However, the seasonal climate simulations do not show evidence of "convergence" to an asymptotic climate state at high resolution. Global convective precipitation increases monotonically with resolution, but frontal precipitation, precipitable water, and cloud cover display a qualitatively different pattern: after undergoing abrupt reductions in the transition from T21 to T42, their global averages show relative increases at finer resolutions. Precipitable water and cloud cover also display a seasonal asymmetry in their responses to increasing resolution. The comparative insensitivity of global cloud cover to resolution is mainly a consequence of compensating tendencies of clouds in different regions. With increasing resolution, decreases in low-latitude clouds that result from drying of the tropical atmosphere are partially offset by increases in high-latitude clouds associated with enhanced relative humidity in response to an intensifying extratropical cold bias.
The large-scale tropical moist processes are modeled more realistically
at T21 than in the finer-resolution simulations, wherein anomalous seasonal
climatic features such as a double ITCZ and underdeveloped summer monsoon
circulation are evident. Although some of these anomalies might ameliorate
if the physical parameterizations were suitably "tuned," these deficiencies
may reflect more fundamental problems related to a mismatch between the
resolution of the model and the implicit spatial and temporal scales of
the parameterizations.(pdf file)
UCRL-MI-123395