Collaborative Research: Understanding Air-Sea Feedbacks to the MJO Through Process Evaluation of Observations and E3SM Experiments
The intraseasonal (30-70 day) Madden-Julian Oscillation (MJO) is a large-scale tropical disturbance that regulates extreme weather events globally, including North American heat waves, tropical cyclones, and flooding. The Rossby wavetrain response to MJO heating transports tropical moisture poleward and induces anomalous circulations that affect the interactions between polar clouds, radiation, and sea ice. The representation of the MJO in many general circulation models (GCMs) is improving, bolstering confidence in future projections of extreme weather globally, but gaps remain for simulating important MJO characteristics, such as its period, intensity, and eastward propagation.
While the MJO is rooted in atmospheric interactions between clouds, radiation, and moist dynamic processes, most GCMs exhibit improvement in MJO performance when the air-sea coupling is introduced, indicating a role for sea surface temperature (SST)-modulated surface fluxes to strengthen the MJO. Some coupled GCMs (CGCMs), however, are overly reliant on ocean feedbacks for MJO skill, suggesting that strong intraseasonal SST fluctuations mask deficiencies in atmospheric physics. Consequently, ocean feedbacks to the simulated MJO should be diagnosed as part of a broad assessment of processes that maintain and propagate MJO convection.
The PIs will document biases in MJO air-sea coupling strength in E3SM and other contemporary Earth System Models, to provide actionable information to E3SM developers for improved model physics, through:
- Applying newly developed air-sea interaction diagnostics to E3SMv1 and CMIP6 simulations to generate MJO air-sea coupling strength metrics.
- Integrating insights from air-sea interaction diagnostics with diagnostics that characterize the spatial and temporal scales of precipitation in model simulations.
- Identifying biases in E3SM atmospheric or oceanic physics that contribute to surface flux biases via careful diagnosis of E3SM variables combined with deep analysis of existing DOE Value-Added Products (VAPs) and other observational data sets.
- Assessing the effects of these biases, and of changes to model physics aimed to reduce them, on the fidelity of the simulated MJO and connected temperature and precipitation extremes over tropical land, using a hierarchy of E3SM atmospheric and air-sea coupled model frameworks.
Benefits of our project include 1) actionable, process-level information for E3SM model developers, 2) the addition of two new diagnostic suites to the PCMDI Metrics Package, and 3) training of one student and one postdoc for running and analyzing E3SM. Our project supports DOE ESMDA priorities by: 1) Focusing on the MJO, which links the tropical water cycle to North American weather extremes; 2) Diagnosing complex behavior of simulations and evaluating the veracity of models through systematic comparison to available observations, and 3) Targeting RGMA Science Topic "the role of ocean fluxes in influencing precipitation and extremes over land." This work supports DOE Climate and Environmental Sciences Division goals to develop, test, and simulate process-level understanding of atmospheric systems and to enhance the impacts of DOE facilities and other community resources to advance climate science.