Collaborative Research: Investigating the Asymmetries and Temporally Varying Nature of Gulf Stream Ring Formation

由于哈特拉斯角和大浅滩之间的墨西哥湾流（GS）流动剧烈蜿蜒，西部边界流延伸将反气旋暖核环（WCR）引入斜坡海，将气旋冷核环（CCR）引入马尾藻海。长期观测表明，在产生的温暖和冷核心环以及政权转变的不对称性。本研究将通过充分利用现有的观测数据集来研究这种变化背后的过程的几种假设。确定GS和环的季节性和年际变化的原因和后果将有助于澄清海洋在气候变化中的作用，并确定系统的要素在多大程度上是可预测的。来自商业捕鱼业的报告指出，最近新英格兰附近的暖水物种增加，这些物种通常与GS有关，因此可能与WCR活动有关。这项工作的结果将在罗得岛商业渔业中心举行的半年度会议上公布，并通过区域和国家媒体向公众公布。安德烈斯将继续她正在进行的外展工作与一所小学，服务于一个传统上在干代表性不足的群体。该项目将支助一名研究生，他将接受高级数据分析和北大西洋变化动态方面的培训。该研究将产生基于观测的衍生产品（例如，根据Clark分析图对40年天气资料的分析表明，环的形成有三个特征，但在动态上还不清楚：（i）在给定年份中WCR的数量不等于CCR的数量（“空间不对称”）;（ii）在2000年发生了一次引人注目的WCR体制转变之后，2000-2018年期间每年形成的WCR通常比CCR多;在此转变之前，（iii）CCRs的形成高峰在冬/春，而WCR的形成高峰在夏/秋（“季节性不对称”）。基于这些观察到的不对称性，人们假设三种不同的环类型（“非对称环”，“夹断环”和“大环分裂”）从流中脱落，并且每种类型由于其各自的形成过程而具有不同的特征。另一个假设是，观察到的空间不对称的相对涡度在整个GS动态链接到观察到的不对称的WCR与CCR形成的年速率。最后，据推测，在分层的季节性变化与CCR形成的WCR的季节性差异，并在环形成的季节性不对称性取决于整个流分层的空间不对称性。为了研究这些不对称性中的每一个，将分析现有的数据集来测试这三个假设。首先，研究人员将确定形成不同环类型的条件。然后，他们将量化一组状态空间参数是否（以及如何）发生变化，以及这些变化是否与观察到的状态转变相关，以确定GS系统是否表现出多重平衡。除了使用克拉克海图导出的WCR和CCR普查外，还将使用沿轨道卫星测高仪、Argo浮标（轨迹和垂直属性剖面）和来自W线计划的现有区域数据集（系泊和船上测量速度和水的性质），夹竹桃项目（温度剖面和速度剖面）和先锋阵列（速度、温度和盐度）。卫星测量的海面高度和海面温度图将提供空间和时间背景。分析计划包括：（1）检查沿着GS路径（75- 55 W）1993-2020年所有可用的沿轨高度计数据;（ii）计算例如按扇区、按环类型和通过集中于特定年份或季节选择的条件平均值，（iii）表征良好采样的个别环事件，以及（iv）使用可用的和导出的长持续时间变量序列来检查状态空间以获得多重均衡的证据（包括相对涡度、层结、输送、流域尺度风、海平面高度），以比较和对比1997-2003年的制度变化期与最近可能的跨越2016年的转变期，2021.该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查进行评估，被认为值得支持的搜索.

As the vigorously meandering Gulf Stream (GS) flows between Cape Hatteras and the Grand Banks, this western boundary current extension sheds anticyclonic warm core rings (WCRs) into the Slope Sea and cyclonic cold core rings (CCRs) into the Sargasso Sea. Long term observations indicate asymmetries in the generation of warm- and cold-core rings as well as a regime shift. This study will investigate several hypotheses for the processes behind this variability by fully exploiting existing observational datasets. Identifying the causes and consequences of seasonal and interannual variability in the GS and rings will help clarify the ocean’s role in climate variability and establish to what extent elements of the system are predictable. Reports from the commercial fishing industry note recent increases off New England in warm water species commonly associated with the GS, and hence likely related to WCR activity. Results from this work will be communicated at semi-annual meetings at the Commercial Fisheries Center of Rhode Island and also to the general public through regional and national media. Andres will continue her ongoing outreach efforts with an elementary school that serves a group traditionally underrepresented in STEM. This project will support a graduate student who will be trained in both advanced data analysis and dynamical aspects of the changes in the North Atlantic. The research will generate observation-based derived products (e.g., CCR census, track census, and a regional Argo-Rings census) which will be made available to others.Analysis of four decades of synoptic data based on Clark Analysis Charts demonstrates three characteristics of ring formation that are not yet understood dynamically: (i) the number of WCRs shed in a given year does not equal the number of CCRs (“spatial asymmetry”); (ii) after a striking WCR Regime Shift in 2000, more WCRs are usually formed each year during 2000-2018 than are CCRs; prior to this shift (during 1980-1999) more CCRs were formed than WCRs (“interannual asymmetry”); and (iii) the formation of CCRs peaks in winter/spring, whereas WCR formations peak in summer/fall (“seasonal asymmetry”). Based on these observed asymmetries, it is hypothesized that three different ring-types (“aneurisms”, “pinched-off rings”, and “large-ring splits”) are shed from the Stream, and that each type has distinct characteristics due to its respective formation processes. An additional hypothesis is that an observed spatial asymmetry of relative vorticity across the GS is dynamically linked to the observed asymmetry in the annual rates of WCR versus CCR formations. Finally, it is hypothesized that seasonal changes in stratification contribute to the difference in the seasonality of WCR versus CCR formations and that seasonal asymmetry in ring formation depends on spatial asymmetry in the stratification across the Stream. To investigate each of these asymmetries, existing datasets will be analyzed to test these three hypotheses. First the researchers will identify the conditions which give rise to formation of the different ring-types. Then they will quantify whether (and how) a set of state-space parameters changes and whether these changes are associated with the observed regime shift, in order to determine whether the GS System exhibits multiple equilibria. In addition to using the Clark Chart-derived WCR and CCR Censuses, ring-types and the system’s asymmetries will be explored with along-track satellite altimetry, Argo floats (trajectories and vertical property profiles) and existing regional datasets from the Line W Program (moored and shipboard measurements of velocity and water properties), the Oleander Project (temperature profiles and velocity sections) and the Pioneer Array (velocity, temperature, and salinity). Maps of satellite-measured sea surface height and sea surface temperature will provide spatial and temporal context. The analysis plan includes (i) examining all available along-track altimeter data from 1993-2020 along the GS path (75-55W); (ii) calculating conditional averages selected, for example, by sector, by ring-type, and by focusing on a specific year or season, (iii) characterizing individual ring events that are well-sampled, and (iv) examining the state-space for evidence of multiple equilibria using available and derived long-duration time-series of variables (including relative vorticity, stratification, transport, basin scale winds, sea surface height) to compare and contrast the regime change period of 1997-2003 with a recent possible shift period spanning 2016-2021.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.