Convective destabilization by a tropopause fold diagnosed using potential-vorticity inversion
Convective destabilization by a tropopause fold diagnosed using potential-vorticity inversion
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DOI：
10.1002/qj.49712656207
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发表时间：
2000-01-01
影响因子：
8.9
通讯作者：
Browning, KA
中科院分区：
文献类型：
--
作者：
Griffiths, M;Thorpe, AJ;Browning, KA
有观测证据表明，当热带气旋的对流层顶褶皱下降到对流层中部时，对流层下部经常会出现不稳定，形成湿对流。在这里，我们认为这样的联系使用所谓的位涡（PV）属性概念的动力学原因。特别是PV反演被用来找到风切变归因于对流层顶折叠本身。然后，该剪切用于量化产生潜在不稳定区域的趋势。对于一个温和的对流层顶褶皱的观测情况下，它被发现，包含在对流层顶褶皱的PV异常贡献了大量的瞬时对流不稳定的意义上增加潜在的不稳定。事实上，在某些地方，它克服了没有褶皱的大气稳定的趋势。另一方面，只有一小部分的区域增加潜在的不稳定性经历了足够的大规模上升，导致对流，它仍然有待观察是否折叠一般作出重大贡献的潜在的不稳定性，实际上可以实现的产生。对流层顶褶皱的重要性，或者说对流层顶低压在对流背景下的重要性，在于它们的水平尺度很小，有可能在局部集中和放大任何对流不稳定。这可能解释了强对流天气爆发的局部性，这对准确预报具有重要意义。目前的数值天气预报模式往往不能非常准确地处理这些小尺度。
There is observational evidence to suggest that at the time tropopause folds in extra-tropical cyclones are descending into the mid troposphere there is frequently a destablization of the lower troposphere to moist convection. Here we consider the dynamical reasons for such a linkage using so-called potential vorticity (PV) attribution concepts. In particular PV inversion is used to find the wind shear attributable to the tropopause fold itself. Then this shear is used to quantify the tendency to generate regions of potential instability. For an observed case of a modest tropopause fold it is found that the PV anomaly contained in the tropopause fold contributed substantially to the instantaneous convective destabilization in the sense of increasing the potential instability. Indeed, at some locations, it overcame a tendency to stabilize by the atmosphere without the fold. On the other hand, only a fraction of the region with increased potential instability experienced sufficient large-scale ascent to lead to convection and it remains to be seen whether folds in general make a significant contribution to the generation of potential instability that can actually be realized. The importance of tropopause folds, or indeed of tropopause depressions in general in the context of convection, is that their small horizontal scale has the potential to focus and amplify any convective destabilization locally. This may account for the localization of outbreaks of severe convective weather which it is important to forecast accurately. Currently numerical weather-prediction models often do not handle these small scales very accurately.