Dear Jonathan and Martin,
I just reread my previous message and realised I had copied and pasted the same text twice, so it doesn't make sense!
What I meant to say is that I have suggested:
tendency_of_thermal_energy_content_of_surface_snow_due_to_rainfall_temperature_excess_above_freezing
for the heat flux name. At the moment it is limited to surface_snow, but we could change it to say ice_and_snow_on_land if necessary.
This fits well with change_over_time_in_thermal_energy_content_of_ice_and_snow_on_land in the other set of LS3MIP proposals.
Sorry for any confusion!
Best wishes,
Alison
------
Alison Pamment Tel: +44 1235 778065
NCAS/Centre for Environmental Data Archival Email: alison.pamment at stfc.ac.uk
STFC Rutherford Appleton Laboratory
R25, 2.22
Harwell Oxford, Didcot, OX11 0QX, U.K.
-----Original Message-----
From: CF-metadata <cf-metadata-bounces at cgd.ucar.edu> On Behalf Of Alison Pamment - UKRI STFC
Sent: 29 June 2018 10:41
To: Juckes, Martin (STFC,RAL,RALSP) <martin.juckes at stfc.ac.uk>; 'Jonathan Gregory' <j.m.gregory at reading.ac.uk>; 'cf-metadata at cgd.ucar.edu' <cf-metadata at cgd.ucar.edu>
Subject: Re: [CF-metadata] Final 17 terms for CMIP6 LS3MIP: Heat flux into snowpack
Dear Martin and Jonathan,
This is just to follow up on my suggestion of using thermal energy content instead of sensible heat flux for proposal 3:
change_over_time_in_thermal_energy_content_of_ice_and_snow_on_land (J m-2).
'The phrase "change_over_time_in_X" means change in a quantity X over a time-interval, which should be defined by the bounds of the time coordinate. The surface called "surface" means the lower boundary of the atmosphere. "Content" indicates a quantity per unit area. Thermal energy is the total vibrational energy, kinetic and potential, of all the molecules and atoms in a substance. The phrase "ice_and_snow_on_land" means ice in glaciers, ice caps, ice sheets & shelves, river and lake ice, any other ice on a land surface, such as frozen flood water, and snow lying on such ice or on the land surface.
In the final set of names (Standard names for LS3MIP: 8 temporal changes + 1 feature depth -
http://mailman.cgd.ucar.edu/pipermail/cf-metadata/2018/020371.html) proposal 1.8 is for change_over_time_in_thermal_energy_content_of_ice_and_snow_on_land (J m-2).
'The phrase "change_over_time_in_X" means change in a quantity X over a time-interval, which should be defined by the bounds of the time coordinate. The surface called "surface" means the lower boundary of the atmosphere. "Content" indicates a quantity per unit area. Thermal energy is the total vibrational energy, kinetic and potential, of all the molecules and atoms in a substance. The phrase "ice_and_snow_on_land" means ice in glaciers, ice caps, ice sheets & shelves, river and lake ice, any other ice on a land surface, such as frozen flood water, and snow lying on such ice or on the land surface.
I think the two names as listed here fit well together, and with the existing name thermal_energy_content_of_surface_snow. This has now convinced me that this is indeed the correct approach to the heat flux name. Do you agree?
Best wishes,
Alison
------
Alison Pamment Tel: +44 1235 778065
NCAS/Centre for Environmental Data Archival Email: alison.pamment at stfc.ac.uk
STFC Rutherford Appleton Laboratory
R25, 2.22
Harwell Oxford, Didcot, OX11 0QX, U.K.
-----Original Message-----
From: Pamment, Alison (STFC,RAL,RALSP)
Sent: 28 June 2018 18:32
To: Juckes, Martin (STFC,RAL,RALSP) <martin.juckes at stfc.ac.uk>; Jonathan Gregory <j.m.gregory at reading.ac.uk>; cf-metadata at cgd.ucar.edu
Subject: RE: [CF-metadata] Final 17 terms for CMIP6 LS3MIP.
Dear Martin and Jonathan,
We are getting very close to agreeing all these names and I'd like to include as many as possible in the standard names update next week. Unless anyone objects I am going to accept and include the following proposals as written in
http://mailman.cgd.ucar.edu/pipermail/cf-metadata/2018/020350.html:
1.1 canopy_albedo (1)
7.1 downward_liquid_water_mass_flux_into_groundwater (kg m-2 s-1)
7.5 land_surface_liquid_water_amount (kg m-2) as I haven't received any further comments on these.
The only other ones still under discussion are the river transport and heat flux into snow pack names.
5.1, 5.2. As stated previously, I did in fact publish the river names in Version 55 of the standard name table as river_water_volume_transport_into_cell and river_water_volume_transport_out_of_cell but Jonathan pointed out that it would be better to avoid mention of grid cells. I think we are now close to agreeing aliases for these. There seem to be two alternatives on the table:
inward_water_volume_transport_along_river_channel
outward_water_volume_transport_along_river_channel
OR
incoming_water_volume_transport_along_river_channel
outoing_water_volume_transport_along_river_channel.
The latter reflects the use of incoming/outgoing in radiation names. My (slight) preference is for the first pair because we are trying to avoid the impression of water entering/leaving the channel itself and I think incoming/outgoing might be a bit misleading, but if others prefer the second option I will go with the majority decision. Please can we have a quick vote on which is the preferred option?
