Dependence of MJO Precipitation Maintenance on Convective Processes

Seasonal to subseasonal (S2S) variability in tropical precipitation and mid-latitude weather is largely controlled by the evolution of tropical precipitation phenomenon. At subseasonal timescales, the Madden-Julian Oscillation (MJO) dominates variability in precipitation. Cloud systems in the MJO release latent heat, which produces a Rossby wave response that propagates in wave trains away from the equator and impacts extreme weather events through Earth’s middle latitudes. However, numerical models of the atmosphere, including NOAA’s Global Forecast System and Climate Forecast System, struggle to demonstrate skill in tropical rainfall beyond about 21 days even though observational analysis strongly suggests that the MJO is related to extreme weather events in the United States at much longer lead times. One particular difficulty in modeling the MJO is what is known as the “barrier effect”, which is the tendency for the convective envelope to stall over the Maritime Continent without reaching the Western Pacific. Numerical models of the global atmosphere dissipate the MJO convection more frequently over the Maritime Continent than is indicated in observations. As a result, most general circulation models are biased in that the mid-latitude weather events that are connected to MJO activity in the Western Pacific are not well predicted. Guided by theoretical descriptions of MJO as a moist equatorial wave, we will use a combination of observations and numerical models to evaluate hypotheses related to the physical processes that control maintenance or decay of the MJO-related moisture anomaly over the Maritime Continent. Our work will incorporate physical parameterizations used in NOAA numerical models with the intention that NOAA’s operational forecast suite can take advantage of our findings more quickly than if other non-NOAA modeling frameworks were used.
As the global climate continues to warm during upcoming decades, improving short- to medium-range predictability of extreme weather events linked to S2S tropical variability will be essential to mitigating the damage and loss of property and human lives in the United States and throughout the world. Improving our understanding of S2S variability—and specifically the MJO—in the current climate will allow the scientific community to more accurately assess the impacts of the MJO on extreme events that impact the United States in a warmer climate. Our research will contribute to the CPO’s mission of increasing resilience of the United States and its strategic geopolitical partners as society encounters uncertain future climate-related challenges. Specifically, our research will explore how unrealistic assumptions made in some of NOAA’s physical parameterizations of the atmosphere may negatively impact the numerical representation of processes that are important for short- and medium range predictability of tropical precipitation and related mid-latitude weather phenomena in both the current and in future, warmer climates.