Sensitivity of climate feedbacks to vertical resolution in a General Circulation Model

2021 ◽  
Author(s):  
William Ingram ◽  
Andrew C. Bushell
Keyword(s):  
General Circulation Model ◽  
General Circulation ◽  
Circulation Model ◽  
Vertical Resolution ◽  
Climate Feedbacks

scholarly journals Convection–Climate Feedbacks in the ECHAM5 General Circulation Model: Evaluation of Cirrus Cloud Life Cycles with ISCCP Satellite Data from a Lagrangian Trajectory Perspective

2012 ◽  
Vol 25 (15) ◽  
pp. 5241-5259 ◽  
Author(s):  
Swati Gehlot ◽  
Johannes Quaas
Keyword(s):  
General Circulation Model ◽  
Model Evaluation ◽  
General Circulation ◽  
Trajectory Analysis ◽  
Deep Convection ◽  
Circulation Model ◽  
Life Cycles ◽  
Cirrus Clouds ◽  
Climate Feedbacks ◽  
Lagrangian Trajectory

Abstract A process-oriented climate model evaluation is presented, applying the International Satellite Cloud Climatology Project (ISCCP) simulator to pinpoint deficiencies related to the cloud processes in the ECHAM5 general circulation model. A Lagrangian trajectory analysis is performed to track the transitions of anvil cirrus originating from deep convective detrainment to cirrostratus and thin cirrus, comparing ISCCP observations and the ECHAM5 model. Trajectories of cloudy air parcels originating from deep convection are computed for both, the ISCCP observations and the model, over which the ISCCP joint histograms are used for analyzing the cirrus life cycle over 5 days. The cirrostratus and cirrus clouds originate from detrainment from deep convection decay and gradually thin out after the convective event over 3–4 days. The effect of the convection–cirrus transitions in a warmer climate is analyzed in order to understand the climate feedbacks due to deep convective cloud transitions. An idealized climate change simulation is performed using a +2-K sea surface temperature (SST) perturbation. The Lagrangian trajectory analysis over perturbed climate suggests that more and thicker cirrostratus and cirrus clouds occur in the warmer climate compared to the present-day climate. Stronger convection is noticed in the perturbed climate, which leads to an increased precipitation, especially on day−2 and −3 after the individual convective events. The shortwave and the longwave cloud forcings both increase in the warmer climate, with an increase of net cloud radiative forcing (NCRF), leading to an overall positive feedback of the increased cirrostratus and cirrus clouds from a Lagrangian transition perspective.

scholarly journals Importance of the Vertical Resolution in Simulating SST Diurnal and Intraseasonal Variability in an Oceanic General Circulation Model

2017 ◽  
Vol 30 (11) ◽  
pp. 3963-3978 ◽  
Author(s):  
Xuyang Ge ◽  
Wanqiu Wang ◽  
Arun Kumar ◽  
Ying Zhang
Keyword(s):  
Temperature Gradient ◽  
General Circulation Model ◽  
General Circulation ◽  
Circulation Model ◽  
Vertical Resolution ◽  
Vertical Temperature Gradient ◽  
Vertical Temperature ◽  
Sst Variability ◽  
Oceanic General Circulation Model ◽  
High Vertical Resolution

Abstract In this paper, the influence of high vertical resolution near the surface in an oceanic general circulation model in simulating the observed sea surface temperature (SST) variability is investigated. In situ observations of vertical temperature profiles are first used to quantify temperature variability with depth near the ocean surface. The analysis shows that there is a sharp vertical temperature gradient within the top 10 m of the ocean. Both diurnal and intraseasonal variabilities of the ocean temperatures are largest near the surface and decrease with the ocean depth. Numerical experiments with an oceanic general circulation model are next carried out with 1- and 10-m vertical resolutions for the upper ocean to study the dependence of the simulated SST and vertical temperature structure on the vertical resolution. It is found that the simulated diurnal and intraseasonal variabilities, as well as the associated vertical temperature gradient near the surface, are strongly influenced by the oceanic vertical resolution, with the 1-m vertical resolution producing a stronger vertical temperature gradient and temporal variability than the 10-m vertical resolution. These results suggest that a realistic representation of SST variability with a high vertical resolution in the upper ocean is required for a coupled atmosphere–ocean model to correctly simulate the observed tropical intraseasonal oscillations, including the Madden–Julian oscillation and the boreal summer monsoon intraseasonal oscillation, which are strongly linked with the underlying SST.