3. The heat flux name has caused a lot of discussion - thank you to Karl, Martin and Jonathan who have all commented on this one so far. We have three current suggestions:
I suggested surface_downward_sensible_heat_flux_due_to_rainfall_temperature_excess_above_freezing which avoided saying 'anomaly'; Jonathan wasn't sure about using 'sensible' heat flux in this context and suggested simply omitting it: surface_downward_heat_flux_due_to_rainfall_temperature_excess_above_freezing;
Martin is suggesting surface_downward_sensible_heat_flux_due_to_rainfall_temperature because the concept of a sensible heat flux is intrinsically related to the existence of a temperature anomaly.
I note that in the definitions of three of the four existing sensible heat flux names we say 'The surface sensible heat flux, also called "turbulent" heat flux, is the exchange of heat between the surface and the air by motion of air' so, on reflection, I agree with Jonathan that this makes the use of 'sensible' rather problematic in this case.
Martin mentioned the concept of heat content, and thinking again about the quantity we are trying to describe, I think it would be correct to regard it as the addition of heat content to the snow pack due to the interception of rainfall that has a higher temperature. Martin has also pointed out that the reference state is important, which is why I originally suggested 'excess_above_freezing'. Could we call it tendency_of_heat_content_of_surface_snow_due_to_rainfall_temperature_excess_above_freezing? We do have an existing name thermal_energy_content_of_surface_snow which says 'Thermal energy is the total vibrational energy, kinetic and potential, of all the molecules and atoms in a substance' so we could alternatively say tendency_of_thermal_energy_content_of_surface_snow_due_to_rainfall_temperature_excess_above_freezing. I note also that we have the name soil_thermal_capacity defined as 'Thermal capacity, or heat capacity, is the amount of heat energy required to increase the tempe rature of 1 kg of mater
ial by 1 K. It is a property of the material' so it would seem we have used the terms 'thermal_energy' and 'heat_energy' interchangeably.
My new suggestion does of course assume that the rain is definitely falling onto snow, but we have recently discussed names for 'snow and ice on land' if that is a more appropriate surface type.
Best wishes,
Alison
------
Alison Pamment Tel: +44 1235 778065
NCAS/Centre for Environmental Data Archival Email: alison.pamment at stfc.ac.uk
STFC Rutherford Appleton Laboratory
R25, 2.22
Harwell Oxford, Didcot, OX11 0QX, U.K.
-----Original Message-----
From: CF-metadata <cf-metadata-bounces at cgd.ucar.edu> On Behalf Of Martin Juckes - UKRI STFC
Sent: 26 June 2018 12:17
To: Jonathan Gregory <j.m.gregory at reading.ac.uk>; cf-metadata at cgd.ucar.edu
Subject: Re: [CF-metadata] Final 17 terms for CMIP6 LS3MIP.
Dear Jonathan,
I'd like to pick up on a comment which you made in the thread about ocean terms "expressed_as_heat_content" (
http://mailman.cgd.ucar.edu/pipermail/cf-metadata/2018/020364.html). You refer to the fact that "thermal energy" is sometimes used in the standard names. I've looked into this to try to understand different usages both within the standard name list and elsewhere.
We have two names referring to thermal energy (always as thermal energy content):
* change_over_time_in_thermal_energy_content_of_vegetation_and_litter_and_soil
* thermal_energy_content_of_surface_snow
and 4 referring to sensible heat (always as sensible heat flux):
* integral_wrt_time_of_surface_downward_sensible_heat_flux
* surface_downward_sensible_heat_flux
* surface_upward_sensible_heat_flux
* upward_sensible_heat_flux_in_air
Usage of "sensible heat" vs. "thermal energy" outside the CF standard names is variable, but there appears to be a consensus that "sensible heat" is not really a measure of the energy but a measure of the energy released or absorbed as a result of temperature changes. This is consistent with the terms we have. Energy fluxes at the surface are partitioned into radiative, latent and sensible heat fluxes.
"thermal_energy_content" appears to be equivalent to "heat_content", which is used in 16 oceanographic terms and is part of the discussion on the thread I've linked to above, except that "heat_content" is only used in the construct "X_expressed_as_heat_content". This makes sense, as "heat_content" is a rather ambiguous concept, and it is the specification of "X" which makes the oceanographic terms precise.
"thermal energy" is related to "internal energy", but, as far as I can make out, "internal energy" is a thermodynamic state function which is well defined, while "thermal energy" is sometimes taken as a measure of heat needed to reach the current state which depends on the thermodynamic pathway take, and sometimes defined in terms of the kinetic and potential energy of molecules. The two thermal energy content terms in the CF standard names are less precisely defined than the oceanographic heat content terms, but I think this reflects the state of the art in the different domains, with heat content being a more central concern in oceanography.
After reading this, I can see that sensible heat fluxes are, in some sense, intrinsically related to a temperature anomalies, so there is no need to put "anomaly" explicitly in the name, so I would be happy to go with surface_downward_sensible_heat_flux_due_to_rainfall_temperature. As I understand it, we are looking at terms in a heat budget, where the heat is measured relative to a reference state at zero Centigrade, so that adding rain water at zero Centigrade leaves the heat content unchanged. If we were looking at the full thermodynamic energy, then there is of course a certain amount of energy in water at zero Centigrade, so this concept of a reference state is important in all these sensible heat flux and heat content terms.
regards,
Martin
________________________________
From: CF-metadata <cf-metadata-bounces at cgd.ucar.edu> on behalf of Martin Juckes - UKRI STFC <martin.juckes at stfc.ac.uk>
Sent: 12 June 2018 16:01
To: Jonathan Gregory; cf-metadata at cgd.ucar.edu
Subject: Re: [CF-metadata] Final 17 terms for CMIP6 LS3MIP.
