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Frequently Asked Questions about the Oval

The meaning of the oval color

Question

On the CANOPUS activity color scale, does green mean little auroral activity and white mean high auroral activity, or is this an indication as to the colors in the aurora? The real-time auroral oval uses magnetometer data from a north-south line through Manitoba.

Answer

The disturbance in the magnetic field, caused by ionospheric electric current, is used as an indicator of the location of the aurora, which occurs in a belt region centered on the magnetic pole. The color of the oval in the central panel is used to indicate the strength of the magnetic disturbance seen along the Manitoba line, it has nothing to do with the color of the aurora itself.

The meaning of the yellow dots

Question

What do the little yellow dots mean on the charts mean?

Answer

The three panels on the left side show latitude profiles of the Northward (X) , Eastward (Y) and vertical (Z) magnetic disturbance components. The dots show the measurements and the lines show the disturbances at other locations as inferred from a model fit to the measurements. Based mainly on the inflection points of the Z component, the poleward and equatorward limits of the auroral oval (belt) are estimated for the longitude of Manitoba. Next a model of the auroral oval is used to estimate its location elsewhere (other longitudes) based on its Manitoba location. This oval is displayed in the large panel. On this panel, the yellow dots represent the locations of the magnetometers along the Manitoba "line".

The RISK factor

Question

If I interpret the RISK chart properly, there seemed to be very high auroral activity at about 4:00 AM our time (10:00 AM UT Nov 8th) which, of course I missed, since I was asleep at that time. Is this interpretation correct? If so, what should I have seen at my latitude at that time if I was watching?

Answer

We estimate the "risk" to technology systems, which may result from these ionospheric currents. Damage to power systems, telephone systems, and pipelines can result from changing of the (ionospheric) currents. The risk is taken to be related to the size of the central hole in the oval. The furthest south the Aurora is, the bigger the risk of damage.

Solar Forecasting

Question 1

Exactly how far into the future are your aurora predictions?

Do you know of anyone who does do 45 day predictions?

Would you be able to explain your process of producing one?

Answer 1

These are difficult questions.

The name of our game is "NOWCASTING" , that is we make no attempt to forecast the future in any way. We attempt as best we can ,with the data we produce, to generate a description of what is happening NOW.

There is a Canadian group in the business of forecasting at site http://www.spaceweather.gc.ca/forecasting_e.shtml, they use all the tools that they can assemble.

Another website forecasting auroral activity comes from Lethbridge Alberta. Sorry I don't know what it is.

The solar rotation of 27.5 days provides a basis for the type of forecasting you want to do, rest assured all forecasting efforts use solar data as a basic input. However the variance of response of the earth's magneotsphere to solar forcing is such that this is really and art, not a science at present.

Amoung the best models of short time scale responses I've seen are from Joel Fedder at NRL. He uses the solar wind energy inputs to the magneotosphere in a gridded MHD model to calculate the response. To do that for 45 days would require a supercomputer of massive size.

A reasonable approximation to the oval can be obtained by drawing two circles on the earth's surface with two different radii and centres displaced towards midnight. Try a radii of 14 and 17 degrees (latitude equivalent) with centres 4 and 7 degrees from the (magnetic pole) on the midnight side.

As we inherited the software used to do the real time oval calculations, we are not familiar with its content. We do know that real auroral occurence data was analysed to produce the oval latitude as a function of magnetic local time, which is used in the plots. That kind of data can be found in the literature, but we do not know if the numbers used in real time oval have been published.

Question 2

From what I have read on other web sites, tonight might be a "good watching" night. Does your organization predict times of high auroral activity? If so, how far in advance.?

Answer 2

We refer to this kind of modelling as "now casting", We do not make predictions for the future. You might look at http://www.spaceweather.gc.ca/myservlet/geomag/forecast/main_e.jsp for one attempt at predictions.

The apparent distortion of the Auroral Oval Latitude Grid

Question

The circles on your map seem to show 40° at the bottom of Florida and the Gulf of California.. which my USA map shows at around 26°.

What do the circles on your map represent?

Answer

The circles are indeed circles of latitude, but they are circles of magnetic latitude, as the Latitude Grid is based on a polar coordinate system aligned with the geomagnetic dipole field.
The Grid has the following characteristics:

  • its 0° Longitude (corresponding to the geomagnetic prime meridian) is the great circle passing through the true and the magnetic North Poles, and thus lies about 104° west of Greenwich, and
  • its 90° Latitude (i.e. the magnetic pole itself) is 11.5° to the South of the earth geographic pole along the geomagnetic prime meridian.

    Thus, the Grid in use is not aligned with respect to the Greenwich coordinate system, but is in fact tilted 11.5° and rotated towards the americas.

    Please note that the continents position is approximate, and that their shape is increasingly distorted in the lower latitudes.


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