Studies of the Early-1990s Climate Shift in the Pacific and Its Linkage to the Atlantic Multi-decadal Oscillation

太平洋及其上覆大气的气候变化具有全球性的影响，其原因和后果是气候动力学的重要课题。 其中之一是20世纪90年代初的太平洋气候转移，其中：（1）厄尔尼诺/南方涛动（ENSO）事件的发生地点从赤道东太平洋转移到赤道中太平洋;（2）北方季风的年际变率急剧下降;（3）热带西太平洋海平面开始以更快的速度上升;（4）北赤道流和逆流南移。 该项目检验的假设是，1990年代的气候变化与太平洋副热带高压的增强有关，太平洋副热带高压是一个准静止的高海平面气压区，从加州海岸延伸到日期变更线之外，覆盖了北太平洋副热带的大部分地区。 当副热带太平洋高压加强时，绕其环流的地面风场加快，这种较高的风速具有加强该地区海气耦合的作用。 该奖项下的工作审查了海洋-大气耦合的加剧在多大程度上可能导致上述四种气候变化影响。 该项目进一步检验了太平洋高压的加强是对同时发生的大西洋多年代际振荡（AMO）逆转的响应的假设。 AMO是一种缓慢变化的海表温度（SST）变化模式，其中赤道以北的大西洋比平均温度更高或更低，大约在1990年左右从较冷的SST过渡到较暖的SST。 这项研究是使用一套以各种方式配置的气候模型模拟来测试假设的。 在一种配置中，全球范围内规定了SST，在大西洋上施加AMO模式，以便可以评估太平洋高压对AMO的响应。 其他配置使用部分或完全交互式海洋模式，允许太平洋高压的变化影响SST和次表层海洋。 这些配置允许在海洋-大气耦合的变化和他们的假设后果进行examined. Although其科学利益，1990年代太平洋气候转变具有社会重要性，由于其全球性的影响。 季风系统的变化对水资源是重要的，而从东太平洋到中太平洋ENSO事件的转变对这些事件对美国天气和气候的影响有影响。 此外，该项目还为一名博士后助理和两名研究生提供支助和培训，从而为这一领域的下一代研究人员提供支持。

Changes in the climate of the Pacific Ocean and overlying atmosphere have worldwide consequences, and the causes and consequences of such changes are important topics in climate dynamics. One such change is the Pacific climate shift of the early 1990s, in which 1) the location of El Nino/Southern Oscillation (ENSO) events shifted from the eastern equatorial Pacific to the central equatorial Pacific; 2) the year-to-year variability of the Northern Hemisphere monsoons decreased dramatically; 3) sea level in the western tropical Pacific began rising at a faster rate; and 4) the north equatorial current and countercurrent migrated southward. This project tests the hypothesis that the 1990s climate shift is related to an intensification of the subtropical Pacific high, a quasi-stationary region of high sea level pressure which extends past the dateline from the California coast and covers much of the subtropical North Pacific. When the subtropical Pacific high intensifies the surface winds circulating around it speed up, and the higher speed has the effect of strengthening the coupling of the ocean and atmosphere in the region. Work under this award examines the extent to which the intensification of ocean-atmosphere coupling can lead to the four climate shift impacts listed above. The project further tests the hypothesis that the intensification of the Pacific high occurred in response to the reversal of the Atlantic Multi-decadal Oscillation (AMO) which occurred at the same time. The AMO is a slowly varying mode of sea surface temperature (SST) variation in which the Atlantic north of the equator is either warmer or colder than average, with a transition from colder to warmer SSTs around 1990. The research is conducted using a suite of simulations from a climate model configured in various ways to test the hypotheses. In one configuration SSTs are prescribed globally, with the AMO pattern imposed in the Atlantic so that the response of the Pacific high to the AMO can be assessed. Other configurations use a partially or fully interactive ocean model, allowing the changes in the Pacific high to affect SSTs and the subsurface ocean. These configurations allow the changes in ocean-atmosphere coupling and their hypothesized consequences to be examined.Aside from its scientific interest, the 1990s Pacific climate shift has societal importance due to its worldwide impacts. The variability of monsoon systems is consequential for water resources, while the shift from eastern to central Pacific ENSO events has implications for the impacts of these events on the weather and climate of the US. In addition, the project provides support and training for a postdoctoral associate and two graduate students, thereby providing for the next generation of researchers in this field.