Dear Jonathan,
(1) downward flux of heat in rainfall
OK, I can see the problem. surface_downward_sensible_heat_flux is currently defined to be the downward flux of sensible heat associated with air motions. That doesn't look right to me. Rain clearly has sensible heat and clearly carries it downwards. "Sensible heat" is widely used synonym for thermal energy, so I don't think we can justify restricting it to apply only to the thermal energy of air.
I still think it is better to use "anomaly" ... it would not break anything and would make the term clearer.
(2) I can see your point about a lake. I was thinking of rivers, and at any point on the river the water is flowing from upstream to downstream of that point. A lake is a special case in that it is a flat area, so it is normal to speak of upstream and downstream areas relative to the lake. For a grid cell with complex sub-grid topography, I think it is more natural to talk about inward and outward flow.
regards,
Martin
________________________________
From: CF-metadata <cf-metadata-bounces at cgd.ucar.edu> on behalf of Jonathan Gregory <j.m.gregory at reading.ac.uk>
Sent: 12 June 2018 14:50
To: cf-metadata at cgd.ucar.edu
Subject: Re: [CF-metadata] Final 17 terms for CMIP6 LS3MIP.
Dear Martin and Alison
> surface_downward_sensible_heat_flux_due_to_rainfall_temperature_anomal
> y
>
> The rainfall temperature anomaly is the temperature of the snow relative to the zero Celsius. The sensible heat flux due the rainfall temperature anomaly is the product of three terms: the rainfall mass flux, the specific heat capacity of the rain and the temperature anomaly.
I following your reasoning and thanks for the explanation. I don't like "temperature flux" either. (In oceanography, I don't like the concept itself, because the zero of temperature is arbitrary, and a temperature flux tells you nothing about heat convergence.) To me "sensible heat flux" doesn't seem right for this quantity, because that term is always used for turbulent heat fluxes in air. This is a bit different. Also, "anomaly" isn't right, because we use this to mean a difference from climatology. I would therefore favour being more explicit, and more closely related to the description of the proposers, which refers specifically to rainfall onto snow. What about
heat_flux_into_surface_snow_due_to_rainfall_temperature
> 5. River in- and out-flow [2]
> inward_water_volume_transport_in_river_channel
> outward_water_volume_transport_in_river_channel
It's good to base them on existing names, but I don't follow why you think from_upstream and to_downstream don't work. If we are thinking of a cell, or in non-model terms some body of water like a lake, the inflow is necessarily from upstream, and the outflow is to downstream. That's the way gravity works.
:-)
Best wishes
Jonathan
>
> 3.1 hfrs Heat transferred to snowpack by rainfall [W m-2]
>
> I have heard back from Hyungjun Kim, and this term should represent the same thermodynamic quantity as the variable hfrainds, which was in CMIP5 with temperature_flux_due_to_rainfall_expressed_as_heat_flux_into_sea_water. The definition of this CF term, which Alison has copied into the discussion below, make it clear that it relates to the flux of sensible heat (i.e. thermal energy) associated with the a temperature anomaly relative to zero Celsius. The fact that it is not the full thermal energy of the rain drops, but only an anomaly component evidently makes the naming harder. The phrase "temperature flux" appears to come from some work by Stommel, who made use of a related term, albeit with different units. I agree with Karl that it is not a very helpful term here, and it would be even more unhelpful if we take it out of the oceanography context and into a land snow term.
>
> Oceanographers refer to the "temperature anomaly relative to zero Celsius" as "the temperature in units of degrees Celsius", which is obviously correct -- up to a point, yet, in an obscure way, not quite right when transplanted into the CF list and the mandated adoption of the UNIDATA interpretation of units. Converting "emperature in units of degrees Celsius" to Kelvin gives a different answer to converting "temperature anomaly relative to zero Celsius" to Kelvin: here we want the latter, so it is important to be explicit that we are talking about a temperature anomaly.
>
> The word "anomaly" is most often used in the CF standard names to refer to an anomaly relative to climatology, but I think we can use it for an anomaly relative to 0 degC -- unless there is a better word?
>
>
> Hence, I suggest:
>
> surface_downward_sensible_heat_flux_due_to_rainfall_temperature_anomal
> y
>
> The rainfall temperature anomaly is the temperature of the snow relative to the zero Celsius. The sensible heat flux due the rainfall temperature anomaly is the product of three terms: the rainfall mass flux, the specific heat capacity of the rain and the temperature anomaly.
>
>
> For the term hfrs this should be used with area type snow. The name temperature_flux_due_to_rainfall_expressed_as_heat_flux_into_sea_water could be aliased to this new term, and hfrainds would then need to use area type ice free sea.
>
>
> > 5. River in- and out-flow [2]
> > river_water_volume_transport_into_cell
> > river_water_volume_transport_out_of_cell
>
>
> Jonathan has suggested using "upstream" and "downstream" instead of into/out_of cell ... to avoid making the term specific to model grid cells. I don't think that will work here. The key concept is flow inwards vs. flow outwards across the boundary of the cell. It could be expressed relative to a region which defaults to the grid cell. But the terms could be expressed in a more generic way.
