teos-10 slides for oceanography

7/23/2019 TEOS-10 Slides for Oceanography

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Trevor J McDougall

University of New South Wales

The International Thermodynamic

Equation of Seawater 2010

Ocean Physics, School of Mathematics and Statistics

Introductory lecture slides


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These slides provide a short

summary of the use of TEOS-10

in oceanoraphy

The official guide to TOS!"# is

$O% et al& '(#"#)* the front cover

is shown&

The www&TOS!"#&orgwe+ site

serves the comuter software,

including algorithms to evaluate all

the thermodynamic roerties of iceand moist air&
http://www.teos-10.org/http://www.teos-10.org/


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- The "./# $nternational 0uation of State 'OS!/#) has served the

community very well for 1# years&

- OS!/# rovides searate algorithms for density, sound seed,

heat caacity and free2ing temerature&

- 3owever, OS!/# does notrovide e4ressions for entroy,

internal energy and most imortantly enthalpy&

- 5ll such thermodynamic roerties are +est derived from a single

6i++s function so that the roerties are totally consistent with

each other&

- The TOS!"# 'Thermodynamic E0uation Of Seawater 7 (#10)

6i++s function incororates the most recent la+oratory data,ma8ing the algorithms more accurate, e& g&

! the roerties of ure water are more accurate than in OS!/#,

! the temerature scale has +een udated from $PTS!9/ to $TS!.#&

! the density of very cold +rac8ish water is significantly imroved&

!ac"round to TEOS-10


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- S%O:;$5PSO Wor8ing 6rou "(< settled on a definition of the:eference %omosition of seawater& This was a necessary first

ste in order to define the 6i++s function at very low salinities&

This :eference %omosition, consisting of the ma=or

comonents of Standard Seawater, was determined from earlier

analytical measurements&

- The definition of the :eference %omosition ena+led the

calculation of the 5+solute Salinity of seawater that has this

:eference %omosition 'ma8ing use of modern atomic weights)&

- The roerties of seawater have +een defined u to highertemeratures '/#>%* useful for desalination lant design) and to

higher 5+solute Salinities '"(# g 8g!"* useful for secial laces

such as Shar8 ?ay, Western 5ustralia)&

#eatures of the new International

Thermodynamic Equation of Seawater 2010


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$hemical $omposition of Standard

Seawater the %eference $omposition

Using the available information and 2005atomic weight estimates, mole fractions of

standard seawater can be determined.

The Na+ contribution is determined by the

requirement to achieve eact chargebalance.

The resulting !Reference Composition"

is shown to the right.

Millero, @& J&, :& @eistel, D& 6& Wright and T& J&McDougall, (##/A The comosition ofStandard Seawater and the definition of the:eference!%omosition Salinity Scale&Deep-Sea Research$, &&, B#!


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%eference Salinity as a steppin stone to /solute Salinity

- Practical Salinity is calculated from the conductivity of seawater,

and is not the mass fraction of salt in seawater&

- The thermodynamic roerties of seawater are more closely

deendent on the mass fraction '5+solute Salinity S5) of dissolved

material, not the conductivity or Practical Salinity SP&

- $n articular, the density of seawater is a function of S5not of SP&3ence we need to use 5+solute Salinity in order to accurately

determine the hori2ontal density gradients 'for use in the Cthermal

wind e0uation)&

- The hori2ontal density gradient is used via the Cthermal wind

e0uation to deduce the mean ocean circulation&

- 3ence an accurate evaluation of the oceanEs role in heat transort

and in climate change re0uires the use of 5+solute Salinity&


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%eference Salinity as a steppin stone to /solute Salinity

- :eference Salinity S:is defined to rovide the +est availa+leestimate of the 5+solute Salinity S5of +oth

'i) seawater of :eference %omosition,

'ii) Standard Seawater 'North 5tlantic surface seawater)&

- S:

can +e related to Practical Salinity SP

'which is +ased on

conductivity ratio) +y

S:F '1B&"9B #G;1B) g 8g7"4 SP&

- The difference +etween the new and old salinities of

H#&"9B #G g 8g7"'H#&G


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ow is the TEOS-10 is #unction used3

