Abstract
Simulations of the global climate system at storm-resolving resolutions of 2 km are now becoming feasible and show promising realism in clouds and precipitation. However, shortcomings in their representation of microscale processes, like the interaction of cloud droplets and ice crystals with radiation, can still restrict their utility. Here, we illustrate how changes to the ice microphysics scheme dramatically alter both the vertical profile of cloud-radiative heating and top-of-atmosphere outgoing longwave radiation (terrestrial infrared cooling) in storm-resolving simulations over the Asian monsoon region. Poorly-constrained parameters in the ice nucleation scheme, overactive conversion of ice to snow, and inconsistent treatment of ice crystal effective radius between microphysics and radiation alter cloud-radiative heating by a factor of four and domain-mean infrared cooling by 30 W m−2. Vertical resolution, on the other hand, has a very limited impact. Even in state-of-the-art models then, uncertainties in microscale cloud properties exert a strong control on the radiative budget that propagates to both atmospheric circulation and regional climate. These uncertainties need to be reduced to realize the full potential of storm-resolving models.
Highlights
Simulations of the global climate system at storm-resolving resolutions of 2 km are becoming feasible and show promising realism in clouds and precipitation
Ice clouds may become a primary roadblock in the era of storm-resolving modeling, and here, we target their impact on the radiative budget of the Asian monsoon region, a key area for the global climate system[9,10]
We begin by illustrating the range in tropical-mean profiles of uppertropospheric cloud-radiative heating (H), produced by three different global coarse-resolution simulations and from CloudSat/ CALIPSO measurements
Summary
Simulations of the global climate system at storm-resolving resolutions of 2 km are becoming feasible and show promising realism in clouds and precipitation. As the turbulent updrafts from which it initiates may extend over only tens of meters These models generate more realistic spatial fields of vertical motion, cloud condensate, and precipitation and improve tropical cyclogenesis and the diurnal cycle of precipitation relative to coarser resolution models[1,3,4]. Ice clouds may become a primary roadblock in the era of storm-resolving modeling, and here, we target their impact on the radiative budget of the Asian monsoon region, a key area for the global climate system[9,10] Ice clouds both reflect incoming ultraviolet radiation and absorb and reemit outgoing infrared radiation, generating a dipole of in-cloud heating and cloud-top cooling[11,12]. We provide initial estimates for how much cloud-radiative heating can vary with these ice microphysical properties
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