>
>
> I also notice that we already have a CF term water_volume_transport_in_river_channel which we should perhaps adapt here. We could also follow the convention established for upward/downward and put the directional modifier in front of the term being modified. hence:
>
> inward_water_volume_transport_in_river_channel
>
> outward_water_volume_transport_in_river_channel
>
>
> "An inward flux or transport is the sum of all transport that is directed inwards across the boundary of an area. By default the area is a model grid cell, but other areas may be specified using a region coordinate" , and similar for outward.
>
>
> However, I can see that the first of these terms might be misread as transport *into* the rive channel, rather than transport *in* the channel. Any other suggestions?
>
>
> regards,
>
> Martin
>
>
>
> ________________________________
> From: Pamment, Alison (STFC,RAL,RALSP)
> Sent: 11 June 2018 11:13
> To: Juckes, Martin (STFC,RAL,RALSP); cf-metadata at cgd.ucar.edu
> Subject: RE: Final 17 terms for CMIP6 LS3MIP.
>
> Dear Martin, Karl and Jonathan,
>
> I wrote most of this email late on Friday evening, before Martin and Karl's comments over the weekend. However, I think it is largely consistent with the later discussion. I have amended my comments on the evaporation (2.1, 2.2), evapotranspiration (2.3) and heat flux into snow pack (3) names to reflect the latest position.
>
> Thanks all for the very quick and helpful responses. I think we are making good progress on these names. Jonathan, I'm afraid I haven't seen your comments from earlier last week - they don't seem to have appeared on the mailing list.
>
> These proposals have raised a number of important questions. I'll try to address the broad issues first before going through the names again in turn.
>
> 1. 'Canopy' versus 'Vegetation'
>
> In the context of discussing canopy evaporation/sublimation, Karl wrote the following:
> > Is there a precise definition of canopy?How does it differ from
> > "vegetation"?A definition I found says "The canopy refers to the
> > highest layer of vegetation in a forest or woodland, made up of the
> > crowns of its tallest trees." I would be surprised if modelers are
> > using the term in this sense. If "canopy" is restricted to "trees" (or tallest trees), how are they defined since some shrubs seem to have similar characteristics as trees.Why would modelers want to isolate water evaporation from the canopy, rather than considering water evaporation from all the vegetation?If "canopy" includes all vegetation that "hides" the surface soil from above, wouldn't all plants do that?If so, why not just say "vegetation"
> > (meaning surface vegetation) and avoid use of "canopy" in standard names.
>
> The AMS Glossary entry for 'canopy' says: 'The vegetative covering over a surface. The canopy is often considered to be the outer surfaces of the vegetation. Plant height and the distribution, orientation, and shape of plant leaves within a canopy influence the atmospheric environment and many plant processes within the canopy.' I think this is consistent with Karl's interpretation. Certainly I think the existing names don't mean only the tops of trees, rather 'canopy' has indeed been used as short hand for 'the parts of plants that protrude into the air and prevent light and precipitation from reaching the surface directly'.
>
> We use 'vegetation' in standard names such as carbon_mass_flux_into_soil_from_vegetation_excluding_litter where it can mean any part of the plant, including roots. 'Vegetation' is also used as an area type. Thus I think canopy does have a more specific meaning. I suggest that we replace the current not very helpful definition of canopy: '"Canopy" means the plant or vegetation canopy' with the one from the AMS Glossary, but that we retain it as a separate term.
>
> 2. Albedo
> Jonathan has pointed out that an albedo of a particular surface type such as 'ice' is not the same as an albedo assuming_condition because the former is an observable surface characteristic while the latter is purely a model construct. This is a good point - thank you. I agree that we should retain surface_albedo_assuming_deep_snow and surface_albedo_assuming_no_snow as separate quantities. However, I think we are agreed that we should have a single surface_albedo name and use area_types in the circumstances where the surface type truly is different and no additional conditions are being assumed.
>
> 3. Evaporation
> Karl made some important points about the definition of evaporation, evapotranspiration and sublimation. Clearly we need to remain consistent with previous usage of these terms - I have taken this into account in my comments on some of the individual names.
>
> > 1.1 albc Canopy Albedo
> > canopy_albedo (1)
> > "Canopy" means the plant or vegetation canopy. Albedo is the ratio of outgoing to incoming shortwave irradiance.
>
> I think we are all agreed that canopy_albedo should be a separate standard name and certainly it is different from a surface albedo. Using the updated definition of canopy we would now have:
> 'Albedo is the ratio of outgoing to incoming shortwave irradiance. "Canopy" means the vegetative covering over a surface. The canopy is often considered to be the outer surfaces of the vegetation. Plant height and the distribution, orientation, and shape of plant leaves within a canopy influence the atmospheric environment and many plant processes within the canopy. Reference: AMS Glossary http://glossary.ametsoc.org/wiki/Canopy.'
>
> Okay?
>
> This name is still under discussion.
>
> > 1.2 albsn Snow and Ice Albedo [1]
> > Albedo of snow and ice covered surface.
> > snow_and_ice_albedo
> > Snow and ice albedo.
> > -- OR --
> > This could be handled with existing name surface_albedo and a new
> > area type "snow_or_ice". [Note that "landice" appears to exclude ice
> > on lakes, which may be a significant component of this albedo]
>
> I think we are agreed now to use the existing surface_albedo name for this quantity. The definition would be amended to read as follows:
> 'The surface called "surface" means the lower boundary of the atmosphere. Albedo is the ratio of outgoing to incoming shortwave irradiance. To specify the nature of the surface a cell_methods attribute should be supplied as described in Chapter 7.3.3 of the CF Conventions.'
