Air-sea sensible and latent heat fluxes are fundamental to tropical cyclone (TC) energetics, but the impacts of seastate-dependent sea spray heat fluxes on TC structure and intensity are poorly understood. We explore these impacts herein by implementing a recently-developed parameterization for air-sea heat fluxes with seastate-dependent spray physics into a fully coupled atmosphere-wave-ocean model, the Unified Wave INterface–Coupled Model. We conduct model experiments with and without spray for four TCs covering wide ranges of intensity and structure. The effects of spray on model TCs in the open ocean can be summarized in three stages. 1) Spray evaporative cooling dominates in boundary layers (BLs) of tropical storms and weak hurricanes (i.e., with 10-m windspeeds ≲ 30–40 m s-1 and relatively small waves), which hinders intensification. 2) Further TC intensification increases spray generation, producing positive spray sensible heat fluxes (i.e., warming) under the eyewall. This warming is favorable for intensification, but inefficiency caused by cooler BL inflow continues to inhibit eyewall deep convection, and spray continues to oppose intensification overall. 3) Further increase of spray production from continued TC intensification (i.e., past Category 3) ultimately allows spray to promote intensification by warming the BL and enhancing eyewall deep convection. Spray’s tendency to oppose intensification of weak TCs is consistent with the relatively rare occurrence of major hurricanes. However, if a TC intensifies beyond stage 2, spray can support rapid intensification. We also find that enhanced spray generation by wave dissipation in the coastal zone may strengthen landfalling TCs.

Large-scale convection associated with the Madden-Julian Oscillation (MJO) initiates over the Indian Ocean and propagates eastward across the Maritime Continent (MC). Over the MC, MJO events are generally weakened due to complex interactions between the large-scale MJO and the MC landmass. The MC barrier effect is responsible for the dissipation of 40-50\% of observed MJO events and is often exaggerated in weather and climate models. We examine how MJO propagation over the MC is affected by two aspects of the MC - its land-sea contrast and its terrain. To isolate the effects of mountains and land-sea contrast on MJO propagation, we conduct three high-resolution coupled atmosphere-ocean model experiments: 1) control simulation (CTRL) of the 2011 November-December MJO event, 2) flattened terrain without MC mountains (FLAT), and 3) no-land simulation (WATER) in which the MC islands are replaced with 50 m deep ocean. CTRL captures the general properties of the diurnal cycle of precipitation and MJO propagation across the MC. The WATER simulation produces a more intense and smoother-propagating MJO compared with that of CTRL. In contrast, the FLAT simulation produces much more convection and precipitation over land (without mountains) than CTRL, which results in a stronger barrier effect on MJO propagation. The land-sea contrast induced land-locked convection weakens the MJO’s convective organization. The land-locked convective systems over land in FLAT are more intense, grow larger, and last longer, which is more detrimental to MJO propagation over the MC, than the mountains that are present in CTRL.