Standard names: improved permafrost characterization

[nicholas512]

The following terms are related to the characterization of permafrost; we aim to adopt them within the NSERC PermafrostNet research network as a means to promote data interoperability. We foresee applications both for the publication of observational data in an interoperable way, and for land surface models that increasingly take permafrost into consideration.

Proposer's name Nick Brown & Michel Paquette (@MichelPqt) Date 2021-05-04

Term: mass_fraction_of_gravel_in_soil Description: "Mass fraction" is used in the construction "mass_fraction_of_X_in_Y'', where X is a material constituent of Y. It is evaluated as the mass of X divided by the mass of Y (including X). It may be expressed as a fraction, a percentage, or any other dimensionless representation of a fraction. Units: 1

Term: mass_fraction_of_sand_in_soil Description: "Mass fraction" is used in the construction "mass_fraction_of_X_in_Y'', where X is a material constituent of Y. It is evaluated as the mass of X divided by the mass of Y (including X). It may be expressed as a fraction, a percentage, or any other dimensionless representation of a fraction. Units: 1

Term: mass_fraction_of_silt_in_soil Description: "Mass fraction" is used in the construction "mass_fraction_of_X_in_Y'', where X is a material constituent of Y. It is evaluated as the mass of X divided by the mass of Y (including X). It may be expressed as a fraction, a percentage, or any other dimensionless representation of a fraction. Units: 1

Term: mass_fraction_of_clay_in_soil Description: "Mass fraction" is used in the construction "mass_fraction_of_X_in_Y", where X is a material constituent of Y. It is evaluated as the mass of X divided by the mass of Y (including X). It may be expressed as a fraction, a percentage, or any other dimensionless representation of a fraction. Units: 1

Term: mass_fraction_of_organic_matter_in_soil Description: "Mass fraction" is used in the construction "mass_fraction_of_X_in_Y", where X is a material constituent of Y. It is evaluated as the mass of X divided by the mass of Y (including X). It may be expressed as a fraction, a percentage, or any other dimensionless representation of a fraction Units: 1

Term: frozen_ground_thermal_conductivity Description: Thermal conductivity is the constant k in the formula q = -k grad T where q is the heat transfer per unit time per unit area of a surface normal to the direction of transfer and grad T is the temperature gradient. Thermal conductivity is a property of the material. Units: W m-1 K-1

Term: frozen_ground_thermal_capacity Description: Thermal capacity, or heat capacity, is the amount of heat energy required to increase the temperature of 1 kg of material by 1 K. It is a property of the material. Units: J kg-1 K-1

Term: soil_water_ph Description: soil_water_ph is the measure of acidity of soil moisture, defined as the negative logarithm of the concentration of dissolved hydrogen ions in soil water. Units: 1

Term: volume_ratio_of_ice_to_ground_pores Alias: ice_saturation_index Description: "Ratio_of_X_to_Y" means X/Y. Ground pores is the volume of the porosity of the ground under natural, unfrozen conditions. Units: 1

Term: volume_fraction_of_excess_ice_in_the_ground Alias: excess ice Description: "Volume fraction" is used in the construction "volume_fraction_of_X_in_Y", where X is a material constituent of Y. It is evaluated as the volume of X divided by the volume of Y (including X).The phrase “excess_ice” means the volume of ice in the ground which exceeds the total volume of the saturated ground under thawed conditions. Units: 1 Source: https://nrc-publications.canada.ca/eng/view/ft/?id=69fb8993-1baa-4225-b33a-6a02341d383d https://doi.org/10.1002/ppp.458

Term: depth_of_surface_thaw_in_permafrost Definition: depth_of_surface_thaw is the instantaneous depth of the downward penetration of thaw from the ground surface at a given time. Permafrost is soil or rock that has remained at a temperature at or below zero degrees Celsius throughout the seasonal cycle for two or more consecutive years. The maximum measurable depth_of_surface_thaw_in_permafrost value as recorded at the end of a thawing season corresponds to the permafrost_active_layer_thickness Units: m

On the use of term “ground”: We note that existing terms use either “soil”, “bedrock”, or more recently, “solid_earth_subsurface”. For our applications, “soil” is too specific (we measure these properties beyond where plants sink their roots) and “solid_earth_subsurface” includes soil and bedrock, but is limited by the notion of a material defined as “solid earth”. As an example typical of permafrost applications, beds of massive ice several meters thick or layers of buried vegetation do not intuitively fit the definition of “solid earth” whereas in natural language, “ground” incorporates all soil phases and components including air, water, sediment or rock, and organic matter, and could be the preferred terminology.

