Lecture 15 Outline of Last Lecture I. RemindersII. Weather of the dayIII. The issue with cloud droplets becoming rain droplets IV. How does rain form?V. Ice FormationVI. Ice nucleiVII. Ice NucleationVIII. Process by which Ice grows Outline of Current Lecture II. RemindersIII. Weather of the dayIV. Reviewa. Warm Rainb. Cold Rainc. Auto Conversiond. Ice Nucleie. Bergeron ProcessV. Processes by which Ice GrowsVI. Wet process procedureCurrent LectureReminders:Test next WednesdayMicrophysics Homework is due next week! Microphysics lecture stuff will be on the test. Tornados are not going to be on the test, but the homework will be due next Friday. Weather of the dayNow we will look at the storm we have been looking at all week. We are looking at a part of the 250 mb map at6z. We can see a jet reaching up through the east side of the trough. The yellows mean there will be 120 knots.An interesting feature here is the kink in the height lines. We can see a little ridge going into the trough. In that area there will be some curvature divergence. If we look at a surface map at the same time, the area of curvature divergence is in the middle sort of. There is a 996 mb line. That is impressive for this time of year. The isobars are close together over Wisconsin it will be a breezy day on Monday. The red right over us is Atm Ocn 100 1nd Editionprecipitation. That means 1 inch of rain over 6 hours, a lot of rain from that short time period. It will be rainy and windy on Monday. A very interesting weather situation we are in.Global view we are going to be looking at. We are going to look at the energy of the tropics and how it relates to what is going on here. We are looking at the JAPE model. The jet available potential energy is what JAPE means. The JAPE bubble is elevated above the tropical atmosphere. What happens is the jet streams are associated with that. The color blue means motion raises and red means it is sinking. We are in a rising motion right now over the Western Hemisphere. Usually rising is in the Western Pacific. But this unusual rising may be associated with cyclones happening right now. The jet streams are in yellow; they hug the boundaries of the JAPE bubble. From the side of this model we are looking at we see the jet streams are around the boundary. They exist because of the energy in the polar jet. The jet streams effectively seal the flow off so it can’t move toward the pole.Bubble air starts at around 10 km above the ground and goes to 18 km. As we know, the tropopause is much higher in the tropics. The reason for this is this energy that is trapped that cannot get out from this JAPE bubble. What is happening at this time of a year is that the polar activity is getting weaker and drying up. The opportunity for the jet to bleed off energy to polar latitude is starting to go away because the southern hemisphere is warming now that they are moving into spring. Polar jets are starting to form in the Northern Hemisphere. We are at a strange period in-between losing polar jets in the Southern Hemisphere, and waiting to create them in the Northern hemisphere as our winter comes on. Bubble is getting bigger and bigger and is waiting for a place to give off energy.Scandinavia had its first snowfall earlier this week. This means that it was allowing the thermal contrast between cold and warmer Europe to create a front. There is now a polar jet forming over the front. This provides an opportunity for the JAPE bubble to dump its energy. Many people died in a flood in Genoa Italy. The reason this happened is because of the eruption of the tropical bubble to the north. If we had had a polar ice cap all year long we would have developed a polar front earlier. We waited so long for this, and once it did, energy exploded into it and produced an epic killer storm.Polar jet is forming over Canada right now as well. We can see the bubble arching up, and is going to plug into the polar jet surge and dump more energy into there in the next couple days. This will then produce aheavy storm over us for next week. These are all global events. The situation has been building over the last couple decades. Normal routes that occur as seasons change are erupted or changed. What happens is that there is excess energy built, and then when it tries to evolve itself it leads to epic events. Bubble is already losing some impact into the Scandinavia region so we aren’t going to have a terrible horrible storm. But we can’t tell people in Italy this isn’t important. Their storm was deadly. Back to lectureReview:Warm Rain: Collision-coalescenceWhat happens when you have warm rain is that droplets evolve to a bimodal distribution. There are 2 maximums in size if you plot size verse radiance. Or otherwise known as size verse the number of small droplets and then the number of large droplets. The number of droplets in-between is not much. How does this happen?What happens is that as you start to form larger droplets, the largest of those droplets, which are almost big cloud droplets and not necessarily rain, are big enough to fall relative to the other droplets. These larger droplets start to fall and when they do they collide with the smaller droplets that are still there and make thembigger. This of course means that smaller droplets are removed. When these smaller droplets collide with the larger droplets they get bigger and bigger and change there shape. A small droplet is spherical. A large droplet tends to be shaped like a teardrop almost. The reason for this is that the flow goes around the droplet when the droplet is falling, and then creates circulations inside the droplet, which cause a depression in the middle.As the droplets get bigger the air around them deforms them. The droplets become hydrodynamically unstableand then they explode. What holds these droplets together from exploding at first is the surface tension between them. The surface tension holds it together but when the droplets are big enough the surface tensioncan no longer hold it together, and then the whole droplet explodes apart. What then happens is that the droplet will turn into many droplets of many sizes but overall smaller than at its largest form. Even though these droplets are smaller, they are still bigger than cloud droplets. The new somewhat smaller droplets continue to fall and collect cloud droplets as they fall. We know that the biggest droplets can’t get bigger. The size at which the rain cannot get any