Lecture 28 Outline of Last Lecture I. ReminderII. Current WeatherIII. ReviewIV. Ocean CurrentsV. Basic Ocean CirculationsVI. How do ocean currents affect weather and climate?VII. Thermohaline CirculationOutline of Current Lecture II. ReminderIII. Current WeatherIV. Global Warming and Thermohaline circulationV. Consequences of Global Warming to Thermohaline CirculationVI. A Local Thermohaline Circulation in MediterraneanVII. El NinoCurrent LectureReminderHomework due November 26, 2014 TYU Ch 5: 1,2,3,8,9,13; TYPSS Ch 5: 3TYU Ch 23: 1,2,3,4,5,6,7,8,10,13,19; TYPSS Ch 23, noneTYU Ch 24; 1,5,7,9,10,14,18,19,22,23,25 TYPSS Ch 24: 4Current WeatherThere is a big trough at the 250 mb level over Canada and it is extending down into the Midwest. The trough is usually associated with a lot colder air aloft and at the surface. If we go ahead in time to Tuesday we can see that the trough has extended even further into the Midwest. It may even get colder by Tuesday. But as we get to later next week the trough is over Canada, but it moves over to the East. So the trough is extending toward New England instead of the Great Lakes. It may warm up a little bit into later next week. Atm Ocn 100 1nd EditionAt 850 mb the purples and pinks are more than 10 degrees below 0. The blues are starting to move up into Wisconsin by Thursday and Friday so perhaps by the end of next week it won’t be quite so cold. Jet stream is a boundary where the air is trying to be pushed forward. Global Warming and Thermohaline circulation• Gulf Stream transports warm water from tropics to North AtlanticThis keeps Europe warm for its latitude:• London at same latitude as Hudson Bay• Sweden at same latitude as Greenland• Gulf Stream driven by:Wind stress from the North Atlantic GyreThermohaline circulation…subduction (sinking of high density water under lower density water) of cold salty water from Arctic, draws up Gulf Stream to replace the water mass lost. • Subduction driven by:– Very cold water produced by long winter nights– Increased water density due to increased salinity of water in contact with the forming Arctic ice. Freezing of ice cap, forces salt out of the ice thereby increasing salinity (saltiness) of water in contact with the developing iceThe amount of salt in the water rises as evaporation continues. That makes the water get heavier. Ice floats on the top of the water because ice is less dense than water. If the ice caps melt, we would expect subduction that creates circulation to the north would probably shut down. The Gulf Stream would shut down which would make Europe get extremely cold. The Carbon Dioxide we put in the air will build up fast because our natural absorbers will not work as well. “Runaway greenhouse” is that the greenhouse effect is going to start going against us basically. Carbon dioxide will not be able to be absorbed effectively by oceans.We have already reached beyond the tipping point. We have passed it. In our lifetime we will see the planet warm significantly. When the circulation shuts down, we can wind up freezing Europe, and be in a big ice age again like the movie Day After Tomorrow. Regardless of what happens, we are under this bad system that was in control but now it really isn’t. It is very hard to predict. Some predict that the ice caps will completely melt, but they have been very slow. But it is shocking how fast this whole phenomenon is happening. We continue to run models, every year it gets a little more frightening. Consequences of Global Warming to Thermohaline Circulation• Ice cap melts creating an excess of floating fresh water in the Arctic Ocean• Permafrost and glaciers, particularly in Siberia, melt, causing huge flux of warm fresh water into Arctic Ocean via northward draining rivers. • Low density water inhibits subduction and supply of deep water to the cold conveyor belt• Gulf Stream slows, and turns east at much lower latitude because it is no longer being driven northward• Cessation of northward heat transport causes Europe, and northeast North America to become colderThere is a cascading feedback loop that does not seem to be getting any better. High clouds stop the radiation and they reradiate it to other directions. The radiation temperatures it will emit at are much colder than the ground, so much less radiation. The clouds will trap the heat even more. If it is lowclouds, they are warm like the earth. They intercept radiation and will radiate it back at a high temperature, and that light will be greater. Low clouds can actually help prevent global warming.A Local Thermohaline Circulation in MediterraneanTH circulation driven by relationship between evaporation, precipitation, runoff and heating that all affect water densityThe water is saltier in the Mediterranean. The Southern Mediterranean is where it gets the saltiest. There is the difference of salinity or saltiness. Thermohaline- a salty temperature circulation El Nino• Original definition: Annual warming of water off of the Coast of Peru around Christmas. “El Nino” referred to the Christ child.• Since early 1980’s new definition: Warm water occurring off of the Peru and reaching out to the dateline that tends to occur periodically every 2-5 years.This shuts down the fishing because the water is so warm. There is a diagram that shows this. It isn’t at Christmas; it’s a little later. We can see the temperature anomaly, the temperature of the water compared to what it normally is. The reddish color is the warm anomaly. In 2010 the equator is right where the warm water is. The Eastern Half was very warm compared to what it normally would be. When this happens it modifies weather systems. The inner tropical convergence zone is driven by warm air in tropics. But the oceans and warm water temperatures mostly drive this. The sun shines on the water in the tropics and the water temperature rises because it has a high heat capacity. The water getting warm makes the whole atmosphere there warm compared to normal. This makes more thunderstorms and the inner tropical convergence zone has a high intensity because of the warm water. Also the Hadley Cell circulation is very strong during this.It will create weather systems in LA that usually don’t happen because of the cold water. California will feel like Seattle because jet streams and weather systems because of El Nino will hit it. A lot of