Dear all,
I have talked to the people who are working with ocean models and
asked for a definition of SST from the modellers viewpoint.
They think it doesn't exist. In the modeL world SST is the temperature of
the first layer or the 'mixed layer' if the mixed layer exists in the model.
So, the problem is, that we have the CF-Name sea_surface_temperature
but not a definition. What does mean 'near' the surface ?
I agree with Alison, that sea temperature depending on different
physical processes should have there own standard names like
sea_surface_temperature_in_subskin_layer
sea_surface_temperature_in_skin_layer...
or
SSTsubskin
SSTskin...
--It will be very, very difficult to change many of the
--names for GHRSST-PP now but of course, this can be done with effort.
The 'CF Controlled Vocabulary' could be a solution of this problem.
See Frank Toussaint's email with subject 'CF Controlled Vocabulary'.
Best wishes
Heinke
Heinke H?ck
Max-Planck-Institut fuer Meteorologie Tel +49 40 41173-465
Abteilung Modelle und Daten Fax +49 40 41173-400
Bundesstr. 53
D-20146 Hamburg Germany
Email: heinke.hoeck at zmaw.de
http://www.mad.zmaw.de/
Craig Donlon wrote:
> Hi Alison:
>
> (Ken and JF, the thread can be picked up here:
> http://mailman.cgd.ucar.edu/pipermail/cf-metadata/2007/date.html#1609)
>
> I missed your mail and the subsequent threads for some reason - the
> most up to date entries I have are from the recent message sent by Nan
> (thanks Nan!). So I'll try and cover the details as best I can for
> all concerned.
>
> All of the names that are being proposed have been the subject of
> great debate within the GHRSST-PP community and are the result of long
> discussions at several international meetings. The names are used for
> every data set produced by GHRSST-PP every day 24/7 and as the
> GHRSST-PP uses netCDF (and tries to be CF-1.0 Compliant) it was
> appropriate to try and obtain ratification for the long and standard
> names proposed. It will be very, very difficult to change many of the
> names for GHRSST-PP now but of course, this can be done with effort.
>
> For the benefit of everyone concerned, here are the full definitions
> (reported in Donlon et al., J Climate 2002 and updated and reported in
> BAMS this August). The following is taken from
> https://www.ghrsst-pp.org/SST-Definitions.html
>
>
> SST is a difficult parameter to define exactly because the upper ocean
> (~10 m) has a complex and variable vertical temperature structure that
> is related to ocean turbulence and the air-sea fluxes of heat,
> moisture and momentum. A framework is required to understand the
> information content and relationships between measurements of SST made
> by different satellite and in situ instruments, especially if these
> are to be merged together. The definitions of SST developed by the
> GHRSST-PP SST Science Team (agreed at the 2nd and 3rd GHRSST-PP
> workshops) achieve the closest possible coincidence between what is
> defined and what can be measured operationally, bearing in mind
> current scientific knowledge and understanding of how the near surface
> thermal structure of the ocean behaves in nature.
>
> The interface temperature (SSTint)
> At the exact air-sea interface a hypothetical temperature called the
> interface temperature (SSTint) is defined although this is of no
> practical use because it cannot be measured using current technology.
> (NOTE- this is probably not required but was included for
> completeness)
> [Proposed CF-names: SSTint, interface_SST, interface_sea_surface_temperature]
>
> The skin sea surface temperature (SSTskin)
> The skin temperature (SSTskin) is defined as the temperature measured
> by an infrared radiometer typically operating at wavelengths 3.7-12 ?m
> (chosen for consistency with the majority of infrared satellite
> measurements) that represents the temperature within the conductive
> diffusion-dominated sub-layer at a depth of ~10-20 ?m. SSTskin
> measurements are subject to a large potential diurnal cycle including
> cool skin layer effects (especially at night under clear skies and low
> wind speed conditions) and warm layer effects in the daytime. (NOTE:
> Discussion on frequency is of secondary importance here - the main
> issue is that the SSTskin is that retrieved using an infrared
> radiometer)
> [Proposed CF-names: SSTskin, skin_layer_SST, skin_layer_sea_surface_temperature]
>
>
> The sub-skin sea surface temperature (SSTsub-skin)
> The subskin temperature (SSTsubskin) represents the temperature at the
> base of the conductive laminar sub-layer of the ocean surface. For
> practical purposes, SSTsubskin can be well approximated to the
> measurement of surface temperature by a microwave radiometer operating
> in the 6-11 GHz frequency range, but the relationship is neither
> direct nor invariant to changing physical conditions or to the
> specific geometry of the microwave measurements. (NOTE: Discussion on
> frequency is of secondary importance here - the main issue is that the
> SSTsub-skin is that retrieved using a microwave radiometer)
> [Proposed CF-names: SSTsubskin, Sub-skin_SST, sub-skin_sea_surface_temperature]
>
>
> The surface temperature at depth (SSTz or SSTdepth)
> All measurements of water temperature beneath the SSTsubskin are
> referred to as depth temperatures (SSTdepth) measured using a wide
> variety of platforms and sensors such as drifting buoys, vertical
> profiling floats, or deep thermistor chains at depths ranging from
> 10-2 - 103m. These temperature observations are distinct from those
> obtained using remote sensing techniques (SSTskin and SSTsubskin) and
> must be qualified by a measurement depth in meters (e.g., or SST(z)
> e.g. SST5m).
