生代早期的构造事件有关,中新世的隆升时间可以作为印－藏碰撞效应到达香山地区的时限,显示青藏高原东北边界新生代的变形隆升时间较前人研究结果早,且存在多期隆升。  相似文献   

Chironomid-based water depth reconstructions: an independent evaluation of site-specific and local inference models   总被引：1，自引：1，他引：0  

Stefan Engels  Les C. Cwynar  Andrew B. H. Rees  Bryan N. Shuman 《Journal of Paleolimnology》2012,48(4):693-709

Water depth is an important environmental variable that explains a significant portion of the variation in the chironomid fauna of shallow lakes. We developed site-specific and local chironomid water-depth inference models using 26 and 104 surface-sediment samples, respectively, from seven kettlehole lakes in the Plymouth Aquifer, southeast Massachusetts, USA. Our site-specific model spans a depth gradient of 5.6?m, has an $ {\text{r}}_{\text{jack}}^{2} $ of 0.90, root mean square error of prediction (RMSEP) of 0.5?m and maximum bias of 0.7?m. Our local model has a depth gradient of 11.7?m, an $ {\text{r}}_{\text{jack}}^{2} $ of 0.71, RMSEP of 1.6?m and maximum bias of 2.9?m. Principal coordinates of neighbourhood matrices (PCNM) analysis showed that there is no influence of spatial autocorrelation on the site-specific model, but PCNM variables explained a significant amount of variance (4.8%) in the local model. This variance, however, is unique from the variance explained by water depth. We applied the inference models to a Holocene chironomid record from Crooked Pond, a site for which multiple, independent palaeohydrological reconstructions are available. The chironomid-based reconstructions are remarkably similar and show stable water depths of ~5?m, interrupted by a 2-m decrease between 4,200 and 3,200?cal a BP. Sedimentological evidence of water level fluctuations at Crooked Pond, obtained using the so-called Digerfeldt approach, also shows a drop in water depths around that time. The period of reconstructed lower water levels coincides with the abrupt decline in moisture-dependent hemlock in this region, providing further evidence for this major palaeohydrological event. The site-specific model has the best performance statistics, but the high percent abundance of fossil taxa from the long core that are absent or rare in the training set makes the site-specific reconstruction unreliable for the period before 4,400?cal a BP. The fossil taxa are well represented in the local model, making it the preferred inference model. The strong similarity between the chironomid-based reconstructions and the independent palaeohydrological records highlights the potential for using chironomid-based inference models to determine past lake depths at sites where temperature was not an influencing factor.  相似文献