<p>I found a quote from <a href="https://www.researchgate.net/publication/224934523_Subsurface_Flows_in_and_Around_Active_Regions_with_Rotating_andNon-rotating_Sunspots" rel="nofollow noreferrer"><strong>K. Jain <em>et al.</em></strong></a>  which <strong>defines a Magnetic Activity Index</strong> might be pointing you in the correct direction - for me it still sounds rather abstract:</p>
<blockquote>
<p>To obtain the MAI, we convert magnetogram data to absolute values, average over the length of a ring day and <a href="https://en.wikipedia.org/wiki/Apodization" rel="nofollow noreferrer">apodise</a> them into circular areas to match the size of the <a href="https://en.wikipedia.org/wiki/Dopplergraph" rel="nofollow noreferrer">Dopplergram</a> patches used in the ring-diagram analysis.</p>
</blockquote>
<p>However, I also found <a href="http://hmi.stanford.edu/teams/rings/modules/maicalc.html" rel="nofollow noreferrer">http://hmi.stanford.edu/teams/rings/modules/maicalc.html</a> which contains a link a source code repository. The man-page of <strong>maicalc</strong> states:</p>
<blockquote>
<p>maicalc takes as its input a dataset of records representing solar magnetograms during a selected interval, and produces as its output the values of the Magnetic Activity Index (MAI) appropriate for a selected set of target locations as they would be mapped and tracked by mtrack for the duration of the input data interval and apodized by pspec3.</p>
</blockquote>

CC BY-SA 4.0
2020-12-30T22:48:48.017Z
2020-12-31T09:48:30.363Z
2020-12-31T09:48:30.363Z
B--rian
<p>I am looking for a description about how this number called Magnetic Activity Index (MAI) is calculated. All I know is that the processing pipeline of the <a href="http://hmi.stanford.edu/" rel="nofollow noreferrer">instrument HMI</a> calculates it. But I would like to know <em>how</em> this quantity is defined and computed! I have not yet found anything on google about it, not even an article.</p>

CC BY-SA 4.0
2020-10-27T08:59:11.970Z
Is this the HMI you are refering to ? http://hmi.stanford.edu/
usernumber
CC BY-SA 4.0
2020-10-27T15:56:01.240Z
Yes it is! I visited this website, but the magnetic activity index is not mentioned
Vanessa
<observational-astronomy><the-sun>
How does the Helioseismic and Magnetic Imager (HMI) compute the Magnetic Activity Index (MAI)?
Vanessa
# How does the Helioseismic and Magnetic Imager (HMI) compute the Magnetic Activity Index (MAI)?

(Asked by: username_0 on 2020-10-27)

I am looking for a description about how this number called Magnetic Activity Index (MAI) is calculated. All I know is that the processing pipeline of the [instrument HMI](http://hmi.stanford.edu/) calculates it. But I would like to know *how* this quantity is defined and computed! I have not yet found anything on google about it, not even an article.

**Tags:** observational-astronomy, the-sun
> **Comments:**
> **username_1**: Is this the HMI you are refering to ? http://hmi.stanford.edu/  
> **username_0**: Yes it is! I visited this website, but the magnetic activity index is not mentioned  

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## 1 answers

### Answer by username_2 on 2020-12-30. Score: 1

I found a quote from [**K. Jain *et al.***](https://www.researchgate.net/publication/224934523_Subsurface_Flows_in_and_Around_Active_Regions_with_Rotating_andNon-rotating_Sunspots) which **defines a Magnetic Activity Index** might be pointing you in the correct direction - for me it still sounds rather abstract:

> To obtain the MAI, we convert magnetogram data to absolute values, average over the length of a ring day and [apodise](https://en.wikipedia.org/wiki/Apodization) them into circular areas to match the size of the [Dopplergram](https://en.wikipedia.org/wiki/Dopplergraph) patches used in the ring-diagram analysis.

However, I also found <http://hmi.stanford.edu/teams/rings/modules/maicalc.html> which contains a link a source code repository. The man-page of **maicalc** states:

> maicalc takes as its input a dataset of records representing solar magnetograms during a selected interval, and produces as its output the values of the Magnetic Activity Index (MAI) appropriate for a selected set of target locations as they would be mapped and tracked by mtrack for the duration of the input data interval and apodized by pspec3.


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