[JonathanGregory]

Dear Nick

Thanks for your proposals. It will be good to make standard names more appealing to permafrost experts. Here are some comments.

mass_fraction_of_X_in_soil is fine, following other patterns, and all the X are present in existing names except gravel.

frozen_ground_thermal_capacity is like the existing soil_thermal_capacity, but we also have specific_heat_capacity_of_sea_water, which has the same canonical units (J kg-1 K-1). I would say that the latter is the common physical term for this quantity, so I would suggest your name should be specific_heat_capacity_of_frozen_ground, and we should make soil_thermal_capacity an alias of specific_heat_capacity_of_soil. Maybe thermal_conductivity_of_frozen_ground would also be a bit clearer? There are no existing thermal conductivity names except for soil.

Does volume_ratio_of_ice_to_ground_pores mean the fraction of the volume which is pores, and that these pores are entirely filled with ice? If so, could it be called volume_ratio_of_pores_in_ground, or volume_ratio_of_ice_in_ground?

Reading the description of volume_fraction_of_excess_ice_in_the_ground and the subsequent discussion of ground, I realise I am not sure what you actually mean by it. I think it might be solid_earth_subsurface, which you mention, and is used in one existing name to mean the solid (whatever it is) underneath the snow, seasonal ice or permanent ice, whose definition explicitly states that solid_earth_subsurface includes permafrost. But you also say, "Beds of massive ice several meters thick or layers of buried vegetation do not intuitively fit the definition of solid earth." Maybe they don't in general, but they do in the context of that existing standard name (if the vegetation is a compact solid, I suppose). Would it be bad? What do you mean by "beds of massive ice"? Is that pure ice? If so, is it permafrost? Isn't permanent ice on the surface an incipient ice-cap? Maybe you mean a pingo?

Best wishes

Jonathan

[MichelPqt]

Hi Jonathan,

Thank you for commenting on this issue.

About volume_fraction_of_ice_to_ground_pores, in permafrost the volume of ice can largely exceed pore saturation, and this ratio is basically an ice saturation index which helps determine whether excess ice is present or not. In this sense, it is different from a volume_ratio_of_pores_in_ground (since it can exceed the volume of pores). In the case of volume_ratio_of_ice_in_ground, this would be the volume of ice / volume of ground, which is not typically measured in permafrost studies (Volumetric ice content is widely used, as the volume_fraction_of_frozen_water_in_soil).

The discussion on ground vs solid_earth is important. solid_earth seemed to have appeared during a previous discussion to replace "soil", yet its use over ground (which was also suggested) wasn't discussed. ground is much more inclusive, because by definition it includes everything below the surface. In the case of beds of massive ice, we are talking about deep and thick, sometimes almost pure ice formations within permafrost, where ice is the principal component of the ground. A pingo typically contains such ice, but so does many other frost mounds, and this can also be buried glacial ice, buried sea / lake ice, or ice wedges. In addition, permafrost often forms in peatlands, where the ground is composed of vegetation and ice only (for example). In all cases, these material, and especially the high frozen water component fit poorly the concept of the rarely used solid_earth. They could be considered as solid_earth if we insist on using the term, but it would have to be better defined as an alias for ground, and not simply the "solid" portion of the ground. You also noted that there are uses of soil that would require a duplicate term to account for the ground or the solid_earth (volume_fraction_of_frozen_water_in_soil, specific_heat_capacity_of_soil, etc.). Since for now solid_earth is only used once in the convention, and is rarely used in the general literature, we figured it would be a good time to discuss its meaning and usage, and potentially replacing it with the widely used and accepted ground.

