Universal Time and Magnetic Local Time
I am a computer science major in New Mexico. The summer before last I did research on the ionosphere and, yet, I have not found a good explanation/definition of magnetic local time (MLT) and/or universal time (UT). I used a computer language called Interactive Data Language to graph sets of data from magnetometers in the North Polar Region..
Would you explain these items and how they relate to the study of science research of the earth's magnetic fields and magnetic storms, etc.?
Thank you very much!!!
Kind of hard to work on a house when the foundation is shaky, no? Your teachers and your texts should really answer those questions, but let me try, anyway.
How do you measure time? A good "clock" is the rotation of the Earth, and in early times this was checked by the position of the Sun. When the Sun was highest above the horizon--and exactly to the south--the time was noon, and the interval from one noon to the next was a DAY, or more precisely a solar day.
Universal Time is essentially the time in Greenwich, England, and serves as reference time for astronomical events (e.g. the observed onset of the 1987 supernova). It's sort of a "world time" not tied to any local clock. There exists a small correction, but if the above is good enough for you, you may skip the next 2 paragraphs.
[ As it happens, the Sun's position among the stars also varies, and that motion contributes to the length of the day (about 4 minutes--see web site). Unfortunately, that contribution varies slightly throughout the year, because the Earth's uneven motion around the Sun, etc., so the "noon-to-noon" day varies slightly in length. Astronomers use instead a MEAN SOLAR DAY averaged over the year, which is a good gauge of the Earth's rotation.
But measuring time in mean solar days is not all. One must also decide when each day begins! Astronomers have agreed that each mean day begins with (mean) midnight at the Royal Astronomical Observatory in Greenwich, England, and time defined that way is known as UNIVERSAL TIME (UT). "Greenwich Mean Time" (GMT) is similar, but is counted from noon.]
So, UNIVERSAL TIME essentially measures time, using the rotation of the Earth around its axis. LOCAL TIME (LT), on the other hand, measures not time but position relative to the Sun.
Suppose you cover the Earth with a network of lines of latitude and longitude
(see on the web http://www.phy6.org/stargaze/Slatlong.htm )
The at UT=0 it is midnight in Greenwich, 11 am in Russia, 6 pm in the Eastern US, and so forth; these are the LOCAL TIMES at these locations. Three hours later you add 3 hours to all these local times--and so forth, for other locations and other times. The local time at each location depends on the difference between its longitude ("meridian") and the longitude where it happens to be midnight. (You need not use time zones, but take the exact difference in longitude, for exact local time.) Your local time is 12 noon if your location faces the Sun, LT=24 (midnight) if it faces away from the Sun, and other values of LT for other relative positions of the Sun.
One can similarly cover the Earth with lines of MAGNETIC LATITUDE and LONGITUDE, the latter converging not at the geographic poles but at the magnetic poles. As the globe rotates, we can say as before that all points on the same magnetic longitude have a certain MAGNETIC LOCAL TIME (MLT). We have MLT=12 (noon) on the magnetic meridian (magnetic line of longitude) facing the Sun, and MLT=0 (or 24) on the meridian facing the opposite direction, and so on,. It is completely similar to ordinary LT.
Why is MLT important? Because the shape of the magnetic environment of the Earth--the magnetosphere--is determined by the solar wind, which "blows" almost exactly from the sun. So at MLT=12 a point faces in the"upwind" direction, and at MLT=24 in the "downwind" direction. Phenomena related to the action of the solar wind on the Earth's magnetic field, such as the polar aurora or daily magnetic variations, depend very much on MLT.
Hope this makes it clear.
Does the magnetosphere affect weather?
I was wondering if the magnetosphere affected the Earth's weather in any way?
And if so please explain in detail.
I don't think so, we have no evidence for it. For at least two reasons, we do not expect any, either.
First, our atmosphere is electrically neutral and does not conduct electricity (below 50 km, anyway--and weather stays below 10-20 km). Substances of this kind (except maybe permanent magnet, a very special case) do not react to magnetic fields. When a doctor puts your body inside the strong magnet of an MRI machine, you feel no difference, except maybe for the loud noise that machine makes.
Second, weather gets its energy from heat deposited by sunlight on the surface of Earth. The energy of the magnetosphere, on the other hand, comes from the solar wind. A beam of the solar wind as wide as the magnetosphere carries only about 1/3500 as much energy as sunlight hitting Earth, and only about 1% of that is given to the magnetosphere. Of that, only a fraction reaches the upper atmosphere. It seems too little to make a difference, and it is not clear how it might move further down.
Practically all that energy, by the way, is channeled to the auroral zone, near the poles. As was said--no clear correlation has been observed, there or elsewhere. You may not get a scientist to say "absolutely no," but "very unlikely" may be just as good.