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Climate Model Resolution

 

The following images were created to help illustrate the differences in climate model resolution.

 

11.13 KM or .1 degree resolution

55 KM or .5 degree resolution

111 KM or 1 degree resolution

300 KM or 2.8 degree resolution

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In each case, the visualization was generated beginning with 8 KM/pixel NASA imagery*.  The imagery was then resampled to generate a height map and image overlay that represent 4 different model resolutions: .1 degree, .5 degree, 1 degree, and 2.8 degree. *Input imagery courtesy of Blue Marble Next Generation, Reto Stockli, NASA Earth Observatory.

 

"Resolution is an important concept in many types of modeling, including climate modeling.Spatial resolution specifies how large (in degrees of latitude and longitude or in km or miles) the grid cells in a model are. Temporal resolution refers to the size of the time steps used in models; how often (in simulated or "model time") calculations of the various properties being modeled are conducted (12-hour time steps are typical).

 

Models use grids of "cells" to establish the locations at which to perform calculations and thus make estimates of the traits (temperature, wind speed, etc.) that are of concern for that model. A typical climate model might have grid cells with a size of about 100 km (62 miles) on a side. Although we know that traits like temperature vary continuously across the face of the Earth, calculating such properties for the entire globe is beyond the reach of even the fastest supercomputers. Instead, the models typically use an algorithm that might be expressed as "calculate the temperature at a point, then move 100 km west and calculate temperature again; then move another 100 km west and repeat; once you've gone all the way around the globe, move 100 km north and repeat the process; and so on". In effect, the model places "virtual weather stations" at 100 km intervals and reports the calculated properties at each of the "weather stations". The "virtual weather stations" are located at the corners of the grid cells. So, for a model with 100 km resolution, we only know the predicted temperature (wind speed, etc.) at 100 km intervals. We can interpolate values in between "weather stations", but the reliability of such interpolations is limited.

 


 


Models can be generated with higher or lower resolutions. The grid cells could be reduced in size to 50 km, thus requiring more cells to cover Earth's surface and increasing resolution; or could be enlarged to 200 km, requiring fewer cells and decreasing resolution. More (and smaller) cells lead to increased computing time; there are simply more "virtual weather stations" at which atmospheric variables must be calculated. Higher resolution models provide much more detailed information, but at the cost of longer run times for the models on supercomputers.


Remember, atmospheric models (including climate models) also have grid cells in the vertical direction, representing the variations that come with altitude in Earth's atmosphere. The images shown here just depict resolution in latitude and longitude directions.” – excerpted from “Windows to the Universe”