Climate Statistics in Global Simulations of the Atmosphere, from 80 to 2.5 km Grid Spacing

Abstract

Basic climate statistics, such as water and energy budgets, location and width of the InterTropical Convergence Zone (ITCZ), trimodal tropical cloud distribution, position of the polar jet and land-sea contrast remain either biased in coarse-resolution General Circulation Models or are tuned. Here we examine the horizontal resolution dependency of such statistics in a set of global convection-permitting simulations integrated with the ICOsahedral Non-hydrostatic (ICON) model, explicit convection and grid spacings ranging from 80 km down to 2.5 km. The impact of resolution is quantified by comparing the resolution-induced differences to the spread obtained in an ensemble of eight distinct global storm-resolving models. Using this metric, we find that, at least by 5 km, the resolution-induced differences become smaller than the spread in 26 out of the 27 investigated statistics. Even for 9 (18) of these statistics, a grid spacing of 80 (10) km does not lead to significant differences. Resolution down to 5 km matters especially for net shortwave radiation, which systematically increases with resolution due to reductions in low cloud amount over the subtropical oceans. Further resolution dependencies can be found in the land-to-ocean precipitation ratio, in the latitudinal position and width of the Pacific ITCZ and in the longitudinal position of the Atlantic ITCZ. Also in the tropics, the deep convective cloud population systematically increases at the ex

Shallow Cumulus Cloud Feedback in Large Eddy Simulations – Bridging the Gap to Storm Resolving Models

“…and colder in the boundary layer, relative humidity is enhanced and saturation is more likely leading to more widespread cloud formation at coarser resolutions. Hohenegger et al (2020) found similar characteristics in global simulations with explicit convection and grid spacings ranging between 2.5 and 80 km.…”

“…8) and therefore the cloud feedback strength increases at coarse resolutions. Hohenegger et al (2020) who investigated grid spacings ranging from 2.5 km to 80 km found that cloud cover increases up to 80 km horizontal resolution, which would, provided the results found here carry over also to even coarser resolutions, translate into further increased cloud feedback. At high resolutions, on the contrary, the trade wind cumulus cloud feedback converges to near-zero values.…”

Mesoscale marine tropical precipitation varies independently from the spatial arrangement of its convective cells

“…A detailed description of the underlying model and a validation of the results can be found in Hohenegger et al . (). In terms of precipitation distribution, the model was found to produce 8% more tropical mean precipitation than observed.…”

“…The model also captures the tropical short‐wave and long‐wave radiation budget at the surface within 1 and 5.7 W·m −2 , respectively, and within 9.9 amd 4 W·m −2 at the top of the atmosphere. The biases are comparable to the biases in the other storm‐resolving models participating in the DYAMOND intercomparison project (table 6 in Stevens et al ., and table 2 in Hohenegger et al ., ).…”

Stürmische Zeiten für die Klimaforschung

“…In dieser Hinsicht erscheint es hilf reicher, zu bestimmen, wann Abweichungen von einer realistischen Klimadarstellung, die durch eine ungenügende Auflösung bedingt sind, kleiner werden als rein numerisch bedingte Unterschiede, die durch eine Veränderung der übrigen Parametrisierungen verursacht werden. In einer aktuellen Studie [17] haben wir hierzu bei einer 40tägigen globalen Klimasimulation die Auflösung systematisch von 80 km bis zu 2,5 km halbiert, ohne andere Parameter der Auflösung anzupassen. Die daraus resultierenden Unter schiede haben wir mit der Standardabweichung eines Ensembles aus acht globalen sturmauflösenden Klima modellen, die parallel das Klima über den gleichen Zeit raum simulierten, verglichen.…”