ATMS 120 1st Edition Lecture 8 Outline of Last Lecture I Radar II How radar works III What radar measures Outline of Current Lecture II Doppler effect and radar III Radar operation modes IV Radar estimated precipitation V Extra tropical cyclones A Characteristics B Origins and tracks Current Lecture I Example have you ever heard a car horn blaring continuously as it was driving past you on the road The horn appeared to have different pitches as it was in different positions compared to you When the car is far from you your ear hears a lower pitch sound In contrast when the car is closer to you your ear hears a higher pitch sound The same concept applies to Doppler radar If a rain drop is moving toward or away from the radar then the frequency and phase of the echo it will make will be higher or lower From this change in frequency and phase we can determine the wind speed and direction When looking at a Doppler radar screen red shows precipitation that s being blown away from the radar antenna Green and blue show that precipitation is being blown toward the radar antenna Storms move from blue to red Doppler radars can indicate tornadoes from hook echoes as discussed before and also by red green couplets that indicate precipitation movement in opposite directions yet within the same small area II There are two types of operation modes in radar clear air mode and precipitation mode Clear air mode is a very sensitive radar and can pick up many different things instead of precipitation This types of radar gets echoes from birds bugs dust turbulence in moisture content and even light snow All of this collectively is commonly called ground clutter These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Precipitation mode is designed to see rain This type of radar only gets echoes from precipitation III Radar estimated precipitation is a great tool for monitoring flood potential It can add up the echoes over time to compile an estimate of how much precipitation is going to fall in a certain area IV Extra tropical cyclones are larger than typical tropical cyclones that go through the eastern coast of the United States Extra tropical cyclones are found in the mid latitude and polar regions of the US and can produce severe weather of all types in surrounding areas all around it A Winds and clouds circulate in a counter clockwise direction The shape of these cyclones looks like a comma This is because there is a dry slot that happens in the southwestern part of the cyclone Air masses from different locations compete to be in the same area In the central part of the United States sometimes the continental arctic air mass wins causing cold weather Sometimes the maritime tropical air mass wins causing warmer weather Paying attention to the track of the cyclone can indicate what type of weather a certain area is going to get To the south there are thunderstorms To the east there is heavy rain To the north northeast there is freezing rain and sleet To the west backside there is snow B Typically cyclone tracks move from the southwest to the northeast and they usually take 2 5 days to cross the US Alberta Clipper moves quickly along the US Canada border They bring very cold air and blizzards to the northern plains of the US Colorado Low tracks across the central US from Colorado through Chicago to the northeast These types of cyclones bring rain to the University of Illinois Ark La Tex Low the name of this cyclone track tells us where these cyclones start They track to the south of the University of Illinois and bring snow there Gulf Low very powerful because they extract heat and moisture directly from the Gulf of Mexico Hatteras Low also very powerful and rack up the east coast These cyclones are also called Nor easters because of the strong onshore northeast winds