Diurnal convection near coasts in the tropics is usually manifest as late afternoon convection over land that frequently moves offshore overnight into the early morning while growing upscale into…

Diurnal convection near coasts in the tropics is usually manifest as late afternoon convection over land that frequently moves offshore overnight into the early morning while growing upscale into organized mesoscale convective systems (MCSS). This offshore propagation of diurnal convection (OPDC) can impact local extreme precipitation and influence remote extreme events by seeding easterly waves (EWS) that can develop into tropical cyclones (TCS) or initiating rossby waves that generate atmospheric rivers and cause flooding along the western coast of the USA. Hence, OPDC plays an important role in global water and energy cycles. Despite their importance, IT is unknown how well earth system models (ESMS) simulate the day-to-day variability in OPDC that observations show. Therefore, the overarching goal of our project is to provide a diagnostic framework to assess the day-to-day variability of OPDC in ESMS and to identify process-level sources of biases for simulated OPDC in those models, such as biases in regional atmosphere and ocean environmental conditions and/or biases in the response of convection to its environment. Our work plan is to: 1. Assess the fidelity of tropical OPDC characteristics (i.e., frequency, intensity, and propagation speed and distance) in ESMS relative to observations with the far east pacific serving as an initial test region. CMIP6 and other ESM databases, such as the MDTF timeslice runs, will be used. 2. Relate biases in OPDC to biases in environmental conditions (i.e., regional background flows and moisture, atmospheric instability) and the resolution of physical features. 3. Link biases in OPDC to biases in the response of convection to its environment, and to biases in dynamical processes (i.e., air-sea interactions, vorticity stretching) that foster offshore propagation and the upscale growth of convection. 4. Expand diagnostics applied to the east-pacific region (objectives 1-3) to a selection of coastal locations across the globe where OPDC has either 1) a diversity of behavior or 2) interactions with larger-scale phenomena such as the MJO or TCS. 5. Perform idealized and/or mechanism-denial simulations with ESMS or cloud resolving models to more fully probe and understand model deficiencies related to OPDC. 6. Quantify changes in OPDC in the tropics under climate change and relate those changes to changes in regional flows, moisture, stability, and air-sea feedbacks. This work will result in a process-oriented diagnostic (POD) that will contain several diagnostic components of tropical OPDC. The POD will be integrated into the model diagnostics task force (MDTF) software package. Targeting OPDC in ESMS addresses two of the key sought after diagnostic development areas in the mapp diagnostics call of: 1) advancing the simulation of climate and weather extremes, particularly tropical and extratropical storms, mesoscale convective systems, and atmospheric rivers and 2) addressing model precipitation biases and how they drive key societal impacts such as floods, droughts. This work also contributes to noaas long-term climate research goal to advance understanding of earths climate system...to enhance societys ability to plan and respond to climate variability and climate change, as OPDC and its changes under future warming impact local and remote extreme events. 3