>
> Okay?
>
> In addition we would introduce two new area_types as suggested by Martin:
> > ice_on_land
> 'The area type ice_on_land means Ice in glaciers, ice caps, ice sheets & shelves, river and lake ice, and any other ice on a land surface, such as frozen flood water. This is distinct from the area type 'land ice' which has a narrower definition.'
>
> > The combined term could be ice_and_snow_on_land
> 'The area type ice_and_snow_on_land means ice in glaciers, ice caps, ice sheets & shelves, river and lake ice, any other ice on a land surface, such as frozen flood water, and snow lying on such ice or on the land surface.'
>
> Are these definitions okay?
>
> This name is still under discussion.
>
> > 2. Evaporation and transpiration fluxes [3] Variations on the theme of the existing water_evaporation_flux term.
> > 2.1 ec water_evaporation_flux_from_canopy_due_to_interception (kg
> > m-2 s-1) ' "Water" means water in all phases. Evaporation is the
> > conversion of liquid or solid into vapor. (The conversion of solid
> > alone into vapor is called > "sublimation".) In accordance with
> > common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics. The specification of a physical process by the phrase "due_to_" process means that the quantity named is a single term in a sum of terms which together compose the general quantity named by omitting the phrase. "Canopy" means the plant or vegetation canopy. "Canopy interception" is the precipitation, including snow, that is intercepted by the canopy of a tree and then evaporates from the leaves.'
>
> Karl wrote:
> > a) This seems quite obscure."interception of what?"[snow fall,
> > yes?]Would water_evaporation_flux_from_canopy_snow work?
> >
> > b) How else does snow accumulate on the canopy except by falling as snow?
> >
>
> Naively, I would have thought that both rain and snow could be intercepted. Some of the rain will drip from the leaves onto the ground, while some will sit on the leaves as water droplets and eventually evaporate into the air. Certainly some snowfall would also be intercepted.
>
> > c) It appears that "evaporation" here must surely include
> > sublimation (as discussed in 1 above), which I think is good.
>
> Certainly the definition as given above does include sublimation.
>
> Karl makes the point that in CMIP5
> > a) "water_evaporation_flux" has included "transpiration" and
> > included water_sublimation_flux from all parts of the surface (soil
> > and vegetation)
> and that it is important we do not alter or confuse this interpretation in the current set of proposals.
>
> I understand the proposed quantity to mean the evaporation (including sublimation) of any precipitation that falls and comes to rest on the canopy. I think it doesn't include transpiration, nor does it include evaporation from the ground. We do have existing names canopy_water_amount and change_over_time_in_canopy_water_amount. Following this pattern, perhaps we could call the proposed quantity:
>
> tendency_of_canopy_water_amount_due_to_evaporation_of_intercepted_prec
> ipitation (kg m-2 s-1) 'The phrase "tendency_of_X" means derivative of
> X with respect to time. "Amount" means mass per unit area. "Water"
> means water in all phases. "Canopy" means the vegetative covering over
> a surface. The canopy is often considered to be the outer surfaces of
> the vegetation. Plant height and the distribution, orientation, and
> shape of plant leaves within a canopy influence the atmospheric
> environment and many plant processes within the canopy. Reference: AMS
> Glossary http://glossary.ametsoc.org/wiki/Canopy.' The specification
> of a physical process by the phrase "due_to_" process means that the
> quantity named is a single term in a sum of terms which together
> compose the general quantity named by omitting the phrase.
> "Intercepted precipitation" is the precipitation, including snow, that
> is intercepted by the vegetation canopy and then evaporates without
> ever reaching the surface or entering the plant through its roots.
> Evaporation is the conversion of liquid or so
lid into vapor. (The conversion of solid alone into vapor is called "sublimation".) Evaporation of intercepted precipitation excludes plant transpiration and evaporation from the surface beneath the canopy.'
>
> This avoids calling it a 'water_evaporation_flux' while (I hope) still accurately representing the quantity. Is this an acceptable compromise?
>
> This name is still under discussion.
>
> > 2.2 eow Open Water Evaporation [kg m-2 s-1]
> >
> > A new term "water_evaporation_flux_from_open_water" would work here,
> > but it might make more sense to define an area type for open water and use the existing standard name "water_evaporation_flux".
>
> The definition of the existing water_evaporation_flux says:
> 'Water means water in all phases. Evaporation is the conversion of liquid or solid into vapor. (The conversion of solid alone into vapor is called "sublimation".) In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics. Unless indicated in the cell_methods attribute, a quantity is assumed to apply to the whole area of each horizontal grid box. Previously, the qualifier where_type was used to specify that the quantity applies only to the part of the grid box of the named type. Names containing the where_type qualifier are deprecated and newly created data should use the cell_methods attribute to indicate the horizontal area to which the quantity applies.'
>
> Regarding "open water" Martin wrote:
> > The phrase "open water" appears to have different meanings for
> > oceans and freshwater. For freshwater it means areas that are free
> > of vegetation or other obstacles. I'm not sure it is really right
> > for an area type: when used in the context of swimming, "open water"
> > means water some distance from the shore or banks, but for evaporation it just means evaporation from the water/air interface as opposed to evaporation of water which is in contact with a solid boundary. We could, perhaps, use "fresh_free_water_surface" (Areas where there is a free interface between freshwater and the atmosphere without vegetation or other obstructions).
