Collaborative Research: Improving the representation of the Quasi-biennial Oscillation and its surface impacts in NCAR climate models

合作研究：改善 NCAR 气候模型中准两年期振荡及其地表影响的表征

• 批准号: 2109996
• 负责人: Chuntao Liu
• 金额: $ 5.99万
• 依托单位: Texas A&M University Corpus Christi
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-09-01 至 2024-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2109996&HistoricalAwards=false
• 关键词: Collaborative; Research; Improving; representation; Quasi

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).The winds of the equatorial stratosphere (say 20 to 50 kilometers above the surface) blow steadily and consistently around the equator, but their direction somehow reverses from easterly to westerly every 28 months or so. This wind reversal, called the Quasi-biennial Oscillation (QBO), is thought to have a number of consequences including influences on the Madden-Julian Oscillation (MJO), a large-scale pattern of winds and rainfall in the tropics; the North Atlantic Oscillation (NAO), a circulation pattern that influences weather in the eastern US and western Europe; and the paths of storms that move along the jet stream in the North Pacific. The slow progression of the QBO could thus impart some long-range predictability to worldwide weather. But weather and climate models are not good at simulating the QBO and their inability to reproduce it may be standing in the way of better forecasts.The QBO is largely driven by atmospheric gravity waves, waves similar to ocean waves except that they can propagate vertically as well as horizontally and thus can transport momentum upward to drive the QBO. The gravity waves are generated by deep convective clouds, commonly pictured as pistons that make waves by pumping the ambient air up and down with their rising and sinking motions. Such wave generation does occur but it tends to make waves which have relatively fast propagation speeds, while observations suggest that much of the momentum flux that matters for the QBO comes from slowly propagating waves.Work performed here explores an alternative wave generation mechanism in which deep convective clouds generate waves by blocking the horizontal wind near the cloud tops. Winds aloft are commonly stronger than winds at the surface, so air rising in a cloud is likely to be moving more slowly than ambient air when it reaches the top of the cloud. The rising air can thus present an obstacle to the upper-level wind, which flows over or around it generating waves in the same way as water flowing over rocks in a stream. Such waves will be stationary relative to the convective clouds that generate them, which move slowly relative to the ground. This mechanism could therefore explain the discrepancy in phase speed between waves generated by piston-like vertical motion and observations that find momentum flux from waves with slower phase speeds.The primary activity in the project is adding a representation of the cloud-as-obstacle generation mechanism to the Whole Atmosphere Community Climate Model (WACCM). A number of comparisons are performed between the properties of simulated waves (momentum flux in particular) and observations from satellites and stratospheric balloons, and further work examines QBO simulations driven by the waves. WACCM is currently able to simulate the QBO using only the piston mechanism but it does so by artificially reducing the phase speed of the waves by a factor of four. Further work examines the impact of the QBO on the MJO and other circulation patterns.The work has societal relevance due to the potential value of better QBO simulation for long-range weather forecasting, as noted above. The work also has relevance for space weather since convectively-generated gravity waves can propagate into the ionosphere and cause disruptions in communications and navigation. An extended version of WACCM known as WACCM-X is used to study such effects, thus there is a direct pathway for the work to benefit the space weather research community.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.

该奖项的全部或部分资金来自2021年美国救援计划法案（公法117-2）。赤道平流层（比如地表以上20至50公里处）的风稳定而持续地绕着赤道吹，但它们的方向不知何故每28个月左右就会从东风转成西风。这种风逆转被称为准两年期涛动（QBO），被认为会产生多种后果，包括对马登-朱利安涛动（MJO）的影响，这是热带地区的一种大规模风和降雨模式;北大西洋涛动（NAO），一种影响美国东部和西欧天气的环流模式;以及北太平洋急流沿着移动的风暴路径。 QBO的缓慢发展因此可以为全球天气提供一些长期的可预测性。 但是天气和气候模型并不擅长模拟准两年振荡，它们无法再现准两年振荡，这可能会妨碍更好的预报。准两年振荡主要是由大气重力波驱动的，这种波类似于海浪，但它们可以垂直传播，也可以水平传播，因此可以向上输送动量，从而驱动准两年振荡。 重力波是由深对流云产生的，通常被描绘成活塞，通过它们的上升和下沉运动将周围的空气上下泵动而产生波浪。 这种波的产生确实会发生，但它往往使波具有相对较快的传播速度，而观测表明，大部分的动量通量的问题QBO来自缓慢传播wave.Work这里进行的探索另一种波的产生机制，其中深对流云产生波阻挡附近的云顶的水平风。 高空的风通常比地面的风更强，因此当空气到达云层顶部时，在云中上升的空气可能比周围空气移动得更慢。因此，上升的空气可以对上层风构成障碍，上层风在其上方或周围流动，产生波浪，就像水流在溪流中流过岩石一样。 这种波相对于产生它们的对流云是静止的，对流云相对于地面移动缓慢。 因此，这一机制可以解释由活塞状垂直运动产生的波与观测结果之间的相位速度差异，而观测结果发现相位速度较慢的波的动量通量。该项目的主要活动是将云作为障碍物产生机制的表示添加到全大气社区气候模式（WACCM）中。 大量的比较之间的属性的模拟波（特别是动量通量）和观测卫星和平流层气球，进一步的工作探讨QBO模拟驱动的波。WACCM目前能够仅使用活塞机制来模拟QBO，但它通过人为地将波的相速度降低四倍来实现。 进一步的工作研究QBO对MJO和其他环流模式的影响。如上所述，由于更好的QBO模拟对长期天气预报的潜在价值，这项工作具有社会意义。 这项工作还与空间气象有关，因为对流产生的重力波可传播到电离层，造成通信和导航中断。 WACCM的扩展版本WACCM-X被用于研究此类影响，因此有一个直接的工作途径使空间天气研究界受益。该奖项反映了NSF的法定使命，并被认为值得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来支持。