AGS-PRF: Understanding Historical Trends in Tropical Pacific Sea Surface Temperature Patterns

海洋表面温度(SST)变暖是温室气体水平上升的预期结果，在过去几十年中，全球SST急剧上升。但是，尽管西太平洋显著变暖，东热带太平洋并没有像预期的那样变暖。东太平洋没有变暖的原因尚不清楚，而且没有变暖与模式模拟中的SST趋势模式形成了鲜明对比，模式模拟通常显示出一种类似厄尔尼诺的模式，东部变暖更严重。观测和模拟的太平洋趋势模式之间的对立引起了气候科学家的极大兴趣，因为变暖模式对区域气候影响和温室气体增加导致的总体变暖都很重要。这里进行的研究试图理解模拟和观测之间太平洋变暖模式差异的物理机制。该项目涉及完全复杂的气候模型和Zebiak-Cane(ZC)模型之间的比较，ZC模型是一个高度理想化的大气-海洋模型，旨在捕捉厄尔尼诺的基本动力学。该模式产生了与观测结果类似的SST趋势模式，从而为理解产生这种模式的物理机制提供了一个重要的参考点。这项工作包括在ZC模型中添加机制，并在完全复杂的气候模型中禁用相同的机制，以了解特定机制的影响。一个关键的考虑因素是平均状态偏差在模拟模式中的作用，因为早期的工作表明，模拟产生了不正确的趋势模式，这是由于众所周知的“冷舌”偏差，即赤道东太平洋的冷SST条带太长太冷。由于SST模式对区域气候影响的影响，这项工作具有实际意义和科学意义。这些包括太平洋热带气旋(飓风和台风)的分布和强度，以及太平洋变暖对美国西南部干旱的影响。此外，该奖项还规定了一名博士后研究员(PRF)的职业发展，该研究员将与芝加哥大学的导师Tiffany Shaw和Malte Jansen合作。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Warming sea surface temperatures (SSTs) are an expected consequence of rising greenhouse gas levels, and the past several decades have seen a dramatic increase in global SST. But the eastern tropical Pacific has not warmed as expected despite substantial West Pacific warming. The reasons for the absence of East Pacific warming are not clear and the lack of warming stands in contrast to the SST trend patterns in model simulations, which typically show an El Nino-like pattern with greater warming to the east. The opposition between observed and simulated Pacific trend patterns has attracted considerable interest among climate scientists, as the warming pattern matters for both regional climate impacts and the overall amount of warming caused by greenhouse gas increases.Research conducted here seeks to understand the physical mechanisms that account for the difference in Pacific warming patterns between simulations and observations. The project involves comparisons between full-complexity climate models and the Zebiak-Cane (ZC) model, a highly idealized atmosphere-ocean model built to capture the basic dynamics of El Nino. The model produces an SST trend pattern similar to the observations and thus provides an important point of reference for understanding the physical mechanisms that produce the pattern. The work involves adding mechanisms to the ZC model and disabling the same mechanisms in a full-complexity climate model to understand the effects of particular mechanisms. A key consideration is the role of mean state bias in the simulated pattern, as earlier work suggests that simulations produce an incorrect trend pattern due to a well-known "cold tongue" bias in which the strip of cold SST along the eastern equatorial Pacific is too long and too cold.The work is of practical as well as scientific interest due to the implications of the SST pattern for regional climate impacts. These include the distribution and intensity of Pacific tropical cyclones (hurricanes and typhoons) and the effect of Pacific warming on drought in the US Southwest. In addition, the award provides for the career development of a Postdoctoral Research Fellow (PRF), who will work with mentors Tiffany Shaw and Malte Jansen at the University of Chicago.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.