Assessing and Understanding Oceanic Climate Forcing on Decadal Climate Variability from Surface Heat Flux

评估和理解海洋气候对地表热通量十年间气候变化的影响

• 批准号: 2321042
• 负责人: Zhengyu Liu
• 金额: $ 65.24万
• 依托单位: Ohio State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-08-15 至 2026-07-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2321042&HistoricalAwards=false
• 关键词: Assessing; Understanding; Oceanic; Climate; Forcing

The North Atlantic and North Pacific are both home to large-scale sea surface temperature (SST) variations that last for years and even decades. An example is the Atlantic Multidecadal Oscillation (AMO), in which a large portion of the Atlantic north of the equator warms and cools over periods of perhaps 20 to 40 years. The low-frequency variability of North Pacific and North Atlantic SST must be driven by some combination of oceanic and atmospheric forcing, but their roles are not well understood and there is still some debate as to which is dominant. An important consideration is that low-frequency SST variability can be generated by changes in evaporation and surface heat exchange accompanying the passage of weather systems even though the movement of weather systems is much faster than the SST variability. If the slow variations of SSTs are driven by the "weather noise" of fast-moving systems the prospects for long-term SST prediction are somewhat limited, while a strong role for ocean dynamics, perhaps involving slow fluctuations of the global overturning circulation, could mean that SST anomalies can be predicted years in advance.Work under this award seeks to quantify the contributions of atmospheric and oceanic forcing to low-frequency SST variability using a simple stochastic model. The gist of the model is that atmospheric and oceanic forcing can be distinguished by looking at the timing of SST and surface heat flux anomalies, where the surface heat flux refers to both the evaporation and heat exchange occurring at the ocean surface and changes in surface sunlight and infrared radiation caused by changes in cloud cover. If an SST change is driven by the atmosphere it should be preceded by the surface heat flux anomaly that caused it. On the other hand an SST change driven by the ocean is likely to produce a change in surface heat flux that acts to damp the SST anomaly, for instance an ocean-driven warm anomaly would likely produce a surface heat flux that has a cooling effect. In that case the heat flux anomaly would be roughly synchronous with the SST anomaly but with opposite sign. The model used here includes explicit representations of both atmospheric and oceanic damping and treats the oceanic forcing as a red noise process. The model is used to analyze SST variability in observational datasets and output from climate models using standard and enhanced horizontal resolution. Simulations with modified versions of the Community Earth System Model (CESM) are then used to identify mechanisms of SST variability.The work has societal value as it addresses the question of long-range SST prediction. The slow variations of SST have a number of human impacts, for instance the number of severe Atlantic hurricanes roughly doubles from the cold phase of the AMO to the warm phase, and the AMO is implicated in the great Sahel drought of the mid-20th century. The extent to which the AMO and other forms of low-frequency SST are predictable is not known, and an understanding of the driving mechanisms is essential for an assessment of predictability and to provide useful guidance as to how predictive models might be developed. In addition, the project provides support and training for two graduate students, thereby providing for the future workforce in this research area.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.

北大西洋和北太平洋都是持续数年甚至几十年的大型海面温度（SST）变化的所在地。 一个例子是大西洋多年代振荡（AMO），其中赤道北部的大部分地区很大一部分在大约20到40年的时间内冷却。 北太平洋和北大西洋SST的低频可变性必须由海洋和大气强迫的某种结合驱动，但是它们的作用尚不清楚，并且仍然存在一些主导的争论。 一个重要的考虑因素是，即使天气系统的移动速度比SST变异性快得多，伴随着天气系统的通过的蒸发和表面热交换的变化可以通过蒸发和表面热量交换的变化产生低频SST变异性。 如果SST的缓慢变化是由快速移动系统的“天气噪声”驱动的，那么长期SST预测的前景有限，而海洋动力学的强大作用，也许涉及全球翻转循环的缓慢波动，可能意味着SST异常可以提前几年预测。根据该奖项，工作旨在量化使用简单的随机模型对大气和海洋强迫对低频SST变异的贡献。该模型的要旨是，可以通过查看SST和表面热通量异常的时间来区分大气和海洋强迫，其中表面热通量是指海面上发生的蒸发和热交换以及表面阳光的变化以及由云覆盖变化引起的红外辐射。 如果SST的变化是由大气驱动的，则应在引起它的表面热通量异常之前。另一方面，由海洋驱动的SST变化很可能会导致表面热通量的变化，从而引起SST异常的作用，例如，海洋驱动的温暖异常可能会产生具有冷却效果的表面热通量。 在这种情况下，热通量异常将与SST异常大致同步，但符号相反。 这里使用的模型包括大气和海洋阻尼的明确表示，并将海洋强迫视为红噪声过程。 该模型用于使用标准和增强的水平分辨率分析观测数据集中的SST变异性和气候模型的输出。 然后使用改良版本的社区地球系统模型（CESM）的模拟来识别SST变异性的机制。该工作具有社会价值，因为它解决了长期SST预测的问题。 SST的缓慢变化具有许多人类的影响，例如，从AMO的冷阶段到温暖阶段，严重的大西洋飓风的数量大约翻了一番，而AMO则与20世纪中叶的萨赫勒干旱有关。 AMO和其他形式的低频SST的预测程度是不清楚的，并且对驾驶机制的理解对于评估可预测性和提供有关如何开发预测模型的有用指导至关重要。 此外，该项目为两名研究生提供了支持和培训，从而为该研究领域提供了未来的劳动力。该奖项反映了NSF的法定任务，并被认为是值得通过基金会的知识分子和更广泛影响的评估评估的评估值得支持的。 。