New approaches to investigate the influence of orographic and dynamic blocking on large-scale atmospheric flow

• Main Author: Spensberger, Clemens
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: The University of Bergen 2015
• Subjects: Meteorology; Atmospheric dynamics; Orographic blocking; Dynamic blocking; Rossby wave breaking; Numerical modelling; Quasi-geostrophy; Semi-geostrophy; Bedymo; Terrain-following coordinate; Jet streams; Storm track; Jet variability; Storm track variability; Jet axis; Deformation; Lee cyclogenesis; Arctic; Greenland; North Atlantic; North Atlantic oscillation
• Online Access: https://hdl.handle.net/1956/10589

Orographic and dynamic blocks have a profound influence on both weather and climate. The persistence of dynamic blocks can, for example, lead to the build-up of extreme temperature anomalies or droughts. In addition, previous studies linked dynamic blocks to Rossby wave breaking events, which can be associated with extreme precipitation. Dynamic blocks occur preferentially at certain locations, and therefore influence local climate. A important climatic effect of orographic blocks is to act as a temperaturebarriers. For example, the North-Atlantic would be significantly colder during winter if Greenland did not shield the North-Atlantic from the climatological cold pool over the Canadian Arctic. Thus, both types of blocking contribute to the zonal asymmetries in the climate and in the atmospheric circulation. Unfortunately, our understanding of the dynamics of both types of blocking is still far from complete. One of the main challenges in trying to grasp the essentials of blocking is the importance of non-linear effects. These effects are important, because the flow diversion around a block constitutes a large deviation from an unblocked basic state, such that the differences in the advection cannot be neglected. For that reason, previous studies proposed different indicators to capture the transition from linear flow over to non-linear flow around orography. Despite this effort, none of the proposed indicators is generally applicable. Furthermore, it is unclear how dynamic blocks interact with breaking Rossby waves and whether variability indexes like the North-Atlantic Oscillation are resulting from variability of blocking and/or wave breaking. In this thesis, I pursue three novel approaches to enhance the understanding of blocking. First, I demonstrate that deformation is a suitable diagnostic for detecting and quantifying the magnitude of orographic and dynamic blocks. Consequently, deformation helps to investigate the splitting of synoptic systems at the Rocky-Mountain barrier. Furthermore, I show that the ...