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The El Niño-Southern Oscillation (ENSO) phenomenon is the most well-known natural climate variability mode, is stationary, and dominates the central-eastern tropical Pacific on interannual time scales. The Madden-Julian Oscillation (MJO) is the leading mode of variability in the tropics on subseasonal time scales and propagates eastwards, circumnavigating the globe in approximately 30 to 90 days. Atmospheric rivers (ARs) are extratropical weather systems characterized by streams of water vapor moving in the sky, analogous to rivers that are streams of water moving over land.
Personnel: Dr. Lais Fernandes and Dr. Paul Loikith (PI). Funding provided by the NASA Modeling, Analysis, and Prediction Program.
During the extended cool-season (November-March), when ENSO and MJO are more mature and ARs are more active over the North Pacific, changes in the atmospheric background and the MJO by ENSO may affect how MJO modulates ARs across the North Pacific. This work assesses how ENSO influences the MJO modulation of North Pacific ARs and their landfalling precipitation over western North America, from November through March. We show below that the background changes produced by the opposite ENSO states, El Niño and La Niña, modify the structure and propagation of the MJO’s convection, and the associated MJO extratropical teleconnection, affecting MJO-AR connections over the North Pacific.
El Niño effect on the MJO-AR connections
MJO convection (blue contours) over the western and central Pacific is shifted eastward and is enhanced during the El Niño phase, influencing the development of the MJO teleconnection pattern (black contours) associated with North Pacific ARs. The MJO teleconnection is triggered east of 180° in MJO phases 7+8 under El Niño years, propagating towards western subtropical North America. In phase 1 and El Niño, the MJO teleconnection strengthens as it propagates towards extratropical North America, probably related to delayed MJO teleconnection signals triggered from the enhanced MJO convection in phase 8. As the MJO convection and teleconnection shift to the east, the upper-level cyclonic flow associated with increased AR activity appears along the western North American coast, persisting until phase 1. Although the teleconnection pattern weakens in phases 7-8, the slower MJO eastward propagation in phases 6-8 allows the anomalous integrated water vapor transport (IVT) cyclonic flow (purple vectors) to be established over the subtropical northeastern Pacific, with a northeastward IVT component coupled to the enhanced MJO convection over the western (phase 7) and central (phase 8) Pacific, supporting increased AR activity (yellow and red shadings).
Percentage changes in AR frequency, 300 hPa streamfunction (continuous/dashed contours represent positive/negative values, 6×10^5 𝑚^2 𝑠^(−1) interval), integrated water vapor transport (IVT) (purple vectors), and outgoing longwave radiation (OLR) (brown/blue contours represent positive/negative values, 5 𝑊/𝑚^2 interval) anomalies from MJO phase 6 through phase 1 in all years (a-d) and El Niño years (e-h). Dots, contours, and vectors represent AR frequency and MJO anomalies with p < 0.1 from a t-test.
La Niña effect on the MJO-AR connections
Several effects of La Niña on the atmospheric basic state and MJO characteristics support the persistence of increased AR activity (yellow and red shadings) from phases 4 through 5 over the northeastern Pacific and across the central North Pacific in phase 3. For instance, the MJO convection (blue contours) intensifies in phase 3 under La Niña conditions, favoring a stronger coupling between anomalous northeastward IVT (purple vectors) in the western North Pacific and the MJO convection over the eastern Indian Ocean. The strongest suppressed MJO convection (brown contours) and the related teleconnection pattern (black contours) shift eastwards in phase 4 and La Niña, favoring increased AR frequency and enhanced eastward IVT anomalies closer to the western US in phases 4+5. Also, the northeastward elongation of the subtropical jet over the northeastern Pacific in La Niña (not shown) favors a persistent and enhanced extratropical cyclonic flow in the teleconnection pattern of the MJO in phases 4-5 over the Gulf of Alaska. Furthermore, the slower eastward MJO propagation in phases 4-5 due to warmer SSTs and intensified convection over the Maritime Continent in La Niña likely favors a second coupling between anomalous eastward IVT over the subtropical western North Pacific and moisture from the MJO convection over the Maritime Continent in phase 5 establishing a long corridor of increased AR activity towards the west of US.
