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Analysis of Tropopause Variability in Observations and in an Idealized Model

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Analysis of Tropopause Variability in Observations and in an Idealized Model UNIVERSIDAD COMPLUTENSE DE MADRID FACULTAD DE CIENCIAS FÍSICAS Departamento de Física de la Tierra, Astronomía y Astrofísica I (Geofísica y Meteorología) TESIS DOCTORAL Analysis of tropopause variability in observations and in an idealized model Análisis de la variabilidad de la tropopausa en observaciones y en un modelo idealizado MEMORIA PARA OPTAR AL GRADO DE DOCTOR PRESENTADA POR Jesús Ángel Barroso Pellico Director Pablo Zurita Gotor Madrid, 2018 © Jesús Ángel Barroso Pellico, 2017 Universidad Complutense de Madrid Facultad de Ciencias Físicas Departamento de Física de la Tierra, Astronomía y Astrofísica I (Geofísica y Meteorología) Analysis of tropopause variability in observations and in an idealized model Análisis de la variabilidad de la tropopausa en observaciones y en un modelo idealizado Memoria para optar al grado de doctor presentada por Jesús Ángel Barroso Pellico Director: Pablo Zurita Gotor III IV Contents Summary.......................................................................................................... VII Resumen.......................................................................................................... XI List of abbreviations......................................................................................... XIV 1. Introduction and objectives.................................................................................. 1 1.1 Properties of the tropopause.......................................................................................3 1.1.1 Definitions of the tropopause......................................................................... 4 1.1.1.1 Thermal tropopause............................................................................... 4 1.1.1.2 Dynamical tropopause.......................................................................... 6 1.1.1.3 Chemical tropopause............................................................................. 8 1.1.2 Meridional structure of the tropopause........................................................ 10 1.1.3 Tropopause Inversion Layer........................................................................... 13 1.1.4 Variability of tropopause pressure................................................................. 14 1.2 Theories on the average height of the tropopause................................................... 18 1.3 Brewer-Dobson Circulation……………………………………………………………………………….. 23 1.3 Motivation and objectives.......................................................................................... 25 1.4 Thesis outline............................................................................................................. 27 2. Data: radiosondes, reanalysis and model....................................................... 29 2.1 IGRA dataset............................................................................................................... 30 2.2 NCEP/NCAR reanalysis............................................................................................. 36 2.3 ERA-interim reanalysis.............................................................................................. 39 2.4 The idealized model.................................................................................................. 42 3. Methodology................................................................................................. 51 3.1 Tropopause height determination............................................................................. 51 3.2 Tropopause-based coordinates................................................................................. 54 3.3 Time-series analysis................................................................................................... 55 3.31 Anomalies........................................................................................................ 55 3.3.2 Time filtering................................................................................................. 56 V 3.4 Principal Component Analysis................................................................................. 59 3.5 Composite and regression maps............................................................................... 62 3.6 Eddy and Eliassen-Palm fluxes................................................................................. 63 4. Objective definitions for the tropopause....................................................... 71 4.1 Optimal thermal tropopause.................................................................................... 71 4.1.1 Definitions of the thermal tropopause......................................................... 71 4.1.2 Critical lapse rate of maximum curvature................................................... 74 4.1.3. Lapse rate distribution near the tropopause level...................................... 77 4.2 Maximum-curvature tropopause............................................................................. 79 4.3 Maximum-stratification tropopause........................................................................ 83 4.4 Discussion.................................................................................................................. 86 5. Seasonal variability of the extratropical tropopause...................................... 91 5.1 Seasonal cycle in the reanalysis................................................................................. 93 5.1.1 Observed characteristics of the seasonal cycle............................................. 93 5.1.2 Forcings of the seasonal cycle....................................................................... 96 5.2 Seasonal cycle in the idealized model...................................................................... 98 5.2.1 Description of the simulations...................................................................... 98 5.2.2 Tropospheric seasonal cycle and orographic influences............................. 99 5.2.2.1 Characteristics of the seasonal cycles.................................................... 99 5.2.2.2 Dynamical analysis of the seasonal cycles............................................ 104 5.3 Discussion.................................................................................................................. 107 6. Intraseasonal variability of the extratropical tropopause............................... 111 6.1 Modes of variability of the extratropical tropopause............................................... 112 6.2 Dynamical analysis of the intraseasonal variability................................................ 115 6.2.1 Composite eddy forcing................................................................................ .115 6.2.2 Forcings on tropopause variability............................................................... 121 6.3 Modes of variability in the idealized model............................................................ 124 6.3.1 Description of the simulations...................................................................... 124 6.3.2 Analysis of the modes of variability.............................................................. 125 VI 6.4 Intraseasonal variability of the extratropical-mean tropopause............................ 131 6.5 EOFs of the SH tropopause...................................................................................... 134 6.6 Discussion................................................................................................................. 137 7. Concluding remarks...................................................................................... 141 References........................................................................................................ 144 List of publications and meeting contributions…………………………………………………...162 VII Summary Introduction The focus of this thesis is the study of the extratropical tropopause. The tropopause is a distinctive feature of the vertical structure of the atmosphere, separating two regions, troposphere and stratosphere, with very different dynamical and chemical characteristics. The abrupt change in air properties found when moving from one layer to another serves as the basis for a wide variety of definitions. The first and most widely used definition is the thermal tropopause, based on the discontinuity in the lapse-rate. The dynamical tropopause is based on the discontinuity in the isentropic potential vorticity. Chemical definitions are also possible, based on the discontinuity in the concentration of tracer gases above and below the tropopause. The greatest variability in tropopause height is found in midlatitudes in synoptic scales, associated with the potential vorticity anomalies caused by the eddies at levels close to the tropopause. Seasonal variability, of lesser amplitude, has the form of a single wave in midlatitudes of both hemispheres and in the southern polar latitudes -where the cycle is inverted with respect to midlatitudes, while some regions of the Arctic exhibit a double-wave seasonal cycle. Previous studies attributed this interhemispheric asymmetry to the different strength of the residual circulation in both hemispheres, due to the different land-sea distributions. The tropopause has been traditionally explained as the transition from a stratospheric temperature profile in radiative equilibrium to a dynamically adjusted profile in the troposphere. Radiative-convective models seem to work well for the tropical regions, while in the extratropics it is less clear which dynamical
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