|Atoms: Molecules: Molecular Bonding|
|Newton's Cradle Potential Energy Pendulum|
|BLACK HOLE PHYSICS|
he present atmosphere of the Earth is probably not its original atmosphere. Our current atmosphere is what chemists would call an oxidizing atmosphere, while the original atmosphere was what chemists would call a reducing atmosphere. In particular, it probably did not contain oxygen.
The oxygen so characteristic of our atmosphere was almost all produced by plants (cyanobacteria or, more colloquially, blue-green algae). Thus, the present composition of the atmosphere is 79% nitrogen, 20% oxygen, and 1% other gases
Layers of the Atmosphere
|Layers of the Earth's atmosphere|
The structure of the ionosphere is strongly influenced by the charged particle wind from the Sun (solar wind), which is in turn governed by the level of Solar activity. One measure of the structure of the ionosphere is the free electron density, which is an indicator of the degree of ionization. Here are electron density contour maps of the ionosphere for months in 1957 to the present. Compare these simulations of the variation by month of the ionosphere for the year 1990 (a period of high solar activity with many sunspots) and 1996 (a period of low solar activity with few sunspots):
Consequences of Rotation for Weather
The Earth is a spinning globe where a point at the equator is travelling at around 1100 km/hour, but a point at the poles is not moved by the rotation. This fact means that projectiles moving across the Earth's surface are subject to Coriolis forces that cause apparent deflection of the motion.
|The Coriolis force deflects to the right in the Northern hemisphere and to the left in the Southern hemisphere when viewed along the line of motion.|
If solar heating were the only thing influencing the weather, we would then expect the prevailing winds along the Earth's surface to either be from the North or the South, depending on the latitude. However, the Coriolis force deflects these wind flows to the right in the Northern hemisphere and to the left in the Southern hemisphere. This produces the prevailing surface winds illustrated in the adjacent figure.
For example, between 30 degrees and 60 degrees North latitude the solar convection pattern would produce a prevailing surface wind from the South. However, the Coriolis force deflects this flow to the right and the prevailing winds at these latitudes are more from the West and Southwest. They are called the prevailing Westerlies.The adjacent animation shows GOES-8 weather satellite images over a 72-hour period from Dec. 29, 1996, through Jan. 1, 1997. This is a geosynchrous satellite, which means that it orbits the Earth with the same period as the Earth's rotation and therefore appears to be essentially motionless over a fixed position on the Earth's surface. For GOES-8 this fixed position looks down on North and South America.
In these composite images red indicates visible light (reflected sunlight), green indicates the 11 micron IR channel (thermal emission), and blue indicates the 3.9 micron channel (thermal + sunlight). At night the images are blue and green. The three periods of daylight in this 72 hour sequence are clearly visible as red-orange regions moving from East to West (right to left). In the IR channels, the natural intensity pattern has been inverted: warmer is darker, so that cool cloudtops stand out brightly.
One can see clearly the pronounced cloud flows associated with the strong westerlies at mid-latitudes in each hemisphere. (This is taken in Northern hemisphere Winter, so the heavier cloud cover in that hemisphere is not surprising.) Less obvious are the easterly trade winds and the polar easterlies, though one can see vestiges of each if one looks carefully. Also apparent are the swirling motions associated with frontal systems. These are particularly pronounced at the boundaries between the mid-latitude westerly and polar wind flows in each hemisphere.
Here is a similar weather animation (1.49 MB animated GIF) using GOES-8/9 IR images for North America over a 2 day period from December 31, 1996 through January 1, 1997. The large weather systems that move ashore from the Pacific in this animation produced catastrophic flooding in California, Oregon, and Washington in early January, 1997.
|Low pressure systems (left) and high pressure systems (right) in the Northern hemisphere
The aurora, or northern and southern lights, are often visible from the surface of the Earth at high northern or southern latitudes. Auroras typically appear as luminous bands or streamers that can extend to altitudes of 200 miles (well into the ionosphere).The following figures show three examples of the often spectacular visible light display associated with auroras.
|Southern aurora from the Space Shuttle Endeavor (Ref)||Northern aurora over Lake Superior (Ref)||Northern aurora over Circle, Alaska (Ref)|
Here is another image of the southern aurora taken from the Space Shuttle. The aurora changes with time, often looking like moving curtains of light. Here are some MPEG and QuickTime film clips that illustrate the time dependence of the auroral display.
