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

Meteorology

90

180

270

0 or 360N

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 from90°S to 90°N

Norman, OK is located at35.22°N latitude97.45°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