SHW Ch. 1 - Properties of the Atmosphere
Troposphere: a thin layer of air that contains 90% of the full atmosphere's mass; its depth varies from 8 km (5 miles) at the poles to 18 km (11 miles) at the equator; all of our "weather" occurs in the troposphere
~78% nitrogen; ~21% oxygen; remainder trace gases (carbon dioxide, ozone, hydrocarbons, argon)
WATER: only substance in the known universe that can exist in all three phases simultaneously at the usual temperatures and pressures at the earth's surface; liquid (hazy droplets, cloud droplets, raindrops); solid (snow, ice pellets, hail); gas (water vapor)
Aerosol: invisible tiny particles in the atmosphere
TEMPERATURE: the average kinetic energy of the molecules in a substance; Fahrenheit scale, Celsius scale, Kelvin scale; Figure 1.1
F = [C * (9/5)] + 32 ; C = (F - 32) * (5/9) ; K = C + 273.15
World Record Hottest Temp: 136 F at El Azizia, Libya (9/13/1922)
USA Record Hottest Temp: 134 F at Death Valley, CA (7/10/1913)
World Record Coldest Temp: -129 F at Vostok, Antarctica (7/21/1983)
USA Record Coldest Temp: -80 F at Prospect Creek, AK (1/23/1971)
Earth's slightly elliptical orbit and axis tilt of 23.5 degrees creates the seasons; the northern hemisphere is actually farther from the sun in summer than in winter; Figures 1.4, 1.2 & 1.3
Atmospheric Structure: troposphere (tropopause), stratosphere, mesosphere, thermosphere; Figure 1.5
Uneven solar heating of earth from equator to pole drives the weather; polar jetstream (around 50 N/S Lat) and the subtropical jetstream (about 25 N/S Lat); just north of each jetstream stratospheric air often descends in a narrow zone, leading to a tropospheric fold; Figure 1.6
PRESSURE: the weight of a column of air over a unit area; average sea level pressure 14.7 lbs/in2 (29.92" Hg; 1013.25 mb; 1013.25 hPa) at 15 C (59 F); must convert observed station pressure (Altimeter) to SLP for plotting; Figures 1.7, 1.8 & 1.9
World Record Highest Pressure: 1084 mb (32.01") at Agata, Siberia (12/1968)
World Record Lowest Pressure: 870 mb (25.70") in the eye of Typhoon "Tip" over the Pacific Ocean (10/1979)
(Properties of the Atmosphere Continued)
MOISTURE: water vapor is invisible; clouds are made up of water droplets and ice crystals; Figure 1.10
Dew point temperature & vapor pressure both measure the absolute amount of moisture in the air; the warmer the air temperature, the more moisture it can hold; Figures 1.11 & 1.12
Relative Humidity = [(vapor pressure) / (saturation vapor pressure) ] x 100%
Phase Change Diagram for Water (Figure 1.14); melting & evaporation; condensation & freezing; sublimation & deposition; Latent Heat
Pure water will not freeze until temp reaches -40 C; water at temps below 0 C are said to be supercooled; ice nuclei (must have a crystal lattice structure similar to that of ice) become active when temp drops to -10 C to -15 C
Graupel: tiny, soft ball of ice; ice crystals collide with supercooled droplets
Hail: continued growth of graupel (wet & dry)
Snowflakes: ice crystals collect other ice crystals
Ice Pellets (sleet): frozen raindrops
WIND: the movement of air; measured by speed & direction (named from where it comes from); a north wind blows from north to south; Figure 1.15
1 knot = 1.15 mph ; 1 knot = 0.51 m/sec
Heating Degree Days (HDD): a measure of energy consumption; heating season runs from July 1st through June 30th of the following year
HDD = 65 - daily mean temp ; e.g., Max=45; Min=14; Mean=29.5 ---> 30
HDD = 65 - 30 = 35 ; HDDs are accumulated throughout the season
Cooling Degree Days (CDD): a measure of energy consumption; air conditioning season runs from Jan. 1st through Dec. 31st of the current year
CDD = daily mean temp - 65 ; e.g., Max=95; Min=64; Mean=79.5 ---> 80
CDD = 80 - 65 = 15 ; CDDs are accumulated throughout the season
Growing Degree Days (GDD): uses a different base temp for each crop; accumulated GDDs indicate when a crop is ready for harvest; Beans (50: 1200-1300; Corn (50: 2200-2800); Cotton (60: 1900-2500); Peas (40: 1100-1200); Rice (60: 1700-2100); Wheat (40: 2100-2400)