Lecture 1 (9/9) METR 1111

Lecture 1 (9/9)METR 1111 Temperature, Humidity, Pressure, Wind, and Latitude & Longitude

Temperature Temperature is the average motion of the molecules of a substance (measured with a thermometer) There are 3 different temperature scales: • Fahrenheit – used to record surface temp in US • Celsius – used overseas & upper air obs. • Kelvin – used in scientific formulas

Conversions for Temperature • C=Celsius, F=Fahrenheit, & K=Kelvin • °C = (°F-32)/1.8 OR °C= (°F-32)*5/9 • °F = (1.8*°C)+32 OR °F=(9/5* °C)+32 • K= °C+273.15 • Note that K does not have degrees(°), but the others do.

Sample Conversions • What is 100 °C in °F and Kelvin? • How do I get there? – Use the formulas • °F = (1.8 * 100 °C) + 32 = 212 °F • K = 100 °C + 273.15 = 373.15 K

Humidity • Humidity is the amount of water vapor in the air. • There’s several ways to measure humidity, but the most useful for meteorologists is the dew point • Dew point temperature is the temperature at which the air would become saturated (and dew would begin forming) • High relative humidity occurs when the temperature is close to the dew point

Pressure • Atmospheric pressure is the force per unit area exerted against a surface by the weight of the air above it. (measured by barometer)

Pressure • If the amount of air molecules above a surface increases, pressure increases too • If the amount of air molecules above a surface decreases, pressure decreases too • High pressure is usually associated with fair wx and Low pressure with stormy wx. • There are several different pressure units

Pressure • These units include: • Inches of Mercury (Hg) • Pascals (Pa) • Millibars (mb) • Meteorologists use millibars most often

Pressure Conversions • Standard sea level pressure is the average pressure on Earth at sea level. • Standard sea level pressure is =29.92 in Hg=1 atm=1013.25 mb =101325 Pa=101325 N/m^2

Winds around High’s &Low’s • Because of the Coriolis force (discussed in a later course) winds in the Northern Hem: • blow counterclockwise (or cyclonically) around Low Pressure • And blow clockwise (or anti-cyclonically) around High Pressure

Winds around High’s and Low’s • If the wind is at your back in the Northern Hemisphere, low pressure is always on your left! (Remember Low pressure = Left!)

Wind • Wind has 2 different measurements (speed and direction) • Wind speed is measured with an anemometer • Wind direction is measured with a vane Vane Anemometer

Units of Wind • Wind speed can be measured in mph, knots, or meters per second • 1 knot = 1.15 miles per hour • 1 m/s = 2.24 miles per hour • Wind Direction tells us FROM WHERE the wind is blowing • Ex: A SW wind means wind is FROM SW

Wind Direction • Wind direction is measured in degrees (like a compass, not like the degrees in math!) 0°=North, 90°=East, 180°=South, 270°=West N 0 or 360 270 90 180 Meteorology

Latitude and Longitude • Latitude and Longitude lines divide up the Earth into a usable coordinate system • Lines from N to S = meridians of Longitude • Longitude measures how far E or W a location is from the Prime Meridian (through Greenwich, England) Values of Longitude go from 180°W to 180°E

Latitude • Lines from E to W (parallel to equator) are meridians of Latitude • Latitude measures how far N or S a location is from the equator. Values of Latitude go from 90°S to 90°N Norman, OK is located at 35.22°N latitude 97.45°W longitude

To do for next time: • Read Chapter 2 in textbook (pg 13-29) • Complete Homework set #1 (You need to print this from the web) • Website: http://weather.ou.edu/~metr1111 • The quiz next time will be over today’s guest speaker, the lecture, & the reading assignment

Lecture 1 (9/9) METR 1111