Examining the Connections between Observed Atmospheric Gravity Waves and Convective Clouds for Improved Climate Simulations

检查观测到的大气重力波和对流云之间的联系以改进气候模拟

• 批准号: 1519271
• 负责人: M Joan Alexander
• 金额: $ 48.98万
• 依托单位: NorthWest Research Associates, Incorporated
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-07-15 至 2019-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1519271&HistoricalAwards=false
• 关键词: Examining; Connections; between; Observed; Atmospheric

Waves in which buoyancy is the restoring force are referred to as gravity waves, and such waves are ubiquitous in the atmosphere. They occur over a broad range of spatial scales but are generally smaller than the frontal weather systems seen on weather maps. They can be generated by a variety of mechanisms including air flow over mountains, the formation of frontal systems, and the vertical motions that accompany convection. Despite their relatively small size, they are thought to play an important role in the atmospheric circulation due to their vertical flux of horizontal momentum, through which they drive the quasi-biennial oscillation in the equatorial stratosphere, modulate the strength of the midlatitude jet streams, and alter the strength of the stratospheric polar vortices, thereby playing a role in the seasonal evolution of the Southern Hemisphere ozone hole. But the small size of the waves and their relatively rapid propagation make it difficult to observe them and examine their generation, propagation, and impacts on the mean flow. Moreover, the waves cannot generally be simulated by global weather and climate models due to their small size, and instead they must represented through parameterizations which estimate their aggregate effects as a function of the resolved flow. While these parameterizations have become quite sophisticated, their validity is difficult to establish, and common circulation biases in models are often ascribed to inadequacies of the gravity wave parameterizations.Work under this award specifically addresses gravity waves generated by convection, motivated by recent observations from balloons and satellites suggesting that that large amplitude gravity waves, of the sort that come from vigorous, small-scale deep convection, account for a larger fraction of the gravity wave momentum flux than previously assumed. Further motivation comes from the availability of the record of tropical convection from the Tropical Rainfall Measurement Mission (TRMM), a satellite record which is now over a dozen years long and can be used to estimate the generation of gravity waves by tropical and subtropical convection. The data is used in conjunction with the gravity wave parameterization from the Community Atmosphere Model, along with observational wind and atmospheric stability data, to estimate the generation, propagation, and momentum flux of convectively generated gravity wave activity. The momentum flux is then compared with estimates calculated from the satellite record of atmospheric temperature from the satellite record of the Atmospheric Infrared Sounder (AIRS). The goal of this effort is to reconcile the large-scale patterns in gravity wave activity observed in the tropics and subtropics with existing knowledge of their convective sources, based on a theoretical understanding of their propagation and mean flow interaction. The reconciliation is expected to require some ad hoc adjustment of free parameters in the parameterization scheme, and the PIs will conduct further experiments to determine how this "tuning" of the parameterization affects the large-scale atmospheric simulation produced by the model. Some work will also consider the generation of gravity waves by convection occurring in the storm tracks of the middle latitudes, using other data sources to estimate convection.The work has broader impacts due to the need for accurate gravity wave parameterizations in weather and climate models. These models are widely used as research tools for a variety of applications, and are also used to provide information to first responders, decision makers, and the general public. In addition, the project supports and trains a graduate student, thereby providing for the future workforce in this research area.

以浮力为恢复力的波称为重力波，这种波在大气中普遍存在。 它们出现在广泛的空间尺度上，但通常比天气图上看到的锋面天气系统要小。 它们可以由多种机制产生，包括气流越过山脉，锋面系统的形成以及伴随对流的垂直运动。 尽管它们的尺寸相对较小，但由于其水平动量的垂直通量，它们被认为在大气环流中发挥重要作用，通过这种通量，它们驱动赤道平流层的准两年振荡，调节中纬度急流的强度，并改变平流层极涡的强度，从而在南半球臭氧洞的季节性演变中发挥作用。 但是，波的尺寸小，传播速度相对较快，因此很难观察它们，也很难检查它们的产生、传播和对平均流的影响。此外，波一般不能模拟全球天气和气候模式，由于其规模小，而是他们必须通过参数化，估计其总的影响，作为一个功能的解决流。 虽然这些参数化已经变得相当复杂，但它们的有效性很难建立，模型中常见的环流偏差通常归因于重力波参数化的不足。该奖项下的工作专门针对对流产生的重力波，受到最近气球和卫星观测的启发，这些观测表明大振幅重力波，小规模的深对流，占一个更大的比重波动量通量比以前假设的。 进一步的动机来自热带降雨测量使命（TRMM）的热带对流记录，这是一个卫星记录，现在已有十几年之久，可用于估计热带和亚热带对流产生的重力波。 这些数据与社区大气模型的重力波参数化结合使用，沿着观测风和大气稳定性数据，以估计对流产生的重力波活动的产生、传播和动量通量。 然后将动量通量与大气红外探测器（AIRS）卫星记录的大气温度卫星记录计算的估计值进行比较。 这项工作的目标是调和大规模的模式，在热带和亚热带地区观察到的重力波活动与现有的知识，其对流源，其传播和平均流相互作用的理论理解的基础上。 协调工作预计需要对参数化方案中的自由参数进行一些特别调整，研究员将进行进一步的实验，以确定参数化的这种“调整”如何影响模式产生的大规模大气模拟。 有些工作还将考虑在中纬度风暴路径上发生的对流产生重力波，使用其他数据来源估计对流，由于需要在天气和气候模型中精确地设定重力波参数，这项工作具有更广泛的影响。这些模型被广泛用作各种应用的研究工具，也用于向第一响应者，决策者和公众提供信息。 此外，该项目还支持和培训一名研究生，从而为该研究领域的未来劳动力提供支持。