Parameter Study of Tropical Cyclones in Rotating Radiative–Convective Equilibrium with Column Physics and Resolution of a 25-km GCM

Abstract

Rotating radiative–convective equilibrium is studied by extracting the column physics of a mesoscale-resolution global atmospheric model that simulates realistic hurricane frequency statistics and then coupling it to rotating hydrostatic dynamics in doubly periodic domains. The parameter study helps in understanding the tropical cyclones simulated in the global model and also provides a reference point for analogous studies with cloud-resolving models. The authors first examine the sensitivity of the equilibrium achieved in a large square domain (2 × 104 km on a side) to sea surface temperature, ambient rotation rate, and surface drag coefficient. In such a large domain, multiple tropical cyclones exist simultaneously. The size and intensity of these tropical cyclones are investigated. The variation of rotating radiative–convective equilibrium with domain size is also studied. As domain size increases, the equilibrium evolves through four regimes: a single tropical depression, an intermittent tropical cyclone with widely varying intensity, a single sustained storm, and finally multiple storms. As SST increases or ambient rotation rate f decreases, the sustained storm regime shifts toward larger domain size. The storm’s natural extent in large domains can be understood from this regime behavior. The radius of maximum surface wind, although only marginally resolved, increases with SST and increases with f for small f when the domain is large enough. These parameter dependencies can be modified or even reversed if the domain is smaller than the storm’s natural extent.

Surface temperature dependence of tropical cyclone‐permitting simulations in a spherical model with uniform thermal forcing

“…As found in the spherical geometry simulations, PI captures the variation in maximum surface wind speed but underestimates the minimum simulated SLP in the rotating RCE simulations (see Zhou et al [] for further discussion). In both cases, we find that the PI calculations are sensitive to the assumption that the surface relative humidity in the TC eyewall, which is nearly saturated in the simulations, is equal to the surface relative humidity of the environment.…”

“…The rotating RCE, f ‐plane simulations also have a decreasing number of TCs as the SST is increased [ Zhou et al , ]. The rate of decrease is ∼12% K −1 in the rotating RCE simulations (dotted line in Figure a), which is an ∼50% higher sensitivity to SST than found in spherical geometry.…”

“…TCs in the rotating RCE simulations are defined with SLP lower than 990 hPa, which corresponds to a 5 hPa anomaly relative to the domain‐mean SLP for the coldest simulation. The domain‐mean SLP increases with temperature (5 hPa over the range of simulations) because the mass of atmospheric water vapor is accounted for in the dynamical core, while the magnitude of SLP anomalies of the weakest TCs [ Zhou et al , , Figure 2] (Figure ) has a stronger temperature dependence. Therefore, the 990 hPa threshold does not influence the results and the comparison between spherical geometry and f ‐plane simulations is consistent across the range of simulated temperatures.…”

Large‐scale character of an atmosphere in rotating radiative‐convective equilibrium

“…Indeed, Zhou et al . [] explored the dependence of the equilibrium state upon domain size using a model similar to Held and Zhao []. They found that as domain size increases, the equilibrium evolves through four regimes: a single tropical depression, an intermittent tropical cyclone with widely varying intensity, a single sustained storm, and finally multiple storms.…”

Understand the Direct Effect of CO2 Increase on Tropical Circulation and TC Activity: Land Surface Warming Versus Direct Radiative Forcing

“…HiRAM is developed based on AM2 (GAMDT, 2004) with increased resolutions and simplified parameterizations for moist convection and stratiform cloudiness. It has thus been used to examine the response of TC activity to climate change in both comprehensive and idealized simulations (Ballinger et al, 2015;Merlis et al, 2013Merlis et al, , 2016Zhou et al, 2014;Zhou et al, 2017). The parameterized convection is made to be less intrusive, allowing explicit convection to make more contributions.…”