Atm Ocn 100 1nd Edition Lecture 4 Outline of Last Lecture I Weather Notes II Composition of Atmosphere III Temperature IV Density V Pressure Outline of Current Lecture II Website of the day Notes III Surface Pressure IV Humidity V Vertical Structure of Atmospheric Temperature Current Lecture Announcements Homework 1 due September 19 Cloud Project Website of the day not sure how important website of the day notes are but I take them anyways just in case Spaceweather com good website to check current conditions A couple of days ago we had some communication problems with our weather maps there was a lot of interference in the air Currently the sun is flaring up which causes radiation After that comes the solar wind which are particles injected by the sun Technically our planet Earth is within the atmosphere of the sun We experience space weather from the sun s weather way out far away We experience winds that come off of the sun Cosmic rays hit the wind and cause auroras to form in the atmosphere When the auroral oval starts to crank we may see that get into Madison If we can see this take a picture of this for extra credit for Cloud Project Put it on Tri pod or put it on a car Exposure for at least 15 seconds you ll gather enough light on the camera to get a good photograph Aurora s can get pretty spectacular One aurora in the past was ripples coming from the horizon one after another very neat Aos wisc edu weather index htm different websites we can go to Climate for sustainability and the Global Environment both different links off of the main AOS website can show how much participation we have had this year If you go to metobs ssec wisc edu aoss tower there are rooftop observations that we can look at Text display shows current temperature wind speed wind direction pressure etc Also shows precipitation which today is very light but annoying If we are curious to do a conversation from knots to miles per hour You multiple knots by 1 15 to get miles per hour Meteorogram a graph that shows the same measurements as text display but on a graph form Annoying rain all day long It is going to take a while to get over us but iti will be light The radar from some of the links we have looked at show slight snow instead of rain Yet most of the time the image of snow is much crisper and well defined set of boundaries Snow that occurred in Denver is mostly over Little flurries is all they have now Computer forecast maps map is based on the observations California is warm because mountains block cold air from coming west Thickness determines how much pressure atmosphere is getting If we still have 47 this afternoon it will be a record low for Madison at this time of year We can see on our weather maps that a big arctic system is moving in Cold air in a couple days will withdraw We will see some very dramatic pictures of this in a few days Back to Class Surface Pressure Surface pressure is on average the weight of the air above you So the pressure on a flat surface is influenced by the weight of the air above you At higher elevations pressure of the surface could be lower Different pressures on the surface moving around why are they different There is high pressure when the weight of the air above that region is greater then the region where you see low pressure If you are in low pressure the air weight is low High pressure air weight is high Why is this If the air weighs less above you air is less dense not as much mass per unit volume It is less dense because the temperature is higher Overall if there is warm air mass above you that means that the surface pressure is lower If there is cold air above you this means that the surface pressure is higher However it is complex because it may have other way around In fact over some warmest areas on Earth like Sahara Desert fro example the pressure is actually higher So because of this example we cannot just say that because of cold air or warm air the pressure is one way or another It really depends on elevation In general pressure drops with height The pressure gets much lower the higher you go Most of our weather we can measure is capped by 10 11 km At the surface which is 1 000 mb by 10 or 11 feet we get 200 or so pressure mb The tropopause is right over 10 km We will go over what the tropopause is later When you are talking about topography in a car going up a mountain means that the pressure goes down and the air expands Going up the mountain the air parcels will get colder and colder But air that has been there a long time has warmed up Denver for example is much warmer then us in the summer even though it is at a high elevation If we take air from Madison and move it up slope to Denver it will raise about 1 5 km which means it will cool about 15 degrees Celsius Which is nearly 30 degrees Fahrenheit If we start with air in Madison at 47 degrees move it up slope all the way to Denver the air would be below 20 degrees Fahrenheit The air that goes to Denver even though moving up slope is modified Humidity A measure of the amount of water vapor in the air Absolute humidity the amount of water in the air measured as Vapor density mass of vapor volume of air Vapor pressure amount of total pressure due to the contribution of water vapor pressure Mixing ratio mass of water per mass of dry air Specific humidity mass of water vapor per total mass of moist air Vapor pressure partial pressure of air in the air Vapor makes up 0 2 percent of the pressure in the air We can look at vapor pressure and tell the actual pressure of how much is in the air Mixing ratio ratio of the mass of water vapor in the air to the mass of the dry air Relative humidity vapor pressure of air per saturation vapor pressure of air This is the humidity relative to how much humidity a parcel can hold before it becomes saturated with humidity and water begins to condense Expressed as a percentage ie multiply the fraction by 100 Relative humidity depends on temperature and the pressure Soon as a parcel gets to saturated value air condenses Only way to get air at higher humidity or vapor then saturation would be to make air extremely clean and that s almost impossible At some given humidity value can say what relative humidity is compared to saturation This is a measurement that affects people We don t care how much humidity in air except for relative humidity Effects …