Diabatic generation of negative potential vorticity and its impact on the North Atlantic jet stream
Diabatic generation of negative potential vorticity and its impact on the North Atlantic jet stream
复制标题
负位涡的非绝热产生及其对北大西洋急流的影响
DOI：
10.1002/qj.3747
复制
发表时间：
2020
影响因子：
8.9
通讯作者：
Harvey B
中科院分区：
文献类型：
--
作者：
Harvey B
在分析和预报产品中，经常在对流层上层急流的赤道侧看到局域负位涡（PV）。它们的位置位于急流的反气旋一侧，通常靠近急流核心，这表明它们与急流最大风速的增强有关。鉴于北半球的PV通常为正，并且在绝热条件下物质上保持不变，负PV的存在表明最近的绝热活动。然而，对其产生的机制和随后的影响了解甚少。在本文中，利用最近一次野外活动的飞机测量结果，为对流层上层急流反气旋侧存在负PV提供了直接观测证据。然后发展理论来理解PV变为负值的过程。关键因素是在垂直风切变存在下的绝热加热，由此产生的PV异常通常是由PV通量“沿等熵斜率向下”引起的。这就解释了为什么在温暖传送带中加热的典型情况下，在靠近喷流核心的对流层上层急流的赤道侧出现负PV值。这些想法用半地转模型来说明，并使用具有在线PV示踪剂诊断的操作预测模型来探索导致观测到的负PV的过程。对急流风和切变的非绝热影响是人们感兴趣的，因为它与极端急流事件和相关飞行水平湍流的可预测性有关，并且对罗斯比波在对流层顶的传播、中纬度天气系统的发展及其随后在地面的影响至关重要。
Localised regions of negative potential vorticity (PV) are frequently seen on the equatorward flank of the upper‐tropospheric jet streams in analysis and forecast products. Their positioning, on the anticyclonic side of the jet and often close to the jet core, suggest they are associated with an enhancement of jet stream maximum winds. Given that PV is generally positive in the northern hemisphere and is materially conserved under adiabatic conditions, the presence of negative PV is indicative of recent diabatic activity. However, little is understood on the mechanisms for its generation and subsequent impacts. In this paper, aircraft measurements from a recent field campaign are used to provide direct observational evidence for the presence of negative PV on the anticyclonic side of an upper‐tropospheric jet. Theory is then developed to understand the process by which PV can turn negative. The key ingredient is diabatic heating in the presence of vertical wind shear, and the resulting PV anomalies are shown to always result from a flux of PV directed “down the isentropic slope”. This explains why, for the typical situation of heating in a warm conveyor belt, negative PV values appear on the equatorward side of the upper‐tropospheric jet stream close to the jet core. These ideas are illustrated with a semi‐geostrophic model and the processes responsible for the observed negative PV are explored using an operational forecast model with online PV tracer diagnostics. The diabatic influence on jet stream winds and shear is of interest because it is pertinent to the predictability of extreme jet stream events and associated flight‐level turbulence, and is crucial to the propagation of Rossby waves at tropopause level, development of midlatitude weather systems and their subsequent impacts at the surface.
登录
查看更多内容
影响因子：
8.9
作者：
C. Grams;H. Wernli;M. Böttcher;J. Čampa;U. Corsmeier;S. Jones;J. Keller;C. Lenz;L. Wiegand-
通讯作者：
C. Grams;H. Wernli;M. Böttcher;J. Čampa;U. Corsmeier;S. Jones;J. Keller;C. Lenz;L. Wiegand-
影响因子：
8.9
作者：
J. Chagnon;S. Gray;J. Methven
通讯作者：
J. Chagnon;S. Gray;J. Methven
影响因子：
8.9
作者：
O. Martínez‐Alvarado;H. Joos;J. Chagnon;Maxi Boettcher;S. Gray;R. Plant;J. Methven;H. Wernli
通讯作者：
H. Wernli
与参数化物理过程的影响相比，动力核心的位涡不守恒
影响因子：
8.9
作者：
L. Saffin;J. Methven;S. Gray
通讯作者：
S. Gray
北极对流层顶褶皱
DOI：
--
发表时间：
1987
期刊：
影响因子：
--
作者：
M. Shapiro;T. Hampel;A. Krueger
通讯作者：
A. Krueger