Lecture 27 Outline of Last Lecture I. RemindersII. Current WeatherIII. General CirculationIV. SSEC Global Satellite and Surface TemperatureV. Solar Absorbed Minus IR EmittedVI. Heat TransportVII. Global Atmospheric CirculationVIII. Rotation produces banding of the General CirculationIX. 3 Celled General CirculationX. 3 Celled Hemispheric CirculationsOutline of Current Lecture II. ReminderIII. Current WeatherIV. ReviewV. Ocean CurrentsVI. Basic Ocean CirculationsVII. How do ocean currents affect weather and climate?VIII. Thermohaline CirculationCurrent LectureThe final will be comprehensive, but it will have an emphasis on the stuff we cover since the 2nd test.Reminder: There is homework due Wednesday the 26th, the day before Thanksgiving. Current WeatherSupposedly we have one inch of snow on this map we are looking at, but that isn’t true. When the first snowfall comes, the climate quickly changes. Northern Wisconsin because they now have snow cover has now entered into winter. Since we did not have a snow fall here, we are still in the “fall” season. This Atm Ocn 100 1nd Editionis based on the energy balance with the sun. Once the snow cover is there, we radiate more energy to space, we don’t absorb as much and everything changes. Winter begins when snow stays on the ground. If you add up when seasons change, we can see when winter begins with snowfall and it ends with the meltingof the ground. It all averages out, the beginning of winter and ending of winter is different every year. Back to lectureThe homework covers the climate stuff. And then Chapter 24 is tropical cyclone stuff. Review:Earth divided into three bands, six bands total. Why is Earth divided into three cells in each hemisphere? It is because of the rotation of the Earth. A circulation means that air will come in at the surface to feed the warm air to the equator and rise over the subtropical convergence zone and then to go poles By the time air goes to the poles, it will go at the speed at the equator part of the earth compared to the speed of the pole. The speedof the pole is 0. The potential wind speed at equator is about 1,000 mph. As the air moves south, it will go about 100 mph and then go toward the west. It is impossible for the wind to traverse the whole hemisphere, before they turn to the right. And end up becoming Westerlies. There is mixed rising motion moving to the south turning to the right and then making a subtropical jet. Or the air rises and turns to the right to make a subtropical jet in the northern hemisphere. In the south the air turns to the right moving toward subtropical convergence zone. In the Southern hemispheres the air turns to the left. The air is going fast at the tropopause, where the inner tropical convergence zone is, because of friction. The ground, through friction, slows it down. So rather then getting faster from the east, the air receives a certain speed and that’s all the speed it will get because friction increases as speed increases. The Earth is moving counterclockwise, so when the air goes to the north should speed up a whole lot but they don’t. It means that air accelerates towards the west, accelerated with Westerly flow; the momentum came from the ground. The Earth provided momentum to increase westerly component. What causes momentum in wind? What causes wind speed?One source of momentum for wind is the ground, the Earth itself. The Earth can provide various degrees of momentum depending on your latitude, because the earth is spinning faster at the equator than at the pole. You get more momentum at the equator then at the pole. How much you pick up depends on your speed relative to the ground. But ultimately, every moment of wind you ever see, horizontal movement, anywhere onthe planet, all that momentum is what causes wind laterally had to come from the ground. If you look at the whole thing added up, only place to get new momentum or any momentum is from the ground.All wind results from the movement of air from one place on the ground to another place where the Earth isspinning at a different speed so there is a relative movement of air to the ground. 3 Celled Hemispheric CirculationsThe actual position of Hadley Cell depends on where the continents are as well as the season. The direct circulation wants to extend to the pole, but it can’t because of angular momentum. We still call it a Hadley Cell. The Polar Front is a circulation too. The cold air sinks and spreads out to the south and then there is a return circulation which produces a polar cell. This is known as a direct cell, as opposed to an indirect cell. The direct cell is thermally direct. This means that the cold air is sinking and the warmer air is rising. The Hadley cell is also a thermally direct situation, warm air rises, and cold air is sinking. That is direct. Opposed would be indirect situation.The energy can be released and be used in the circulation. The energy of the jet streams is grown through this direct circulation. The momentum comes from moving the momentum around, but the energy can be shown to result from the energy released by this direct circulation. Warm air rises; cold air sinks that releases energy. If it’s the opposite need energy to make that happen. That energy can be used to make a subtropical jet and can be used to do other things as well. Also there is a mid-latitude storm track in the middle.The horse latitudes are the calm winds…New StuffOcean CurrentsWhat causes them?– Wind drag. Friction with the wind drags the ocean surface to produce a current. The semi-permanent position of the subtropical high over the north and south Pacific and the north and south Atlantic help drive the anticyclonic Friction with the wind drags the ocean surface to produce a gyre of water in each basin.– Thermohaline circulation. Density variations in water arise from differences in temperature (warmer=> less dense) and salinity (more salty=>more dense). More dense water tends to sink relative to less dense water, giving rise to vertical circulations known as thermohaline circulations. – Interactions of ocean currents with bottom topography and lateral boundaries– Other ocean “weather”, i.e. ocean waves, vorticies, etc.The ocean temperatures are transmitted into the air. Water becomes warmer if the air over the water is warmer and they mix. There can be circulations between warm water on the coast and cooler air that is not in contact with water. Day