Dear Martin et al. Is it sum_x (v'(x) T'(x)) where v'=v-avg_x(v), similarly for T, and x is longitude? In that case I think it would be neat to describe it as a covariance, which like "product" doesn't attribute a physical meaning to it. Could it be called covariance_over_longitude_of_northward_velocity_and_air_temperature where the (important) fact that it is calculated on pressure levels can be adequately indicated by its having a coordinate of pressure, I think. The same quantity could be computed on other sorts of levels.
Best wishes Jonathan ----- Forwarded message from Martin Juckes - UKRI STFC <[email protected]> ----- > PS: Michaela sent another suggestion while I was composing that email: > > > covariance_of_northward_velocity_and_temperature .. which could work, though > I think it would need a prefix of "zonal_isobaric". > > regards, > Martin > > > > > ________________________________ > From: Juckes, Martin (STFC,RAL,RALSP) > Sent: 08 May 2019 09:55 > To: CF-metadata ([email protected]) > Cc: Plummer, David (EC); David Neubauer; [email protected]; RIGOUDY Gaelle; > Michael Schulz; Michaela Hegglin; Taylor, Karl E. > Subject: Standard name of isobaric zonal mean eddy meridional temperature > advection > > > Hello All, > > > For AerChemMIP we need a new standard name for a quantity which is the > isobaric zonal mean of the eddy meridional temperature advection. That is, > the mean wrt. longitude of the product of v' and T', where v' and T' are the > eddy meridional velocity and air temperature respectively and "eddy" denotes > the departure from the isobaric zonal mean. The units should be "K m s-1" > > > This is related to two existing terms: > > 1. northward_heat_flux_in_air_due_to_eddy_advection [W m-2] > 2. product_of_northward_wind_and_air_temperature [K m s-1] > > The first of these involves the eddy advection, but includes a factor of > density and the specific heat constant. Since density is spatially varying, > (1) can not be directly converted to the term we want, though there is an > approximate relationship. > > The second specifies the product, but without reference to the eddies. > > The term "eddy_advection" occurs in 38 existing terms, always in the form > "...._due_to_[...]eddy_advection", describing the part of some process which > can be attributed to some kind of eddy advection. In this case we want a > term for the eddy advection itself. > > In some preliminary discussion we have the following ideas: > > (1) > northward_heat_flux_expressed_as_temperature_flux_in_air_due_to_eddy_advection > -- staying close to the existing heat flux term; > (2) northward_temperature_flux_in_air_due_to_eddy_advection -- more > descriptive > (3) Karl has suggested terms based on "product_of_...", to avoid the use of > "temperature flux", because the notion of "flux" sits uncomfortably with a > non-conservative quantity like temperature. > > In reviewing the use of "eddy_advection" in existing terms, I can see that > the nature of the eddy advection is clearly defined in 27 of them, and the > heat flux term above is the only one for which the user is left to guess. The > standard interpretation would be as a departure from the isobaric zonal mean, > but that is not spelled out in the standard name. > > Combining some of the ideas from Karl and Michaela (suggestion 2 above), I > think we could use: > > > * northward_isobaric_zonal_mean_eddy_advection_of_air_temperature > > This differs from Karl's suggestions in using "eddy_advection" rather than > trying to adapt "product_of" to deal with this use case. > > The phrase "isobaric_zonal_mean_eddy_advection" would be defined as the zonal > mean advection by eddies defined as the departure from the instantaneous > isobaric zonal mean of the velocity and the advected quantity. > > I'm submitting this on behalf of the group, so please consider comments by > Karl and Michaela below. The discussion is still quite open, but I think it > is better to engage with the CF list at this stage (the definition of the > term we want to represent is clear). > > regards, > Martin > ________________________________ > From: Taylor, Karl E. <[email