> (NOTE: I'm happy with Alison and Nan suggestions regarding the use of
> sea_water_temperature followed by a depth attribute. Without the
> depth attribute the data are only of marginal use in data assimilation
> systems and for blending. Many of the problems we have in the
> satellite SST community today stem from the fact that depth was not
> included as an essential component of the measurement. Now that some
> satellite radiometers are providing more accurate and consistent
> measurements of SST than can be obtained in situ (O'Carroll et al
> JTECH, 2007) depth is essential!!) So to answer Alisons question
>
> "We already have the standard name sea_water_temperature which is
> defined as follows: "For the temperature of sea water at a particular
> depth or layer, a data variable of sea_water_temperature with a
> vertical coordinate axis should be used." Would this meet your
> needs?" The answer is YES it does and we will work on this within
> GHRSST-PP.
>
>
> The foundation temperature (SSTfnd) (Please look at figure provided at
> https://www.ghrsst-pp.org/SST-Definitions.html to make sense of this)
> The foundation SST, SSTfnd, is defined as the temperature of the
> water column free of diurnal temperature variability (daytime warming
> or nocturnal cooling) and is considered equivalent to the SSTsubskin
> in the absence of any diurnal signal. It is named to indicate that it
> is the foundation temperature from which the growth of the diurnal
> thermocline develops each day (noting that on some occasions with a
> deep mixed layer there is no clear SSTfnd profile in the surface
> layer). Only in situ contact thermometry is able to measure SSTfnd and
> analysis procedures must be used to estimate the SSTfnd from
> radiometric satellite measurements of SSTskin and SSTsubskin. SSTfnd
> provides a connection with the historical concept of a "bulk" SST
> considered representative of the oceanic mixed layer temperature and
> represented by any SSTdepth measurement within the upper ocean over a
> depth range of 1-20+m. SSTfnd provides a more precise, well-defined
> quantity than previous loosely defined "bulk" SST and consequently, a
> better representation of the mixed layer temperature. In general,
> SSTfnd will be similar to a night time minimum or pre-dawn value at
> depths of ~1-5 m, but some differences could exist. Note that SSTfnd
> does not imply a constant depth mixed layer, but rather a surface
> layer of variable depth depending on the balance between
> stratification and turbulent energy and is expected to change slowly
> over the course of a day.
> [Proposed CF-names: SSTfnd, Foundation_Temperature,
> foundation_sea_surface_temperature]
>
> (NOTE: The main purpose of SSTfnd is to remove from the vocabulary of
> scientists the totally confusing and lazy term bulk SST which is
> meaningless in the context of modern measurements, for data
> assimilation and simply perpetuates confusion and erroneous
> assumptions (Bit harsh, I know, but essentially true!)). To answer
> Alison's question:
>
> "Does this mean that the foundation temperature is measured/modelled
> at the base of the thermocline so that the values are intrinsically
> free of diurnal variation [YES], or is the diurnal variation
> statistically removed from the data [it could be - especially when
> blending data for statistical analyses]?" The answer is yes in both
> cases. I hope that a new 'surface' and associated name can be
> introduced to represent this quantity which is the quantity that most
> global SST analysis systems produce today. There is a nice figure
> showing what SSTfnd is at
> https://www.ghrsst-pp.org/SST-Definitions.html
>
>
> I should note that I had a small WMO/IOC JCOMM task team set up as
> part of the SOT to look at this a year or so ago which concluded at
> this years SOT. The definitions presented above above were adopted by
> the WMO CBS. I Hope this makes things clearer and more straight
> forward and I sense that the main concern is with the in situ folk
> regarding the details and not the principles behind SSTz.
>
> Take care and with best regards
>
> Craig
>
>
>
>
>
>
>
>
>
Received on Wed Aug 15 2007 - 08:03:19 BST
