On the Resolution Sensitivity of Equatorial Precipitation in a GFDL Global Atmospheric Model

Abstract

We performed a series of aquaplanet simulations at the horizontal resolution from 50 to 6 km with identical parameterization settings using the Geophysical Fluid Dynamics Laboratory's Atmosphere Model version 4 implemented with the two‐moment Morrison‐Gettelman cloud microphysics with prognostic precipitation (GFDL AM4‐MG2). At the finer resolution, the global mean resolved‐scale precipitation increases and that from cumulus parameterization decreases. The model also simulates less/thinner clouds over the low latitudes and more/thicker clouds over the high latitudes as the resolution increases. The precipitation over the deep tropics is investigated in detail. We find little resolution sensitivity in the daily mean precipitation extremes. Changes of the equatorial resolved precipitation with resolution cannot be fully explained by the resolution dependence in the vertical velocity amplitude. We report a robust sensitivity in the convective organization over the deep tropics to the model resolution. In simulations of finer resolution, the localized convection is suppressed, and the organized convective system associated with large‐scale circulations becomes more prominent.

ITCZ Response to Disabling Parameterized Convection in Global Fixed‐SST GFDL‐AM4 Aquaplanet Simulations at 50 and 6 km Resolutions

“…We examine simulations from the NOAA Geophysical Fluid Dynamics Laboratory AM4 atmospheric GCM in its alternative "AM4-MG2" configuration, a well-tested configuration that will form the base of future AM models (Guo et al, 2021;Lin et al, 2023). The model employs the standard AM4 physics package (Zhao et al, 2018a;Zhao et al, 2018b), but with more sophisticated microphysics (Gettelman & Morrison, 2015) and a nonhydrostatic solver (Harris et al, 2020).…”

“…The simulations are configured as an aquaplanet with fixed SSTs specified as the Q-control profile from Neale and Hoskins (2000) and perpetual equinox insolation including a diurnal cycle. Details of the model settings are documented in Lin et al (2023).…”