protected]> > Sent: 07 May 2019 23:15 > To: Michaela Hegglin; Juckes, Martin (STFC,RAL,RALSP) > Cc: Plummer, David (EC); David Neubauer; [email protected]; RIGOUDY Gaelle; > Michael Schulz > Subject: Re: vt100 > > I just noticed that there is a standard_name > "product_of_northward_wind_and_air_temperature". Perhaps this could be > modified to something indicating we're only considering the "eddy" > component, e.g., > "eddy_component_of_product_of_northward_wind_and_air_temperature" or > "product_of_northward_wind_and_air_temperature_eddy_components" or > eddy_associated_product_of_northward_wind_and_air_temperature". > best, > Karl > > On 5/7/19 2:23 AM, Michaela Hegglin wrote: > > Hi Martin, Karl, > > > > I got some more input from the DynVarMIP people on this too and Martin has > > analysed this correctly. > > > > It seems that v’T’ * c_p * \rho would give us the correct units in [W/m^2]. > > The c_p factor is trivial, but the density isn't. Since it is requested on > > a specific pressure level, it would depend only on the temperature at 100 > > hPa: \rho = 10^4 Pa/RT. This does add some nonlinearity. To do it > > properly, you’d need the account for variations in \rho (T) in time and > > space. > > > > Hence, would it be possible to keep the calculation as it is done by most > > researchers as v’T’ and rename the variable to > > > > northward_temperature_flux_in_air_due_to_eddy_advection with units of [m K > > s-1]. > > > > Also, by “eddy_advection”, people do mean deviations from the > > instantaneous zonal mean. > > > > If it doesn’t sound like changing the name is a good idea, we could simply > > change the units to [K m s-1], and explain that v’T’ was intended? > > > > This is what people expect to deliver for this variable as Gaelle’s case > > shows too. > > > > > > Michaela > > > > > > > > > >> On 7 May 2019, at 09:30, Martin Juckes - UKRI STFC > >> <[email protected]> wrote: > >> > >> Hi Karl, > >> > >> > >> It would need a new standard name .. perhaps : > >> > >> > >> northward_heat_flux_expressed_as_temperature_flux_in_air_due_to_eddy_advection > >> > >> > >> -- this is the current name with "_expressed_as_temperature_flux" > >> inserted. It would make it clear that it is closely related to > >> northward_heat_flux_in_air_due_to_eddy_advection, but also provide the > >> necessary level of detail for CF. > >> > >> > >> The relationship between the two is not a simple transformation of units: > >> you need to make an assumption about the density and heat capacity of the > >> air (if this is done after the fact it will, I believe, involve some > >> degree of approximation). > >> > >> > >> regards, > >> > >> Martin > >> > >> > >> ________________________________ > >> From: Taylor, Karl E. <[email protected]> > >> Sent: 06 May 2019 16:34 > >> To: Plummer, David (EC); Michaela Hegglin; Juckes, Martin (STFC,RAL,RALSP) > >> Cc: David Neubauer; [email protected]; RIGOUDY Gaelle; Michael Schulz > >> Subject: Re: vt100 > >> > >> Hi Martin, > >> > >> It appears to me that perhaps more important than the inconsistency > >> between standard_name and units, is the issue of whether or not to > >> remove an instantaneous zonal-mean or a local time mean (or perhaps > >> operate without removing any sort of mean). Since the heat flux is > >> simply the temperture flux scaled by the specific heat of air at > >> constant pressure with a value of about 1000 J kg-1 K-1, users can > >> probably guess whether heat flux or temperature flux is actually being > >> reported and correct for it. Users will not generally be able to guess > >> whether deviations from some mean or full quantities are used in > >> calculated the products. > >> > >> Since vt100 is used for a fairly specific "aerochem" diagnostic, I think > >> they should decide what they *really* want (and need for their > >> analysis). Then I think we should make an exception to our rule > >> (because the science apparently demands it) and modify the data request > >> to reflect this. If there is any way we can do this without changing > >> the current standard_name for vt100, that would certainly be best > >> because then all data would be searched for