Regards,

Michel

[nicholas512]

Thanks Jonathan for the quick reply. A few comments to supplement what Michel has said:

• frozen_ground_thermal_capacity vs specific_heat_capacity_of_frozen_ground and frozen_ground_thermal_conductivity vs thermal_conductivity_of_frozen_ground. I don't see a problem with using the terms you suggested. As you pointed out, we based these off the relevant terms for soil, but if the soil ones are going to change too then all the more reason to go with the standard_name_of_X form. This also lends itself nicely to e.g. volumetric_heat_capacity_of_frozen_ground which is also common.
• Regarding volume_fraction_of_excess_ice_in_the_ground, this term measures how much more ice there is in the ground than would otherwise be possible if it were water, given the total pore space. By way of example: if a 1m column of ground with 25% excess ice were to thaw completely, one would be left with 0.25m of water atop a 0.75m column of 100% saturated "ground" (ignoring runoff).

Finally, it may be worthwhile to note that the thermal properties of frozen_ground are sometimes used as counterparts to those same thermal properties of thawed ground (e.g. frozen (λ_f) and thawed (λ_t) thermal conductivities in Nicolsky et al. (2007).

[JonathanGregory]

Dear Michel and Nick

Thanks for your replies. Rereading https://github.com/cf-convention/vocabularies/issues/119 I see that solid_earth was prefixed to solid_earth_subsurface in order to distinguish it from the sea, where subsurface is also used. Although that proposal started with ground, this seems to have been forgotten in the discussion of the distinction between surface and subsurface temperature. There are quite a few existing standard names containing ground_level, and also wrt_ground, grounded_ice, and groundwater, but not ground by itself as a medium. I agree with you that "solid Earth subsurface" means "ground" as a medium, but maybe participants in that earlier discussion (e.g. @taylor13 @awi-gamma @roy-lowry) can remember if there was a reason against it. Otherwise I would favour renaming solid_earth_subsurface_temperature as temperature_in_ground, like temperature_in_surface_snow.

Apart from the question of "ground", I found the two names about volume of ice hard to interpret, so thanks for your explanations. In order to make them more self-explanatory to a non-expert (I think, if I've understood them), would you consider ratio_of_ice_volume_in_frozen_ground_to_pore_volume_in_unfrozen_ground and ice_volume_in_frozen_ground_in_excess_of_pore_volume_in_unfrozen_ground_expressed_as_ratio? Other names use unfrozen or expressed_as (most of the latter are chemical names).

I realise I overlooked depth_of_surface_thaw_in_permafrost before. Since this instantaneous, could it not be called freezing_level_depth_in_ground?

Best wishes

Jonathan

[Polardan]

Hi Nick/Michel,

Regarding: depth_of_surface_thaw_in_permafrost.

Actually: The maximum measurable depth_of_surface_thaw_in_permafrost value as recorded near the end of a thawing season corresponds to the permafrost_active_layer_thickness.

Suggestion: change 'near' to 'at'

Cheers

[nicholas512]

@JonathanGregory

I think that ratio_of_ice_volume_in_frozen_ground_to_pore_volume_in_unfrozen_ground is suitable, provided that the alias ice_saturation_index is also available.

ice_volume_in_frozen_ground_in_excess_of_pore_volume_in_unfrozen_ground_expressed_as_ratio : Just to be sure we're on the same page, the denominator in this ratio is the volume of frozen ground, not the pore volume.

The as_ratio construction leaves a little ambiguity there, which is why I'm a bit hesitant. However, I think that if we were dealing with the extensive property excess ice content [m3] (rather than excess ice as a ratio as proposed) then ice_volume_in_frozen_ground_in_excess_of_pore_volume_in_unfrozen_ground would be a very good name, so maybe all it takes is a bit more clarity in the definition to really spell out what the ratio is. I might think on this for another day or so.

Some concerns I have with freezing_level_depth_in_ground:

• In permafrost, the "freezing level" depth is not unique. Assuming freezing at 0 °C, there could be three or more 0 degree isotherms in the ground column, so the standard name would not suffice to describe what was being measured
• Semantically, the proposed concept of thaw depth is only meaningful when the ground is thawing from the surface downwards

I do see how freezing_level_depth_in_ground provides greater generality, but I think it misses some of the semantic specificity.

