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

飞越北半球或南半球中纬度的喷气式飞机通常会遇到时速超过100英里的东风，大大缩短了向东飞行的时间。对流层上层存在如此强烈的气流对中纬度天气系统产生控制影响，即使急流的细微变化也可能对地面天气产生影响。对温室气体变暖引起的气候变化的模拟通常显示，两个半球的急流都向更高纬度移动，而观测结果表明，已经发生了向极地移动的迹象。极移类似于纵向平均急流的非强制自然变化，其中南北移动是最突出的模式。本奖项下的工作考虑了水分在急流自然南北移动中的作用，以及它们响应温室气体增加而向极地移动的作用。湿气可以通过凝结形成云滴时产生的加热来影响平均喷流位置，而云层通过云辐射效应(CRE)产生额外的加热和冷却，特别是通过将阳光反射回太空来冷却，通过捕获传出的长波辐射来变暖。最近的工作表明，Cres在气候变化模拟中发现的急流向极地漂移中扮演着重要的角色，但确切的机制尚未确定，关于Cres在自然变率中的作用的工作也很少。潜热在极地漂移中的作用也相对未被研究，最近的两项研究对于潜热是减少还是增加了自然产生的急流位移的持久性存在分歧。这项研究使用了一套简化的模型，其中可以控制地添加湿效应，来研究潜热和Cres对南北急流波动和强迫极向漂移的影响。这项工作的另一个资源是为云开-关Klimate相互比较实验(Cookie)产生的模式模拟档案，其中综合了有和没有CRE的气候模式。鉴于急流转移对地面天气的影响，包括它们在确定与锋面风暴和阻塞事件有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助理提供支持和培训，从而发展这一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)计划，每年夏天招募一名本科生。此外，该奖项通过购买和使用DIYnamics项目的旋转水箱来支持高中科学教育，这些水箱用于课堂演示急流、气旋和其他大气环流特征。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。

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.