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The Madden-Julian Oscillation : observation, modeling, and theory

Citation

Yang, Da (2014) The Madden-Julian Oscillation : observation, modeling, and theory. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechTHESIS:05232014-112348842

Abstract

The Madden-Julian Oscillation (MJO) is a pattern of intense rainfall and associated planetary-scale circulations in the tropical atmosphere, with a recurrence interval of 30-90 days. Although the MJO was first discovered 40 years ago, it is still a challenge to simulate the MJO in general circulation models (GCMs), and even with simple models it is difficult to agree on the basic mechanisms. This deficiency is mainly due to our poor understanding of moist convection—deep cumulus clouds and thunderstorms, which occur at scales that are smaller than the resolution elements of the GCMs. Moist convection is the most important mechanism for transporting energy from the ocean to the atmosphere. Success in simulating the MJO will improve our understanding of moist convection and thereby improve weather and climate forecasting.

We address this fundamental subject by analyzing observational datasets, constructing a hierarchy of numerical models, and developing theories. Parameters of the models are taken from observation, and the simulated MJO fits the data without further adjustments. The major findings include: 1) the MJO may be an ensemble of convection events linked together by small-scale high-frequency inertia-gravity waves; 2) the eastward propagation of the MJO is determined by the difference between the eastward and westward phase speeds of the waves; 3) the planetary scale of the MJO is the length over which temperature anomalies can be effectively smoothed by gravity waves; 4) the strength of the MJO increases with the typical strength of convection, which increases in a warming climate; 5) the horizontal scale of the MJO increases with the spatial frequency of convection; and 6) triggered convection, where potential energy accumulates until a threshold is reached, is important in simulating the MJO. Our findings challenge previous paradigms, which consider the MJO as a large-scale mode, and point to ways for improving the climate models.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:The Madden-Julian Oscillation; Atmospheric Convection; Equatorial Waves; Tropical Meteorology
Degree Grantor:California Institute of Technology
Division:Geological and Planetary Sciences
Major Option:Environmental Science and Engineering
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Ingersoll, Andrew P.
Thesis Committee:
  • Bordoni, Simona (chair)
  • Thompson, Andrew F.
  • Waliser, Duane E.
  • Ingersoll, Andrew P.
Defense Date:9 May 2014
Record Number:CaltechTHESIS:05232014-112348842
Persistent URL:http://resolver.caltech.edu/CaltechTHESIS:05232014-112348842
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1175/2010JAS3563.1PublisherArticle adapted for Ch. 2: Testing the Hypothesis that the MJO is a Mixed Rossby-Gravity Wave Packet
http:///dx.doi.org/10.1175/JAS-D-12-0255.1PublisherArticle adapted for Ch. 3: Triggered Convection, Gravity Waves, and the MJO: A Shallow-Water Model
http://dx.doi.org/10.1002/2013GL058542PublisherArticle adapted for Ch. 4: A theory of the MJO horizontal scale
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:8389
Collection:CaltechTHESIS
Deposited By: Da Yang
Deposited On:29 May 2014 21:36
Last Modified:29 Apr 2016 00:16

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