Further extension of skillful prediction of tropical cyclones (TCs) relies on in-depth studies about the intrinsic predictability of TCs. In this study, convection-resolving ensemble forecasts based on the Hurricane Weather Research and Forecasting model were adopted with perturbed initial conditions to study the error growth and intrinsic predictability of TCs. The new aspect of our study is the focus on the sensitivity of TC track and intensity predictability to initial errors in different regions, including (1) the inner core and outer rainbands (0-350 km), (2) the near environment (350-1300 km), and (3) the far environment (1300-3500 km). The results of TC track predictability show that the most sensitive region of initial errors for TC track forecasts is case-dependent. For the TC case with striking track forecast errors (e.g., Typhoon Chan-hom, 2020), the initial errors in the combined region of the TC inner core and outer rainbands produce the largest track uncertainties compared to those in the near and far environment. However, for the TC case with a highly predictable track (e.g., Typhoon Maysak, 2020), the most sensitive region of initial errors is the near environment at early lead times and the far environment later. By contrast, the most sensitive region for TC intensity is the inner core for both cases. The surface wind structure of TC inner core at larger scales (wavenumbers 0-2) can be predicted for more than 3.5 days, while the structure at smaller scales can only be predicted for a few hours.

Studies have long reported the existence of pronounced diurnal and semi-diurnal variations in near-surface winds and divergence over the tropical oceans. Diurnal cycles of convective precipitation and cloudiness in the tropics are also well recognized from in-situ and satellite observations. However, the linkages between diurnal variations in tropospheric circulation, cloudiness and precipitation over the tropical oceans remain to be fully documented and understood. Recently, global storm-resolving models, which do not require convective parameterizations, have created an unprecedented opportunity to investigate the full three-dimensional structure of the diurnal cycle over the tropical oceans. In this study, we used one such model – the Model for Prediction Across Scales (MPAS) – for two main purposes: first, to evaluate the model’s representation of semi-diurnal and diurnal variations in near-surface winds, precipitation, and cloudiness over the tropical oceans; and second, to extend the analyses to provide a full three-dimensional picture of the daily variations in tropospheric circulation and their linkage with the hydrological cycle. A 40-day MPAS simulation (the same as used for DYAMOND-1 global storm-resolving models inter-comparison project) was utilized in this study to examine the large-scale geographical patterns and vertical structures of mean daily variations of zonal and meridional wind components, wind divergence, vertical velocity, cloudiness, water vapor mixing ratio and precipitation. The model shows generally good agreement with the previously reported observational results for near-surface winds and divergence. In particular, MPAS exhibits a pronounced large-scale diurnal cycle in the local Hadley Circulation over the Tropical Pacific Ocean, with lower tropospheric divergence (convergence) relative to the daily mean, maximizing around 1000 (2200) LT. The amplitude of the diurnal variation in near-surface wind divergence at the equator is approximately 0.8×10-6 s-1, or approximately 44% of the daily mean. The vertical structure of this diurnal circulation, along with its signature in vertical velocity and its association with water vapor, cloudiness and precipitation, will be presented.