Bramberger Martina, Alexander M Joan, Grimsdell Alison W
NorthWest Research Associates Boulder CO USA.
J Adv Model Earth Syst. 2020 Aug;12(8):e2019MS001949. doi: 10.1029/2019MS001949. Epub 2020 Jul 29.
Gravity waves (GWs) generated by tropical convection are important for the simulation of large-scale atmospheric circulations, for example, the quasi-biennial oscillation (QBO), and small-scale phenomena like clear-air turbulence. However, the simulation of these waves still poses a challenge due to the inaccurate representation of convection, and the high computational costs of global, cloud-resolving models. Methods combining models with observations are needed to gain the necessary knowledge on GW generation, propagation, and dissipation so that we may encode this knowledge into fast parameterized physics for global weather and climate simulation or turbulence forecasting. We present a new method suitable for rapid simulation of realistic convective GWs. Here, we associate the profile of latent heating with two parameters: precipitation rate and cloud top height. Full-physics cloud-resolving WRF simulations are used to develop a lookup table for converting instantaneous radar precipitation rates and echo top measurements into a high-resolution, time-dependent latent heating field. The heating field from these simulations is then used to force an idealized dry version of the WRF model. We validate the method by comparing simulated precipitation rates and cloud tops with scanning radar observations and by comparing the GW field in the idealized simulations to satellite measurements. Our results suggest that including variable cloud top height in the derivation of the latent heating profiles leads to better representation of the GWs compared to using only the precipitation rate. The improvement is especially noticeable with respect to wave amplitudes. This improved representation also affects the forcing of GWs on large-scale circulation.
热带对流产生的重力波（GWs）对于模拟大规模大气环流，例如准两年振荡（QBO），以及诸如晴空湍流等小尺度现象非常重要。然而，由于对流的表示不准确以及全球云分辨模型的高计算成本，这些波的模拟仍然是一个挑战。需要将模型与观测相结合的方法，以获取关于重力波产生、传播和耗散的必要知识，以便我们可以将这些知识编码到用于全球天气和气候模拟或湍流预测的快速参数化物理过程中。我们提出了一种适用于快速模拟真实对流重力波的新方法。在这里，我们将潜热加热廓线与两个参数相关联：降水率和云顶高度。使用全物理云分辨WRF模拟来开发一个查找表，用于将瞬时雷达降水率和回波顶测量值转换为高分辨率、随时间变化的潜热加热场。然后，这些模拟的加热场被用于强迫WRF模型的理想化干版本。我们通过将模拟的降水率和云顶与扫描雷达观测结果进行比较，以及将理想化模拟中的重力波场与卫星测量结果进行比较来验证该方法。我们的结果表明，与仅使用降水率相比，在潜热加热廓线的推导中纳入可变云顶高度能够更好地表示重力波。这种改进在波幅方面尤为明显。这种改进的表示也会影响重力波对大规模环流的强迫作用。
