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Moist static energy and the Madden-Julian oscillation: understanding initiation, maintenance and propagation through the application of novel diagnostics

Date

2014

Authors

Wolding, Brandon, author
Maloney, Eric, advisor
Johnson, Richard, committee member
Cooley, Dan, committee member

Journal Title

Journal ISSN

Volume Title

Abstract

As the dominant mode of tropical intraseasonal variability, the Madden-Julian Oscillation (MJO) has enormous societal impacts. Despite four decades of research motivated by these impacts, the processes that drive the initiation, maintenance and propagation of the MJO are still poorly understood. The development of large scale moisture anomalies plays an important role in many recent theories of the MJO, including moisture mode theory. This study identifies processes that support the development, maintenance and propagation of moisture anomalies associated with the MJO. A new set of objective MJO diagnostics, obtained as an extension of CEOF analysis, are introduced. These diagnostics provide useful measures of previously overlooked information yielded by CEOF analysis, including an objective measure that allows geographically disparate locations to be compared and contrasted throughout a reference MJO lifecycle. Compositing techniques based on this measure are applied to the MJO in an attempt to determine key physical processes affecting the MSE budget, identify prominent geographical variability of these processes, and highlight changes in the mean state winds and moisture field that explain this variability. The MSE budget reveals that variations in MSE associated with the MJO are largely the result of variations in column integrated moisture content (~90%), the majority of which occur between 850-500 hPa (~75%). Easterly(westerly) low level wind anomalies to the east(west) of the MJO result in a reduction(enhancement) of drying due to horizontal advection, which is only partially offset by a reduction(enhancement) of surface latent heat flux. In the deep tropics (5°N-5°S) of the eastern hemisphere, anomalous horizontal advection is primarily the result of the anomalous winds acting on the mean state moisture gradient. Over the broader tropics (15°N-15°S), the anomalous horizontal advection appears to result primarily from the modulation of synoptic scale eddy activity. The incomplete cancelation that occurs between anomalous horizontal advection and anomalous surface latent heat flux allows for the enhancement(reduction) of MSE to the east(west) of the MJO, enhancing(reducing) convection and helping drive propagation of the MJO. Anomalous vertical moisture advection is the primary process maintaining moisture and MSE anomalies against dissipation by anomalous precipitation throughout the MJO lifecycle. Anomalously positive(negative) vertical moisture advection appears to slightly exceed anomalous precipitation during periods of enhanced(suppressed) convection, suggesting a potential positive feedback that could act to destabilize the MJO. Geographical changes in the MSE budget of the MJO are primarily associated with changes in the mean state winds and the mean state moisture gradient. These results suggest that MJO convective anomalies are maintained by anomalous vertical moisture advection, and that propagation of these convective anomalies results from the large scale asymmetrical dynamical response to equatorial heating occurring in a specific arrangement of mean state winds and mean moisture gradient. The findings of this study support the hypothesis that the MJO is a moisture mode.

Description

2014 Spring.
Includes bibliographical references.

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Subject

intraseasonal oscillation
Madden-Julian oscillation
moisture mode
moisture budget
moist static energy

Citation

Associated Publications