using the same standard > >> name. The units would be inconsistent for some already written data > >> sets, but errata could be recorded by es-docs for those models > >> indicating the error in units. > >> > >> best regards, > >> Karl > >> > >> > >> On 5/4/19 3:28 PM, Plummer, David (EC) wrote: > >>> Hi Michaela > >>> I'll admit to being a bit out of my depth on stratopheric dynamics, > >>> but from a practical standpoint looking at our diagnostic codes that were > >>> developed by Charles McLandress we calculate the eddy meridional heat > >>> flux as the product of the instantaneous deviations around the > >>> instantaneous zonal average of the meridional velocity and temperature. > >>> The end product is the zonal and monthly average of this product. This > >>> calculation does agree with the description of V'T' in the literature > >>> where the primes are used to denote deviations around the zonal mean. > >>> Note that the MIP table for CCMI, which derives from the CCMVal data > >>> request, has the following comment: Zonally averaged meridional heat > >>> flux at 100 hPa as monthly means derived from daily (or higher frequency) > >>> fields > >>> It is really important that the sampling be daily or better because > >>> you want to capture the meridional advection of temperature by transient > >>> eddies. > >>> It is one of the terms in the Transformed Eulerian Mean (TEM) > >>> calculation of the stratospheric residual circulation and the value at > >>> 100 hPa is usually seen as a proxy for the total amount of planetary wave > >>> drag entering the stratosphere. Chapter 4 of the CCMVal report, > >>> Stratospheric Dynamics, used the term 'eddy meridional heat flux' and > >>> referenced a paper by Newman et al. (2001) where this term is referred to > >>> similarly. I have also seen a few articles in the literature where it is > >>> referred to as the 'temperature flux', so that term is not unknown. > >>> David > >>> > >>> ________________________________________ > >>> From: Michaela Hegglin <[email protected]> > >>> Sent: May 4, 2019 6:23 AM > >>> To: Martin Juckes - UKRI STFC; Plummer, David (EC) > >>> Cc: Taylor Karl; David Neubauer; [email protected]; RIGOUDY Gaelle; Michael > >>> Schulz > >>> Subject: Re: vt100 > >>> > >>> Hi all again, > >>> > >>> Indeed, our community was lax about the notation and commonly used 'heat > >>> flux’ instead of the more correct term ’temperature flux’ (K m s-1), > >>> which is a measure for wave activity. The units should remain [K m s-1]. > >>> However, how to get the variable I am still not clear about. Hence, I > >>> have copied in David Plummer who may be able to tell us what it is > >>> exactly what was calculated in CCMVal for the temperature flux (whether > >>> v’T’ or v’*T’ in fact as Martin says below). Then we have clear > >>> instructions and should find the right notation for it. > >>> > >>> Thanks for looking into this, > >>> > >>> Michaela > >>> > >>> > >>>> On 3 May 2019, at 15:47, Martin Juckes - UKRI STFC > >>>> <[email protected]> wrote: > >>>> > >>>> Hello Karl, > >>>> > >>>> > >>>> do you have an idea what to do about this? > >>>> > >>>> > >>>> The variable "vt100" has long name "Northward Heat Flux Due to Eddies", > >>>> > >>>> standard name: "northward_heat_flux_in_air_due_to_eddy_advection" and > >>>> units "W m-2". > >>>> > >>>> > >>>> AerChemMIP, who requested the variable, really wanted a meridional > >>>> temperature flux (units "K m s-1") and at least one group (CNRM) has > >>>> submitted temperature flux data with metadata as above saying it is a > >>>> heat flux. > >>>> > >>>> > >>>> At the moment only two groups have published vt100 data (CNRM and IPSL), > >>>> but it is likely that many more have produced the data and are in the > >>>> process of preparing it for publication. > >>>> > >>>> > >>>> Michaela has suggested an "errata" for the data request, but I don't > >>>> think this helps: if we decide to make a change, the easiest approach > >>>> would be to update the request. The only reason for not doing this is > >>>> that we have committed to not changing the definitions of variables -- > >>>> but that is a significant