ENVXR 202: EARTH, AIR, WATER EXPERIMENTAL PROJECTS for Water (W) 25 Feb 2003 As we said about the Energy experiments, this hand-out is meant to get you started. After progressing with these basic questions, please pose some of your own questions of the experiment, and report on them in your lab-book. Often this will involve changing something about the experiment to see the effect on the primary phenomenon. A useful idea is, when looking at a steady process (like a steady tornado) you can often learn something by seeing how it develops from ‘the beginning’; in this case watching the tornado develop as the flow is turned on, and by doing something to change its intensity. Another tactic is to change the ‘environment’ of the experiment; in this case the tornado is very sensitive to the symmetry of the tank; if it is not round, or the drain is not in the center, or there is a ‘mountain’ somewhere at the base of the fluid, it may be disorganized, it can develop oscillations, or it may not form at all. These are useful observations (telling us why tornadoes are only found where conditions are right). W1 OCEAN WAVES Waves on water are generated by wind and flow, and can control the flows of rivers and streams (where they can ‘stand still’). This cxperiment involves finding the relation between frequency and wavelength, looking at the velocity of the, fluid beneath the waves, seeing the great behavioral difference between waves in shallow water and in deep water, watching the increase in amplitude of the motion when waves approach a shore. This will involve both a long, thin Plexiglas channel and a smaller glass fish-tank, Images of the motion of the fluid can be made with a digital camera, Storm surges are great invasions of coastal lowlands by wind-driven waves; if they come at high tide they can be particularly bad, and they (not the wind) account for the majority of damage when hurricanes come to land. In the low-lying country of Bangladesh tropical cyclones can send ocean water over vast areas of the Ganges/Brahmaputra river delta, leading to major loss of lift. Ocean waves also have analogs in many other systems, for example something like the refraction of light beams is seen as waves approach a beach. 1. Set up the long (8-foot) plexiglass channel with about 5 cm. of water in it. Using a small piece of plexiglass as a paddle make waves (try to avoid making scratches, by taping up the end of the paddle). 2. Set up a smaller tank…aquarium or short plexiglass tank…and make waves in deep water (at least 25 cm deep). How do they differ from waves in shallower water, say 5 cm. deep (you can compare simply by reducing the water depth here), and in very shallow water (less than 1 cm deep)? 3. Observe the motion of particles floating beneath the surface and on the surface. Describe the velocity pattern of water beneath a wave. 4. Visit the flume and try making surface waves using a plate (aluminum or plexiglas) as a wave maker). In the ‘peninsula’ experiment (W4 part 4.) look at waves that try to move upstream through the narrows where the flow is strong. This is a modelof the waves you experience as a kayaker in Puget Sound or the San Juan Islands: big waves are found in unexpected places because of the pattern of the strong tidal flow. (It would be possible to make digital images of the particles and waves with our lab camera). W2 OCEAN ESTUARIES AND TIDES Estuaries are formed where rivers spill into the sea, They are often regions of great biological productivity, with biological food chain active from microscopic plankton to large sea creatures and birds. At one end the ocean provides salty, dense water rich with nutiients; at the other, the river water is very buoyant and floats out over the salt water. The tides totally change the circulation: these mix up the river water and lead to an ‘overturning circulation’ (seaward at the top, landward at the bottom). The strength of this circulation far cxceeds the simple river inflow, and it is important in ventilating the estuary with oxygen and nutrients. In this experiment we want to explore the overturning circulation, its dependence on tides and river flow and other mixing. There may be ridges on the seafloor that are involved, and layering of the density is important to examine. A separate hand-out exists for starting up this experiment. (This was attached to the paper hand-out). W3 CIRCULATION OF THE GLOBAL OCEAN AND CLIMATE CHANGE At a much larger scale than an ocean estuary, we find some similar events: the entire global ocean has a circulation that involves sinking at high Iatitude, and rising elsewhere. This kind of circulation, sometimes known as a ‘conveyor belt’ brings nutrients to the sea surface where in the sunlight they make for very active growth. PhytopIankton, the ‘grass of the seas’, grow there and lead to a whole spectrum of animal life A fundamental property is the ‘layering’ of the ocean, with dense (cold or salty) waters at the bottom and buoyant (warm or fresh) waters at the top. It is very difficult to move vertically against this density difference. In the experiment we want to observe the form of the ocean circulation when at the surface the water is made dense or less dense by cooling and heating or by ‘rainfall’ and evaporation. 1. One of the simplest ways to begin is to use a small amount of crushed ice to cool the surface and observe the circulation that follows, using colored dyes, ink, or small particles in the water. The rates of circulation can be observed, as well as internal wave motions, where regions of different density move in a ‘silent surf.’ 2. Put saline water (made by dissolving 10 g of salt per 100 g of water) in a spray-bottle. It’s density will be close to 10% greater than fresh water. Instead of crushed ice, spray this water on the surface of the experiment near one end, and used dyes to trace the circulation that develops. This is a similar circulation, showing that evaporation at the sea surface or rainfall (which change the surface salinity) can drive deep-ocean circulation. (Please be careful not to spray the salt water anywhere but in the tank, and wipe up salt crystals which appear elsewhere). 3. Note the vertical motion of the fluid, comparing the sinking regions with the regions of rising water (this is an appropriate model of the global ocean circulation, andits form largely controls where