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[k-index] - [faq]

K-Index FAQ

What is K Index?

The K-index, and by extension the Planetary K-index, are used to characterize the magnitude of geomagnetic storms. Geomagnetic storms in turn are caused by disturbances that propagate away from the Sun, travel through interplanetary space. Eventually, they reach Earth, and interact with radio signals vital to global positioning systems.  

Kp indicates the variation resulting from disturbances in the Earth’s magnetic field. Based on the value, the Space Weather Prediction Centre (SWCP) issue geomagnetic alerts and warnings.

How is it calculated?

The data is recorded from across 13 subaural observatories with 11 distributed in the northern hemisphere and 2 in the southern hemisphere.

observatories map.png Figure 1.  Distribution of subarual observatories (courtesy of the Solar-Terrestrial Centre)

The K-index is represented as a quasi-logarithmic local index of the 3-hourly range in magnetic activity relative to an assumed quiet-day curve for a single geomagnetic observatory site. Essentially, it is a measurment of the variation from the expected norm.  

It is based on 3-hour measurements of variations from the calculated norm based for each of the past three days. 

Who does it affect most?

Essentially, anyone transmitting radio signals which reflect off of or pass through the ionosphere. So any drone pilot utilising a positioning system.

Beyond this, some principal users affected by geomagnetic storms are the electrical power grid and spacecraft operations.

How does it affect GPS? 

There are multiple ways space weather impacts Global Navigation Satellite System (GNSS) function: 

Ionosphere Corrections

As GNSS signals travel between your ground station receiver and satellites, they pass through the ionosphere. Contained within the ionosphere is charged plasma which bends the path of radio signals. In the absence of space weather, it is accurately modelled and positioning systems precisely compensate for the bends it causes.  However, in the event of space weather with a disturbed ionosphere, the models are no longer effective and cannot accurately predict the variations.

Loss of Satellite Connections

The signal-to-noise ratio is reduced impacting the receivers connection with satellites. The effects of this will fluctuate rapidly during higher geomagnetic disturbances. Accuracy will typically drop from less than a meter to tens of meters depending on the severity of the storm and could significantly impact your flight.  

When and where are these disturbances most likely?

In higher latitudes, major storms are more common with increasingly dynamic enhancements observed. These result in much larger errors introduced into the GNSS positioning calculations.  Countries such as Norway often experience positioning error due to these higher ionosphere disturbances. Last year Norway launched improved systems to track the known errors in GPS signals. These extrapolate ionosphere disturbances more precisely so they can be accounted for and more effectively compensated against. 

At lower altitudes along the earth’s magnetic equator, more localised variations are possible. Here there are additional factors which impact geomagnetic interference here including current systems and electric fields both creating instabilities in the ionosphere.

They are most significant immediately after sunset, which may increasingly have the potential to impact drone pilots with their successful night wavers.  

It should be noted that these, although not influencing space weather, have the potential to contribute to your positioning system's effectiveness and reliability alongside space weather disturbances.

Should I still fly my drone?

Geomagnetic storms are relatively infrequent. It's important fly with an appropriate number of sattelites in order to avoid GNSS failures and to improve accuracy. Localised variations, as well as more immediate hazards radio transmissions are more likely to impact your operations. However, K-Index is easy enough to account for and is worth checking each time. Safety is paramount.  

Table 1. General impact and flight suitability:

Kp Value

Impact on Drone Operations*

1 - 3

Safe, unlikely to lose noticeable accuracy

4 - 5

Safe, slight chance of accuracy loss

6

Safe, up to 5% accuracy loss

7 - 9 

Avoid operating, potential for loss of GPS connection

and radio signal interference

*Remember, localised variations can impact

We will be including K-Index in our updated weather reporting. Our source will be the three hourly feed published by NOAA Space Weather.     

References:

Space Weather Prediction Service - http://www.swpc.noaa.gov/impacts/space-weather-and-gps-systems

International Service of Geomagnetic Indiceshttp://isgi.unistra.fr/indices_kp.php

Solar-Terrestrial Centre of Excellence - http://www.stce.be/news/243/welcome.html

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