<p>I would agree with your hypothesis, but I must point out that it will likely break down further and further as you approach the tropopause. Whether the ISA model is actually a average, I cannot say. However, the idea that the ISA model is a horizontal average is plausible.</p>

CC BY-SA 3.0
2017-05-09T22:36:02.423Z
2017-05-09T22:36:02.423Z
BarocliniCplusplus
<p>I have a newbie question...</p>

<p>I always used the <a href="https://en.wikipedia.org/wiki/International_Standard_Atmosphere#/media/File:Comparison_International_Standard_Atmosphere_space_diving.svg" rel="nofollow noreferrer">International Standard Atmosphere model</a> whenever I needed to calculate the temperature in a given altitude.
It always looked accurate to me...  </p>

<p>However, doing some work using <a href="https://www.ncdc.noaa.gov/data-access/model-data/model-datasets/global-forcast-system-gfs" rel="nofollow noreferrer">GFS data</a>, I found something intriguing..</p>

<p>At a given high altitude (let's say : 150 hpa/44000ft), the temperature I saw in the GFS model was almost always colder than the ISA temperature for that altitude</p>

<p>This was mostly TRUE for latitudes between -30 and 30º, and the OPPOSITE for abs(latitudes) > 30º.   </p>

<p>Example:</p>

<p><a href="https://i.sstatic.net/fyeNC.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/fyeNC.png" alt="enter image description here"></a></p>

<p>So, I came with a hypothesis... Want I want to know if it is crazy or not.</p>

<ul>
<li>The ISA model is an average model. Temperatures in the tropics are lower (for high altitudes) and the temperatures near the poles are higher. The final average is the ISA model.</li>
</ul>

<meteorology><temperature><weather-forecasting><gfs>
ISA Model and GFS data
guilhermecgs
# ISA Model and GFS data

(Asked by: username_0 on 2017-05-08)

I have a newbie question...

I always used the [International Standard Atmosphere model](https://en.wikipedia.org/wiki/International_Standard_Atmosphere#/media/File:Comparison_International_Standard_Atmosphere_space_diving.svg) whenever I needed to calculate the temperature in a given altitude.
It always looked accurate to me...

However, doing some work using [GFS data](https://www.ncdc.noaa.gov/data-access/model-data/model-datasets/global-forcast-system-gfs), I found something intriguing..

At a given high altitude (let's say : 150 hpa/44000ft), the temperature I saw in the GFS model was almost always colder than the ISA temperature for that altitude

This was mostly TRUE for latitudes between -30 and 30º, and the OPPOSITE for abs(latitudes) > 30º.

Example:

[![enter image description here](https://i.sstatic.net/fyeNC.png)](https://i.sstatic.net/fyeNC.png)

So, I came with a hypothesis... Want I want to know if it is crazy or not.

* The ISA model is an average model. Temperatures in the tropics are lower (for high altitudes) and the temperatures near the poles are higher. The final average is the ISA model.

**Tags:** meteorology, temperature, weather-forecasting, gfs


---

## 1 answers

### Answer by username_1 on 2017-05-09. Score: 1 | Accepted answer

I would agree with your hypothesis, but I must point out that it will likely break down further and further as you approach the tropopause. Whether the ISA model is actually a average, I cannot say. However, the idea that the ISA model is a horizontal average is plausible.


---

