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Kyle MacRitchie
and
Paul E. Roundy

Abstract

Previous works have shown that most of the rainfall embedded within the Madden–Julian oscillation (MJO) occurs in large eastward-moving envelopes of enhanced convection known as super cloud clusters. Many of these superclusters have been identified as convectively coupled Kelvin waves. In this work, a simple composite-averaging technique diagnoses the linear and nonlinear contributions to MJO potential vorticity (PV) structure by convection collocated with Kelvin waves. Results demonstrate that PV is generated coincident with active convection in Kelvin waves, but that this PV remains in the environment after Kelvin wave passage and becomes part of the structure of the MJO. Analysis of the Tropical Rainfall Measuring Mission (TRMM) rainfall suggests that 62% of the total rainfall within the MJO occurs within the active convective phases of the Kelvin waves (88% higher than the rain rate that occurs outside of the Kelvin waves), supporting the hypothesis that diabatic heating in cloud clusters embedded within the Kelvin waves generates this PV.

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Paul E. Roundy
,
Kyle MacRitchie
,
Jonas Asuma
, and
Timothy Melino

Abstract

Composite global patterns associated with the El Niño–Southern Oscillation (ENSO) and the Madden–Julian oscillation (MJO) are frequently applied to help make predictions of weather around the globe at lead times beyond a few days. However, ENSO modulates the background states through which the MJO and its global response patterns propagate. This paper explores the possibility that nonlinear variations confound the combined use of composites based on the MJO and ENSO separately. Results indicate that when both modes are active at the same time, the associated patterns in the global flow are poorly represented by simple linear combinations of composites based on the MJO and ENSO individually. Composites calculated by averaging data over periods when both modes are present at the same time more effectively describe the associated weather patterns. Results reveal that the high-latitude response to the MJO varies with ENSO over all longitudes, but especially across the North Pacific Rim, North America, and the North Atlantic. Further analysis demonstrates that the MJO influence on indexes of the North Atlantic Oscillation is greatest during La Niña conditions or during periods of rapid adjustment in the phase of ENSO.

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Howard J. Diamond
,
Carl J. Schreck III
,
Emily J. Becker
,
Gerald D. Bell
,
Eric S. Blake
,
Stephanie Bond
,
Francis G. Bringas
,
Suzana J. Camargo
,
Lin Chen
,
Caio A. S. Coelho
,
Ricardo Domingues
,
Stanley B. Goldenberg
,
Gustavo Goni
,
Nicolas Fauchereau
,
Michael S. Halpert
,
Qiong He
,
Philip J. Klotzbach
,
John A. Knaff
,
Michelle L'Heureux
,
Chris W. Landsea
,
I.-I. Lin
,
Andrew M. Lorrey
,
Jing-Jia Luo
,
Kyle MacRitchie
,
Andrew D. Magee
,
Ben Noll
,
Richard J. Pasch
,
Alexandre B. Pezza
,
Matthew Rosencrans
,
Michael K. Tippet
,
Blair C. Trewin
,
Ryan E. Truchelut
,
Bin Wang
,
Hui Wang
,
Kimberly M. Wood
,
John-Mark Woolley
, and
Steven H. Young
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