Does increasing horizontal resolution improve the simulation of intense
tropical rainfall?
Abstract
We examine tropical rainfall from Geophysical Fluid Dynamics
Laboratory’s Atmosphere Model version 4 (GFDL AM4) at three horizontal
resolutions of 100 km, 50 km, and 25 km. The model produces more intense
rainfall at finer resolutions, but a large discrepancy still exists
between the simulated and the observed frequency distribution. We use a
theoretical precipitation scaling diagnostic to examine the frequency
distribution of the simulated rainfall. The scaling accurately produces
the frequency distribution at moderate-to-high intensity (≥10 mm day-1).
Intense tropical rainfall at finer resolutions is produced primarily
from the increased contribution of resolved precipitation and enhanced
updrafts. The model becomes more sensitive to the grid-scale updrafts
than local thermodynamics at high rain rates as the contribution from
the resolved precipitation increases. On the contrary, the observed
tropical precipitation extremes do not show a strong sensitivity to the
grid-scale updrafts.