The Ap-index provides a daily average level for geomagnetic activity. Because of the non-linear relationship of the K-scale to magnetometer
fluctuations, it is not meaningful to take the average of a set of K-indices. Instead, every 3-hour K-value will be converted back into a linear
scale called the a-index. The average from 8 daily a-values gives us the Ap-index of a certain day. The Ap-index is thus a geomagnetic activity
index where days with high levels of geomagnetic activity have a higher daily Ap-value.
How do you determine the Ap-index?
The daily Ap-value is obtained by averaging the eight 3-hour values of ap for each day. To get the these ap-values you first need to convert
the 3-hour Kp-values to ap-values. Be aware that we use the official, finalized Kp which comes from the GFZ in Potsdam, Germany. This Kp-index
works slightly different then the preliminary Kp-index. Read about this in our Kp-index help article. To make it a bit more clear on how you can
determine the Ap for a certain day, we will work with an example: we take one day with the following measured Kp-values: 0+, 2-, 2o, 3o, 7-, 8o,
9- and 9o. The next step would be to convert these Kp-values to ap-values. The table at the bottom of this article will help you with this. When
we are done converting we get these eight ap-values: 2, 6, 7, 15, 111, 207, 300 and 400. The average of these eight values will give you the Ap for
that day. The day that we used in this example day would have an Ap-value of 131. The table below will let you convert the Kp-values to ap-values.
||Kp in decimals
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Current data suggest that it is not possible to see aurora now at middle latitudes
The strength of the interplanetary magnetic field is moderate (10.39nT), the direction is North (4.71nT).
Sunday, 28 May 2017 - 14:50 UTC
Wednesday, 24 May 2017 - 13:30 UTC
Thursday, 18 May 2017 - 13:22 UTC
Today's space weather
|Predicted Kp max
|M-class solar flare
|X-class solar flare
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Space weather facts
|Last geomagnetic storm:||2017/05/28||Kp7 (G3)|
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