>
> I think perhaps we could just say "fresh_free_water" and the definition would be 'An area type of fresh_free_water means a free interface between freshwater and the atmosphere without vegetation or other obstructions'.
>
> The standard name definition doesn't mention anything about transpiration and, for the open water quantity, no vegetation is involved. To avoid confusion with the total evaporation/evapotranspiration quantity, I suggest we introduce a new standard name of surface_water_evaporation_flux. It would be defined exactly as above, except for one additional sentence saying that transpiration is NOT included in this name.
>
> This name is still under discussion.
>
> > 2.3 et Total Evapotranspiration [kg m-2 s-1]
> > "Evapotranspiration" is a new concept to the CF standard names, but appears to be clearly defined.
> > evapotranspiration_flux (kg m-2 s-1) "Evapotranspiration refers to
> > the flux of water into the atmosphere from a combination of
> > transpiration by plants and evaporation from soil and other land surfaces."
>
> Karl wrote:
> > If you want to introduce "evapotranspiration_flux", you would have
> > to make "water_evaporation_flux" an alias. It would be o.k. to
> > define "transpiration_flux" as a new name identifying the portion of
> > "water_evaporation" (i.e., "evapotranspiration") that is due to
> > transpiration.I think it would be a mistake to change the meaning of
> > water_evaporation_flux so that it excludes the portion due to
> > transpiration.water_evaporation_flux has been in use too long with
> > the original meaning."evapotranspiration" is *not* a new concept in
> > CF, it is a suggested new name for "evaporation".My vote would be
> > *not* to replace "evaporation" with "evapotranspiration"; the
> > atmosphere doesn't care that a portion of the evaporating water
> > traveled through the plant roots and exited through stomata in the
> > leaves; it still ends up in the atmosphere as vapor.
>
> In view of this, Martin has suggested that we should make the existing water_evaporation_flux name into an alias of water_evapotranspiration_flux and adding to the definition. I agree this would be a very good step. So then we would have:
> water_evapotranspiration_flux
> 'Water means water in all phases. "Evapotranspiration" means all water vapor fluxes from the surface: liquid evaporation, sublimation and transpiration.
> Evaporation is the conversion of liquid or solid into vapor. (The conversion of solid alone into vapor is called "sublimation".) Transpiration is the process by which water is carried from the roots of plants and evaporates from the stomata. In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics. Unless indicated in the cell_methods attribute, a quantity is assumed to apply to the whole area of each horizontal grid box.'
>
> Keeping the reference to cell_methods in the definition is useful because it potentially allows the use of area type to describe evapotranspiration from different types of vegetation in a single grid box, even if there is no requirement to do that at the moment. I have also added a definition for 'transpiration' (which we haven't had before).
>
> Taking this approach of having separate surface evaporation and evapotranspiration fluxes in proposals 2.2 and 2.3 seems to me the tidiest and least confusing way of accommodating the CMIP6 quantities while not introducing inconsistencies with CMIP5. I note that this does raise an interesting wrinkle as regards aliases: currently water_evaporation_flux has an alias of water_evaporation_flux_where_sea_ice which clearly would not include vegetated areas and is therefore more akin to the surface_water_evaporation_flux name I am now suggesting for 2.2. I think it makes sense to list water_evaporation_flux_where_sea_ice as an alias of surface_water_evaporation_flux, rather than water_evapotranspiration_flux. We have never 'transferred' an alias in this way before, but I think it is the best approach to preserving the meaning of all the terms, past and present. Do others agree?
>
> This name is still under discussion.
>
> > 3. Heat fluxes [2]
> > 3.1 hfrs Heat transferred to snowpack by rainfall [W m-2]
> > A variation of "temperature_flux_due_to_rainfall_expressed_as_heat_flux_into_sea_water".
> >
> > temperature_flux_due_to_rainfall_expressed_as_heat_flux_into_snow_an
> > d_ice (W m-2)
>
> Karl wrote:
> > I must have missed the discussion about this, but does
> > temperature_flux_due_to_rainfall_expressed_as_heat_flux_into_sea_wat
> > er make sense? Our use of flux as a short-hand for "flux density"
> > (as formally used in physics)wouldn't seem to apply to
> > "temperature", which is a property of a material not something that
> > can flow from one place to another.Does it mean
> > "heat_flux_into_sea_water_due_to_rainfall_added_at_a_different_tempe
> > rature"?Or is it the
> > "tendancy_of_sea_water_temperature_due_to_rainfall"? Or something
> > else?
>
> This name was introduced some years ago (possibly for CMIP5, but I can't quite remember). I do recall it being discussed for quite a while on the list before being agreed. I'm not keen on having 'temperature_fluxes' either! It is defined as:
> 'The quantity with standard name temperature_flux_due_to_rainfall_expressed_as_heat_flux_into_sea_water is the heat energy carried by rainfall entering the sea at the sea surface. It is calculated relative to the heat that would be carried by rainfall entering the sea at zero degrees Celsius. It is calculated as the product QrainCpTrain, where Qrain is the mass flux of rainfall entering the sea (kg m-2 s-1), Cp is the specific heat capacity of water and Train is the temperature in degrees Celsius of the rain water entering the sea surface. In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics. The specification of a physical process by the phrase due_to_process means that the quantity named is a single term in a sum of terms which together compose the general quantity named by omitting the phrase.'
> So it is a heat flux, but a relative one.
