Collaborative Research: Study of the Relationship between Regionally Localized and Zonally Symmetric Anomalously Persistent Weather States

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。低频大气变异性，从一个星期到几个月的时间尺度，将通过确定比大多数其他状态持续时间更长的少数流动状态来研究。这种状态被广泛地称为流态。这些制度对中期预报很重要，因为它们的高持久性可能转化为更高的可预测性。它们被认为是由于在地形存在下的行星波/纬向平均流相互作用（太平洋和大西洋纬向/阻塞流模式），或快速天气涡旋的低频组织及其随后对大尺度流的反馈（与环状模态相关的模式）而产生的。理论证据表明，上述两种状态类型具有不同的空间格局和持续特征；据推测，第一种类型的制度往往更受地理限制，比第二种类型的制度更不持久。进一步推测，驱动这两种型态的动力过程可能重合，从而产生混合型态，如北大西洋涛动。这些假设将结合观测分析、理论模拟和大气环流模式（GCM）实验进行探讨。研究人员先前的工作中出现了一项新技术，该技术将被用于分离北半球大气流动观测中的制度，方法是将它们定义为流动序列的片段，其中线性统计预测的技巧异常低；这些计算将对二维场和纬向平均场进行。一组理想化的、准地转的、斜压模型和简化物理的一般环流模型的长时间模拟将在广泛的参数范围内进行和分析。附加的实验将包括制度发作的案例研究和模拟手术切除潜在重要的相互作用；这些分析将阐明导致政权行为的过程。这项研究的更广泛影响与中长期天气预报问题的社会意义有关。该项目将加强两个机构之间的科学伙伴关系，并进一步发展研究生课程和大气动力学和统计方法方面的培训。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Low-frequency atmospheric variability, with time scales from one week to a few months, will be studied by identifying a small number of flow states that persist longer than most other states. Such states are widely referred to as flow regimes. The regimes are important for medium-range forecasting since their elevated persistence may translate into enhanced predictability. They are thought to arise due to planetary wave/zonal mean flow interaction in the presence of topography (Pacific and Atlantic zonal/blocked flow regimes), or low-frequency organization of the fast synoptic eddies and their subsequent feedback onto the large-scale flow (regimes associated with annular modes). Theoretical evidence suggests that the above two regime types have different spatial patterns and persistence characteristics; it is hypothesized that the regimes of the first type tend to be more geographically confined, and less persistent than the regimes of the second type. It is further conjectured that dynamical processes that drive the two types of regimes are likely to coincide, resulting in mixed regime types such as the North Atlantic Oscillation. These hypotheses will be explored using a combination of observational analyses, theoretical modeling, and General Circulation Model (GCM) experiments. A new technique, which emerged from the investigators' previous work, will be used to isolate regimes in the observations of the Northern Hemisphere's atmospheric flow by, defining them as the episodes of flow sequences for which linear statistical forecasts have an abnormally low skill; these calculations will be performed for two-dimensional, as well as for the zonally averaged fields. A set of long simulations of idealized, quasi-geostrophic, baroclinic models, and simplified-physics general circulation models will be performed and analyzed for a wide range of parameters. Additional experiments will include case studies of regime episodes and simulations subjected to surgical removal of potentially important interactions; these analyses will elucidate processes responsible for regime behavior.The broader impacts of this study relate to the societal significance of the problem of medium- and long-range weather forecasting. The project will strengthen scientific partnerships between the two institutions and further the development of graduate curricula and training in atmospheric dynamics and statistical methods.