August 25, 2018 Magnetic Disturbance - Peak Dst 174 nT

Science Center Objects

Space Weather Events of August 25, 2018

A magnetic storm transpired on 2018 August 25-27. Ground-based magnetic observatory data do not show any clear indication that this storm commenced with a sudden impulse, and, indeed, space-weather summaries issued by National Oceanic and Atmospheric Administration (NOAA) and the U.S. Air Force (USAF) report a storm-time maximum solar wind velocity of a relatively modest 553 km/s (as opposed to a typical velocity of about 400 km/s). During the storm, the interplanetary magnetic field was, however, rather strong (up to 21 nT), and this might have contributed to a geoeffective driving of magnetospheric convection.

The Kyoto World Data Center storm-time disturbance index, produced using data from 4 ground-based observatories, 2 operated by the USGS (Honolulu and San Juan), 1 by the Japan Meteorological Agency, 1 by the South African National Space Agency, attained a maximum -Dst=174 nT (at 07:00 and 08:00 UT on August 26). The USAF mid-latitude activity range index, obtained using data from 8 observatories: 5 operated by the USGS (Boulder, Fredericksburg, Fresno, Newport, Sitka), 3 by Natural Resources Canada, and 1 by the British Geological Survey, attained a maximum Kp=7. The related geomagnetic disturbance scale produced by NOAA attained a level of G3 (strong). At high latitudes, the USGS-Schlumberger magnetic observatory at Deadhorse Alaska showed a declination range of approximately 7 degrees, enough to be easily seen on a compass.

Geomagnetic and geoelectric timeseries obtained at the Boulder magnetic observatory are shown in Figure 1 – measured geomagnetic variation had a range of more than 200 nT; measured geoelectric had a range of about 50 mV/km. The same figure also shows a predicted geoelectric field obtained by convolving the geomagnetic field variation with local Earth-surface impedance. The discrepancy between the predicted and measured geoelectric time series is smaller than the measured signal. Analyses like this are being used by scientists of the USGS Geomagnetism Program to validate geoelectric estimation methods – intense magnetic storms can generate geoelectric fields of sufficient strength to interfere with the transmission of electric power.

The USGS Geomagnetism Program operates 14 observatories across the United States and Territories. Data from these observatories and the research USGS Geomagnetism Program scientists contribute to an interagency project within the Federal Government known as Space Weather Operations, Research, and Mitigation (SWORM) and which is coordinated by the National Science and Technology Council of the Office of Science and Technology Policy.

Prepared on 2018 September 13 by Jeffrey J. Love, E. Joshua Rigler, and Greg Lucas