>
> It has been suggested that we might call this one:
> heat_flux_into_snow_and_ice_on_land_due_to_rainfall
> Martin wrote:
> I believe that the heat flux here depends on the temperature of the
> target medium (or, rather, the difference in temperature between the target and source) So adapting the definition of the existing name would give us something like:
> 'The quantity with standard name heat_flux_into_snow_and_ice_due_to_rainfall is the heat energy carried by rain falling onto the snow and ice. It is calculated as the product QrainCpTdiff, where Qrain is the mass flux of rainfall reaching the snow and ice surface, Cp is the specific heat capacity of water and Tdiff is the difference in temperature of the rain water and the frozen surface. In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics. The specification of a physical process by the phrase due_to_process means that the quantity named is a single term in a sum of terms which together compose the general quantity named by omitting the phrase.'
>
> However, I see that none of us is currently very clear about what this quantity really means and Martin is seeking further clarification. I will await the outcome of that before proceeding any further with this name.
>
> This name is still under discussion.
>
> > 3.2 hfsbl Energy of sublimation [W m-2]
> > Variation of: surface_upward_latent_heat_flux The definitions of latent heat flux state that the latent heat flux includes sublimation heat flux, so it makes sense to use the same pattern:
> > surface_upward_sublimation_heat_flux (W m-2)
> 'The surface called "surface" means the lower boundary of the atmosphere. "Upward" indicates a vector component which is positive when directed upward (negative downward). Sublimation is the conversion of solid into vapor. In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics.'
>
> Karl wrote:
> > I've never seen the term "sublimation heat flux" used, although I
> > guess its meaning is clear enough.Does anyone know of a different
> > term meaning "heat flux from the surface to the atmosphere due to
> > sublimation of surface ice, frost, and snow?
>
> Martin has now suggested we call this one surface_upward_latent_heat_flux_due_to_sublimation. I think that is fine. I had already accepted this name so I will amend it. It will still be included in the June update.
>
> > 4. Nudging increments [2]
>
> (4.1 nudging_increment_in_mass_content_of_water_in_soil (kg m-2) has already been accepted).
>
> > 4.2 nudgincswe Nudging Increment of Water in Snow [kg m-2]
> > nudging_increment_in_surface_snow_and_ice_amount
> The definition would be as follows:
> 'A "nudging increment" refers to an amount added to parts of a model system. The phrase "nudging_increment_in_X" refers to an increment in quantity X over a time period which should be defined in the bounds of the time coordinate. The surface called "surface" means the lower boundary of the atmosphere. "Amount" means mass per unit area.'
>
> I asked about the areas of snow and ice and Martin suggested:
> Can we use "nudging_increment_in_snow_and_ice_on_land_amount", following my suggestion for the area type above?
>
> I think that's good. The area type was 'ice_and_snow_on_land' so we should have them in the same order in the standard name. Also, I think ice_and_snow_amount_on_land is easier to understand, so we'd have:
> nudging_increment_in_ice_and_snow_amount_on_land (kg m-2) ''A "nudging
> increment" refers to an amount added to parts of a model system. The phrase "nudging_increment_in_X" refers to an increment in quantity X over a time period which should be defined in the bounds of the time coordinate. The surface called "surface" means the lower boundary of the atmosphere. "Amount" means mass per unit area. "Ice and snow on land" means ice in glaciers, ice caps, ice sheets & shelves, river and lake ice, any other ice on a land surface, such as frozen flood water, and snow lying on such ice or on the land surface.'
>
> This name is accepted for publication in the standard name table and will be added in the June update.
>
> > 5. River in- and out-flow [2]
> > water_volume_transport_in_river_channel and
> > water_volume_transport_into_sea_water_from_rivers exist. The new variables represent cell averages of river fluxes directed inwards and outwards respectively.
> > 5.1 rivi River Inflow Water flux from upstream [m3 s-1]
> > river_water_volume_transport_into_cell
> > '"Cell" refers to a model grid-cell. "River water" refers to the water (liquid and solid) in the fluvial system (stream and floodplain).'
> ' "Cell" refers to a model grid-cell. The extent of an individual grid cell is defined by the horizontal coordinates and any associated coordinate bounds or by a string valued auxiliary coordinate variable with a standard name of "region". "Water" means water in all phases. "River" refers to water in the fluvial system (stream and floodplain).'
>
> Martin has confirmed that this name does include water in all phases, which was the only outstanding question.
>
> This name is accepted for publication in the standard name table and will be added in the June update.
>
> > 5.2 rivo River Discharge [m3 s-1]
> > river_water_volume_transport_out_of_cell
> ' "Cell" refers to a model grid-cell. The extent of an individual grid cell is defined by the horizontal coordinates and any associated coordinate bounds or by a string valued auxiliary coordinate variable with a standard name of "region". "Water" means water in all phases. "River" refers to water in the fluvial system (stream and floodplain).'
>
> Martin has confirmed that this name does include water in all phases, which was the only outstanding question.
>
> This name is accepted for publication in the standard name table and will be added in the June update.
>
> > 6. Roots [1]
> >
> > > 6.1 rzwc Root zone soil moisture [kg m-2]
> > > This is a variation on mass_content_of_water_in_soil_layer, but with a layer defined by the presence of roots rather than a coordinate range (cf.
> > > "stratosphere" in atmosphere).
> >
> > mass_content_of_water_in_soil_layer_defined_by_root_depth
> > ' "Content" indicates a quantity per unit area. The content of a
> > soil layer is the vertical integral of the specified quantity within
> > the layer. The quantity with standard name
> > mass_content_of_water_in_soil_layer_defined_by_root_depth is the vertical integral between the surface and the depth to which plant roots penetrate. A coordinate variable or scalar coordinate variable with standard name root_depth can be used to specify the extent of the layer. "Water" means water in all phases.'
