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1. Gravity Waves:

[NASA image]

Description:

Two unique types of waves ripple through the Indian Ocean in this spectacular true-color Moderate Resolution Imaging Spectroradiometer (MODIS) image, taken by the Terra satellite on November 11, 2003. In the upper western portion of the image, atmospheric gravity waves ripple the surface of the ocean, and are mirrored by wave clouds in the atmosphere directly above. In the lower eastern portion, a mixture of atmospheric gravity waves and internal waves fan out from the coast. Sunglint (sunlight reflecting from rough surface waters and back into MODIS's "eye") slants across this portion of the image, which makes the different types of waves easier to see.

2. Seismic Waves:

In a longitudinal wave (or p-wave) the particle displacement is parallel to the direction of wave propagation. The animation shows a one-dimensional longitudinal plane wave. The particles do not move with the wave; they simply oscillate back and forth about their individual equilibrium positions. Pick a single particle and watch its motion. The wave is seen as the motion of the compressed region (ie, it is a pressure wave), which moves from left to right. [Animation by Dr. Dan Russell]

3. Electromagnetic Waves:

E-m fieldwork in Ethiopia, using specialized geophysical equipment developed at Edinburgh. The electromagnetic measurements are used to probe the deep structure of the East African Rift.

This site was on the rift floor. The escarpment of the rift can be seen in the backgound. The small hut closest to the camera, behind the horse is a grain store - it sits off the ground. By monitoring the changing magnetic and electric fields, the sub-surface electrical resistivity can be determined. Information from several kilometers depth can be recovered, even from light portable equipment, by analysing waves of a suitable frequency. The computer, which controls all the e-m kit, was placed under the acacia tree to the left in order to keep it cool, while the e-m sensors were buried in the field, in the foreground of the photograph. The e-m data are currently being analysed as part of an Honours undergraduate project. [Photographer KAW]

4. Planetary Waves and Ozone Holes:

Most of the world's ozone-destroying pollutants come from the northern half of our planet. Yet Earth's yawning ozone hole straddles the south pole - not the north. Why?

Huge planet-girdling atmospheric waves suppress ozone holes over Earth's northern hemisphere. These giant atmospheric waves, spawned by land features such as the Himalayas, damp the formation of a northern ozone hole and, as a result, Northern cities remain safe from unwelcome doses of solar ultraviolet radiation. The north-south difference is an indirect result of the way land is distributed around Earth - that is, unevenly. Most of our planet's land and its highest mountains are in the northern hemisphere as a result of plate tectonic processes.

In years when planetary waves (or "long waves") in the Northern Hemisphere are unusually weak, an ozone hole can form over the Arctic. Blue and purple indicate regions of low stratospheric ozone.

1. Convection in the Earth's Mantle

The animation shows how the hot silicate rock of the Earth's mantle is stirred by heat trying to escape. The heat is partly generated by the radioactive decay of natural elements like uranium, and partly is primordial heat left over from the time of the Earth's formation and the separation of iron into the core. The hot rock (yellow) rises slowly as the denser cold rock (blue) sinks. The layer is at least 700 km thick, and could be as thick as 2900 km. The rock is at temperatures of order 1000 to 2000°C and creeps like a very viscous fluid. Its viscosity is about 20 orders of magnitude greater than that of water so velocity is only centimeters per year, and the time interval of this animation is of order 10 million years. [Greg Houseman]

2. Exploring the Earth's Mantle

Convection and the release of heat from the Earth's core drives further convection to release heat from the mantle. Convection in the mantle drives plate tectonic motions of the sea floor and continents. It is possible to use P waves and S waves travelling through the mantle from earthquakes to map out this convection, much like a hospital CAT scan can map out bones and organs with x-rays. In this view of a flattened-out mantle, the blue blobs show where colder, denser material is sinking into the mantle. Near the surface, most of the colder material is in the ancient roots of continental cratons. Subducting slabs of oceanic lithosphere also appear, being recycled into the mantle from oceanic trenches. [Original image from the Harvard Seismology Lab]

3. Convection in the Earth's Atmosphere

Hurricane Felix
Description:

Hurricane Felix is prominently featured, as a swirl of clouds at the left-centre, in this SeaWiFS image captured on September 14, 2001.

As you can see, dust from Africa is being drawn into the storm. Hurricanes are the most powerful storms on Earth. They not only cause destruction, but are important meteorological phenomena. Felix, along with its impact on sea-surface temperatures, is being studied as part of a final year Honours project. [NASA imagery]

4. Convection in the Earth's Core

The Earth's magnetic field is fading. Today it is about 10 percent weaker than it was when German mathematician Carl Friedrich Gauss started keeping tabs on it in 1845, scientists say. If the trend continues, the field may collapse altogether and then reverse. Compasses would point south instead of north.

The magnetic field is generated deep inside the Earth where the heat of the planet's solid inner core churns a liquid outer core of iron and nickel. The solid inner core is thought to be a mass of iron about the size of the moon that is heated to several thousand degrees Celcius. Heat radiated by this inner core builds up at its boundary with Earth's liquid outer core, causing the fluid there to expand. When it expands it becomes a little less dense and more buoyant. So it starts to rise. In this classic form of convection, hot fluid rises, then cools off and sinks again. The convection generates an electric current and, as a result, a magnetic field.

A snapshot of the 3D magnetic field structure simulated with the Glatzmaier-Roberts geodynamo model. Magnetic field lines are blue where the field is directed inward and yellow where directed outward. The rotation axis of the model Earth is vertical and through the center. A transition occurs at the core-mantle boundary from the intense, complicated field structure in the fluid core, where the field is generated, to the smooth, potential field structure outside the core. The field lines are drawn out to two Earth radii. Magnetic field is wrapped around the "tangent cylinder" due to the shear of the zonal fluid flow. [Image by Gary Glatzmaier]

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Examples of projects and posters from the final year Geophysics and Meteorology course

WIND FARMS: THE CONSISTENCY OF SUPPLY ISSUE by NICHOLAS JOHNSON

Abstract

WIND FARMS: Full Report

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Examples of projects and posters from the final year Meteorology course

ATMOSPHERIC POLLUTANTS IN AND AROUND MANCHESTER, UNITED KINGDOM by CHRISTINA ROBERTSON

Example project - Atmospheric pollutants

COLD-WAKE PRODUCTION BEHIND TROPICAL STORMS IN THE WESTERN NORTH PACIFIC by JULIA PEREZ

Example poster - Cold wakes behind hurricane tracks

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Banner images

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Dangerous beauty. Polar stratospheric clouds are common in Antarctica, but a rare sight in the Arctic. They form when temperatures in the stratosphere become extremely cold - below -78° C. They spell trouble for ozone; tiny ice crystals and droplets within the clouds provide surfaces where CFCs are converted into ozone-destroying molecules. [Credit: Lamont Poole, NASA]

Seismic Lines. When an earthquake or explosion happens, shock waves, also called seismic waves, travel through the ground and reflect off rocks in the subsurface the same way that ripples in a pond reflect off a boat in the water. Because boundaries between different rocks often reflect seismic waves, geophysiscists use these waves to generate pictures of what the subsurface looks like. It is much the same as using sonar to create a profile of the ocean floor, except seismic waves are used instead of sound waves. Dynamite explosions or vibrator trucks are used to create the seismic waves, and geophones laid out in lines measure how long it takes the waves to leave the seismic source, reflect off a rock boundary, and return to the geophone. The resulting two-dimensional image, which is called a seismic line, is essentially a cross-sectional view of the earth oriented parallel to the line of geophones.