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Last Post 10/21/2008 12:27 PM by  Kris Sigsbee
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10/21/2008 11:31 AM


    After discussing the lessons, how are auroras formed? Is there a specific pattern to when you can see the northern lights?

    Mr. Bilotta's Fifth Grade class

    Deer Crossing Elementary School

    Tags: aurora, Substorms

    Emilia Kilpua

    New Member

    New Member

    10/21/2008 12:19 PM


    Auroras or northern lights are caused by fast electrons that hit the atoms or molecules in the

    Earth's atmosphere. Electron collision makes the molecule excited and after a while it

    returns to a normal state and releases a burst of light that we see as aurora. The color of auroras depend on the

    depth the electorns reach in the atmosphere and what kind of particle they collide with. For example green color

    is produced by electrons colliding with Hydrogen atoms.

    People used to have many different explanations for the aurora.

    Accroding to an old Finnish folk tail auroras were sparkled up by an artic fox running along

    the mountains in the north sweeping up snow with its tail. Actually, the finnish name for aurora

    is "revontulet" that is translated as "fox" and "fire"

    Kris Sigsbee

    Basic Member

    Basic Member

    10/21/2008 12:27 PM

    Hello Fifth Graders from Deer Crossing Elementary!

    The aurora borealis (northern lights) and aurora australis (southern lights) occur as the result of a complicated interaction between the solar wind and the Earth's magnetic field or magnetosphere. On the day side of the Earth, the solar wind compresses the Earth's magnetic field. On the night side of the Earth, the solar wind stretches the Earth's magnetic field out into a long tail, which scientists call the magnetotail. The transfer of solar wind energy from the day side magnetosphere to the night side is very important to the formation of the aurora.

    The sequence of processes that result in spectacular auroral displays with ribbons of light that wiggle and swirl across the sky is called a "substorm." A typical auroral substorm has three phases: growth, expansion, and recovery.

    During the growth phase of a substorm, solar wind energy is transported from the dayside magnetosphere and stored on the nightside in the magnetotail through the processes of magnetic reconnection and convection. In magnetic reconnection, the solar wind magnetic field can briefly merge with the Earth's magnetic field to allow solar wind particles and energy to enter the magnetosphere. When a magnetic field line in the Earth's magnetosphere merges with a solar wind magnetic field line, it gets blown away by the solar wind (or convected) towards the night side magnetosphere. This deposits a lot of magnetic energy in the magnetotail. The growth phase of an average substorm might last 1-2 hours.

    The expansion phase of a substorm starts when the energy stored in the magnetotail is explosively released. This is the phase when the most brilliant auroral displays occur, and it typically lasts about 30 minutes, although it can be longer.

    During the recovery phase, the aurora fade and the magnetosphere becomes quiet again. I'm not quite sure how long a typical recovery phase takes - sometimes this phase lasts only a few minutes, other times it is much longer.

    This entire cycle only takes 2-4 hours, so it can repeat several times a night. However, unlike eruptions of the Old Faithful Geyser in Yellowstone National Park, substorms do not occur on a regular, predictable schedule. The length of a substorm and the auroral display depends upon solar wind conditions and how much solar wind energy has been stored in the Earth's magnetotail. There is no specific pattern to the occurrence of substorms that repeats regularly every night.

    However, during the spring and fall, substorms are more likely to occur due to the alignment of the Earth's magnetic axis relative to the solar wind magnetic field. The solar wind magnetic field is like an extension of the Sun's magnetic field out into interplanetary space. Although the solar wind magnetic field direction can vary on time scales of just a few minutes, there are also larger scale magnetic field structures in the solar wind that vary much more slowly. These larger scale structures are what causes the seasonal variations in the occurrence of aurora because during the spring and fall, they create conditions that are more favorable for magnetic reconnection. You can learn more about the seasonal variations here:

    Of course, during certain times of the 11 year solar cycle, you are also more likely to see aurora. During solar maximum, solar activity like coronal mass ejections (CMEs) and solar flares are more common. These types of disturbances are even more effective at causing geomagnetic storms and substorms than the more gentle solar wind variations we see all of the time.


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