<p>They're not directly equivalent.  I think the problem is that &quot;absolute humidity&quot; is used to mean both &quot;a measurement of the actual humidity content of the air&quot; (&quot;absolute&quot; as in &quot;non-relative&quot;) and, in some sources, &quot;mass of water vapor per unit volume&quot; - which is temperature-dependent as well (using <span class="math-container">$PV=nRT$</span> at fixed pressure and mass: <span class="math-container">$V$</span> varies with <span class="math-container">$T$</span>).</p>
<p>I think this <a href="https://web.archive.org/web/20170120174947/https://www.nasa.gov/centers/dryden/pdf/87878main_H-937.pdf" rel="nofollow noreferrer">technical note</a> covers it.  Key points:</p>
<ul>
<li>Vapor pressure is a function of dew point alone (Eq. 16 - remaining variables are constants).</li>
<li>Absolute humidity is a function of vapor pressure <em>and temperature</em> (Eq. 3).</li>
<li>Thus, absolute humidity is a function of both dew point and temperature (Eq. 20).</li>
</ul>
<p>The reason they appear to be directly related, like in the dataset you looked at, is that <span class="math-container">$T$</span> (in Kelvin) only varies by 20% or so in a typical temperature range (e.g., -20 to +40 C = 253 to 313 K), so it doesn't affect things that much.</p>
<p>That technical note does work as a citation for dew point being an absolute measurement of humidity, since it corresponds directly to vapor pressure in Eq. 16.</p>

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2023-08-30T18:23:11.030Z
2024-09-19T19:48:51.710Z
2024-09-19T19:48:51.710Z
damp_civil
<p>I am looking for a reference (e.g. book, peer-reviewed paper) that asserts that
absolute humidity is &quot;equivalent&quot; to the dew-point temperature.</p>
<p>Such statement should be true, AFAIU. Online, <a href="https://www.quora.com/Why-is-the-dew-point-a-consequence-of-the-absolute-humidity" rel="nofollow noreferrer">people say</a> <a href="https://www.memphisweather.blog/2013/08/how-humid-is-it-why-dew-point-is.html" rel="nofollow noreferrer">they are the same</a>, in scientific publications they look almost linearly related in some range of temperatures <a href="https://www.naun.org/main/NAUN/mechanics/19-574.pdf" rel="nofollow noreferrer">here, figure 4</a>, I tested their relation on data I have and their correlation is <span class="math-container">$ &gt; 0.98$</span>.</p>
<p>But I am unable to find a reference that states the absolute humidity and the dew-point temperature are &quot;equivalent&quot;, &quot;highly correlated (under reasonable conditions)&quot;, or that &quot;one can serve as a proxy for the other&quot;. Please help me find such reference.</p>

<meteorology><temperature><humidity>
Dew-point temperature and absolute humidity
Yair Daon
# Dew-point temperature and absolute humidity

(Asked by: username_0 on 2023-08-30)

I am looking for a reference (e.g. book, peer-reviewed paper) that asserts that
absolute humidity is "equivalent" to the dew-point temperature.

Such statement should be true, AFAIU. Online, [people say](https://www.quora.com/Why-is-the-dew-point-a-consequence-of-the-absolute-humidity) [they are the same](https://www.memphisweather.blog/2013/08/how-humid-is-it-why-dew-point-is.html), in scientific publications they look almost linearly related in some range of temperatures [here, figure 4](https://www.naun.org/main/NAUN/mechanics/19-574.pdf), I tested their relation on data I have and their correlation is $ > 0.98$.

But I am unable to find a reference that states the absolute humidity and the dew-point temperature are "equivalent", "highly correlated (under reasonable conditions)", or that "one can serve as a proxy for the other". Please help me find such reference.

**Tags:** meteorology, temperature, humidity


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## 1 answers

### Answer by username_1 on 2023-08-30. Score: 3 | Accepted answer

They're not directly equivalent. I think the problem is that "absolute humidity" is used to mean both "a measurement of the actual humidity content of the air" ("absolute" as in "non-relative") and, in some sources, "mass of water vapor per unit volume" - which is temperature-dependent as well (using $PV=nRT$ at fixed pressure and mass: $V$ varies with $T$).

I think this [technical note](https://web.archive.org/web/20170120174947/https://www.nasa.gov/centers/dryden/pdf/87878main_H-937.pdf) covers it. Key points:

* Vapor pressure is a function of dew point alone (Eq. 16 - remaining variables are constants).
* Absolute humidity is a function of vapor pressure *and temperature* (Eq. 3).
* Thus, absolute humidity is a function of both dew point and temperature (Eq. 20).

The reason they appear to be directly related, like in the dataset you looked at, is that $T$ (in Kelvin) only varies by 20% or so in a typical temperature range (e.g., -20 to +40 C = 253 to 313 K), so it doesn't affect things that much.

That technical note does work as a citation for dew point being an absolute measurement of humidity, since it corresponds directly to vapor pressure in Eq. 16.


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