Understanding How Latent Heat Release and Cloud Radiative Effects Shape Jet Variability and Jet Shifts Under Climate Change

在北半球或南半球的中纬度地区飞行的喷气式飞机通常会遇到时速超过100英里的东风，这大大减少了向东飞行的时间。对流层上层这种强气流的存在对中纬度天气系统产生了控制性影响，即使是急流的细微变化也可能对地面天气产生影响。由温室效应变暖引起的气候变化的模拟通常显示出喷射气流在两个半球向高纬度地区移动，而观测显示出向极地移动已经发生的迹象。向极地移动与纵向平均急流的非强迫自然变率相似，其中南北移动是最突出的模式。该奖项下的工作考虑了水汽在喷射气流的自然南北向移动及其因温室气体增加而向极地移动中的作用。湿气可以通过凝结形成云滴时产生的加热作用来影响平均喷流位置，而云通过云辐射效应（cre）产生额外的加热和冷却作用，特别是通过将阳光反射回太空而产生的冷却作用和通过捕获向外的长波辐射而产生的增温作用。最近的研究表明，cre在气候变化模拟中发现的喷流向极地漂移中发挥了重要作用，但其确切机制尚未确定，关于cre在自然变率中的作用的研究也很少。潜热在向极地漂移中的作用也相对未得到检验，最近的两项研究在潜热是否减少或增加自然发生的射流位移的持久性方面存在分歧。本研究采用一套可控制地加入湿润效应的简化模式，研究潜热和cre对南北向急流波动和强迫向极地漂移的影响。这项工作的另一个资源是为“云开-关气候对比实验”（COOKIE）制作的模式模拟档案，在该实验中，综合气候模式与cre和cre相结合。考虑到急流变化对地表天气的影响，包括它们在确定与锋面风暴和阻塞事件相关的极端事件的频率和严重程度方面的作用，这项工作具有社会意义。该项目为研究生和博士后研究员提供支持和培训，从而发展该研究领域的科学队伍。该项目还通过斯克里普斯本科生研究奖学金（SURF）项目每年夏天招收一名本科生。此外，该奖项还通过购买和使用来自动力学项目的旋转水箱来支持高中科学教育，这些水箱用于教室演示急流、旋风和大气环流的其他特征。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Jets flying over the middle latitudes of either the Northern or Southern Hemisphere commonly encounter eastward winds with speeds over 100 miles per hour, substantially reducing flight times going east. The presence of such strong flow in the upper troposphere exerts a controlling influence on middle latitude weather systems and even subtle changes in the jet streams can be consequential for surface weather. Simulations of climate change due to greenhouse warming typically show shift of the jet streams toward higher latitudes in both hemispheres, and observations show indications that poleward shifting has already occurred. The poleward shift is similar to the unforced natural variability of the longitudinally averaged jet streams, in which north-south shifting is the most prominent mode.Work under this award considers the role of moisture in the natural north-south shifting of the jet streams and their poleward movement in response to greenhouse gas increases. Moisture can affect the mean jet position through the heating that occurs when it condenses to form cloud droplets, and the clouds cause additional heating and cooling through cloud radiative effects (CREs), in particular cooling by reflecting sunlight back to space and warming by the trapping of outgoing longwave radiation. Recent work suggests that CREs play a strong role in the poleward drift of jets found in climate change simulations, but the exact mechanism has not yet been determined and little work has been done on the role of CREs in natural variability. The role of latent heating in the poleward drift is also relatively unexamined, and two recent studies disagree as to whether latent heating reduces or increases the persistence of naturally occurring jet displacements.The research uses a suite of simplified models, in which moist effects can be added in a controlled manner, to study the influence of latent heating and CREs on north-south jet fluctuations and forced poleward drift. A further resource for the work is the archive of model simulations produced for the Clouds On-Off Klimate Intercomparison Experiment (COOKIE), in which comprehensive climate models are integrated with and without CREs.The work has societal relevance given the effects of jet shifts on surface weather, including their role in determining the frequency and severity of extreme events associated with frontal storms and blocking events. The project provides support and training to a graduate student and postdoctoral research associate, thereby developing the scientific workforce in this research area. The project also recruits an undergraduate student each summer through the Scripps Undergraduate Research Fellowship (SURF) program. In addition, the award supports high school science education through the purchase and use of rotating tanks from the DIYnamics Project, which are used for classroom demonstrations of jet streams, cyclones, and other features of the atmospheric circulation.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.