<p>The Tetens coefficents are the empirically derived coefficients of an equation for calculating the saturation vapour pressure of water. From <a href="https://en.wikipedia.org/wiki/Clausius%E2%80%93Clapeyron_relation#Meteorology_and_climatology" rel="nofollow noreferrer">wikipedia</a>:</p>
<blockquote>
<p>a very good approximation can usually be made using the August-Roche-Magnus formula (usually called the Magnus or Magnus-Tetens approximation, though this attribution is historically inaccurate):</p>
<p><span class="math-container">$e_s(T)= 6.1094 \exp \left( \frac{17.625T}{T+243.04} \right)$</span></p>
<p>e_s(T) is the equilibrium or saturation vapor pressure in hPa as a function of temperature T on the Celsius scale. Since there is only a weak dependence on temperature of the denominator of the exponent, this equation shows that saturation water vapor pressure changes approximately exponentially with T.</p>
</blockquote>

CC BY-SA 3.0
2014-09-04T03:45:25.443Z
2014-09-04T03:45:25.443Z
2020-06-18T08:25:19.090Z
naught101
<p>Tetens coefficients appear in a few meteorological/climatological models that I've been looking at,for example <a href="http://apsrunet.apsim.info/svn/apsim/tags/Apsim70/Model/MicroMet/MicroMet.for" rel="nofollow">APSIM</a>:</p>

<pre><code>svp_A = 6.106
svp_B = 17.27
svp_C = 237.3
</code></pre>

<p>These same values appear in at least two other models, but I can't find any documentation about what they represent, or where they come from. What are these numbers?</p>

<p><strong>Edit:</strong> <a href="http://onlinelibrary.wiley.com/doi/10.1029/2000JD900061/pdf" rel="nofollow">Oroud, I. M., 2001, <em>Dynamics of evaporation from saline water bodies</em></a> uses these constants and references <em>Tetens, O. 1930 <strong>"Uber einige meteorologische Begriffe."</strong> Z. Geophys. 6: 297-309</em>, but that text doesn't appear to be available online, or in my university's library.</p>

CC BY-SA 4.0
2023-01-23T01:33:05.287Z
For future reference: Text can be accessed online [here](https://e-docs.geo-leo.de/handle/11858/7532), p. 297ff.
dimfalk
<meteorology>
What are Tetens coefficients?
naught101
# What are Tetens coefficients?

(Asked by: username_0 on 2014-07-02)

Tetens coefficients appear in a few meteorological/climatological models that I've been looking at,for example [APSIM](http://apsrunet.apsim.info/svn/apsim/tags/Apsim70/Model/MicroMet/MicroMet.for):

```
svp_A = 6.106
svp_B = 17.27
svp_C = 237.3

```

These same values appear in at least two other models, but I can't find any documentation about what they represent, or where they come from. What are these numbers?

**Edit:** [Oroud, I. M., 2001, *Dynamics of evaporation from saline water bodies*](http://onlinelibrary.wiley.com/doi/10.1029/2000JD900061/pdf) uses these constants and references *Tetens, O. 1930 **"Uber einige meteorologische Begriffe."** Z. Geophys. 6: 297-309*, but that text doesn't appear to be available online, or in my university's library.

**Tags:** meteorology

> **Comments:**
> **username_1**: For future reference: Text can be accessed online [here](https://e-docs.geo-leo.de/handle/11858/7532), p. 297ff.  

---

## 1 answers

### Answer by username_0 on 2014-09-04. Score: 4 | Accepted answer

The Tetens coefficents are the empirically derived coefficients of an equation for calculating the saturation vapour pressure of water. From [wikipedia](https://en.wikipedia.org/wiki/Clausius%E2%80%93Clapeyron_relation#Meteorology_and_climatology):

> a very good approximation can usually be made using the August-Roche-Magnus formula (usually called the Magnus or Magnus-Tetens approximation, though this attribution is historically inaccurate):
>
> $e\_s(T)= 6.1094 \exp \left( \frac{17.625T}{T+243.04} \right)$
>
> e\_s(T) is the equilibrium or saturation vapor pressure in hPa as a function of temperature T on the Celsius scale. Since there is only a weak dependence on temperature of the denominator of the exponent, this equation shows that saturation water vapor pressure changes approximately exponentially with T.


---