@rom a 6i++s function, all of the thermodynamic roerties of seawater

can +e determined +y simle differentiation and alge+raic maniulation&


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.odular nature of TEOS-10


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/solute Salinity /nomaly

- Practical Salinity SPreflects the conductivity of seawaterwhereas the thermodynamic roerties are more accurately

e4ressed in terms of the concentrations of all the comonents

of sea salt& @or e4amle, non!ionic secies contri+ute to density

+ut not to conductivity&

- The 6i++s function is e4ressed in terms of the 5+solute SalinityS5'mass fraction of dissolved material) rather than the Practical

Salinity SPof seawater&

- S5 F '1B&"9B #G;1B) g 8g7"4 SP

S#x,y,p( )


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ow can we calculate 3

- The 5+solute Salinity 5nomaly is determined +y

accurately measuring the density of a seawater samle in thela+oratory using a vi+rating +eam densimeter&

- This density is comared to the density calculated from the

samleEs Practical Salinity to give an estimate of

! We have done this to date on /"" seawater samles from

around the glo+al ocean&

- We e4loit a correlation +etween and the silicate

concentration of seawater to arrive at a comuter algorithm, a

loo8!u ta+le, to estimate

S5F '1B&"9B #G;1B) g 8g7"4 SP

S

#

S

#

S

#

S

#

S

#= S

#x,y,p( ) .

S# x,y,p( )


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4here have the )11 samples come from3


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4hat is the spatial distriution of 3S#


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4hat is the spatial distriution of 3S#


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This figure is for data from theworld ocean +elow "### m&

This imrovement is mainly due

to using S5rather than SP&

The red data uses S:in lace of

S5&

Improvement in calculatin the hori5ontal density radient

9#I of the data

is imroved +y

more than (I&

$p = pS# p

S# S%

6orthward density radient

improvementinTEOS-10vsEOS-)0

This shows that for calculating

density, the other imrovements

in TOS!"# are minor comared

with accounting for comosition

anomalies&


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The 6orth 7acific8 109 chane in the thermal wind with TEOS-10

imp

rovementinTEOS-10

vsEOS-)0

6orthward density radient


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4hy adopt /solute Salinity 3S#

- The ure water content of seawater is K" 7 ##"S5;'g ;8g)L not

K" 7 ##"SPL& Since S5and SPdiffer numerically +y a+out#&G


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The air!sea heat flu4 is a well!defined 0uantity,

and it can +e measured&

?ut what is the heat flu4 carried +y seawater

That is, how would we calculate the meridionalheat flu4 carried +y the ocean circulation

This meridional heat flu4 is the main role of the

ocean in climate and in climate change* +ut

how can we evaluate this heat flu4

4hat is the :heat content; of seawater3


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The Ocean


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The concept of potential temperature

Potential temerature, , involves a thought e4eriment&

ou ta8e your seawater samle at ressurepand

you mentally ut an insulating lastic +ag around it,

and then you change its ressure& Usually you move

the lastic +ag to the sea surface whereprF # d+ar&Once there, you Cmeasure the temerature and call

it Cotential temerature&

$n ocean models the air!sea heat flu4 enters the

ocean as a flu4 of otential temerature, using a

constant secific heat caacity&


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7resent oceanoraphic practice reardin :heat;

To date we oceanograhers have treated otential temerature

as a conservative varia+le&

We also mi4 water masses on diagrams as though +oth

salinity and otential temerature are conserved on mi4ing&

$n ocean models, air!sea heat flu4es cause a change in using

a constant secific heat caacity 'whereas in fact varies +y

BI at the sea surface)&

That is, we treat Cheat content as +eing roortional to

-3ow good are these assumtions

- %an we do +etter

S

cp

.


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The #irst >aw of Thermodynamics in terms of

The @irst aw of Thermodynamics is written in terms of enthaly as

dh

dt

$

dP

dt

= F% F& +

We would li8e the +rac8et here to +e a total derivative, for then we

would have a varia+le that would +e advected and mi4ed in theocean as a conservative varia+le whose surface flu4 is the air!sea

heat flu4&

$f we ta8e thermodynamic reasoning leads toh= S#,,p( ) ,

T0+ t( )T0+ ( )

cp pr( ) dd t+ p( ) T0+ t( )T pr( ) dS

#

d t

= F% F& +

h


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Specific heat capacity at constant pressure?cp? @ "-1A-1atpB 0 dar


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7otential enthalpy? and $onservative Temperature?