The delicate colors are caused by energetic electrons colliding with oxygen and nitrogen molecules in the atmosphere. This excites the molecules, and when they decay from the excited states they emit the light that we see in the aurora.
The collisions of trapped charged particles with atmospheric molecules causes spectacular effects in the visible spectrum, but these excited molecules can also emit radiation in other wavelength bands. The following figures show aurora imaged in the ultraviolet (UV) and X-ray regions of the spectrum.
|Imaging the Earth
We have seen a number of images of Earth in visible light, but mostly at large scale from a great distance. Here are two images from space of smaller objects on the Earth that we will be interested in looking for on other planets and moons: a canyon system, and an active volcano.
We shall find canyon systems and active volcanoes on other objects in the Solar System to are not too different from these images. Here is a set of links to satellite imaging of the Earth.
The Earth at NightThere is one aspect of the Earth's appearance that we do not expect to be repeated in the near future for other objects in the Solar System: at night the artificial light associated with human civilization is very visible from space. The following image shows the appearance of the United States at night as observed from a composite of many satellite passes.
The major source of light is from cities, but by looking carefully you can even see things like lights scattered in the Gulf of Mexico south of Louisiana that are from oil platforms (Ref). The photograph is from Defense Meteorological Satellite Program (DMSP) images.
Imaging in Ways other than Visible LightBecause our eyes are sensitive to visible light, our prejudice is to view things at those wavelengths. However, we now have instruments at our disposal that permit observations in many wasy other than the visible light region of the electromagnetic spectrum. These often offer considerable advantage; for example radar cuts through the ever-present thick cloud cover to give us images the surface of Venus that we could not obtain at visible wavelengths.
Infrared and more Exotic ImagingWe have seen in the preceding sections examples of imaging the Earth in the infrared, ultraviolet, and X-ray regions of the spectrum. Here we show additional examples of IR images, and a more exotic technique combining magnetic and gravitational data that can even locate objects beneath the surface of the planet.
The middle figure shows a composite of local gravity and magnetic field variation data to image a 112-mile wide relic meteor crater in Yucatan that presently lies below several hundred meters of sedimentary rock. This crater, called Chicxulub, is famous because it is the leading candidate for the site of the asteroid impact that is thought to have killed the dinosaurs 65 million years ago in the K-T extinction (Ref).
The right image shows a GOES-8 weather satellite image in the 6.7 micron IR channel that is sensitive to the distribution of water vapor in Earth's atmosphere (Ref). The imager on this satellite records radiation emitted by water vapor in the upper troposphere. Regions with high concentrations of water vapor are bright, while dark spots signal lower water vapor concentrations.
Surface Temperature MapsInfrared radiation is basically radiant heat. Therefore, IR detected from satellites can be used to determine the temperature of objects. The following image shows a color-coded map constructed from a composite of satellite data and surface observations giving surface temperatures on the Earth (Ref).
Sea Surface Temperature MapsSimilar methods as described above may be used to construct color coded maps of surface seawater temperatures. Here is an example (Ref):
In 1976 the Viking 1 and 2 landers undertook searches on the Martian surface for the chemical evidence of present or past life on Mars. The images shown below give a picture of one of the backup landers, and two different views of the Martian surface as photographed from Viking 1.
|Viking lander (Ref) and two views of the Martian surface from Viking 1(Ref)|
In addition to photgraphing the surface, the Viking landers undertook a series of experiments at two points on the surface to find evidence for life.
Hindumal Kot Road, Abohar-152116 (Punjab), INDIA
01634 - 231112 -16, 232235
firstname.lastname@example.org & email@example.com