Diabatic processes modifying potential vorticity in a North Atlantic cyclone
Diabatic processes modifying potential vorticity in a North Atlantic cyclone
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DOI：
10.1002/qj.2037
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发表时间：
2013-07
影响因子：
8.9
通讯作者：
J. Chagnon;S. Gray;J. Methven
中科院分区：
文献类型：
--
作者：
J. Chagnon;S. Gray;J. Methven
位涡（PV）由于其物质守恒和可逆性，简洁地描述了大尺度大气流动的演变。然而，温带气旋中的非绝热过程可以改变PV并影响中尺度天气和天气尺度波型的演变。在这项调查中，修改PV的非绝热过程诊断在气象局统一模式（MetUM）模拟的北大西洋气旋使用一组PV示踪剂。非绝热PV的结构内的热带气旋的调查和连接的过程负责它。在中尺度上，一个三极的非绝热PV产生的对流层顶褶皱向下延伸到冷锋。该结构的结果从偶极子在加热的正面界面，由于冷凝在温暖的传送带两侧的褶皱和蒸发的降水在干燥的侵入和下面的上侧。在与对流层顶相交的等熵面上，平流层一侧产生正的非绝热位涡，对流层一侧产生负的非绝热位涡。平流层非绝热PV主要由长波冷却产生，由于对流层顶的湿度梯度很大，长波冷却在对流层顶达到峰值。对流层非绝热PV局部来源于长波辐射，非局部来源于与大尺度云、对流和边界层方案相关的加热顶部的平流。在大多数地区，对流层顶本身的位涡没有非绝热修正，但非绝热位涡异常会通过它们诱导的风和随后的平流间接影响对流层顶。讨论了这种非绝热PV偶极子对天气尺度波型演变的影响。
Potential vorticity (PV) succinctly describes the evolution of large‐scale atmospheric flow because of its material conservation and invertibility properties. However, diabatic processes in extratropical cyclones can modify PV and influence both mesoscale weather and the evolution of the synoptic‐scale wave pattern. In this investigation, modification of PV by diabatic processes is diagnosed in a Met Office Unified Model (MetUM) simulation of a North Atlantic cyclone using a set of PV tracers. The structure of diabatic PV within the extratropical cyclone is investigated and linked to the processes responsible for it. On the mesoscale, a tripole of diabatic PV is generated across the tropopause fold extending down to the cold front. The structure results from a dipole in heating across the frontal interface due to condensation in the warm conveyor belt flanking the upper side of the fold and evaporation of precipitation in the dry intrusion and below. On isentropic surfaces intersecting the tropopause, positive diabatic PV is generated on the stratospheric side, while negative diabatic PV is generated on the tropospheric side. The stratospheric diabatic PV is generated primarily by long‐wave cooling which peaks at the tropopause itself due to the sharp gradient in humidity there. The tropospheric diabatic PV originates locally from the long‐wave radiation and non‐locally by advection out of the top of heating associated with the large‐scale cloud, convection and boundary layer schemes. In most locations there is no diabatic modification of PV at the tropopause itself but diabatic PV anomalies would influence the tropopause indirectly through the winds they induce and subsequent advection. The consequences of this diabatic PV dipole for the evolution of synoptic‐scale wave patterns are discussed.