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Possible ambiguity of wind_from_direction_at_surface regarding degrees #153
Description
The name wind_from_direction_at_surface has units of degrees, and the description says "Direction, from north, of wind speed closest to surface".
The _at_surface part of the name has ambiguities, but those are being discussed in #151, and are not the point of this issue.
The question I have here is about the orientation of the degrees. Does a wind blowing out of the south, towards the north, have a direction of zero degrees or 180 degrees? Is a west-to-east wind 90 degrees or 270? I think the answers are 180 and 270, but it seems like it's possible for there to be some confusion on this, and it would be nice to make it more explicit in the description.
Activity
svahl991 commentedon Jul 7, 2026
Tagging @rajichidamb on this issue since we discussed looking into the standard that CRTM uses for this, as it appears to be opposite the standard meteorological definition.
dudhia commentedon Jul 7, 2026
Yes 180 and 270.
Also I prefer wind_direction over wind_from_direction which sounds a bit awkward. I guess they are trying to avoid ambiguity, but the meaning of wind direction is quite standard.
rajichidamb commentedon Jul 7, 2026
Talked to BenjaminTJohnson, confirmed that in CRTM the wind direction from South to North corresponds to zero degrees and is following the Oceanographic standard definition.
mkavulich commentedon Jul 7, 2026
The CF names have two definitions for wind direction (differences in italics, important definition in bold):
wind_from_direction: Wind is defined as a two-dimensional (horizontal) air velocity vector, with no vertical component. (Vertical motion in the atmosphere has the standard name upward_air_velocity.) In meteorological reports, the direction of the wind vector is usually (but not always) given as the direction from which it is blowing (wind_from_direction) (westerly, northerly, etc.). In other contexts, such as atmospheric modelling, it is often natural to give the direction in the usual manner of vectors as the heading or the direction to which it is blowing (wind_to_direction) (eastward, southward, etc.) "from_direction" is used in the construction X_from_direction and indicates the direction from which the velocity vector of X is coming.wind_to_direction: Wind is defined as a two-dimensional (horizontal) air velocity vector, with no vertical component. (Vertical motion in the atmosphere has the standard name upward_air_velocity.) In meteorological reports, the direction of the wind vector is usually (but not always) given as the direction from which it is blowing (wind_from_direction) (westerly, northerly, etc.). In other contexts, such as atmospheric modelling, it is often natural to give the direction in the usual manner of vectors as the heading or the direction to which it is blowing (wind_to_direction) (eastward, southward, etc.) "to_direction" is used in the construction X_to_direction and indicates the direction towards which the velocity vector of X is headed. The direction is a bearing in the usual geographical sense, measured positive clockwise from due north.So as I expected, there are contexts where both the wind velocity vector (2.) and wind source vector (1.) are used. The definition of the "direction" is defined in what seems to be the typical way for geoscience contexts: 0 is the north direction, increasing clockwise.
Given this information, and especially with the fact that JEDI seems to have to deal with a mix of definitions, I would propose we maintain
wind_from_direction, add awind_to_directionwhere needed, and define "direction" the same way it is defined in the CF names above.svahl991 commentedon Jul 7, 2026
Sounds good. Thanks for the speedy answer @mkavulich . I know this issue isn't fully resolved, but since JEDI moves fast, I will proceed as if both
wind_from_directionandwind_to_directionare valid ESM names, with 0 degrees being north for both, and degrees going clockwise.Tagging @BenjaminTJohnson
BenjaminRuston commentedon Jul 8, 2026
yes thanks @svahl991 think we can get this fixed in the CRTM interface, and since it's 180-degrees out of phase think the CRTM emissivity models (SURFEM) for ocean emissivity is the primary one here will actually provide the same estimate for that
but let's keep and maintain the JEDI convention in JEDI and treat CRTM as external and have conversion to its convention as the SURFEM ocean model is a community model and not something under CRTM control:
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2022EA002785
Improve definitions and usage of "surface" vs "surface_adjacent_layer…
mkavulich commentedon Sep 1, 2026
Resolved by #155