Column of water in the sea

Storyboard

In the case of the ocean, the density of water, depending on its temperature and salinity, varies with depth. For this reason the pressure cannot be calculated with the traditional pressure formula for the water column. It is necessary to consider the effect of the variation in density and calculate by integrating the mass along the column the pressure that occurs at the depth that we wish to estimate.

>Model

ID:(1598, 0)



Characterization of the ocean layers

Definition

Ekman's transport causes the boundaries between the surface and deepest layers in the ocean to shift. These are characterized by sudden changes in parameters depending on the temperature. In particular there are changes in:

Temperature (thermocline)
Salinity (halocline)
Density (pycnocline)

ID:(11684, 0)



Column with variable density

Image

To calculate the pressure under the sea at a given depth, one must first estimate the mass of a volume element at a certain depth:

The problem in this case is that the density is not constant so the typical relationship of the pressure of the water column cannot be applied.

ID:(12008, 0)



Density modeling

Note

If you look at the curve of the density of ocean water as a function of depth, you see that it has the shape of an inverted exponential. In other words, the upper part is allowed to compress, reaching a limit where the weight of the column does not lead to greater compression:

ID:(12014, 0)



Column of water in the sea

Storyboard

In the case of the ocean, the density of water, depending on its temperature and salinity, varies with depth. For this reason the pressure cannot be calculated with the traditional pressure formula for the water column. It is necessary to consider the effect of the variation in density and calculate by integrating the mass along the column the pressure that occurs at the depth that we wish to estimate.

Variables

Symbol
Text
Variable
Value
Units
Calculate
MKS Value
MKS Units
$p_0$
p_0
Atmospheric pressure
Pa
$dz$
dz
Column depth element
m
$\rho$
rho
Density of sea water at a given depth
kg/m^3
$\rho_{\infty}$
rho_infty
Density of sea water at depth
kg/m^3
$\rho_w$
rho_w
Density of sea water on the surface
kg/m^3
$z$
z
Depth in the sea
m
$dF$
dF
Force element
N
$\lambda$
lambda
Inverse of reference depth
m
$S$
S
Marine column section
m^2
$p$
p
Pressure
Pa
$dp$
dp
Pressure element
Pa
$dm$
dm
Sea water body element
kg

Calculations


First, select the equation:   to ,  then, select the variable:   to 

Symbol
Equation
Solved
Translated

Calculations

Symbol
Equation
Solved
Translated

 Variable   Given   Calculate   Target :   Equation   To be used



Equations


Examples

Ekman's transport causes the boundaries between the surface and deepest layers in the ocean to shift. These are characterized by sudden changes in parameters depending on the temperature. In particular there are changes in:

Temperature (thermocline)
Salinity (halocline)
Density (pycnocline)

image

To calculate the pressure under the sea at a given depth, one must first estimate the mass of a volume element at a certain depth:

image

The problem in this case is that the density is not constant so the typical relationship of the pressure of the water column cannot be applied.

A water element of a height dz , section S and density \ rho has a mass:

equation

Con la definici n de la fuerza gravitacional

equation=3241

el aumento de la fuerza en funci n de la masa es

equation

Con la variaci n de la masa

equation=12010

y la variaci n de la fuerza en funci n de la masa

equation=12012

con lo que se obtiene

equation

Con la definici n de la presi n

equation=4342

la presi n aumenta con la fuerza seg n

equation

en donde se asume que la secci n no varia.

Con la definici n de la presi n

equation=12009

el aumento de la fuerza

equation=12013

lleva a un aumento de la presi n

equation

If you look at the curve of the density of ocean water as a function of depth, you see that it has the shape of an inverted exponential. In other words, the upper part is allowed to compress, reaching a limit where the weight of the column does not lead to greater compression:

image

If you observe the curve of density with depth you can model this with a value for surface density \ rho_0 \ sim 1,025 , g / cm ^ 3 and a very deep value of \ rho _ {\ infty} \ sim 1,028 , g / cm ^ 3 to which it converges exponentially with an average depth of (reaching 36% of the original value) of about 500 , m whose inverse value We will call \ lambda . In this way we have the model:

equation

Con el incremento de la presi n dp cuando se incrementa la profundidad dz

equation=12011

se puede mediante integraci n calcular la presi n para cualquier profundidad:

equation

Si se emplea la funci n de la densidad

equation=11882

en la ecuaci n de la presi n

equation=11881

se obtiene

equation


>Model

ID:(1598, 0)