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首页> 外文学位 >An investigation of snowcover-atmosphere-ocean interactions in the northern hemisphere with a global atmospheric model coupled to a slab ocean model.
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An investigation of snowcover-atmosphere-ocean interactions in the northern hemisphere with a global atmospheric model coupled to a slab ocean model.

机译：利用全球大气模型和平板海洋模型对北半球积雪-大气-海洋相互作用的调查。

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摘要

The difference between snow versus snow free conditions is the most significant natural, seasonal change the land surface can experience. Snow affects all aspects of the surface energy balance including albedo, sensible and latent heat fluxes, and soil moisture. In addition, the presence or lack of snow plays an important role in modifying the overlying air temperature, propagating from local climate to neighboring regions and even globally through atmospheric teleconnections. Numerous studies to date have investigated the implications of snow forcing the atmosphere and associated circulation, however the cause and effect relationship or direction of forcing has not been decisively demonstrated from observed data alone.GCM studies investigating snow-atmosphere interaction have focused on interaction of Siberian or Eurasian snow cover anomalies with the atmospheric teleconnection modes such as the Arctic Oscillation. Although the tendency has been to concentrate on Eurasia due to the magnitude of snowmass, North American snow cover also produces a weak relationship with downstream climate and an atmospheric teleconnection via enhanced North Atlantic storm track activity.Recent GCM studies of the effects of snow cover on overlying atmospheric conditions and large-scale circulation have primarily used a data ocean model with a fixed seasonal cycle of sea surface temperature (SST) and sea ice cover, based on historical SST records. We explore the influence of this SST boundary condition by comparing the data-forced model with a mixed-layer slab ocean model underneath the NCAR atmospheric GCM. Experimental runs consist of 40-year simulations where each experiment was run once with the data-forced model and once with the mixed-layer slab ocean model in scenarios of anomalously high and low snow cover patterns. Anomalous snow cover patterns were generated from historical snow cover data by choosing minimum and maximum depths observed on a particular day of the year for each grid point.Surface response results include significant SST cooling under maximum North American and Eurasian snow conditions. Locations of SST cooling include local coastal cooling directly downstream of each individual forcing region in addition to upstream centers of remote cooling in the Pacific under anomalously high snow conditions in North America and in the Atlantic under anomalously high Eurasian snow conditions. Significant cooling of surface temperature at 2 m under maximum snow conditions local to each forcing region was evident from both experiments, however values were larger in magnitude and greater in spatial extent when using the slab model.Atmospheric responses to anomalous snow conditions are dominated by a barotropic response under maximum snow conditions throughout much of the mid latitudes in both experiments. Consistent upstream anomalously lower geopotential height and sea level pressure over the Pacific during early winter in particular is evident from the North American Slab experiment, implying a reduced north-south gradient indicating a negative AO phase under maximum snow extent and depth. In contrast, the Data experiment is dominated by weaker and less significant downstream response in both atmospheric fields for both experiments.Areas of positive eddy kinetic energy (EKE) correlate well with steep geopotential height gradient differences between maximum and minimum snow experiments. A dipole of EKE in early winter over the Pacific in both experiments with positive values to the south and negative to the north is indicative of reduced poleward heat flux which may be contributing to a decrease in warm SST advection northwards and the ensuing mid Pacific SST cooling. This proposed pathway is supported by increased zonal wind at 250 hPa collocated with identified regions of sharpened geopotential height gradient, strengthened baroclinicity and positive EKE.The Eurasian experiment shows a similar pathway to the North American experiment, however circulation response is focused downstream of the forcing region in early winter for both Slab and Data experiments. A southward shift of the prevailing East Asia storm track is indicated from a dipole pattern of EKE in the Pacific during early winter when using the Slab model in contrast to strengthening alone with no southward shift under Data conditions. Reduced poleward heat transport associated with a southward shift in the prevailing storm tracks of this region may be influencing the cooling SST trend through reduced warm SST advection to the Aleutian area of the North Pacific.
机译：降雪与无雪条件之间的差异是土地表面可以经历的最重要的自然，季节性变化。降雪会影响表面能平衡的各个方面，包括反照率，显热和潜热通量以及土壤湿度。此外，是否存在积雪在改变上方的气温方面也起着重要作用，气温从局部气候传播到邻近地区，甚至通过大气遥传而在全球范围内传播。迄今为止，已有许多研究调查了积雪对大气和相关环流的影响，但是仅凭观测数据并没有确定性地表明积雪的因果关系或强迫方向。GCM研究积雪与大气相互作用的研究集中在西伯利亚的相互作用大气遥相关模式（例如北极涛动）引起的欧亚或积雪异常。尽管由于积雪的数量级，人们倾向于将注意力集中在欧亚大陆上，但北美积雪也通过增强北大西洋风暴路径活动而与下游气候和大气遥相关产生了较弱的联系。上空的大气条件和大规模的环流主要是根据历史SST记录，使用具有固定的海面温度（SST）和海冰覆盖的季节性周期的数据海洋模型。通过将数据强制模型与NCAR大气GCM下的混合层平板海洋模型进行比较，我们探索了这种SST边界条件的影响。实验运行包括40年的模拟，其中每个实验在数据异常高和低积雪模式的情况下，都使用数据强制模型进行一次，并使用混合层平板海洋模型进行一次。根据历史积雪数据，通过选择一年中特定日期在每个网格点上观察到的最小和最大深度来产生异常的积雪模式。表面响应结果包括在北美和欧亚最大积雪条件下的显着SST降温。 SST降温的位置包括在每个强迫区域下游直接的局部沿海降温，以及北太平洋异常高雪条件下太平洋的远距离降温的上游中心以及在欧亚高雪条件下异常的大西洋的降温的上游中心。从两个实验中都可以看出，在每个受力区域局部的最大降雪条件下，表面温度在2 m处有明显降温，但是使用平板模型时，其值在大小上和空间范围上都较大。在两个实验中，大部分中纬度地区在最大雪况下的正压响应。北美平板实验表明，特别是在初冬期间，太平洋上空的上游异常反常地势高度和海平面压力一直很明显，这意味着北-南坡度减小，表明在最大积雪范围和最大深度下，AO相为负。相比之下，数据实验在两个大气场中都受到较弱和较不显着的下游响应的支配。正涡动能（EKE）的面积与最大雪实验和最小雪实验之间陡峭的地势高度梯度差异有很好的相关性。这两个实验中，太平洋初冬的EKE偶极子都向南和向北均为负值，这表明极向热通量减少，这可能导致北半球温暖的对流平流和随之而来的太平洋中部冷气减少。 。在250 hPa上增加的纬向风与确定的区域具有更强的地势高度梯度，增强的斜压度和正EKE的区域支持了这一拟议的途径。欧亚实验显示了与北美实验相似的途径，但环流响应集中在强迫作用的下游Slab和Data实验都可以在初冬时使用该区域。在冬季，使用Slab模型时，太平洋地区EKE的偶极子模式表明了东亚风暴路径的南移，这与在数据条件下没有单独向南移动的情况相反。与该地区盛行的风暴轨迹向南移动相关的极向热传输减少，可能是由于减少了对北太平洋阿留申地区的暖海涛对流，从而影响了冷海涛动趋势。

著录项

  • 作者

    Henderson, Gina R.;

  • 作者单位

    University of Delaware.;

  • 授予单位 University of Delaware.;
  • 学科 Physical Geography.Climate Change.Atmospheric Sciences.
  • 学位 Ph.D.
  • 年度 2010
  • 页码 150 p.
  • 总页数 150
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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