Lecture 9Outline of Last Lecture I. Weather of the day notesII. Key Forces that Accelerate the AirIII. Force BalancesIV. Pressure Gradient Acceleration FormulaV. Friction Forces Outline of Current Lecture II. Weather of the day (whole lecture today)III. ITCZIV. Force balancesV. Coriolis effectVI. Surface temperatureVII. Weather Prediction for next weekendCurrent LectureAnnouncements:Homework #2 is due next week.Weather of the day: (all that we did today) Right now there is a lot of humidity concentrated in the tropics. Also we can see various weather patterns going on in the tropics. There are different pools of moisture going up from the tropics. There is typhoon activity south towards Japan moving north. There is high humidity along the tropics at a latitude a little north of the equator. A lot of moisture is picked up over the ocean this then converges into a line and rises from there. The belt or line of moisture is considered a “conversion zone”. Conversion is just north or just south of our equator. Inter tropical convergence zone is called ITCZ: inner tropical convergent zoneThis exists because the sun shines stronger or more at lower latitudes than higher latitudes, so they gather more heat. (In terms of ocean temperature and air temperature.) Atm Ocn 100 1nd EditionThe result of this is that the planet needs to mix that heat around. Why does this need to happen? Why can’t tropics get extremely warm and poles get extremely cold?As a whole the sun shines unevenly across the earth. The earth balances that heat by radiating it back to space. The temperature of the earth determines how quickly that radiation goes to space. But radiation occurs over wide surface areas of the earth. So if the temperature is only high at the equator, it would only radiate from the equator, which would mean that it is only a small region radiating to space, but an equilibrium is created or a mixing of air so there are more regions that radiate to space. Air is mixed around so it radiates equally all over the globe to balance sun that is shining the most on low latitudes.So weather mixes heat around the atmosphere and also currents in the ocean. Air is mixed around so radiation can occur in more places therefore radiation can more efficiently move back to space. Earth has to radiate just as much heat that comes from sun to space otherwise there would be a net warming or net cooling of the earth. Weather forms when you heat an area or makes changes in the pressure. We talked about relationship with heat and pressure. In general pressure increases as temperature increases. When air is hot, it expands and the density is lowered. This happens for the hot air in the tropics. There is high pressure at higher levels in the tropics. In the poles, the air diverges away and sinks. The air rises at the equator. An example of this would be fire burning along the convergence line; it would make the air currents rise where it is burning. The air would be pushed out and would sink at the equator.The humidity is high at the equator. Air at its surface is rushing toward the equator, it is also moving over oceans and getting moisture. The max amount of moisture it will have is when it reaches the convergence line.The air as it gets more and more moist, will then rises and create clouds that give a lot of rain or tropical cyclones. That same air is then moved towards the poles and then sinks. The air at the poles is quite dry in comparison to the air at the equator. We can animate Vis5D picture to see how this is happening right now:There is typhoon activity going on in the pacific. In the Atlantic it is calming down. There are occasional dry pushes coming down. There is moisture moving toward the poles from the Gulf of Mexico. There are little extensions of tropical moisture that move to middle latitudes moved by weather systems. There are tropical cyclones moving off of west coast.Weather formed with air off of ITCZ. This then induces other weather in the middle latitudes. In the middle latitudes we can look at pressure at higher levels to get an understanding of some of what is going on. Isobars (lines of consistent pressure) at about 5 km so that means same as pressure height lines at 500 mb. They look the same, represent same thing.In the middle of the atmosphere there are isobars that show variability in pressure. What we see is a line of strong change, or region…There is pressure near poles sign on band of strong pressure gradient (space in-between the lines) The lines that are closely spaced means there is a strong pressure gradient, when the lines are further apart there is weak pressure gradient.By the poles there is strong pressure gradient but at the equator there is hardly any pressure gradient. Pressure gradient occurs as a result of air underneath 5 km, lower half of atmosphere; there is a strong thermal contrast of air at poles and air at equator.Air doesn’t just get warmer… if you get across southern United States the temperature is up in the 80’s and you can get to South America same temperature it will not get warmer.North of this land however, there is a strong pressure change, if you go a little distance, such as Alabama to Wisconsin in wintertime, the temperature could go from 60 to -20 in Wisconsin. There is huge variability when you get to bands of the middle latitudes. There is cold air and then warm air, this means there is an existence of a front of semi permanent demarcation north of convergence line, the air becomes cold very quickly here. Pressure gradience is associated with temperature change. Force balances: what does pressure gradient suggest with regard to the winds?Have a strong pressure gradient or closer spacing of these lines of constant pressure, isobars, means that the winds are stronger. Spacing of these lines across middle latitudes suggestive how fast winds are moving. Lines represent the approximate location of the jet stream at 500 mb. 500 mb is not the middle of the jet stream, you would actually have to go higher. But winds already are stronger here. Force balance that occurs: how does it result in the strong winds with pressure gradient? Why does pressure gradient create strong winds by the concept of force balance?If there is a parcel of air blowing along through the westerlys… What are the forces acting upon the parcel?There are 2 major forces acting on the parcel, one force is to the left and one is to the right. The poles have very low