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Si us plau utilitzeu sempre aquest identificador per citar o enllaçar aquest document: https://hdl.handle.net/2445/102496
Subsynoptic characterization of tropopause fold structure with glogal data anlyses and mesoscale WRF simulations
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[eng] In this work, a subsynoptic characterization of tropopause fold structures is derived from one-year of global, high resolution GFS (Global Forecasting System, 0.3 degrees) data analyses and 10 years of daily WRF (Weather Reasearch and Forecasting) mesoscale simulations at 30 km resolution initialized with the Japanese 25-year Re-Analysis (JRA-25, 1.125 degrees). The dynamical tropopause, defined as a constant potential vorticity surface (2 PVU), is an important meteorological concept that under adiabatic and frictionless conditions acts as a material barrier between the troposphere and the stratosphere. Deformations of this layer such as foldings have a relevant influence on midlatitude weather systems and are a major mechanism of extratropical stratosphere-troposphere exchange. In the vicinity of these stratospheric intrusions, large vertical and horizontal gradients of Potential Vorticity (PV) are found, so that high resolution data is required for a direct characterization of these structures. Based on a geometric definition of tropopause folds, a novel objective algorithm has been developed and applied over the 6-hour meteorological fields to unambiguously detect the presence of a folded dynamical tropopause. The methodology applied requires no assumptions on the dynamical origin of the folding, and it registers the main geometric features of each individual folded grid structure such as its horizontal dimensions, depth of penetration, thickness or the gap relative to the upper tropopause. The application of the fold detection algorithm has served to characterize the geographical distribution of folding features on a global basis using one year of GFS data, and on a regional basis using a more robust 10-year WRF climatology over Southwest Europe. The analysis corroborates the differences between subtropics and extratropics in tropopause fold characteristics and formation, and serves to identify the main synoptic upper-level scenarios that drive the intensification of these structures. The geographical distribution and annual variability of stratospheric intrusions detected with the GFS analyses are in line with existing climatologies, supporting the competence of the fold searching algorithm, but providing a more detailed portrait through the higher resolution of the GFS data. The 10-year WRF tropopause fold climatology shows a general good agreement with the one-year GFS observations, although WRF tropopause fold frequencies appear to be lower on average. This can be partly attributed to interannual variability, and partly to underestimation of the total folded area simulated by WRF relative to that observed by GFS, as revealed in individual tropopause fold case studies. Additionally, a product that uses a combination of geometric tropopause fold parameters has been generated (Stratosphere-Troposphere Transport Folding Index, STTFI) to estimate the regions of the globe where the largest amounts of stratospheric air are most likely to be irreversibly transferred into the troposphere due to deep tropopause fold intrusions. Despite its simplicity, the STTFI reproduces the most important features captured in existing Stratosphere-Troposphere Transport (SST) climatologies based on Lagrangian trajectory techniques. Finally, a detailed evaluation on the WRF model ability to simulate tropopause folds has been performed over an entire year (December 2007 - November 2008), with an eye at establishing the role of resolution enhancements at improving their simulation. Qualitative and quantitative comparisons between WRF results and both the initial JRA data and the GFS analyses have been performed over tropopause fold frequencies and individual tropopause fold events. The comparison demonstrates that the WRF forcing is in general able to forecast the main mesoscale features of the tropopause folds, significantly improving their representation with respect to the JRA coarse description of the initial state, particularly at midlatitudes. However, it has been observed that a poor definition of the initial conditions can be an important obstacle in tropopause fold performance, particularly under certain circumstances (e.g. rapidly traveling perturbations entering the domain) in some specific areas (e.g. close to the border of the simulation domain).
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MATEU I SANTAEULÀRIA, Mireia. Subsynoptic characterization of tropopause fold structure with glogal data anlyses and mesoscale WRF simulations. [consulta: 24 de novembre de 2025]. [Disponible a: https://hdl.handle.net/2445/102496]