>
> Martin has agreed this approach. This name is accepted for publication in the standard name table and will be added in the June update.
>
> > 7. Water fluxes [5]
> > 7.1 qgwr Groundwater recharge from soil layer [kg m-1 s-1]
>
> Currently this name is listed as follows:
> liquid_water_mass_flux_from_soil_to_groundwater (kg m-2 s-1) 'In
> accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics. Groundwater is subsurface water below the depth of the water table, including soil moisture and underground aquifers.'
>
> We are still awaiting clarification of the definition of groundwater and we will need to wait for the outcome of that before we can finalise this name.
>
> This name is still under discussion.
>
> > > 7.2 sblnosn Sublimation of the snow free area [kg m-2 s-1]
> > >
> > > This is a variation of the CMIP5 variable "sbl" which used the
> > > existing term surface_snow_and_ice_sublimation_flux. Here, we just drop "and_ice" > to get a term referring to the ice only.
> > > surface_ice_sublimation_flux
>
> Alison wrote:
> > Looking at existing names I see we also have
> > surface_snow_sublimation_amount. Rather than talking about
> > sublimation amount in one name and sublimation flux in others I
> > think it would make sense to take a more uniform approach. I think
> > the primary purpose of the existing
> > surface_snow_and_ice_sublimation_flux
> > name is to describe changes at the surface, rather than a water vapour flux into the atmosphere. Hence I suggest introducing aliases:
> > surface_snow_sublimation_amount ->
> > tendency_of_surface_snow_amount_due_to_sublimation
> > surface_snow_and_ice_sublimation_flux ->
> > tendency_of_surface_snow_and_ice_amount_due_to_sublimation
> > and calling the proposed quantity:
> > tendency_of_ice_amount_due_to_sublimation.
> > None of these names specify that the snow and ice are located on land, so as with the albedo and evaporation names we probably need to use them in > conjunction with an area type. Do you agree with this approach?
>
> Martin wrote:
> > Yes, this is good.
>
> Okay, thank you, these changes are agreed. I will create the aliases and add the new name as follows:
> tendency_of_surface_ice_amount_due_to_sublimation (kg m-2 s-1) 'The
> phrase "tendency_of_X" means derivative of X with respect to time. "Amount" means mass per unit area. The specification of a physical process by the phrase "due_to_" process means that the quantity named is a single term in a sum of terms which together compose the general quantity named by omitting the phrase. Sublimation is the conversion of solid into vapor. Unless indicated in the cell_methods attribute, a quantity is assumed to apply to the whole area of each horizontal grid box.'
>
> This name is accepted for publication in the standard name table and will be included in the June update.
>
> > > 7.3 snmsl Water flowing out of snowpack [kg m-2 s-1]
> > > This is a variation of snm [surface_snow_melt_flux], but considering only the component of the flux into soil:
> > >
> > > surface_snow_melt_flux_into_soil
>
> Alison wrote:
> > For this name I suggest a different form:
> > liquid_water_mass_flux_into_soil_due_to_surface_snow_melt (kg m-2
> > s-1) 'In accordance with common usage in geophysical disciplines,
> > "flux" implies per unit area, called "flux density" in physics. The
> > specification of a physical process > by the phrase "due_to_" process means that the quantity named is a single term in a sum of terms which together compose the general quantity named by omitting the phrase. The phrase "surface_snow" means snow lying on the surface.'
>
> Martin wrote:
> > Yes, this looks good to me. Longer, but the additional clarity justifies this.
>
> Okay, thank you. This name is accepted for publication in the standard name table and will be added in the June update.
>
> (7.4 canopy_snow_amount has already been accepted.
>
> > 7.5 sw Surface Water Storage (excluding snow) [kg m-2]
> > The existing term surface_water_amount refers to ".. the amount on
> > the ground, excluding that on the plant or vegetation canopy", and
> > "water" is assumed to refer to all phases. There is a term
> > "land_based_water_amount" under discussion for PMIP which refers to
> > "This quantity is often known as Terrestrial Water Storage. It
> > includes surface water (water in rivers, wetlands, lakes, snow,
> > vegetation and
> > reservoirs) and subsurface water (soil moisture, groundwater)".
> >
> > Assuming that this term is intended to be a variation on the first,
> > surface_water_amount, and the amount includes only liquid phase water (excluding snow and ice):
> > surface_liquid_water_amount
>
> This name is currently listed as:
> land_surface_liquid_water_amount (kg m-2) 'The surface called
> "surface" means the lower boundary of the atmosphere. "Amount" means mass per unit area. The quantity with standard name land_surface_liquid_water_amount includes water in rivers, wetlands, lakes, snow, vegetation and reservoirs.'
>
> We are still awaiting clarification of the definition of land water and we will need to wait for the outcome of that before we can finalise this name.
>
> This name is still under discussion.
>
> Best wishes,
> Alison
>
> ------
> Alison Pamment Tel: +44 1235 778065
> NCAS/Centre for Environmental Data Archival Email: alison.pamment at stfc.ac.uk
> STFC Rutherford Appleton Laboratory
> R25, 2.22
> Harwell Oxford, Didcot, OX11 0QX, U.K.
>
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Received on Fri Jun 29 2018 - 03:49:41 BST
