Increased Model Resolution

Increased Model Resolution

Average Precipitation Rate (mm/day) for North America 1996-2005 from Willmott-Matsuura Climatology and 0.25-degree Resolution CCSM4

The other revolution in climate simulation is increased model resolution. As computers have gotten more and more powerful, models are able to be run at higher and higher resolution. These plots show mean annual precipitation for North America in mm/day. The top plot comes from an observational data set over a 10-year period. The bottom plot shows results from an atmospheric model run at a quarter-degree grid spacing, using actual SSTs to capture the model response to processes like ENSO. That's equivalent to about a 25-km grid box size, the same as many weather forecast models. We can now run global models over decades to centuries at the same spatial resolution as forecast models. And as we can see here, models are beginning to capture not just the large, general features of precipitation, but even details down to small scales.

And models have been run down to even finer resolution. One of these images is the result of a climate model initialized with observations, like a forecast model, and run at 5-km resolution to simulate a particular storm system. The other image is the satellite observation of the actual storm system.

Image A

Simulated Infrared Image from 5-km Goddard Earth Observing System Model, Version 5 (GEOS-5) 90-hr Forecast valid 6 Feb 2010

Image B

Simulated Infrared Image from 5-km Goddard Earth Observing System Model, Version 5 (GEOS-5) 90-hr Forecast valid 6 Feb 2010

Which image do you think is the result of the model simulation? (Choose the best answer.)

Image A

Simulated Infrared Image from 5-km Goddard Earth Observing System Model, Version 5 (GEOS-5) 90-hr Forecast valid 6 Feb 2010

Image B

GOES Infrared Image 6 Feb 2010

The correct answer is (a) Image A is the model simulation, but it's quite difficult to tell. The model simulates even small-scale features like cloud streets that broadly match the observations.

So not only are models getting more complex, but there is a parallel path wherein models are being run with increasing horizontal resolution, in both the atmosphere and the ocean. In general, the more we increase resolution, the more improvement we see in the model simulations. However, not all model fields are improving with increased resolution, and increasing resolution further may not yield significant improvement. Biases still remain, but many are now clearly related to parameterization schemes.