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@MichelPqt - any further comments?

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@Polardan thanks for pointing this out. I will edit the original issue unless there are any objections.

[JonathanGregory]

Dear @nicholas512

I think that ratio_of_ice_volume_in_frozen_ground_to_pore_volume_in_unfrozen_ground is suitable, provided that the alias ice_saturation_index is also available.

We introduce aliases to correct mistakes or change our mind while retaining backward-compatibility, not to provide synonyms. In cases like this, where there's a commonly used but less self-explanatory phrase, it's usual to mention it in the definition e.g. "This is often known as X". Then people will find it by searching the standard name table, if they include the help text in the search. Would that be OK?

In ice_volume_in_frozen_ground_in_excess_of_pore_volume_in_unfrozen_ground_expressed_as_ratio, the denominator of the ratio is the volume of frozen ground, not the pore volume.

I see, thanks. I misunderstood - an illustration of how careful and clear we have to be! How about ice_volume_in_frozen_ground_in_excess_of_pore_volume_in_unfrozen_ground_expressed_as_fraction_of_frozen_ground_volume?

I appreciate your points regarding the thaw depth. This quantity seems similar to the existing depth_at_shallowest_isotherm_defined_by_soil_temperature. On the pattern, could we call it depth_at_shallowest_freezing_isotherm_in_ground?

By the way, do you need to name ground_temperature? You haven't requested it, but I suppose you wouldn't want to use the existing soil_temperature.

Best wishes

Jonathan

[MichelPqt]

Dear @JonathanGregory,

On the discussion surrounding depth_of_surface_thaw_in_permafrost, I think its important to avoid any reference to temperature or thermal conditions in the name. This is because ground often thaws while remaining cryotic (with temperature <0°C), due to salinity content or other factors. In many case, this measurement is performed by probing the ground, and therefore the thermal conditions are not as important as the phase of the ice cement / water in the ground. The use of thaw also relates to the dominant condition of the ground (frozen), which is affected by the passing warm conditions, and therefore thaws seasonally and briefly. Therefore, it is not a depth to an isotherm, rather a surface_thickness_of_unfrozen_ground, or thickness_of_unfrozen_ground_from_the_surface. I'm not sure these are well constructed, however.

Regards,

Michel

[JonathanGregory]

Dear @MichelPqt

Ah, I see, thanks. Your suggestions make sense, but I'm slightly doubtful about whether surface might be confusing. What do you think of thickness_of_unfrozen_ground_layer or depth_at_base_of_unfrozen_ground? Since depth means a distance below the surface, the second is clearest in specifying that it refers to a layer which extends from the surface downwards.

Best wishes

Jonathan

[nicholas512]

@JonathanGregory

Thanks for the clarification about aliases.

ice_volume_in_frozen_ground_in_excess_of_pore_volume_in_unfrozen_ground_expressed_as_fraction_of_frozen_ground_volume : I think this is clear. The definition will have to change to reflect the different name and to replace the alias information. Something along the lines of:

ice_volume_in_frozen_ground_in_excess_of_pore_volume_in_unfrozen_ground_expressed_as_fraction_of_frozen_ground_volume represents the fractional amount of "excess ice" in frozen ground. Excess ice is the volume of ice in the ground which exceeds the total pore volume that the ground would have under natural unfrozen conditions. Due to the presence of ground ice, the total water content of a frozen soil may exceed that corresponding to its normally consolidated state when unfrozen. As a result, upon thawing, a soil containing excess ice will settle under its own weight until it attains its consolidated state. Reference: van Everdingen, R. O. editor 1998: Multi-language glossary of permafrost and related ground ice terms. International Permafrost Association.

ground_temperature: In my opinion this would be a good term to have (or temperature_in_ground as you suggest above) for the reasons laid out by Michel. The reason we didn't propose it because of possible overlap with solid_earth_subsurface_temperature. However, if this is a case where renaming or adding an alias is appropriate I'd be happy to update the issue to include it.

