The evolution of the Brewer-Dobson circulation and the ozone layer during the last three decades

• Autores: Albert Ossó Castillón
• Directores de la Tesis: Jeroni Lorente Castelló (dir. tes.)
• Lectura: En la Universitat de Barcelona ( España ) en 2014
• Idioma: inglés
• Tribunal Calificador de la Tesis: David Thompson (presid.), Ileana Blade Mendoza (secret.), Alvaro Corral Cano (voc.)
• Materias:
  • Ciencias de la tierra y del espacio
    • Ciencias de la atmósfera
      • Química atmosférica
      • Dinámica atmosférica
    • Climatología
      • Climatología analítica
      • Climatología física
• Enlaces
  • Tesis en acceso abierto en:  TDX  Dipòsit Digital de la UB  TESEO 
• Resumen

  • In 1985 Joseph Farman and his colleagues of the British Antarctic Survey published a paper [Farman et al. 1985] showing that the total ozone content of the atmosphere during the Antarctic spring had decreased dramatically between 1975 and 1984. Subsequent studies confirmed this decrease and the term Antarctic ozone hole became popular. The occurrence of this phenomenon revitalized the interest of the climate community in the stratosphere. Since then many remarkable advances have been made in our understanding of stratospheric processes. These advances have been possible by the advent of remote sensing measurements of the atmosphere together with the sophistication of the atmospheric simulations. Nowadays it is known that stratospheric climate is determined by a complex coupling of dynamic, radia­tive and chemical processes.The view of the stratosphere as an isolated layer have changed completely and today it is widely accepted that both the tropospheric pro­cesses a.ect the stratospheric climate, and the other way around, the stratospheric processes a.ect the climate in the troposphere. Despite all the progresses made, our knowledge is far to be complete. There are still large uncertainties about how climate change is a.ecting the stratosphere and to what extent it will in.uence the stratospheric ozone recovery. Moreover recent studies [e.g., Thompson et al. 2012] evidenced that there are important discrepancies among observational data sets and between observations and numerical simulations of recent stratospheric temperature trends. OVERVIEW The aim of this thesis is to contribute on the understanding of the past evolution of the ozone layer and the Brewer-Dobson circulation. With this objective the following question will be addressed: 1. To what extent are the long-term trends of total ozone a.ected by the North Atlantic Oscillation (NAO) during winter and summer seasons? 2. How robust are the observed trends in the Brewer-Dobson Circulation (BDC)? 3. Is the current generation of coupled atmosphere-ocean global circulation mod­els (AOGCMs) and coupled climate-chemistry models (CCMs) reproducing the observed stratospheric temperature trends over the last three decades? Chapter 1 presents an introduction to the basic concepts that are transverse to chapter 2 and chapter 3. First, a description of the mean state of the stratosphere is provided. Then, an introducing of the basic equations used to describe the strato­sphere followed by a description of the mechanisms involve in the troposphere­stratosphere exchange processes is presented. Finally a description of the basic processes involved in the production, transport and destruction of ozone are re­viewed. Chapter 2 deals with question 1 and is built on the bases of the article Ossó et al. [2012]. In this chapter the in.uence of the North Atlantic Oscillation on the total ozone content of the atmosphere is examined during winter and summer seasons. Chapter 3 deals with questions 2 and is built on the bases of the article Ossó et al. [2014]. First, a brief review of our current understanding of the stratospheric temperature trends is provided. Then, residual vertical velocity trends and temper­ature trends from the CCM WACCM output is examined. Finally, stratospheric temperatures are used to infer trends in the BDC during the last 3 decades. Chapter 4 presents a brief discussion on the performance of the current AOGCMs and CCMs on reproducing the stratospheric temperature trends derived from ob­servation. Finally a summary and outlook of the thesis is provided in chapter 5. This PhD study is primary built on the following peer-reviewed publications: • Ossó, A., Y. Sola, J. Bech, and J. Lorente, 2011: Evidence for the in.uence of the NAO on total ozone column at northern low-and mid-latitudes during winter and summer seasons. J. Geophys. Res., 116, D24. • Ossó, A., Y. Sola, K. Rosenlof, B. Hassler, J. Bech, J. Lorente, 2014: How robust are trends in the Brewer-Dobson Circulation derived from observed stratospheric temperatures? (Submitted to Journal of Climate 04-17-2014). • Thompson, D.W.J., D.J. Seidel, W.J. Randel, C. Zou, A.H. Butler, C. Mears, A.Ossó, C. Long, R. Lin, 2012: The mystery of recent stratospheric tempera­ture trends. Nature 491, 692–697. Other contributions made during this thesis: • Bech J., Y. Sola, A. Ossó, J. Lorente, 2014: Analysis of 14 years of broadband ground based solar UV index observations in Barcelona. Int. J. Climatol. • Sola, Y., J. Lorente, A. Ossó, 2012: Analyzing UV-B narrowband solar irra­diance: Comparison with erythemal and vitamin D production irradiances. Journal of Photochem.Photobiol. B 117, 90-96.