A Guide to Understanding and Predicting Space Weather

by Meghan Mella
Revised by Philip Fernandes

In case there weren't enough links below, let's start with this animation.In this video you can see a quick version of how aurora is created. At the beginning we see a solar flare and the rush of solar wind toward the earth. At the boundary of the earth's magnetic field the solar wind pushes on the sunward side of the earth's field and stretches out the tail on the anti-sunward side. As this stretching is occuring, the auroral oval is widening and moving southward. At some point, the system breaks, and the field lines snap back to a more dipole-like configuration, sending large amounts of plasma toward the earth along the field lines. All of this activity produces large currents flowing in various directions, and also causes the aurora. So the important things to look at when monitoring and predicting the space weather would be things like the sun, the solar wind, the shape of the earth's magnetic field, and the currents detected at earth.

 

Let's jump right in and start looking at some data. We will begin by looking at an abridged version of the links list. This will include the most interesting and most important data – the data that we in the field are watching closely, as they update pixel by pixel. The easiest way to do this is through the Viewista site. Download this document for short, simple instructions to log into Viewista.

 

ACE – Measurements in the Solar Wind

At this point, you should hopefully be viewing the RENU_short Viewista page. If you've had any problems, you can find all of this data on Dartmouth's Real Time Space Weather page. The first data from the ACE satellite. ACE is a satellite that sits at a point of gravitational equilibrium between the earth and the sun, but is much closer to the earth (about 1.5 million km) than to the sun (about 148.5 million km). The delay time from when ACE sees something to when we see it is on the order of one hour, but varies with increases or decreases in the solar wind velocity. It is important to recognize that ACE is measuring properties of the solar wind. The 7 day plot shows data over the last week, but the 6 hour plot gives a much clearer indication of the current solar wind properties. The most important parameter is Bz, the z–component of the sun's magnetic field. When Bz goes negative, the solar wind strongly couples to the Earth's magnetosphere. Think of Bz as the door that allows transferring of significant amounts of energy. The more negative Bz goes, the more energy that can be transferred, resulting in more geomagnetic activity. Other parameters to watch are the density and the solar wind velocity, as these determine just how much energy is transferred when Bz is negative.

 

GOES – Measurements of the Earth's Magnetic Field

Next is the GOES magnetometer data. GOES are satellites in geosynchronous orbit, so they are measuring properties inside the earth's magnetosphere. This plot is showing the one minute average of the parallel component of the earth's magnetic field. The red line is from the geostationary satellite orbiting over the east coast, and the blue GOES is over Alaska, approximately. So if the earth's magnetic field were a perfect dipole, the magnetic field would not vary as the satellite rotated from the sun side of the earth to the anti-sunward side of the earth. However, because the earth's magnetic field is compressed on the sunward side and stretched into the tail on the antisunward side, the satellites measure a varying magnetic field as the earth rotates. On this plot the 'M' and 'N' mark midnight and noon respectively. If the parallel component of the field gets very low near midnight (in other words, the tail is very stretched out) that is almost a sure sign that there will be aurora.

 

EISCAT – Probing the Ionosphere with an Incoherent Scatter Radar

Let's next look at data from EISCAT, the European incoherent scatter radar. The first place to look is the RENU rocket campagin EISCAT page. The first plot, the top–left plot, displays electron density versus altitude. The higher the electron density, the better chance for the type of activity we are hoping to launch into. See the EISCAT sample data link below to see how to locate the F and E regions of the ionosphere. The top–right plot gives the velocity of the ions, in the z direction (either upflow or downflow). We are looking for an ion upflow event, meaning the Vi will get more positive with altitude. Again see the EISCAT sample data page for an example of ion outflow. The other two plots give ion and electron temperature. The RENU science includes both ion and electron heating, so we are looking for temperature enhancements in both of these plots.

 

These four plots are line plots from a larger data set. EISCAT consists of two radar dishes – a 32m dish and a 42m dish. We will examine the data from the 42m dish, found here. The focus is the same with these data as with the line plots. Here, the enhancements will show up as different colors, typically reds and pinks. See the sample data link to compare the line plot with the full data set.

 

     EISCAT Sample Data

 

Cameras and Imagers

There is not a lot to say about these; we're looking for aurora! Just remember that these are very sensitive instruments, so what you see from the instrument is an intensified version of what you would see if you were to step outside and look up at the sky. Often, the instruments will observe aurora that is too dim to see with the naked eye.

 

Long Range Trends and Predictions

Let's examine some of the Long Range links. These are typically visited once or twice per day (maybe once at the beginning of the window, and once at the end). They indicate trends in solar and geomagnetic activity, which help with predicting future activity.

 

The first set of data we looked at, the ACE data, also has a 7 day plot to give a recent history of solar wind properties.

 

There is also the Kp: General Activity Index. Kp is an auroral index, ranging from 0 to 9, that is derived from ground based magnetometers. Indices of 5 or higher indicated storm level geomagnetic activity. There is also a Kp Condegram which displays the data in terms of the sun's 27 day rotation. Other Condegrams can be found here.

 

Other interesting sites include:

Solar Dynamics Observatory: Here you can watch as active regions (bright) or coronal holes (dark) appear on the sun. We typically begin seeing their effects here on earth when the feature reaches the right–most edge (the limb) of the image.

Kjell Henriksen Observatory general website

Space Weather

Today's Space Weather - A site that posts space weather daily, hosted by the Space Environment Center (SEC).

Space Weather Now - Another space weather site, hosted by the SEC.

SuperDARN - A site containing a model and data about the polar cap electric fields.

Andoya Rocket Range - This site has lots of great pictures of the RENU project.

Back to the Space Weather page.