Lecture 19 Outline of Last Lecture I. Weather of the dayII. What causes a thunderstorm to break, weaken, or collapseIII. 3 Stages of an Air Mass ThunderstormIV. Effects of Wind ShearV. Introduce Environmental Wind Shear to Prevent BreakdownVI. Frontal Thunderstorm VII. Squall Line Growtha. Other picturesVIII. Three-Dimensional Effect of Wind ShearIX. Supercell Soundinga. Pictureb. EchoOutline of Current Lecture II. Weather of the dayIII. ReviewIV. DiagramV. Lifecycle of a SupercellVI. Where Supercells FormVII. Tornados Current LectureWeather of the dayDark colors on an infrared image show warmer areas while lighter colors depict cooler areas. Something we might be able to see is that there is a little lighter of an area on this image of Wisconsin. The little area of lighter colors that show up in the middle of the image is valley fog from this morning. This is slightly colder than the area around it. Also though the valley fog is not as warm as clouds to the West. Looking at a picture where we can see region of high moisture, we can see the tropics. The line is called the inner tropical convergence zone. This is where the winds from the northern and southern hemisphere come together. This plot is showing the total integrated moisture in account. Right along this line the moisture is deeper because it is coming together between the northern and southern hemispheres and then being lifted up. We can see roll offs of this going up and developing into tropical storms. Atm Ocn 100 1nd EditionRight now we can see that there is a tropical storm forming in the Caribbean and moving up through the western tip of Cuba. In about 2 or 3 days we will see it come through into the Gulf and then it will move over Tampa. This is unusual and it is so far into advance we can’t know for sure if it will happen. If this does happen and there is a disturbance that moves into there it is interesting because the water there is warm. This is significant because hurricanes can develop in warm water conditions. In the Caribbean there is deep warm water. In the Gulf there is a shallow part of warm water. The water in the Gulf is not deep warm water as it is in the Caribbean. Hurricanes need a lot of warm water to be strong. Energy that the tropical cyclone uses is from this warm water. The energy of a tropical cyclone is usually proportional to how strong the water is. Deep warm water is driven into the Gulf of Mexico from the Caribbean. This occurrence is called a loop current. Sea Height Anomaly charts show how deep the warm water goes into the Gulf of Mexico. Water getting warmer and deeper is one of the reasons sea level rises with global warming. We had a strong loop current sitting over the Golf in 2005. Hurricane Katarina went over that loop current and became very strong. Hurricanes become very strong on the loop current, but as they approach other places they weaken. We are talking about this today because as we have already said we currently have a loop current. And there is a chance that there could be a storm that would move across the loop current and then intersect with Florida. There are different progs about this predication so there is a lot of spread; there is no certainty of what is goingto happen. But we will keep checking on this. It is hard to get tropical storms at this time of year because there westerly flows moving in so wind shear coming in could shred the tropical storm even if it is warm. If we don’t have the wind shear and we do have warm water then a tropical cyclone could happen. It would weaken though before hitting the shore of Florida because as a tropical cyclone get into cooler waters it weakens. But it still can have strong affects. This is the website we looked at today. www.aomi.noaa.gov/phod/cyclone/data/go.htmlBack to lectureReview: Last time we looked at this kidney shaped echo with a hook on the end of it. It is a very beautiful structure to a storm. It is very robust you see it over and over again. If storm chasers are out looking for a storm they love to see this. You want to be in the clear air so you can see the storm moving. You want to be to the right side of the hook. This is a structure of a supercell, Wind turns clockwise as you get higher. When windturns like that we say it has helicity. Example: We are facing toward the east and the west is behind us. The eraser is in the middle and is suspended above the ground. The ground is easterly flow, which is toward us. Above there is westerly flow in wind shear profile. The eraser would turn clockwise we can see that. The spiral pattern occurs when southern winds go through the erasers. This is helicity. If there is an updraft in the middle of the erasers turning they will be pushed up. If they are pushed up and keep turning now they are turning with a cyclonic circulation or a counterclockwise circulation and a clockwise circulation on the other. If there is no helicity, or no southerly wind, there will be two equal storms one turning cyclonically and one anticyclonically. If you have no helicity the cyclones would be the same strength. Coriolis doesn’t have much effect on these little storms. If you do have helicity the southerly flow is going through the erasers, if we tilt them up the flow would go up and then down through the other one. The one that is moving toward the right will have air pumped into it, which will make it stronger. The left storm is being suppressed. While the right moving storm becomes stronger the left one dissipates and dies. You end up with just one spinning right moving storm. This is the image we are seeing on the screen now, the echo picture. We have southerly flow in this picture, which is part of a big cyclone system. The right moving supercells are the strongest they rotate cyclonically or counterclockwise. If we observed wind flow in the southern hemisphere it would actually going the other way. If we use our right hands and curl our fingers around our thumb points in the direction the flow would have to be in order to have positive helicity. Diagram:The region is the forward flanking downdraft. The downdraft is air sinking from above, which is a divergent outflow, which is cool. It is cooled because of evaporational cooling. There is a protective front as well which is the front associated with a thunderstorm. The front will organize and cold air will come out of the downdraft and push against the front. Then air will rotate and collect air from middle levels.