Video Portrays Impact on Earth of Space Weather Event

Contact: David Hosansky UCAR Communications P.O. Box 3000 Boulder, CO 80307-3000 Telephone: (303) 497-8611 Fax: (303) 497-8610 E-mail: hosansky@ucar.edu

What:	Colorful computer animations created by physicist Gang Lu and her colleagues at the National Center for Atmospheric Research portray the growth and movement of a geomagnetic storm as it develops above the Earth. The animations will be on view and S-VHS videotapes will be available.
Where:	The NOAA Space Environment Center Research-to-Operations Meeting takes place at the National Institute of Standards and Technology (NIST) building, 325 Broadway, Boulder.
When:	The video-poster session is Thursday, April 22, 11:30 a.m.-2:00 p.m. and 5:00-6:00 p.m.

Advancing space weather research

New computer animations from the National Center for Atmospheric Research reveal the dramatic growth and development of the geomagnetic storm of January 10-11, 1997. Geomagnetic storms begin when coronal mass ejections on the sun's surface launch interplanetary shock waves. When those shock waves reach the Earth's magnetic field, they may disrupt radio transmission, affect satellite communications, or interrupt electrical power supplies. They also produce the beautiful aurora borealis and aurora australis (the northern and southern lights).

The NCAR team's research will help scientists understand and predict near-Earth space weather.

Background

Animations of 10-11 January 1997 Geomagnetic Substorm

Prepared for the Space Weather Workshop at the Space Environment Center in Boulder, Colorado, April 19-23, 1999

1. Animation of the Evolution of the Magnetic Cloud (not created at NCAR; courtesy of the International Solar Terrestrial Program). An artist's illustration of an interplanetary shock wave leaving the sun's corona and entering the Earth's magnetosphere. The star represents the SOHO satellite poised to detect the arrival of the magnetic cloud.

The next four animations are based on observations and a computer model simulation of the geomagnetic storm of January 10-11, 1997. Running time for each loop averages 60 seconds.

2. Auroral Energy Flux and Electric Potential for 10-11 January (magnetic polar view) 7MB MPEG. This loop shows energetic electrons, measured in kilo-electron volts, precipitating from the magnetosphere into the Earth's upper atmosphere, where they increase the ionization rate and ionospheric conductivity. These are the particles responsible for creating visible auroras. The contours show the electric potential in kilovolts (kV). The higher the electric potential gradient, the faster the ions move and the more energy is transferred. Data are from satellite measurements taken at about 800 kilometers (500 miles) and radars sensing at 300-400 km (190-250 mi) altitude.

3. Difference in Total Electron Content for 10-11 January 1997 (geographic polar view) 5Mb MPEG. The Northern Hemisphere is on the left and the Southern Hemisphere is on the right in this animation, which shows the increase and decrease of total electron content (TEC) with respect to the nonstorm, or quiet-time, background. TEC is the integration of electron density over an altitude range between 95 and 600 km (60 and 370 mi), plotted in TEC units (TECUs). TECUs are 10¹⁶ electrons per meter squared (m²); higher TECUs represent greater electron column density.

4. Total Electron Content for 10-11 January 1997 (global view) 5Mb MPEG. This loop shows the global distribution of total electron content. The center of the frame (12 local time) is solar noon, the most direct line between the sun and the Earth. The Earth rotates through that noon point over a two- day period. The unit of measure for height-integrated total electron density is electrons per square centimeter (cm²).

5. Height-Integrated Joule Heating and Neutral Temperature Variation for 1011 January 1997 (satellite view) 8Mb MPEG. This loop illustrates the lag time between Joule heating and the heating of the thermosphere at about 300 km (190 mi) above the Earth's surface. Joule heating takes place when ions collide with neutral particles, transferring the ions' kinetic energy into thermal energy. By 07:00 Universal Time (UT, or midnight Mountain Standard Time) on January 10 the big substorm--and Joule heating--has begun (globe on the left). About 20 minutes later the temperature of the neutral particles begins rising (globe on the right). The first increases can be seen in the aurora zone over the Northern Hemisphere; the heating ripples outward rapidly until temperatures have increased over the entire hemisphere by about 8:10 UT. When the storm subsides at about 13:40 UT on January 11, Joule heating quiets down, but elevated temperatures persist in the thermosphere for about 24 to 30 hours afterwards.

The animation portrays the changes in temperature of neutral particles (TN) at 300 km (190 mi) from the quiet-time background, with no storm activity. The measure of height- integrated Joule heating is microwatts per square meter (mW/m²). Temperatures are shown in kelvins (K).

Data sources

These animations are based on data from satellites operated by the U.S. Air Force, the National Oceanic and Atmospheric Administration, and NASA; high-frequency ground-based radars operated by the Johns Hopkins University; and ground magnetometers located around the world. The data were fitted into a numerical simulation model created by Raymond Roble of the National Center for Atmospheric Research, and the model output was used to create the animations. Model results were then compared with observations from additional sources, including several U.S. universities.

Definitions

The magnetosphere is the irregularly shaped region enveloping the Earth from several thousand kilometers down to about 1,000 km (600 miles) above the surface. The magnetosphere is characterized by charged particles influenced by the Earth's magnetic field. Many Earth-orbiting satellites operate in the magnetosphere.

The ionosphere begins within the edge of the magnetosphere, about 1,000 km (600 mi) out from the Earth's surface, and extends down to about 50 km (30 mi) above the Earth. Ionized particles in this region make reflection of radio-wave transmissions possible.

The thermosphere is the outermost layer of the Earth's atmosphere, encompassing the main body of the ionosphere at about 1,000 km (600 mi) and extending down to meet the next atmospheric layer (the mesosphere) at about 90 km (56 mi). The thermosphere is collocated with the ionosphere.

Research by Gang Lu, Arthur Richmond, Raymond Roble, Maura Hagan, and Thomas Holzer, High Altitude Observatory, National Center for Atmospheric Research. Video production by Benjamin Foster and Gang Lu.

Funding for this research was provided by the National Science Foundation and the International Solar Terrestrial Program.