A New Method to Construct a Horizontal Resolution‐Dependent Wind Speed Adjustment Factor for Tropical Cyclones in Global Climate Model Simulations. Issue 11 (8th June 2020) - Moon, Yumin
Abstract: A new method to construct a horizontal resolution‐dependent wind speed adjustment factor for evaluating tropical cyclones (TCs) in global climate models (GCMs) is presented. In contrast to the previous studies that used idealized axisymmetric wind fields, this study analyzes 48 hr of 10‐s surface wind fields from 1‐km TC simulations. The adjustment factor is derived from filtering the simulated TC wind fields onto various horizontal grid spacings typical of those used in GCMs. The new adjustment factor leads to TCs with greater intensity than the existing adjustment factors for horizontal grid spacings smaller than 30 km. This difference is attributed to more realistic wind fields in the TC simulations that contain highly asymmetric, localized patches of higher wind speeds instead of axisymmetric wind fields. Applying the new adjustment factor to select GCM simulations suggests the common interpretation of low‐intensity bias in GCM‐simulated TCs might be slightly exaggerated. Plain Language Summary: It has long been recognized that the intensity of tropical cyclones (maximum sustained surface wind speed) in global climate model simulations needs adjustments as the horizontal grid spacing of the climate models is not yet fine enough, resulting in the representative errors in the simulated tropical cyclone structures. This study presents a new method to construct a horizontal resolution‐dependent tropical cyclone intensity adjustment factor that can be used when evaluating tropical cyclones in climate model simulations. Our new method uses tropical cyclone simulations performed with 1‐km horizontal grid spacing, in which tropical cyclone structures are realistically captured. Applying the new adjustment factor increases the interpreted intensity of simulated tropical cyclones, which suggests that the common interpretation of low‐intensity bias in climate model‐simulated tropical cyclones in comparison to the observations might be slightly exaggerated. Key Points: A new method of constructing a tropical cyclone intensity adjustment factor for global climate model simulations is proposed The new intensity adjustment factor uses high‐resolution tropical cyclone simulations and is horizontal resolution‐dependent Using the new adjustment indicates the low‐intensity bias in global climate model‐simulated tropical cyclones might be slightly exaggerated