Percentage changes in AR frequency, 300 hPa streamfunction (continuous/dashed contours represent positive/negative values, 6×10^5 𝑚^2 𝑠^(−1) interval), integrated water vapor transport (IVT) (purple vectors), and outgoing longwave radiation (OLR) (brown/blue contours represent positive/negative values, 5 𝑊/𝑚^2 interval) anomalies from MJO phase 2 through phase 5 in all years (a-d) and La Niña years (e-h). Dots, contours, and vectors represent AR frequency and MJO anomalies with p < 0.1 from a t-test.
Results described here show that both El Niño and La Niña nonlinearly affect the connections between MJO and North Pacific ARs and the MJO-AR landfalling precipitation over western North America, corroborating previous studies describing nonlinear interactions between MJO and ENSO across the North Pacific and western North America. These findings indicate an urge to consider changes in the impacts of the intraseasonal signal of MJO on North Pacific ARs due to different ENSO background states, with possible implications for subseasonal predictions of ARs. For instance, both El Niño and La Niña background states favor increased AR frequency and landfalling precipitation lasting longer over western North America, for example, impacts in phase 4 last until phase 5 in La Niña, and those in phase 8 last until phase 1 in El Niño.
Composites of precipitation anomalies (𝑚𝑚 𝑑𝑎𝑦^(−1)) in MJO phases 4-5 in all years and La Niña years (a-d) and in MJO phases 8-1 in all years and El Niño years (e-h). Gray lines delimit values with p < 0.1 from a t-test.
Publications:
Fernandes, L. G., and Loikith, P. C. 2024: Does El Niño affect MJO-AR connections over the North Pacific and associated North American precipitation? Climate Dynamics, https://doi.org/10.1007/s00382-024-07177-3.
Fernandes, L. G., Wheeler, M. C., Grimm, A. M., Arcodia, M. C. 2025: Ocean-atmosphere interactions: Madden-Julian Oscillation and the El Niño-Southern Oscillation. Atmospheric Oscillations: Sources of Subseasonal-to-Seasonal Variability and Predictability, Guan, B., Ed. Elsevier, https://doi.org/10.1016/B978-0-443-15638-0.00017-4.
Fernandes, L. G., Loikith, P. C., Mora, M. La Niña Effects on the MJO Modulation of North Pacific Atmospheric Rivers and Associated Western North American Precipitation. Manuscript submitted to the Journal of Geophysical Research (JGR): Atmospheres.
Presentations:
La Niña Effects on the MJO Modulation of North Pacific Atmospheric Rivers and Associated Western North American Precipitation. Laís G. Fernandes, Paul C. Loikith, and Margarita Mora, American Geophysical Union Fall Meeting, Washington, D.C., December 2024 (poster by Laís Fernandes).
Does El Niño affect MJO-AR connections over the North Pacific and associated North American precipitation? Laís G. Fernandes and Paul C. Loikith, International Atmospheric River Conference, San Diego, California, June 2024 (poster by Laís Fernandes).
ENSO and MJO Effects on North Pacific AR Speed and Propagation. Margarita Mora, Laís G. Fernandes, and Paul C. Loikith, American Meteorological Society Annual Meeting, Baltimore, Maryland, January 2024 (talk by Margarita Mora).
Does El Niño affect MJO-AR connections over the North Pacific and associated North American Precipitation? Laís G. Fernandes and Paul C. Loikith, American Geophysical Union Fall Meeting, San Francisco, California, December 2023 (poster by Laís Fernandes).
ENSO and MJO Effects on North Pacific AR Speed and Propagation. Margarita Mora, Laís G. Fernandes, and Paul C. Loikith, American Geophysical Union Fall Meeting, San Francisco, California, December 2023 (poster by Margarita Mora).
ENSO Modulation of MJO Teleconnections to the Lifecyle of North Pacific Atmospheric Rivers and their Precipitation Extremes. Laís G. Fernandes and Paul C. Loikith. Annual Meeting of the American Meteorological Society, Denver, Colorado, January 2023 (talk by Laís Fernandes).
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