Changes between Initial Version and Version 2 of Ticket #152
 Timestamp:
 07/13/16 00:57:28 (3 years ago)
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Ticket #152 – Description
initial v2 3 3 The proposal is to make it clear that use of `where` for nonspatial dimensions is allowed by adding examples in section 7. It is also necessary to provide these examples to clarify the subtle differences implied by different formulations of the `cell_methods` statement. 4 4 5 The following should be added as a new example in section 7.3.3: 5 == New example for timevarying area fractions == 6 7 ''The following new example and explanatry text should be added in section 7.3.3:'' 6 8 7 9 Example 7.8: Time mean over area fractions which vary with time … … 15 17 16 18 float partial_mean(lat,lon): 17 partial_mean:cell_methods: area: mean where sea_ice over sea time: mean19 partial_mean:cell_methods: area: mean where sea_ice over sea time: mean 18 20 }}} 19 21 20 22 When the area fraction is varying with time, there are several different ways in which a time mean can be formulated. Three of these are illustrated in this example. Suppose, for instance, we are averaging over three time steps and the data at one grid point is 10, 6, 2 with area fractions .75, .50, .25. The values of the simple_mean, weighted_mean and partial mean are, respectively, (10 6 2)/3 = 6, (10*.75  6*.5 2*.25)/(.75+.5+.25) = 7.33 , and (10*.75  6*.5 2*.25)/3 = 3.667. The partial mean provides the contribution to the mean over the entire grid from a specified area type. The simple mean is weighting each time period equally, while the weighted mean provides equal weighting to each unit area of `sea_ice`. 23 24 In example 7.8, `time` could be replaced by any other coordinate over which an average is taken, such as an ensemble index. 25 26