Simulating the QBO in an Atmospheric General Circulation Model: Sensitivity to Resolved and Parameterized Forcing

2016 ◽  
Vol 73 (4) ◽  
pp. 1649-1665 ◽  
Author(s):  
James A. Anstey ◽  
John F. Scinocca ◽  
Martin Keller
Keyword(s):  
Gravity Wave ◽  
General Circulation Model ◽  
General Circulation ◽  
Atmospheric General Circulation Model ◽  
Circulation Model ◽  
Wave Drag ◽  
Vertical Resolution ◽  
Atmospheric General Circulation ◽  
Downward Influence ◽  
Seasonal Synchronization

Abstract The quasi-biennial oscillation (QBO) of tropical stratospheric zonal winds is simulated in an atmospheric general circulation model and its sensitivity to model parameters is explored. Vertical resolution in the lower tropical stratosphere finer than ≈1 km and sufficiently strong forcing by parameterized nonorographic gravity wave drag are both required for the model to exhibit a QBO-like oscillation. Coarser vertical resolution yields oscillations that are seasonally synchronized and driven mainly by gravity wave drag. As vertical resolution increases, wave forcing in the tropical lower stratosphere increases and seasonal synchronization is disrupted, allowing quasi-biennial periodicity to emerge. Seasonal synchronization could result from the form of wave dissipation assumed in the gravity wave parameterization, which allows downward influence by semiannual oscillation (SAO) winds, whereas dissipation of resolved waves is consistent with radiative damping and no downward influence. Parameterized wave drag is nevertheless required to generate a realistic QBO, effectively acting to amplify the relatively weaker mean-flow forcing by resolved waves.

scholarly journals Extreme Precipitation in an Atmosphere General Circulation Model: Impact of Horizontal and Vertical Model Resolutions

2015 ◽  
Vol 28 (3) ◽  
pp. 1184-1205 ◽  
Author(s):  
Claudia Volosciuk ◽  
Douglas Maraun ◽  
Vladimir A. Semenov ◽  
Wonsun Park
Keyword(s):  
General Circulation Model ◽  
Extreme Precipitation ◽  
General Circulation ◽  
Large Scale ◽  
Circulation Model ◽  
Generalized Extreme Value Distribution ◽  
Precipitation Extremes ◽  
Vertical Resolution ◽  
Physical Processes ◽  
The Impact

Abstract To investigate the influence of atmospheric model resolution on the representation of daily precipitation extremes, ensemble simulations with the atmospheric general circulation model ECHAM5 at different horizontal (from T213 to T31 spectral truncation) and vertical (from L31 to L19) resolutions and forced with observed sea surface temperatures and sea ice concentrations have been carried out for January 1982–September 2010. All results have been compared with the highest resolution, which has been validated against observations. Resolution affects both the representation of physical processes and the averaging of precipitation across grid boxes. The latter, in particular, smooths out localized extreme events. These effects have been disentangled by averaging precipitation simulated at the highest resolution to the corresponding coarser grid. Extremes are represented by seasonal maxima, modeled by the generalized extreme value distribution. Effects of averaging and representation of physical processes vary with region and season. In the tropical summer hemisphere, extreme precipitation is reduced by up to 30% due to the averaging effect, and a further 65% owing to a coarser representation of physical processes. Toward middle to high latitudes, the latter effect reduces to 20%; in the winter hemisphere it vanishes toward the poles. A strong drop is found between T106 and T63 in the convection-dominated tropics. At the lowest resolution, Northern Hemisphere winter precipitation extremes, mainly caused by large-scale weather systems, are in general represented reasonably well. Coarser vertical resolution causes an equatorward shift of maximum extreme precipitation in the tropics. The impact of vertical resolution on mean precipitation is less pronounced; for horizontal resolution it is negligible.

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