The meandering flows of the red and green dye are very similar to the flow patterns of the real atmosphere; they carried heat from an area of a higher temperature to an area of lower temperature. This was done via the convection of heat; heat was transferred through the representational atmosphere (room-temperature water) from the outer warm wall to the inner cold wall. This process was aided and made efficient by the meandering flows of the jet streams which formed vortices like movements. In the demonstration, this was observed because the red and green dye moved in opposing directions. These movements created flows that were analogous to the troughs and ridges that are found in the development extratropical cyclones. Vortices that rotated counterclockwise were considered cyclones while those that rotated clockwise were considered anticyclones because the experiment aimed to model the Northern hemisphere. They rotated to bring cold water back to the outer walls and warm water to the inner walls, thus exchanging heat. This demonstrates a real atmospheric occurrence: storms transfer heat from tropics to the Artic. Without meandering, circular jet streams are not efficient.
Describe the difference in the behavior of dye dropped in (i) nonrotating fluid, (ii) rotating fluid with no thermal contrast, and (iii) rotating fluid with thermal contrast.
Dye dropped in non-rotating fluid merely diffused into the water in a stochastic fashion. Without the rotating movement of the turntable, the Coriolis effect is not represented. The dye does not move in a curved pattern because there is a lack of rotation to cause this change in motion. This would represent the equator where the effect of Coriolis force is zero because the effect of the earth's rotation there is zero.
Dye dropped in rotating fluid with no thermal contrast penetrated down to form a column. The dye did not spread horizontally as it just maintained vertical coherence. Food coloring is heavier than water thus it tends to sink downwards. This proves that an energy source for jet streams are temperature gradients. Potential energy lies in cold water that tends to sink and hot water that tends to rise.
Dye in a rotating fluid with rotating fluid and thermal contrast will form vortices that represent meandering flows of the polar and subtropical jet streams in the Earth’s atmosphere. The dyes moved in opposing directions in a vortex like shape/fashion of eachother. The dyes were used to trace the patterns of the flow. These flows can carry warm water towards the pot of ice which represents the transfer of heart from the tropics to the Artic.
All three scenarios demonstrate that rotation and a temperature gradient are essential to the formation of extratropical cyclones.
For the sink experiment, explain why the rotating case develops an intense vortex and the surface of water is severely depressed, whereas this doesn’t happen in the non-rotating case? In what ways is the rotating case analogous to a hurricane?
The spin of the vortex in the sink (and hurricane) is due to the vertical stretching of the water column that is rotating because the apparatus is rotating. The water in the sink has angular momentum which is aided by the initial angular momentum of the spinning water. Without the rotation, this initial angular momentum would not be provided and the rest would not be possible. The swirl of water is sucked toward the sink hole (center), decreasing its distance from the axis of rotation so the vortex speeds up due to the conservation of momentum. The equation of angular momentum is given by initial momentum*radius*circulation (which all equates to the constant). However, the circulation can change and become more intense. Water is loss when it drains down the sinkhole and so the remaining swirl of water has a decreasing radius. The following is true C1*R1=C2*R2 given that C1 is circulation and R1 is radius for a wide/slow swirl and C2 and R2 refer to a intense vortex like swirl . As follows, the equation for the circulation as the radius decreases is C2=(C1xR1)/R2. If R2 is a smaller value than the circulation would be at a higher intensity, thus a smaller radius has a tremendous effect.
Like in the sink experiment, hurricanes have an initial angular momentum: the Coriolis effect, or the rotation of the Earth. If this force was absent like at the equator and the air can’t rotate which means the genesis of a tropical cyclone is impossible. This is analogous for hurricanes because winds have angular momentum (the differences between air and water can be disregarded in this case). Winds spiral towards the eyewall of the hurricane. The conservation of angular momentum allows a hurricane to spin faster as it moves towards the center of circulation—although not certain, one of the reasons behind the formation of the eye—and it requires wind speed to increase as the wind’s distance from the center decreases. Once the sink is plugged up or the hurricane hits land, they lose power because their energy source is depleted.
In the non-rotating case, we did not observe swirling of dye around the sink. However, as long as the Earth underneath the tank is rotating (which it is), in principle it should be possible to observe a swirling motion in a similar experiment. How would you design an experiment to increase the chance to observe a swirling motion around a sink without rotating the tank or tweaking the shape of sink?
It is within the realm of reason to design an experiment to observe the Coriolis effect. In order to do so, the draining of the sink must be drastically slowed down to the extent of where the Earth’s rotation could have an effect on the water. In the demonstration in the lab, the sink water was drained too quickly. However, in hurricanes the Coriolis effect is obvious in the swirl because they last for several days to over a week. Since the Earth needs one day’s time to make one rotation, then the Coriolis effect occurs with the earth’s rotation. Therefore, the sink experiment must last for at least one rotation of the Earth (one day) in order to produce an observable effect.
The specific design would include a very large tank of water with relatively small drain to let water out slowly. The water will continue to steadily drain for several days so the Earth has completed several revolutions also; hence, the swirl of the water would mimic that of hurricanes.