Geomagnetic teams across the globe measure and monitor the Earth's magnetic field to provide Space Weather warnings of solar disturbances and forecast magnetic storms that can affect human activities.

GNS Science currently runs a magnetic observatory in Canterbury, north-west of Christchurch, and at Scott Base in Antarctica. GNS Science also supports the Apia magnetic observatory in Samoa, which is run by the Samoan Government, with assistance from New Zealand and other countries.

We continuously record changes in the Earth's magnetic field at these geomagnetic observatories using instruments that we call magnetometers. These magnetometers can record the rapid changes of the Earth's magnetic field (also known as geomagnetic field changes) associated with solar storms, as well as other geologic processes.

We use magnetometer data recorded at a 1-second sampling rate as input to compute 1-minute averages of geomagnetic field changes that are local to each 'geomag' network site.

The resulting geomagnetic basic time series have no adjustments made to them, so they may contain offsets, spikes, and daily and seasonal variations at individual sites that can also occur due to various causes. For example, introduction of magnetic objects like a vehicle being parked close to the magnetometer can cause contamination of the data, or even a large earthquake can influence the data quality.

Also worth noting is that the Intermagnet data products use additional constants which results in the magnetic field intensity being distributed differently across the individual magnetic field components and the vector component values deviate from the basic data shown in Tilde.

Data Names and Aspects

The magnetic field measured by a magnetometer on the ground is typically described by a vector field, with the intensity (or strength) being different for the different vector components. The direction of a vector (or arrow) can be thought of as the direction of the magnetic field. The length of the arrow can be thought of as the strength of the field, i.e. the longer the arrow, the stronger the field.

Magnetic intensity is measured in nanoTesla (nT) units.

The magnetic field intensity at almost all the geomag network sites are measured by both a fluxgate magnetometer, and a proton (or scalar) magnetometer. The sensor codes are 50 and 51, respectively. The EY2M and SMHS stations are only equipped with a fluxgate magnetometer.

The geomag domain fluxgate magnetometers, except for the one at SMHS, have three components.

The magnetic east component (Y) was set to zero at the time a fluxgate magnetometer was installed, aligning the magnetometer’s north-south axis to magnetic north. Since then, Y fluctuates around magnetic east-west direction with positive values in eastward direction, while the magnetic north component (X) fluctuates around magnetic north-south direction with positive values in northward direction.

The horizontal intensity (H) of the magnetic field is derived from the measured horizontal magnetic field components X and Y.

The intensity of the total vector field (F) can be calculated from the three magnetic field components X, Y and the Z measured by the fluxgate magnetometer. The intensity of the total scalar field (S) is measured directly by the proton magnetometer.

The magnetic field rate of change is the variation in intensity of the horizontal magnetic field from one minute to the next. Units are nanoTesla per minute (nT/min).

Rate of change can be calculated in different ways. The rate of change we named dH is calculated by dH/dt = H(t+1) - H(t) where t is a 1-minute timestep and H = sqrt(XX + YY). The absolute rate of change (R absolute) is calculated from the absolute value of H, and therefore represents the rate of horizontal change independent on what the scaling of each component (X and Y) is.

Data Access

Basic time series data and a few other derived products are available through Tilde, GeoNet’s Time Series API. In Tilde, geomagnetic data are available through the geomag data domain.

There are three avenues to access geomagnetic data through Tilde:

• Tilde API
• Tilde Data Discovery tool which allows you to discovery what data is available at different sensor locations and for what time periods the data is available for.
• Tilde Data Exploration tool which allows you to look at multiple data streams for different stations or multiple data streams from one station.

Station Metadata

GeoNet's network map can be used to investigate the magnetometer stations that are part of the geomag network. Station metadata XML files are available on the GeoNet data repository.

Data Products

Other available geomagnetic data products available can be discovered through the New Zealand Geomagnetic Database GNS Science dataset catalogue. Data can be accessed via the Tilde Time Series Data Discovery tool or via the Tilde API. Data are available in CSV or JSON format.

The Intermagnet geomagnetic observatory data products’ naming convention is different from the station codes and names used in Tilde.