[JonathanGregory]

Dear Nick @nicholas512

Sorry, of course - we've already discussed this. I'm still in favour of renaming solid_earth_subsurface_temperature as temperature_in_ground or ground_temperature, with solid_earth_subsurface_temperature becoming an alias. I hope others will comment who contributed to the earlier discussion.

Thanks

Jonathan

[MichelPqt]

Hi @JonathanGregory and @nicholas512,

Here's a recap of the discussion so far:

There was a compelling argument to rename solid_earth_subsurface_temperature to temperature_in_ground, since ground is more inclusive to a range of material and phases and more widely used than solid_earth. solid_earth_subsurface_temperature would become an alias.

The submission volume_fraction_of_excess_ice_in_the_ground, was modified to: ice_volume_in_frozen_ground_in_excess_of_pore_volume_in_unfrozen_ground_expressed_as_fraction_of_frozen_ground_volume, with the definition: ice_volume_in_frozen_ground_in_excess_of_pore_volume_in_unfrozen_ground_expressed_as_fraction_of_frozen_ground_volume represents the fractional amount of "excess ice" in frozen ground. Excess ice is the volume of ice in the ground which exceeds the total pore volume that the ground would have under natural unfrozen conditions. Due to the presence of ground ice, the total water content of a frozen soil may exceed that corresponding to its normally consolidated state when unfrozen. As a result, upon thawing, a soil containing excess ice will settle under its own weight until it attains its consolidated state. Reference: van Everdingen, R. O. editor 1998: Multi-language glossary of permafrost and related ground ice terms. International Permafrost Association.

The submission: volume_ratio_of_ice_to_ground_pores should be modified to ratio_of_ice_volume_in_frozen_ground_to_pore_volume_in_unfrozen_ground. The description should be changed to: "Ratio_of_X_to_Y" means X/Y. Pore volume is the volume of the porosity of the ground under natural, unfrozen conditions. This is often known as "ice saturation index". Units: 1

The submission depth_of_surface_thaw_in_permafrost was modified to thickness_of_unfrozen_ground_layer or depth_at_base_of_unfrozen_ground. Both seem fine to me, and @JonathanGregory suggested depth_at_base_of_unfrozen_ground should be preferred since depth already implies a dimension. The definition would be: Definition: depth_at_base_of_unfrozen_ground is the instantaneous depth of the downward penetration of thaw from the ground surface at a given time. Permafrost is soil or rock that has remained at a temperature at or below zero degrees Celsius throughout the seasonal cycle for two or more consecutive years. The maximum measurable depth_at_base_of_unfrozen_ground value as recorded at the end of a thawing season corresponds to the permafrost_active_layer_thickness. Units: m

The submissions frozen_ground_thermal_conductivityand frozen_ground_thermal_capacity should be changed to thermal_conductivity_of_frozen_ground and specific_heat_capacity_of_frozen_ground, with the following descriptions:

Description: Thermal conductivity is the constant k in the formula q = -k grad T where q is the heat transfer per unit time per unit area of a surface normal to the direction of transfer and grad T is the temperature gradient. Thermal conductivity is a property of the material. Units: W m-1 K-1

Term: specific_heat_capacity_of_frozen_ground Description: Thermal capacity, or heat capacity, is the amount of heat energy required to increase the temperature of 1 kg of material by 1 K. It is a property of the material. Units: J kg-1 K-1

The following submissions seemed fine, but I received comments that asked for the grain-size scale to be divulged in the description:

Term: mass_fraction_of_gravel_in_soil Description: "Mass fraction" is used in the construction "mass_fraction_of_X_in_Y'', where X is a material constituent of Y. It is evaluated as the mass of X divided by the mass of Y (including X). It may be expressed as a fraction, a percentage, or any other dimensionless representation of a fraction. Grain-size class distribution is based on the Udden-Wentworth scale Units: 1

