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Storm track response to perturbations in climate

Citation

Mbengue, Cheikh Oumar (2015) Storm track response to perturbations in climate. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z9FT8J05. http://resolver.caltech.edu/CaltechTHESIS:05112015-075223217

Abstract

This thesis advances our understanding of midlatitude storm tracks and how they respond to perturbations in the climate system. The midlatitude storm tracks are regions of maximal turbulent kinetic energy in the atmosphere. Through them, the bulk of the atmospheric transport of energy, water vapor, and angular momentum occurs in midlatitudes. Therefore, they are important regulators of climate, controlling basic features such as the distribution of surface temperatures, precipitation, and winds in midlatitudes. Storm tracks are robustly projected to shift poleward in global-warming simulations with current climate models. Yet the reasons for this shift have remained unclear. Here we show that this shift occurs even in extremely idealized (but still three-dimensional) simulations of dry atmospheres. We use these simulations to develop an understanding of the processes responsible for the shift and develop a conceptual model that accounts for it.

We demonstrate that changes in the convective static stability in the deep tropics alone can drive remote shifts in the midlatitude storm tracks. Through simulations with a dry idealized general circulation model (GCM), midlatitude storm tracks are shown to be located where the mean available potential energy (MAPE, a measure of the potential energy available to be converted into kinetic energy) is maximal. As the climate varies, even if only driven by tropical static stability changes, the MAPE maximum shifts primarily because of shifts of the maximum of near-surface meridional temperature gradients. The temperature gradients shift in response to changes in the width of the tropical Hadley circulation, whose width is affected by the tropical static stability. Storm tracks generally shift in tandem with shifts of the subtropical terminus of the Hadley circulation.

We develop a one-dimensional diffusive energy-balance model that links changes in the Hadley circulation to midlatitude temperature gradients and so to the storm tracks. It is the first conceptual model to incorporate a dynamical coupling between the tropical Hadley circulation and midlatitude turbulent energy transport. Numerical and analytical solutions of the model elucidate the circumstances of when and how the storm tracks shift in tandem with the terminus of the Hadley circulation. They illustrate how an increase of only the convective static stability in the deep tropics can lead to an expansion of the Hadley circulation and a poleward shift of storm tracks.

The simulations with the idealized GCM and the conceptual energy-balance model demonstrate a clear link between Hadley circulation dynamics and midlatitude storm track position. With the help of the hierarchy of models presented in this thesis, we obtain a closed theory of storm track shifts in dry climates. The relevance of this theory for more realistic moist climates is discussed.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:storm tracks, climate change, extratropics, Hadley cell, tropical-extratropical interaction, extratropical circulation
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Aeronautics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Schneider, Tapio
Thesis Committee:
  • Meiron, Daniel I. (chair)
  • McKeon, Beverley J.
  • Ravichandran, Guruswami
  • Teixeira, Joao
  • Schneider, Tapio
Defense Date:6 May 2015
Non-Caltech Author Email:C.Mbengue (AT) wolfson.oxon.org
Funders:
Funding AgencyGrant Number
NSFAGS-1019211
Record Number:CaltechTHESIS:05112015-075223217
Persistent URL:http://resolver.caltech.edu/CaltechTHESIS:05112015-075223217
DOI:10.7907/Z9FT8J05
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1175/JCLI-D-13-00404.1DOIArticle adapted for ch. 2
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:8854
Collection:CaltechTHESIS
Deposited By: Cheikh Mbengue
Deposited On:19 May 2015 16:29
Last Modified:12 Apr 2016 17:39

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