reason. > >>>> > >>>> > >>>> regards, > >>>> > >>>> Martin > >>>> > >>>> > >>>> > >>>> > >>>> > >>>> > >>>> > >>>> > >>>> ________________________________ > >>>> From: Michaela Hegglin <[email protected]> > >>>> Sent: 02 May 2019 16:23 > >>>> To: Michael Schulz > >>>> Cc: Juckes, Martin (STFC,RAL,RALSP); Taylor Karl; David Neubauer; > >>>> [email protected]; RIGOUDY Gaelle > >>>> Subject: Re: vt100 > >>>> > >>>> Hi all, > >>>> > >>>> Thank you, Gaelle, for this helpful and important information. > >>>> > >>>> My rather limited understanding is that the fields that were defined and > >>>> produced in CCMI could be converted in Wm-2 by integration of the fields > >>>> involving air density and the heat capacity (cp), however, this would > >>>> not be the fields that users would look for nor would know of how to > >>>> use/interpret/compare to old studies easily. > >>>> > >>>> So, yes, Martin, if there is a way to remedy the problem with leaving > >>>> the units but changing the standard name (or by putting a caveat around > >>>> that variable used in CMIP6) that would be great… > >>>> > >>>> Michaela > >>>> > >>>> > >>>>> On 2 May 2019, at 16:12, Michael Schulz <[email protected]> wrote: > >>>>> > >>>>> Hi Martin, > >>>>> > >>>>> I understand, sorry that this slipped our attention. > >>>>> > >>>>> for curiosity - what happens now? Shouldnt there be some log on errors > >>>>> in the data request? > >>>>> Or would you add a specific clarification to the data request that this > >>>>> variable has been specified with an incompatible unit and standard name? > >>>>> > >>>>> best wishes > >>>>> Michael > >>>>> > >>>>>> On 30 Apr 2019, at 13:44, Martin Juckes - UKRI STFC > >>>>>> <[email protected]> wrote: > >>>>>> > >>>>>> Hello Michaela, Michael, > >>>>>> > >>>>>> > >>>>>> I'm afraid that is not consistent with the CF Convention. The standard > >>>>>> name "northward_heat_flux_in_air_due_to_eddy_advection" is for a heat > >>>>>> flux, so it needs to have units of "W m-2". > >>>>>> > >>>>>> > >>>>>> It looks as though the term was declared in the CCMI tables with an > >>>>>> invalid combination of "units" and "standard_name". In the CMIP6 > >>>>>> request, the "units" have been modified to be consistent with the > >>>>>> "standard_name". > >>>>>> > >>>>>> > >>>>>> The variable "vt100" has already been published in CMIP6 (with units > >>>>>> "W m-2") by IPSL and CNRM, Stéphane Senesi or Gaëlle Rigoudy (copied > >>>>>> in) might be able to comment on how they did this (the question is: > >>>>>> what factor is used to convert v*t into a heat flux? (see, for > >>>>>> example, > >>>>>> https://esg1.umr-cnrm.fr/thredds/dodsC/CMIP6_CNRM/CMIP/CNRM-CERFACS/CNRM-ESM2-1/amip/r1i1p1f2/AERmonZ/vt100/grz/v20181205/vt100_AERmonZ_CNRM-ESM2-1_amip_r1i1p1f2_grz_197901-201412.nc.html). > >>>>>> > >>>>>> > >>>>>> If this issue had come up earlier we could have changed the standard > >>>>>> name and the units ... but we have promised modeling centres not to > >>>>>> change the definitions of variables (beyond clarifications) at this > >>>>>> stage. > >>>>>> > >>>>>> > >>>>>> regards, > >>>>>> > >>>>>> Martin > >>>>>> > >>>>>> ________________________________ > >>>>>> From: Michaela Hegglin <[email protected]> > >>>>>> Sent: 30 April 2019 10:30 > >>>>>> To: Michael Schulz > >>>>>> Cc: Juckes, Martin (STFC,RAL,RALSP); Neubauer David > >>>>>> Subject: Re: vt100 > >>>>>> > >>>>>> Hi again, > >>>>>> > >>>>>> Here more information from David Plummer, I got the units wrong in my > >>>>>> previous email. > >>>>>> > >>>>>> Hope this helps, > >>>>>> > >>>>>> Michaela > >>>>>> > >>>>>> > >>>>>> variable_entry: vt100 > >>>>>> !============ > >>>>>> modeling_realm: atmos > >>>>>> !---------------------------------- > >>>>>> ! Variable attributes: > >>>>>> !---------------------------------- > >>>>>> standard_name: northward_heat_flux_in_air_due_to_eddy_advection > >>>>>> units: K m s-1 > >>>>>> cell_methods: time: mean longitude: mean > >>>>>> long_name: Meridional Heat Flux > >>>>>> comment: Zonally averaged meridional heat flux at 100 hPa as > >>>>>> monthly means derived from daily (or higher frequency) fields. > >>>>>> !