ATMS 120 1st Edition Lecture 17 Outline of Last Lecture I Flood fatalities in US II Flood prone areas in the US III Comparing the 3 types of floods IV Miscellaneous notes Outline of Current Lecture I El Ni o II Global winds trade winds III Graph depictions IV The slosh V Southern oscillation VI Link to precipitation VII Anomalies Current Lecture I Peruvian fisherman fish the nutrient rich cold water off the west coast of Peru Every 2 7 years starting around Christmas the cold nutrient rich waters would warm up unexpectedly and the fish would leave This left the fishermen out of a job so they tried to move inland to farm for the time being but would receive heavy floodwater and wouldn t be able to farm These fishermen called this weather phenomenon El Ni o or The Little Baby referring to the Christ child or Christianity because it would happen around Christmas time So El Ni o technically refers to Jesus We study El Ni o because it changes weather patterns all over the world II We already learned about the trade winds and the westerlies These wind directions over certain latitudes are called wind belts Wind belts are caused by the planet spinning Traveling merchants would sail from Europe south towards Africa where they would pick up supplies and people then they would sail west and be picked up by the trade winds towards the Americas Once they dropped the goods off they would sail back a bit north and take the westerlies back to Europe It was an efficient way of sailing since they could follow the way the wind was taking them and could rely on strong wind power in their favored direction These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute The latitude where it switched from the trade winds to the westerlies is called the horse latitude It was called this because it caused trouble with the ships and if they had horses on board they would just dump them off Ships that saw horse carcasses in the ocean knew that the ship before them had a hard time managing the horse latitude and shifting winds III Under normal conditions it s called a Walker Circulation or Walker Cell As you can see from the image cold waters remain closer to South America Peru and warmer waters stay closer to Australia This image is crucial to understanding El Ni o and La Ni a El Ni o occurs when the Walker Circulation reverses in circulation depicted by the second image La Ni a occurs when the Walker Circulation speeds up in the original direction IV Every 2 7 years the trade winds weaken stop and sometimes reverse High pressure builds over Australia Low pressure builds over Peru Warm water sloshes back across the Pacific Ocean Redistributes clouds and precipitation across 10 000 miles of ocean Under normal conditions warm water gathers by Australia During El Ni o warm water sloshes over by Peru Australia and Peru are the most impacted because they are on either side of an El Ni o V See Saw Sequence of events 1 Surface pressure systems weaken 2 Slows the trade winds might even stop or reverse them 3 Warm water sloshes back to the east 4 Precipitation shifts eastward What is La Ni a After an El Ni o the return to the normal circulation often overshoots Sea surface temperatures are colder than normal Trade winds are stronger than normal Peru during an El Ni o intense precipitation flooding Australia during an El Ni o drought VI VII El Ni o is not the only weather circulation and therefore cannot be the only thing looked at when predicting weather patterns Sea surface temperatures are a good indication of what type of year it is going to be in terms of El Ni o La Ni a For 2014 warm water is sloshing towards Peru which is indicative of an El Ni o year