Wednesday, November 8, 2017

Moderate Geomagnetic Storm Strikes Earth

Credit: NASA

A G2-class (moderately strong) geomagnetic storm that could have noticeable impact on power systems, satellites and could trigger auroras seen as low as New York and Wisconsin, hit Earth on Tuesday, November 7. The storm is stronger than previously expected by National Oceanic and Atmospheric Administration (NOAA) as it forecasted only a G1-class (minor) event.

Geomagnetic storms can increase the density and distribution of density in the upper atmosphere, causing extra drag on satellites in low-earth orbit. The local heating also creates strong horizontal variations in the in the ionospheric density that can modify the path of radio signals and create errors in the positioning information provided by GPS. While the storms create beautiful aurora, they also can disrupt navigation systems such as the Global Navigation Satellite System (GNSS) and create harmful geomagnetic induced currents (GICs) in the power grid and pipelines.

G2-class storm can cause voltage alarms and transformer damage in high-latitude power systems. When it comes to possible impact on spacecraft operations, in result of such storm, corrective actions to orientation may be required by ground control. Moderately strong geomagnetic storm can also spark auroras and cause fading of HF radio propagation at higher latitudes.

Few days ago, NOAA issued a warning forecasting a minor geomagnetic storm on November 7-8, noting that there is some chance that it will get stronger due to recurrent coronal hole high speed streams (CH HSSs) effects. Fast CH HSSs can impact Earth’s magnetosphere enough to cause periods of geomagnetic storming to the G1-G2 levels; although rarer cases of stronger storming may also occur. The larger and more expansive coronal holes can often be a source for high solar wind speeds that buffet Earth for many days.

The G2-class geomagnetic storm currently affecting Earth should get weaker today, turning into a G1-class storm. According to NOAA, these conditions should last until Saturday, November 11. Another minor geomagnetic storm is expected on November 20-22.

In general, solar activity is expected to be at very low levels until December 2 due to an absence of returning sunspots and a spotless solar disk.

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