Lecture 29 Outline of Last Lecture I. ReminderII. Current WeatherIII. Global Warming and Thermohaline circulationIV. Consequences of Global Warming to Thermohaline CirculationV. A Local Thermohaline Circulation in the MediterraneanVI. El NinoOutline of Current Lecture II. RemindersIII. Current WeatherIV. El NinoCurrent LectureRemindersNo formal class next Wednesday, just questions/answersHomework due next Wednesday Another assignment will be due Friday in 2 weeks Due 12/5Weather of the dayThe weather we have right now is very cold for this time of year. This is January typical weather. This weekend the weather is looking a lot warmer than today. But in 8 days there is a colder push developing. Today has a Walker Circulation. What happens during El Nino years with Walker Circulation? Atm Ocn 100 1st EditionIt shifts. The blue air will shift over. It will be in different places when it is not an El Nino year. If an El Nino does set in, the air will move over. That movement is the Southern Isolation. The movement toward the east occurs in conjunction with the El Nino. The El Nino is associated with warm water along the equator. The warmest water works its way eastward. The big question is, the blue pattern is it caused by the conjunction? Or is the conjunction caused by the blue pattern?One theory of El Nino is that the water just starts to come back to the west, and when it does this it will then pile up and warm the water off the coast of South America and so on. A number of things cause El Nino.LectureEl NinoA picture of what El Nino looks like. If you take sea surface temperature today, you compare that to the average. You can see if it is either warm or cold compared to what it normally is.If there is an anomaly of warmth that means it is El Nino. Today it is slightly warmer, but not at El Nino temperatures yet. Another figure shows where the traditional El Nino occurs off the coast of Peru. But the new definition of El Nino is warming in the general eastern side of the Pacific.A walker circulation between El Nino is determined by pressure difference between Tahiti and Darwin. This determines whether the Walker Circulation is the east or to the west. The depth of the warm water can study the El Nino. If we look at a situation in January of 1997 there was deepwarm water. The water then sloshes back. The warm water spreads across the pacific. The El Nino models try to use models of the ocean to try and calculate the slosh and how much it is going to come across. The slosh sometimes only occurs at low water levels so they see the water getting warm below the surface, remaining cold on top. But then warm water can come to surface.Can be difficult to warm the water because it is related to the wind stress at the surface .The Southern Isolationgets into this. The Southern Isolation is going back and forth, not consistent. That is reality. Given changes and weather and movement of the water, it is difficult to predict this. This is a picture of El Nino winter and normal winter. As far as winter and affects on the weather very profound.Water is energy for the atmosphere. It transmits energy into the air through water vapor. What percent of the energy is used to evaporate water? 90%! When we think of the sun warming the ground it really evaporates water more than it warms the ground. 2/3 of earth’s surface is water. Water energy cycle of the atmosphere is the cycle of how the sun’s energy is processed and we how we get energy throughout.On a normal winter we tend to have more westerly flow across the pacific. But in El Nino we get more ridging along the west coast, more strong southerly jet.When the jetstreams do this, more moisture and more water cycle directly into the west coast and cause the west coast to be warm. If we go several years without El Nino Southern California has trouble, serious drought.It has been since 2010 since the last El Nino. Even in Central California there is drought. Californians are hopingfor an El Nino this year. But El Nino because it shifts the pattern around the globe has very strong effects all over the planet. La Nina is opposite of El Nino. The rising motion of Asia is really going it is much stronger rising motion. La Ninais a stronger version of normal. La Nina have patterns that affect the rest of the globe. Things can be stronger then what they usually are. Tend to get more persistent high altitude patterns. El Nino also produces, at least in the tropics, stronger wind shear. The stronger wind shear can change the nature of the convection. Buoys are in the water measuring the temperature of the water. El Niño’s tend to occur on the average of every 3
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