Dear Martin,
Many thanks for making these proposals. I have comments and questions about
some of them. In particular, these proposals have made me think that we can
make better use of area types than we currently do for surface properties and
fluxes such as albedo (1.2), water evaporation (2.2) and snowpack heat flux
(3.1) - I think we should take a common approach to these.
I have accepted a few of the names and there are quite a number more that are
close to acceptance. As with the change_over_time names we need to be clear
which areas are included and excluded for all names and also which phases of
water are included. Please have a look at my comments and let me know what you
think.
Albedo [2]
We already have names such as "soil_albedo" (Soil albedo is the albedo of the
soil surface assuming no snow). Two new terms are requested, for canopy and snow
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.
The name and units are fine. Does the canopy albedo assume no snow, or does it
include snow covered areas of the canopy?
This name is still under discussion. Please see also my related comments on 1.2.
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'm beginning to think that we should have just one surface_albedo name which
would have several aliases (surface_albedo_assuming_deep_snow,
surface_albedo_assuming_no_snow, sea_ice_albedo) and add some more area types.
For your proposed quantity we'd need an area type of something like
land_snow_or_ice as you suggest; we could add deep_snow and no_snow, and
sea_ice already exists. This would be similar to the way in which we deprecated
several surface_temperature_where_X names and made them all aliases of
surface_temperature.
The surface_temperature definition says 'The surface called "surface" means the
lower boundary of the atmosphere. The surface temperature is the temperature at the
interface, not the bulk temperature of the medium above or below. 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.' If we take a
similar approach with the albedo names we should of course add the same recommendation to
use cell_methods to indicate the horizontal area. We would then be able to have the
albedo of any surface that is described in the area_type table without the need to add
further standard names. Do others think that would
be a useful step?
If we do go down the area_type route, I think we'd still need canopy_albedo as
a separate name because it's clearly not the same as the surface, but that name
could also optionally be combined with an area_type of no_snow if only the
albedo of snow free canopy where required.
Regardless of whether we decide to introduce a new standard name or a new area type
for the proposed quantity, we need a clear definition of which ice/snow areas are
included and excluded. I wonder if excluding lake_ice from our definition of
land_ice is a deliberate omission or an oversight? Can we check this point with the
ISMIP6 group? Even if lake_ice is not included in land_ice, we do have an existing
area_type lake_ice_or_sea_ice and we could introduce lake_ice as a distinct
area_type in its own right. I think we'd also need a definition for land_snow,
presumably something like ' "Land snow' means any snow lying on the land
surface, land ice or lake ice.'
If we use surface_albedo, then the area type for this quantity would need to be
land_ice_and_lake_ice_or_land_snow or land_ice_or_land_snow, depending on
whether lake_ice should be included in land_ice. If we introduce a new standard
name the information would have to go in there:
surface_albedo_assuming_land_ice_and_lake_ice_or_land_snow. Both approaches
lead to quite a long string for the surface type, but I think that's the only
way to be clear about the quantity that is being represented. We've used
similar long strings for C4MIP names such as
surface_upward_mass_flux_of_nitrous_oxide_expressed_as_nitrogen_out_of_vegetation_and_litter_and_soil.
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 Interception evaporation [kg m-2 s-1]
water_evaporation_flux_from_canopy_due_to_intersection
"Canopy interception is the precipitation, including snow, that is intercepted by
the canopy of a tree and then evaporates from the leaves",
expanding on the existing name water_evaporation_flux_from_canopy
I assume there's a typo in the proposed name and it should say 'interception'.
Thank you for providing a definition for interception. Adding text from our
usual definitions I think we would end up with:
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.'
Okay?
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".
I agree that using the existing name water_evaporation_flux is a good choice,
although perhaps we should make that one into an alias of
water_evaporation_flux_from_surface which is a more accurate representation of
the quantity. We could certainly introduce a new area_type, but we'd need a
definition of 'open_water'. Does it mean 'ice_free_water'? We already have
ice_free_land and ice_free_sea. Does the open water in this case include the
sea or does it mean only land based water? Does it include rivers, lakes, etc.?
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."
The name and units are fine. Thank you for providing a definition for
evapotranspiration. I think the full definition should read as follows:
' "Evapotranspiration" means the flux of water into the atmosphere from a combination of transpiration by
plants and evaporation from soil and other land surfaces. 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").
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.'
Okay?
One question: does 'other land surfaces' specifically mean dry land, i.e. does
it exclude the open water of proposal 2.2?
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_and_ice (W
m-2)
The name itself does follow existing patterns and the units are correct for a
heat flux. The existing
temperature_flux_due_to_rainfall_expressed_as_heat_flux_into_sea_water name is
defined as follows:
'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.'
Assuming that the proposed name would be defined similarly, it seems to me that
this is another case where we could use area types. The energy being carried by
the rainfall is essentially a surface flux - it depends on where the rain
originated and the properties of the air it has fallen through, rather than the
type of surface it is falling onto. I suggest we could make the existing name
into an alias of temperature_flux_due_to_rainfall_expressed_as_heat_flux. We
could then use this for both the original and proposed quantities if an
appropriate area type is supplied. We already have an area type of sea. Is the
proposed quantity like the albedo in proposal 1.2, i.e. does it mean
land_ice_and_lake_ice_or_land_snow?
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 name and units are fine and the definition can be constructed from existing
text:
'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.'
This name is accepted for publication in the standard name table and will be
added in the June update.
