CLM output latitudes

[samrabin]

With the 15° longitude x 10° latitude grid (f10_f10_mg37), CLM output files have 360/15 = 24 longitudes, and they are as I would expect for a lower-left alignment (0, 15, …, 345). But there are 19 latitudes instead of 180/10 = 18, with latitudes -90, -80, …, -10, 0, 10, …, 80, 90. The inter-latitude spacing is correct, but there's an extra member.

Same for the "2-degree" grid f19_g17, which is actually 2.5° longitude x ~1.894737° latitude. The longitudes look right, but there are 96 output latitudes instead of the expected 95. Again, the problem is not the inter-latitude spacing but rather that there appears to be one extra member.

Why are the files like this, and how are they supposed to be handled? For now, I'm just chopping off the northernmost latitude, but I'm (almost) sure that's not right.

 

[samrabin]

Actually, follow-up question… The latitudes are describing the left edges of the grid, right? There aren't gridcells centered on the prime meridian and international date line?

 

[oleson]

The LATIXY and LONGXY variables on the surface datasets represent the center of each gridcell. For the 10X15 example, the "center" of the northernmost gridcell is 90. The southern boundary is 85, so this gridcell is actually 5deg in latitude instead of 10. Same for the southernmost gridcell.

 

[samrabin]

Huh, that is quite unexpected. Thanks for the clarification!