Term: mass_fraction_of_sand_in_soil Description: "Mass fraction" is used in the construction "mass_fraction_of_X_in_Y'', where X is a material constituent of Y. It is evaluated as the mass of X divided by the mass of Y (including X). It may be expressed as a fraction, a percentage, or any other dimensionless representation of a fraction. Grain-size class distribution is based on the Udden-Wentworth scale Units: 1

Term: mass_fraction_of_silt_in_soil Description: "Mass fraction" is used in the construction "mass_fraction_of_X_in_Y'', where X is a material constituent of Y. It is evaluated as the mass of X divided by the mass of Y (including X). It may be expressed as a fraction, a percentage, or any other dimensionless representation of a fraction. Grain-size class distribution is based on the Udden-Wentworth scale Units: 1

Term: mass_fraction_of_clay_in_soil Description: "Mass fraction" is used in the construction "mass_fraction_of_X_in_Y", where X is a material constituent of Y. It is evaluated as the mass of X divided by the mass of Y (including X). It may be expressed as a fraction, a percentage, or any other dimensionless representation of a fraction. Grain-size class distribution is based on the Udden-Wentworth scale Units: 1

Term: mass_fraction_of_organic_matter_in_soil Description: "Mass fraction" is used in the construction "mass_fraction_of_X_in_Y", where X is a material constituent of Y. It is evaluated as the mass of X divided by the mass of Y (including X). It may be expressed as a fraction, a percentage, or any other dimensionless representation of a fraction Units: 1

Term: soil_water_ph Description: soil_water_ph is the measure of acidity of soil moisture, defined as the negative logarithm of the concentration of dissolved hydrogen ions in soil water. Units: 1

I think this sums it up, anything else to add?

Cheers,

Michel

[JonathanGregory]

Dear @MichelPqt

That looks very good to me. Thanks!

Best wishes

Jonathan

[feggleton]

Hi all,

Thank you for this proposal. I think I have managed to get all the terms and the changes into the cfeditor correctly. I will clarify all below. Please let me know if there are any parts I have got wrong or any more discussions to be had.

Changes to an existing name: solid_earth_subsurface_temperature

Term: temperature_in_ground Definition: The quantity with standard name solid_earth_subsurface_temperature is the temperature at any depth (or in a layer) of the "solid" earth, excluding surficial snow and ice (but not permafrost or soil). For temperatures in surface lying snow and ice, the more specific standard names temperature_in_surface_snow and land_ice_temperature should be used. For temperatures measured or modelled specifically in the soil layer (the near-surface layer where plants sink their roots) the standard name soil_temperature should be used.

Changes need to be made to the definition which I don't think is just a case of switching the name in the first sentence. Do we need to remove the term 'solid earth' if we are now referring to 'ground'?

This term is also referred to in one name which might need to be changed:

soil_temperature Soil temperature is the bulk temperature of the soil, not the surface (skin) temperature. "Soil" means the near-surface layer where plants sink their roots. For subsurface temperatures that extend beneath the soil layer or in areas where there is no surface soil layer, the standard name solid_earth_subsurface_temperature should be used.

Other terms include:

Term:ice_volume_in_frozen_ground_in_excess_of_pore_volume_in_unfrozen_ground_expressed_as_fraction_of_frozen_ground_volume Definition:ice_volume_in_frozen_ground_in_excess_of_pore_volume_in_unfrozen_ground_expressed_as_fraction_of_frozen_ground_volume represents the fractional amount of "excess ice" in frozen ground. Excess ice is the volume of ice in the ground which exceeds the total pore volume that the ground would have under natural unfrozen conditions. Due to the presence of ground ice, the total water content of a frozen soil may exceed that corresponding to its normally consolidated state when unfrozen. As a result, upon thawing, a soil containing excess ice will settle under its own weight until it attains its consolidated state. Reference: van Everdingen, R. O. editor 1998: Multi-language glossary of permafrost and related ground ice terms. International Permafrost Association.

Term:ratio_of_ice_volume_in_frozen_ground_to_pore_volume_in_unfrozen_ground Definition:The phrase "ratio_of_X_to_Y" means X/Y. "X_volume" means the volume occupied by X within the grid cell. Pore volume is the volume of the porosity of the ground under natural, unfrozen conditions. This is often known as "ice saturation index".

