Tropical Convective Variability in the NOAA UFS - A Process - Level Assesment

Incorrect model representations of tropical convective variability and air-sea coupling are known to be important sources of error that strongly impact sub-seasonal predictability in the Tropics, and lead to forecast error propagation from tropics to midlatitudes. In this study, a suite of recently developed diagnostics is used to assess the representation of tropical convective variability and air-sea coupling in the NOAA Unified Forecast System (UFS), and to identify sources of systematic forecast errors and model biases. The diagnostics assess model representation of:

• Moisture-convection coupling
• Relative sensitivity of convection to variations in humidity and/or CAPE
• Relationship between shallow, mid-level, and deep convective cloud populations and moist static energy (MSE) variability
• Relationship between shallow, mid-level, and deep convective cloud populations and upper ocean heat content (OHC) variability
• The role of convection in coupling MSE and OHC variability

Together, the diagnostics provide a deeper process level evaluation of the thermodynamic aspects of tropical convective variability. These diagnostics are applied to a range of UFS simulations, including re-forecasts, climate simulations, and “replay” experiments where the tropics are nudged towards reanalysis. Primary sources of UFS model errors are discussed, and potential approaches for addressing these errors are presented.

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