Intellectual Merit: 

The Madden-Julian oscillation (MJO) is a phenomenon that causes tropical precipitation in the Pacific and Indian Oceans to strengthen and wane every 40-50 days. The MJO produces robust remote connections to other parts of the tropics and higher latitudes and an associated modulation of extreme weather events including hurricanes, atmospheric rivers, blocking, and heat waves. Recent modeling results suggest that MJO circulation anomalies may weaken in a future warmer climate (even though precipitation anomalies increase in amplitude), which may make the MJO less important for impacts and prediction of tropical and midlatitude extreme weather events. This study used various climate and regional models to examine how the MJO and its teleconnections may change in a future warmer climate. We hypothesized going into the project that MJO precipitation anomalies will increase in strength in a future warmer climate, although MJO circulation anomalies and associated teleconnections will decrease in strength. The decrease of MJO remote impacts to other parts of the global may make its impacts on places like North America less predictable in a future warmer climate.

Our major results are as follows: 

1. We showed the changes in MJO precipitation and wind amplitude only become detectable at the end of the 21^stCentury in climate models in a high-end greenhouse gas forcing scenario. However, changes to the ratio of their amplitudes are detectable as early as 2020-2040. Weakened MJO winds per unit precipitation may decrease the impact of the MJO on extreme weather events and their prediction over North America. 

2. An analysis with observed data over the past Century shows that changes to the ratio of MJO wind and precipitation amplitude are already detectable over the observational record, consistent with our hypothesis above.

3. We showed that coupled climate models (where the ocean and atmosphere influence each other) produce a different MJO response in future climate than uncoupled models, even for the same climatological SST warming. 

4. A climate model with a large number of future ensemble members (initiated with slightly different initial conditions) shows that individual model runs with greatest increase in MJO amplitude have a more El Nino-like warming pattern.  Hence, internal variability may produce some uncertainty in future MJO change. 

5. The MJO’s modulation of tropical cyclones may weaken near coastal Mexico and Central America of the east Pacific in a future warmer climate in climate model simulations. This may make the MJO less important in the future for 3-4 week prediction of tropical cyclone activity.  

Broader Impacts:

This work has made significant contributions to the atmospheric sciences by helping us to understand how climate variability may change in the Tropics in a future warmer climate. The Madden-Julian oscillation, an important climate process that modifies hurricane genesis and mid-latitude weather, is a microcosm of all the processes that help to regulate tropical climate variability. Our work has used models to provide valuable insights into how the MJO might change with climate warming, which has important consequences for predicting future events such as blocking, atmospheric rivers, hurricanes, and other extremes.

This NSF-funded project has had a significant and important impact on our understanding of tropical climate processes, particularly those involving tropical precipitation, and how they might change in a warmer climate.  This work has also led to improved understanding of how the midlatitudes are modulated by the MJO, including extreme events including atmospheric rivers, hurricanes, and blocking events, and has opened the prospect for improved prediction of these events on subseasonal timescales. Blocking and atmospheric rivers are associated with extreme flooding events, cold air outbreaks, and other extremes over the United States that are societally relevant. Improving their prediction and understanding will lead to knowledge gains that can be used to better protect life and property.  Our results suggest that the effect of the MJO on these extremes may weaken in future climate due to MJO circulations decreasing, even in the presence of increased MJO precipitation variability. We have also shown that state-of-the-art climate models suggest a diminished influence of the MJO on hurricane formation in the Americas. This finding has important implications for precipitation prediction and protection of life and property in a future warmer climate. 

Last Modified: 09/30/2024
Modified by: Eric D Maloney