Term:depth_at_base_of_unfrozen_ground Definition:The phrase depth_at_base_of_unfrozen_ground is the instantaneous depth of the downward penetration of thaw from the ground surface at a given time. Permafrost is soil or rock that has remained at a temperature at or below zero degrees Celsius throughout the seasonal cycle for two or more consecutive years. The maximum measurable depth_at_base_of_unfrozen_ground value as recorded at the end of a thawing season corresponds to the permafrost_active_layer_thickness.

Term:thermal_conductivity_of_frozen_ground Definition:Thermal conductivity is the constant k in the formula q = -k grad T where q is the heat transfer per unit time per unit area of a surface normal to the direction of transfer and grad T is the temperature gradient. Thermal conductivity is a property of the material.

Term:specific_heat_capacity_of_frozen_ground Definition:Thermal capacity, or heat capacity, is the amount of heat energy required to increase the temperature of 1 kg of material by 1 K. It is a property of the material.

Term:mass_fraction_of_gravel_in_soil Definition:"Mass fraction" is used in the construction "mass_fraction_of_X_in_Y'', where X is a material constituent of Y. It is evaluated as the mass of X divided by the mass of Y (including X). It may be expressed as a fraction, a percentage, or any other dimensionless representation of a fraction. Grain-size class distribution is based on the Udden-Wentworth scale.

Term:mass_fraction_of_sand_in_soil Definition:"Mass fraction" is used in the construction "mass_fraction_of_X_in_Y'', where X is a material constituent of Y. It is evaluated as the mass of X divided by the mass of Y (including X). It may be expressed as a fraction, a percentage, or any other dimensionless representation of a fraction. Grain-size class distribution is based on the Udden-Wentworth scale.

Term:mass_fraction_of_silt_in_soil Definition:"Mass fraction" is used in the construction "mass_fraction_of_X_in_Y'', where X is a material constituent of Y. It is evaluated as the mass of X divided by the mass of Y (including X). It may be expressed as a fraction, a percentage, or any other dimensionless representation of a fraction. Grain-size class distribution is based on the Udden-Wentworth scale.

Term:mass_fraction_of_clay_in_soil Definition:"Mass fraction" is used in the construction "mass_fraction_of_X_in_Y", where X is a material constituent of Y. It is evaluated as the mass of X divided by the mass of Y (including X). It may be expressed as a fraction, a percentage, or any other dimensionless representation of a fraction. Grain-size class distribution is based on the Udden-Wentworth scale.

Term:mass_fraction_of_organic_matter_in_soil Definition: "Mass fraction" is used in the construction "mass_fraction_of_X_in_Y", where X is a material constituent of Y. It is evaluated as the mass of X divided by the mass of Y (including X). It may be expressed as a fraction, a percentage, or any other dimensionless representation of a fraction.

Term:soil_water_ph Definition:soil_water_ph is the measure of acidity of soil moisture, defined as the negative logarithm of the concentration of dissolved hydrogen ions in soil water.

[MichelPqt]

Hi Francesca,

Thank you for your edits. I think you're right that we should remove the reference to solid_earth_subsurface_temperature from the soil_temperature definition, and replace it with temperature_in_ground. For the definition of temperature_in_ground, I would suggest the following change:

Term: temperature_in_ground Definition: The temperature at any given depth (or in a layer) below the surface of the ground, excluding surficial snow and ice (but not permafrost or soil). For temperatures in surface lying snow and ice, the more specific standard names temperature_in_surface_snow and land_ice_temperature should be used. For temperatures measured or modelled specifically for the soil layer (the near-surface layer where plants sink their roots) the standard name soil_temperature should be used.

How does that sound to you @nicholas512 ?

MP

[nicholas512]

@MichelPqt @feggleton This all looks good to me. Good catch on the soil_temperature description.

[feggleton]

Thank you all. If there are no further comments in the next 7 days then these terms can be accepted.

[feggleton]

These terms have now been accepted.

[japamment]

Changes applied in version 78 of the standard name table.