Weather and the Atmosphere RAP Short Course
Syllabus 1) Vertical structure and composition of the atmosphere, basic weather variables 2) Warming Earth and its atmosphere the diurnal and seasonal cycles 3) Humidity, condensation, clouds, fog 4) Cloud development and precpitation 5) Large-scale processes upper-air winds, mid-latitude cyclones, fronts
Syllabus continued 6) Mesoscale processes mountain-valley breezes, sea breezes 7) Severe weather hurricanes, thunderstorms, tornadoes 8) Global climate and climate change 9) Atmospheric optics mirages, rainbows, etc. 10) The weather-forecast process
More about the course Selected topics and lectures from a CU course ATOC 1050 (45, 50-min. classes). The course is aimed at non-science as well as science majors so no math and physics beyond high school are assumed. No meteorologists allowed in class. Text available from NCAR bookstore, but not required Essentials of Meteorology, by Ahrens
Please interrupt with short questions when necessary. If the answer is not also short, I may ask you to see me after class. No exams No homework Course web site with notes at http://www.rap.ucar.edu/general/events.html
Class dates all 1:30-2:20 1) 6 March, Thur 2) 13 March, Thur 3) 20 March, Thur 4) 27 March, Thur 5) 3 April, Thur 6) 10 April, Thur 7) 29 April, Tues 8) 1 May, Thur 9) 8 May, Thur 10) 15 May, Thur
Composition of the Atmosphere
The atmosphere A molecular cocktail
COMPOSITION OF THE ATMOSPHERE NEAR EARTH S SURFACE Permanent gases (percent is the same everywhere) Nitrogen 78 % Oxygen 21 % Hydrogen -.00006 % Others (less than 1 %) ozone, methane, helium, etc. Variable gases (amount depends on place and time) Water vapor 0-44 % Carbon dioxide about.037 %
CO 2 varies with time Upward trend from 1958-2000, plus seasonal variational Not zero
Why the variation with time? Overall upward trend carbon dioxide from combustion by industry, autos, etc. Sawtooth pattern seasonal variation. Q: What would cause winter-summer oscillation? A: Vegetation is active in warm season, consuming carbon dioxide Q: But shouldn t two hemispheres balance? A: More land and vegetation in Northern Hemisphere
Seasonal Variation in Vegetation Equator
Equator Distribution of forests
Water-vapor Content
Content of the atmosphere in addition to gases Mineral particles dust from ground, man-made made pollution Water droplets clouds, fog Water drops rain Ice small crystals, snow flakes, hail
Structure of the atmosphere Varies depending on the meteorological conditions But we can talk about average conditions - horizontal structure (as shown on a weather map) - vertical structure
Vertical structure of the atmosphere First how deep is it? White line is the thickness of the atmosphere (99% of molecules) Earth
Within this thin atmosphere, there are three ways of defining layers How temperature changes with height (increase versus decrease with height) Composition (mixture of gases) Electrical structure
Different Layers of the Atmosphere
A Glossary of Weather Variables Air temperature Air pressure Humidity amount of water vapor Clouds Precipitation rain, snow, hail, etc. Wind direction and speed Visibility
Air Temperature
Temperature Related to rate of motion of molecules: The warmer the air, the more rapidly the molecules move. Primary temperature scales Fahrenheit (F): freezing point of water = 32 F, boiling point = 212 F Celsius (C): freezing = 0 C, boiling =100 C Absolute (A) or Kelvin (K): absolute zero = 0 A = - 273 C (all molecular motion stops) Temperature observations near the surface (2m) are reported in degrees F, and above that are reported in degrees C.
The temperature scales, A
Vertical Temperature Structure of the Atmosphere Commercial Aircraft All the Weather
Denver temperature profile at 5:00 AM 28 Feb 03 Stratosphere Tropopause Troposphere Temp Up
Experiences that confirm that temperature decreases with height It is colder on the tops of mountains Some of the hottest places in the world are below sea level Death Valley, the Dead Sea Commercial aircraft need to be heated
Air Pressure
Why do we care about pressure?
Air Pressure - Definition Pressure = force/area (e.g., pounds per square inch) 1) Hydrostatic pressure weight of the atmosphere above the surface 2) Dynamic pressure force of the wind (e.g., against a door)
Air Pressure - Units In this course, pressure is expressed in millibars (mb) average sea-level pressure = 1013 mb Sometimes (e.g., in weather forecasts) it is given in inches of mercury average = 29.92 in. mercury Surface pressure values are adjusted to sea level, so that values show high and low pressure patterns rather than the elevation of the observation
How is sea-level pressure estimated for plotting on weather maps?
Vertical Pressure Variation in the Atmosphere
Experiences that confirm that pressure decrease with height Ears pop in elevator or driving up mountain Commercial airplanes need to be pressurized - pain in ears when landing Analogy with water ears sometimes hurt as you dive deeply
Air Density
General definition of density - Mass per unit volume Air density Mass (e.g., kilograms) of air molecules per unit volume (cubic meter) More dense Less Dense *********** *********** *********** *********** * * * * * * * * * * * * * * * * * * * *
Density Variation With Height
Sea level
6-77 km, 450 mb,, 4 mi ASL 50 % reduction
20 km, 50 mb,, 12 mi ASL 90 % reduction
Personal experience showing that air density decreases with height It is more difficult to breath at higher elevations fewer oxygen molecules
Humidity A measure of the amount of water vapor in the air There are many different measures of humidity, and a few used in this class are Relative humidity Vapor pressure Dew point temperature
Clouds Percent of sky covered by clouds Types of clouds Cumulus Cirrus Stratus, etc.
Wind Speed miles per hour or knots (nautical miles per hour), meters per second Direction - Given in terms of the direction from which the wind is blowing. A northwesterly wind is blowing from the northwest. Horizontal wind is measured, but vertical wind is also very important
Visibility The maximum distance at which an observer can distinguish an object against the sky as a background May be limited by fog, air pollution, etc.
Precipitation Type of precipitation - rain, snow, sleet, hail, etc. Rate at which it is falling (inches/hour)
Scales of atmospheric motion - Storms of all sizes Mid-latitude cyclones 1000+ mile Hurricanes 500+ miles Thunderstorms 1-100100 miles Tornadoes few hundred yards Turbulence centimeters-meters
Measuring the atmosphere Weather balloons, or radiosondes make upper-air measurements of horizontal wind, temperature and humidity.
Radiosonde helium balloon with measurement instruments
Measuring the atmosphere Weather balloons, or radiosondes make upper-air measurements of horizontal wind, temperature and humidity. Surface weather stations (land and seas) measure horizontal wind, temperature, humidity, cloud cover Satellites can estimate winds, temperature and humidity
Radiosonde launch locations
Surface observations - NWS
Zooming in to see even more Northern Utah