4. Nudging increments [2]
There are no terms referring to "nudging increments" in the CF convention, but there are a number referring to
"flux correction". The following help text is proposed for nudging increments: "A nudging increment refers to
an amount > added to parts of the model system. 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." These should be encoded with cell_methods
"time: > sum" and a bounds variable to give the time over which nudging is summed. The convention requires that,
with this construction, the time periods should be contiguous.
4.1 nudgincsm Nudging Increment of Water in Soil Moisture [kg m-2]
nudging_increment_in_mass_content_of_water_in_soil
Thank you for providing a definition for 'nudging increment'. I think this is
very much modelling jargon, although so is 'flux correction' I suppose. I can't
think of a better phrase, so don't have any real objection to including this
name as it is. The rest of the definition can be constructed from existing text:
'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. "Content"
indicates a quantity per unit area. "Water" means water in all phases. The mass content of water in soil refers to the vertical
integral from the surface down to the bottom of the soil model. The "soil content" of a quantity refers to the vertical integral
from the surface down to the bottom of the soil model. For the content between specified levels in the soil, standard names including
"content_of_soil_layer" are used.'
This name is accepted for publication in the standard name table and will be
added in the June update.
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.'
This seems okay, but I'm wondering if once again this quantity refers to
land_ice_and_lake_ice_or_land_snow as in proposals 1.2 and 3.1? If so, then we
should probably add something to the definition advising on the use of an area
type to describe exactly which areas are affected.
This name is still under discussion.
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).'
I think the suggested name and units look good. I suggest that we add some
advice about grid cell bounds to the definition (similar to ice mass and ice
area names).
' "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).'
Is it correct to say that this one includes "water in all phases", i.e. would it include
ice floating on a river? (This question also applies to proposal 1.3
change_over_time_in_river_water_amount in the thread "Standard names for LS3MIP: 8 temporal
changes + 1 feature depth".
This name is still under discussion.
5.2 rivo River Discharge [m3 s-1]
river_water_volume_transport_out_of_cell
As with proposal 5.1 the name and units look good and I suggest adding advice
about cell bounds to the definition:
' "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).'
Again, does this one include ice floating on a river?
This name is still under discussion.
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_root_zone
"The root zone refers to the soil which surrounds the roots of vegetation."
I think it would be helpful to include 'soil' in the name. We have an existing
name root_depth defined as 'Depth is the vertical distance below the surface.
The root depth is maximum depth of soil reached by plant roots, from which they
can extract moisture.' I suggest we call the proposed quantity
mass_content_of_water_in_soil_layer_defined_by_root_depth. This is a bit like
existing ocean_mixed_layer names, e.g.,
ocean_mixed_layer_thickness_defined_by_temperature. The ocean name definitions
refer to a coordinate variable whose value contains the temperature, etc., that
actually determine the layer thickness. We could do something similar here:
' "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.'
What do you think?
7. Water fluxes [5]
7.1 qgwr Groundwater recharge from soil layer [kg m-1 s-1]
There are no usage of "groundwater" in existing CF terms, the following has
been suggested in connection with the LS3MIP term dgw:
"Groundwater is the water present beneath Earth's surface in soil pore spaces and in
the fractures > of rock formations."
water_flux_from_soil_to_groundwater
I think there's a typo in the suggested units and it should say kg m-2 s-1. I
assume that this quantity must refer to the transfer of liquid water - frozen
soil moisture would have to melt before it could permeate to lower levels,
wouldn't it? Hence I think this name should be
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.'
I notice the wording of the suggested definition of groundwater differs from
the one we have discussed in other LS3MIP proposals, although I think the
meaning is the same. For consistency I have used the same wording as other
proposals for now. I am aware that there is still some work being done on
clarifying 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
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?
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
For this name I suggest a different form:
liquid_water_mass_flux_into_soil_due_to_surface_snow_melt (kg m-2 s-1)
There are a number of reasons for suggesting this. The existing
surface_snow_melt_flux name isn't very clear in my opinion. It doesn't say
where the flux is going (or even that it is a mass flux, although that is
mentioned in the definition). It might even be better to change the existing
name to something like tendency_of_surface_snow_amount_due_to_melting. The
other reason I am suggesting a different form for the proposed quantity is
because of the use of the phrase 'surface_snow' in standard names to mean snow
lying on the surface. I think there's some potential for confusing surface_snow
with a surface_flux (i.e. flux in or out of the atmosphere) when that clearly
isn't intended. The definition would be as follows:
'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.'
Okay?
The sentence explaining that surface_snow means lying snow is new, but I think
we should add it to all existing surface snow names. Do others agree?
This name is still under discussion.
7.4 snwc Snow intercepted by the vegetation [kg m-2]
There is an existing term "canopy_water_amount", hence:
canopy_snow_amount
I think the name and units are fine. The definition would be:
' "Amount" means mass per unit area. "Canopy" means the plant or vegetation canopy. The
phrase "canopy_snow" means snow lying on the canopy.'
This one is a straight forward addition to the standard name table. It is
accepted for publication and will be added in the June update.
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
I note that the PMIP name you refer to is currently listed as
land_water_amount. Given that this variable is related and is clearly limited
to surface water on land (i.e. it excludes surface sea water) I suggest:
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.'
I am aware that there is still some work being done on clarifying 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: [email protected]
STFC Rutherford Appleton Laboratory
R25, 2.22
Harwell Oxford, Didcot, OX11 0QX, U.K.
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