Gravity-wave-induced perturbations in marine stratocumulus
Gravity-wave-induced perturbations in marine stratocumulus
复制标题
重力波引起的海洋层积云扰动
DOI：
10.1002/qj.1952
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发表时间：
2012
影响因子：
8.9
通讯作者：
Allen G
中科院分区：
文献类型：
--
作者：
Allen G
我们讨论了大气重力波在调制东南太平洋云辐射和动力学特性中的作用。 2008 年 10 月期间的卫星图像和卫星检索的云特性显示了重力波列穿过覆盖当地海洋边界层的大规模层积云 (Sc) 云层的三个不同的水平传播过程。在2008年10月7日至9日的一个时期内，波浪将云顶高度调制了高达400 m的峰谷，垂直于天气边界层流传播，相速度为15.3 m s−1，周期为∼1 h，水平波长为55 km。观察到重力波是非色散的。这些波浪首先在 2008 年 10 月 7 日中午开始的 24 小时内出现在南纬 30°、西经 85° 附近的云层中，并在接下来的 48 小时内向东北向秘鲁海岸传播。在此期间，它们引起了云辐射和云动力学特性的可逆和不可逆变化，使得晴空区域在经过的波前的波谷中形成。这些开放单元在重力波通过后仍持续存在很长一段时间，并随背景风向西北平流。利用欧洲中期天气预报中心的分析领域并结合红外和微波卫星图像，我们表明这些重力波是从受干扰的副热带急流中产生的。在所有情况下，波浪的辐射点都与非线性平衡中的大负残差中心重合，这表明与扰动射流相关的急剧发散流的地转调整提供了波浪能量的来源。相反，在更静止的射流条件下没有观察到重力波。本案例研究强调了在对流层中传播的重力波可能对大范围区域的云辐射特性（以及表面辐射预算）产生重要且不可逆的影响。它还强调了天气影响对钪覆盖的海洋边界层的重要性。版权所有 © 2012 英国皇家气象学会
We discuss the role of atmospheric gravity waves in modulating cloud radiative and dynamical properties over the southeast Pacific. Satellite imagery and satellite‐retrieved cloud properties during October 2008 illustrate three distinct episodes of horizontal propagation of gravity wave trains across the large‐scale stratocumulus (Sc) cloud deck capping the local marine boundary layer. In one period, 7–9 October 2008, the waves modulated cloud‐top‐height by up to 400 m peak‐to‐trough, propagating perpendicular to the synoptic boundary layer flow with phase speed 15.3 m s−1, period ∼1 h and horizontal wavelength 55 km. The gravity waves were observed to be non‐dispersive. These waves were first evident in the cloud deck near 30°S, 85°W during a 24 h period beginning at midday on 7 October 2008, and propagated northeastward toward the Peruvian coast for the following 48 h. During this time they induced both reversible and non‐reversible changes in cloud‐radiative and cloud‐dynamic properties, such that areas of clear sky developed in the troughs of passing wave‐fronts. These pockets of open cells persisted long after the passage of the gravity waves, advecting northwestward with the background wind. Using the analysis fields of the European Centre for Medium‐Range Weather Forecasts in conjunction with infrared and microwave satellite imagery, we show that these gravity waves emerged from a disturbed subtropical jet stream. The radiant of the waves was coincident in all cases with centres of large negative residuals in nonlinear balance, suggesting that geostrophic readjustment of sharply divergent flows associated with the disturbed jet provided a source for the wave energy. Conversely, gravity waves were not observed in more quiescent jet conditions. This case study highlights the important and irreversible effects that gravity waves propagating in the troposphere can have on cloud radiative properties (and hence surface radiation budgets) over a very wide area. It also highlights the importance of synoptic influence on Sc‐covered marine boundary layers. Copyright © 2012 Royal Meteorological Society