Lecture 22 Outline of Last Lecture I. Weather of the dayII. Tornado Formation Mechanismsa. Top-Downb. Bottom-upIII. Two Major Types of TornadosIV. Daisy ChainV. Dry SlotsVI. Hook Echo Big PictureVII. Successive tornado genesis Outline of Current Lecture II. Weather of the dayIII. A little more about Tornadosa. Enhanced F Scale for Tornado Damageb. Tornado FrequencyIV. Hail and LighteningV. Origins of hailVI. Ways that ice interacts with supercooled liquid waterVII. Haila. How big?VIII. Supercell structureIX. Hail SwathsCurrent LectureFinal is cumulative. The test next week is not cumulative; it is only on the convection storms. Weather of the dayOn Friday the temperatures look really cold. There is a pretty strong wind at 850 mb for Friday night. The temperature at 850 is -12 degrees Celsius. We can see that it will be very cold and very windy on Friday night. We can brace for the 20’s by this weekend. At 250 mb the Jetstream corresponding to all this…Polar Jetstream is about 140 knots. It is a pretty strong Jetstream and it gets even stronger as it moves south. The Jetstream sits on the boundary between the warm air and the cold air. Ridges and troughs are becoming more amplified and these intensify the cold air that is driving into us. Atm Ocn 100 1nd EditionLectureTornadoEnhanced F Scale for Tornado DamageTornado strength is evaluated by the damage that they do, not by a direct measurement of the wind. We can infer wind from the damage that they do, if there is nothing that is damaged it is hard to figure out how strong a tornado was. The F-numbers go from 0-5. Then there now are the enhanced scales of numbers called the EF numbers, whichagain range from 0-5. That is estimated based on the damage. They types of damages that are done like small barns, one or two family residences, or malls. You can detect a tornado from radar, but you cannot estimate how strong it is until you inspect the damage. After a tornado there is a team that goes out and looks at the damage done and then evaluate it based on the damage criteria. And then you can relate the type of damage to expected wind strength and EF rating on the storm. Degrees of damage that can occur, expected wind speed, etc. Meteorologists correlate type of damages with the EF ratings. The degree increases, as there is worse damage. It is not until you get to EF3 when you see houses extremely damaged. EF4 damages are when a whole house is blown down. The house is destroyed. And then an EF5 damage is when the entire house is gone. You don’t call something EF5 unless you look at area where there were houses and only foundations. If only foundations and no debris, that is considered an EF5 rating. EF5 tornados are really rare. An EF5 storm leaves no debris! All the debris is blown out of the air that would be typical EF5 damage. Tornado Frequency is where tornados usually occur. The region is a good mixed layer from the west coming ofthe mountains, mixed dry layers of air above the surface, the gulf moisture, and polar front brings Jetstream. These three ingredients come together especially in Oklahoma. Texas gets a lot of tornados as well, but not asmany as Oklahoma. The reason is that Texas doesn’t get as good of Jetstream’s so it doesn’t have as many tornados as Oklahoma. Europe gets some tornados but not as much as in the United States. They can get some dry layers, but the moist air is not the same as we have in the United States. They can get dry air, and jetstreams from the north. This shows that Europe gets some ingredients, but they are missing gulf moist air from Mexico so their tornados are not as great as the ones in the United States. Florida gets them too. But not the intense downdrafts like in Oklahoma. A lot of little tornados and water spouts. But they are mostly F0 and F1s. There are not too many EF5 category tornados in Illinois and Ohio because they don’t have dry air from the Rocky’s. Iowa gets good gulf moisture and other ingredients so it could have good tornados. Minnesota is far from the gulf so not much moist air. EF1 is the most likely type of tornado. And EF0 and EF2. EF5 is very rare and EF4 is pretty rare too. EF5 has happened though in states like Alabama, Kansas, and Iowa. Onto today’s topic…Hail and LighteningAlmost all thunderstorms involve the ice phase. And to some extent the ice can get large and often it doesn’t melt before it hits the ground. So in many cases you get hail because that ice didn’t melt. But in certain storms ice can get really large which makes it impossible to melt. The dynamics of the thunderstorm, which could lead to ice, that get super large is part of the problem.Also another part of the problem is how warm it is below a cloud base, which sees if the air is warm enough to melt the ice before it touches the ground. Origins of hailHail is a precipitating ice hydrometeor that forms when an ice particle comes into contact with a super-cooled water particle, causing it to freeze onto the ice particleWe know there is always going to be snow, ice inside the cloud. Ice crystals develop. They can grow by vapor deposition, which is vapor on an ice crystal making it grow bigger. Or after they start falling ice crystals can intercept with smaller cloud droplets and even rain droplets, as they get large enough. Lower part of cloud might be super cold, which could be because there is not enough ice crystals to glaciate the cloud. Ice particles that fall into a lower part of a cloud that produce rain droplets, could then be brought back up, and could be back in top. Then collisions can form which could make a lot of rain in the cloud.Ways that ice interacts with supercooled liquid water• Super-cooled water hydrometeor collects ice– Water hydrometeor is bigger than ice– Diferential fall velocity between water hydrometeor and ice necessary, hence we are talking about rain collecting small ice, usually pristine crystals– Result is rain droplet is caused to freeze (ice is a great ice nucleus!)– Forms frozen rain pellets of full ice density, ie 0.9 g/cm3, which are called by several names:a) Rain pelletsb) High density graupelc) Small hail– Ice pellet falls faster than rain droplet did (less drag)Ice crystals are 2D like a sheet of paper. They can fall quickly. They have a high density if they are collecting raindroplets. They can have low density if they have cloud droplets. When there is fog outside in the winter, it blows against things like