- What is GCM?
- A Global Climate Model (or General Circulation Model, GCM) is a mathematical model of the general circulation of a planetary atmosphere or ocean and based on the Navier-Stokes equations on a rotating sphere with thermodynamic terms for various energy sources (radiation, latent heat).
- - Mechanism of GCM
- Climate models are systems of differential equations based on the basic laws of physics, fluid motion, and chemistry. To "run" a model, scientists divide the planet into a 3-dimensional grid, apply the basic equations, and evaluate the results. Atmospheric models calculate winds, heat transfer, radiation, relative humidity, and surface hydrology within each grid and evaluate interactions with neighboring point.
- - Global Climate Model trends
- A recent trend in GCMs is to apply them as components of Earth system models, e.g. by coupling to ice sheet models for the dynamics of the Greenland and Antarctic ice sheets, and one or more chemical transport models (CTMs) for species important to climate. Thus a carbon CTM may allow a GCM to better predict changes in carbon dioxide concentrations resulting from changes in anthropogenic emissions.
- - Global Climate Model structures & improving parts
- Climate prediction uncertainties depend on uncertainties in chemical, physical, and social models (see IPCC scenarios below). Progress has been made in incorporating more realistic chemistry and physics in the models, but significant uncertainties and unknowns remain, especially regarding the future course of human population, industrym and technology.
- a. Model grids
- Resolution of model is a critical role to simulation global climate. The accuracy of simulating climate highly depends on the spatial resolution of GCM. However, the high resolution is necessary to huge computing source to calculate mathematical model of the general circulation.
- b. Flux correction
- Ocean and atmospheric models have a different implicit flux from the other component. If uncorrected this could lead to a dramatic drift away from observations in the coupled model. However, if the fluxes were 'corrected', the problems in the model that led to these unrealistic fluxes might be unrecognised and that might affect the model sensitivit.
- c. Convection
- Moist convection causes the release of latent heat and is important to the Earth's energy budget. Convection occurs on too small a scale to be resolved by climate models, and hence must be parameterized.
< 50km resolution low-level cloud >
< 25km resolution low-level cloud >
< 14km resolution low-level cloud >
- A method for GCM validation and assessment
- - Diurnal Cycle of Precipitation
- The analysis of diurnal cycle of precipitation is one of the methods that verify performance of the parameterized deep convection scheme of GCM. This cycle driven by variation of solar and long-wave radiation geographical difference, etc (Dai et al, 1999; Lee et al, 2007; Kikuchi et al, 2007) is major phenomenon of hydrological cycle of atmosphere and surface.
In this study, the diurnal variation of precipitation, precipitation frequency, intensity and low-level wind, which has the important role that low-level wind transports moisture from the ocean (Lee et al, 2007; Daran et al, 2010), is analyzed and examined using NASA GEOS-5 10km high horizontal resolution Atmospheric GCM over 2005-2006 summer season (JJA, June to August).
Aiguo Dai (1999), Recent Changes in the Diurnal Cycle of Precipitation over the United States, GRL, 26, 341-344, DOI: 10.1029/1998GL900318
Aiguo Dai, Filippo Giorgi, and Kelvin E. Trenberth (1999), Observed and model-simulated diurnal cycles of precipitation over the contiguous United States, JGR, 104, 6377-6402
Daran L. Rife, James O. Pinto, Andrew J. Monaghan, and Christopher A. Davis (2010), Global Distribution and Characteristics of Diurnally Varying Low-Level Jets, J. Clim., 23, 5041-5064, doi: 10.1175/2010JCLI3514.1
Lee, M. I., and coauthors (2007a), An Analysis of the Warm-Season Diurnal Cycle over the Continental United States and Northern Mexico in General Circulation Models, J. Hydrometeorol., 8, 344-366
Kazuyoshi KiKuchi and Bin Wang (2008), Diurnal Precipitation Regimes in the Global Tropics, J. Clim., 21, 2680-2696