---------------------------------- > >>>>>> ! Additional variable information: > >>>>>> !---------------------------------- > >>>>>> dimensions: longitude latitude time pr100 > >>>>>> type: real > >>>>>> valid_min: -1000.0 > >>>>>> valid_max: 1000.0 > >>>>>> !---------------------------------- > >>>>>> > >>>>>> It is the zonal average of the product of V' x T', where the prime is > >>>>>> the deviation around the zonal average. So the units you get are just > >>>>>> windspeed (m s-1) times temperature (K) -> K m s-1. > >>>>>> > >>>>>> > >>>>>> > >>>>>> ******************************************** > >>>>>> Michaela I. Hegglin > >>>>>> Associate Professor in Atmospheric Chemistry > >>>>>> Department of Meteorology > >>>>>> University of Reading > >>>>>> Lyle Building, 302A > >>>>>> Reading, RG6 6BX, UK > >>>>>> > >>>>>> email [email protected]<mailto:[email protected]> > >>>>>> phone +44 (0)118 378 6693 > >>>>>> fax +44 (0)118 378 8905 > >>>>>> ******************************************** > >>>>>> > >>>>>> On 29 Apr 2019, at 12:56, Michael Schulz > >>>>>> <[email protected]<mailto:[email protected]>> wrote: > >>>>>> > >>>>>> Hi Michaela, > >>>>>> > >>>>>> Can you explain how this vt 100 is calculated? > >>>>>> > >>>>>> Its a ccmi variable in AerChemMIP... > >>>>>> > >>>>>> See below, > >>>>>> Thanks > >>>>>> Michael > >>>>>> > >>>>>> ------- Weitergeleitete Nachricht ------ > >>>>>> Von: Neubauer David > >>>>>> <[email protected]<mailto:[email protected]>> > >>>>>> Datum: Mo. 29. Apr. 2019 um 11:11 > >>>>>> Betreff: RE: vt100 > >>>>>> An: Martin Juckes - UKRI STFC > >>>>>> <[email protected]<mailto:[email protected]>>, Michael > >>>>>> Schulz <[email protected]<mailto:[email protected]>> > >>>>>> Cc: Ferrachat Sylvaine > >>>>>> <[email protected]<mailto:[email protected]>> > >>>>>> > >>>>>> > >>>>>> Hi Michael and Martin, > >>>>>> > >>>>>> we would like to start our simulations soon. Therefore we would need > >>>>>> to know possible pre-factors of "vt100". Thank you for any help you > >>>>>> can provide. > >>>>>> > >>>>>> Kind regards, > >>>>>> David > >>>>>> > >>>>>>>> -----Original Message----- > >>>>>>>> From: Martin Juckes - UKRI STFC > >>>>>>>> [mailto:[email protected]<mailto:[email protected]>] > >>>>>>>> Sent: Freitag, 12. April 2019 17:10 > >>>>>>>> To: Michael Schulz > >>>>>>>> Cc: Neubauer David > >>>>>>>> Subject: Fw: vt100 > >>>>>>>> > >>>>>>>> Hello Michael, > >>>>>>>> > >>>>>>>> > >>>>>>>> Can you help with David's question below about the precise > >>>>>>>> definition of > >>>>>>>> the "vt100" variable requested by AerChemMIP? > >>>>>>>> > >>>>>>>> > >>>>>>>> regards, > >>>>>>>> > >>>>>>>> Martin > >>>>>>>> > >>>>>>>> > >>>>>>>> ________________________________ > >>>>>>>> From: Neubauer David > >>>>>>>> <[email protected]<mailto:[email protected]>> > >>>>>>>> Sent: 12 April 2019 15:39 > >>>>>>>> To: Juckes, Martin (STFC,RAL,RALSP) > >>>>>>>> Cc: Ferrachat Sylvaine > >>>>>>>> Subject: vt100 > >>>>>>>> > >>>>>>>> > >>>>>>>> Dear Martin, > >>>>>>>> > >>>>>>>> > >>>>>>>> > >>>>>>>> In the CMIP6 data request it is written that the units for the > >>>>>>>> variable vt100 > >>>>>>>> (AERmonZ) should be [W m-2]. However, computing the zonal average of > >>>>>>>> the product of the zonal average departures of v and t has the units > >>>>>>>> [m s-1 > >>>>>>>> K-1]. By which factors should this product be multiplied to obtain > >>>>>>>> the zonally > >>>>>>>> meridional averaged heat flux? > >>>>>>>> > >>>>>>>> > >>>>>>>> > >>>>>>>> Thank you in advance for any help you can provide. > >>>>>>>> > >>>>>>>> > >>>>>>>> > >>>>>>>> Kind regards, > >>>>>>>> > >>>>>>>> David > >>>>>>>> > >>>>>>>> > >>>>>>>> > >>>>>>>> -- > >>>>>>>> Dr. David Neubauer > >>>>>>>> ETH Zurich > >>>>>>>> Institute for Atmospheric and Climate Science Universitaetstrasse > >>>>>>>> 16, CHN > >>>>>>>> P17.2 > >>>>>>>> 8092 Zurich, Switzerland > >>>>>>>> phone: +41 44 632 74 26 > >>>>>>>> > > _______________________________________________ > CF-metadata mailing list > [email protected] > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata ----- End forwarded message ----- _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