Just as is the temerature evaluated after an adia+atic change in

ressure, so otential enthaly is the enthaly of a fluid arcel after the

same adia+atic change in ressure&

h0 S#,,0( ) = h S# ,,p( ) v S# ,, p( )0

p

dp .

h0,

T0+ t( )T0+ ( )

cp0 dd t

+ p( ) T0+ t( )T0+ ( )

0( )

dS#dt

= F% F& +

Ta8ing the material derivative of this leads to 'with )h0 = cp0

The Csecific heat is a constant, and the s0uare +rac8et here is very

close to 2ero, even at a ressure of G# MPa F G,### d+ar& This means

that the @irst aw of Thermodynamics can +e accurately written as

dh0

dt = c

p0 ddt

= F% F& +.

cp0


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The difference etween potential temperature

and

$onservative Temperature? '( )


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C to e compared with the error in assumin that

entropy is a conservative varialeD contours in '


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Improvin :eat; $onservation in Ocean .odels

- %onservative temerature is"## times closer to +eing Cheat

than is otential temerature&

- The algorithm for conservative

temerature has +een imorted

into the MOMG code and it isavaila+le as an otion when

running the MOMG code&

- The figures show the e4ected

influence of sea!surface

temerature in the annual

mean, and seasonally&


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This imrovement in the calculation of the Cheat

content of seawater and the Cheat flu4 carried +y the

ocean circulation is ossi+le +ecause the TOS!"#

6i++s function delivers the enthalyof seawater&

Improvin :eat; $onservation in Ocean .odels


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The two "ey chanes to oceanoraphic practice

"& Use of a new salinity varia+le, 5+solute Salinity S5'g;8g) in lace

of Practical Salinity SP'ocean models need to also 8ee trac8 of

another salinity varia+le, called Preformed Salinity S)&

(& Use of a new temerature varia+le, %onservative Temerature

relacing otential temerature.

,


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The official guide to TOS!"# is

$O% et al& '(#"#)* the front cover

is shown&

4loiting the thermodynamic

e0uili+rium roerties +etween

seawater, ice and humid air, means

that we now have very accurate

roerties such as free2ingtemerature, latent heat of

evaoration etc&

TOS!"# is the official

thermodynamic descrition of

seawater, ice and of humid air at

all ressures in the atmoshere&


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This short (/!age document is an

introduction to TOS!"# and to the

6i++s Seawater Oceanograhic

Tool+o4 of comuter algorithms&


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TEOS-108 7ulications and 7eer-%eview


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eostrophic Streamfunction for density surfaces

p(5,0 (5,0 dp0

p

The rms error is imroved +y a factor of "9&

$2 p QQp( ) QQ S# ,,p( ) $$2

Tb

QQ( ) p QQp( )2

QQdp

0

p


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Implementation of TEOS-10

-$n Octo+er (##/, the $nternational 5ssociation for the

Proerties of Water and Steam '$5PWS) adoted TOS!"# asthe thermodynamic e0uation of seawater for industrial and

engineering uroses&

-$n June (##., the $ntergovernmental Oceanograhic

%ommission adoted TOS!"# as the new definition of the

thermodynamic roerties of seawater in oceanograhy,effective from "stJanuary (#"#&

-The descrition of TOS!"# and the TOS!"# comuter

software is availa+le at httA;;www&TOS!"#&org

- Oceanograhic =ournals are now encouraging authors to use

TOS!"#, including the use of 5+solute Salinity& The use ofPractical Salinity and OS!/# in =ournal articles is +eing hased

out over a transition eriod 'B years)&


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Implementation of TEOS-10

- The thermodynamic roerties of seawater are now defined in terms of theTOS!"# 6i++s function for seawater which is a function of 5+solute

Salinity&

- %ontinue to reort Practical Salinity SPto national data +ases since

'i) SPis a measured arameter and

'ii) we need to maintain continuity in these data +ases&! Note that this treatment of wor8ing scientifically with 5+solute Salinity

+ut reorting Practical Salinity to national data +ases is e4actly what

we have +een doing for temerature* we store in situ temerature,

+ut we have done our research and u+lished in otential temerature&


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