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Contents: General Information | Forecasting | Wind chill/Heat Index | Weather modeling | Glossary

Related pages: High Altitude Guide | Temperature Indexes (wind chill, heat index)

Nitrogen 78.08%
Oxygen 20.95%
Water 0 to 4%
Argon 0.93%
Carbon Dioxide 0.036%
Neon 0.0018%
Helium 0.0005%
Methane 0.00017%
Hydrogen 0.00005%
Nitrous Oxide 0.00003%
Ozone 0.00004%
Note: Carbon Dioxide concentration is spread evenly throughout the atmosphere.

Air density as a function of altitude.

There are more complicated formulas which take into account temperature variation.
See High Altitude Guidelines in recreation.

Hypoxia is the effects of an insufficient supply of oxygen to the body. Every person can have different symptoms when suffering from hypoxia (U.S. Air Force aircrews are required to take an altitude chamber ride every three years to reinforce and identify their hypoxic symptoms). Some of the common symptoms are: lightheaded sensation, dizziness, reduced vision, and euphoria.
The Time of Useful Consciousness is a function of altitude. (Assuming you are in a plane which looses pressurization):

	20,000'  5-12 min.
	25,000'  3-5 min.
	30,000'  1-2 min.
	40,000'  9-15 sec.

Note: The boundaries of these areas vary depending on the source.
Classification Altitude pressure (mb)
(mi) (km)
Earth radius 3,963 6,378 1,000
Altitudes below are from the surface
Troposphere 0-10 0-17 1000-200
Stratosphere 10-30 17-50 200-1.5
Near Space 14
Ozone Layer 15 25
Mesosphere: 30-52 50- 85 1.5-0.01
Ionosphere 31-621 50 to >1,000
Thermosphere 52-430 85-690
Space begins 62 100
Exosphere 430-800 690-1,280
Plasmasphere 12-20,000 19-30,000
Magnetosphere 20-35,000 30-56,000

Source: TheOzoneHole.com/atmosphere.htm
See also Satellites and the International Space Station

  • Exosphere: The exosphere is the outermost layer of the Earth's atmosphere. The exosphere goes from about 400 miles (640 km) high to about 800 miles (1,280 km). The lower boundary of the exosphere is called the critical level of escape, where atmospheric pressure is very low (the gas atoms are very widely spaced) and the temperature is very low.
  • Ionosphere: The ionosphere starts at about 30-50 miles (50-80 km) high and continues up to 600 - 1,000 mi. It contains many ions and free electrons (plasma). The ions are created when sunlight hits atoms and tears off some electrons. Auroras occur in the ionosphere.
    The Ionosphere is composed of layers (D, E & F). HF AM Radio waves are refracted (bent) by the F layer, so they are effectively reflected back to earth. They are absorbed by the D layer, which disappears at night.
    High Frequency (HF) (3-30 MHz) radio waves are reflected but VHF (30-300 MHZ) and higher frequencies are usually not. The F2 layer of the Ionosphere and extends upward with decreasing density to a transition height where O+ ions become less numerous than H+ and He+. The transition height varies but seldom drops below 500km at night or 800km in the daytime.
    X-rays associated with a solar flare ionize the ionospheric D-region and increases the absorption of radio signals passing through it. These solar flares can disrupt HF radio propagation and affect GPS accuracy. See:
    Ionosphere and HF and Lower Frequency Radiation at navy.mil
    Ionosphere at NOAA.gov
  • Mesosphere: The mesosphere is characterized by temperatures that quickly decrease as height increases. The mesosphere extends from between 31 and 50 miles (17 to 80 kilometers) above the earth's surface.
  • Stratosphere: The stratosphere is characterized by a slight temperature increase with altitude and the absence of clouds. The stratosphere extends between 11 and 31 miles (17 to 50 kilometers) above the earth's surface. The earth's ozone layer is located in the stratosphere. Ozone, a form of oxygen, is crucial to our survival; this layer absorbs a lot of ultraviolet solar energy. Only the highest clouds (cirrus, cirrostratus, and cirrocumulus) are in the lower stratosphere.
  • Tropopause: The tropopause is the boundary zone (or transition layer) between the troposphere and the stratosphere. The tropopause is characterized by little or no change in temperature altitude increases.
  • Troposphere: The troposphere is the lowest region in the Earth's (or any planet's) atmosphere. On the Earth, it goes from ground (or water) level up to about 11 miles (17 kilometers) high. The weather and clouds occur in the troposphere. In the troposphere, the temperature generally decreases as altitude increases.
  • Thermosphere: The thermosphere is a thermal classification of the atmosphere. In the thermosphere, temperature increases with altitude.
  • Plasmasphere:
    See Plasmasphere at albany.edu
  • Magnetosphere:
    See Plasmasphere at albany.edu
An altitude of 120 km (75 mi) is where atmospheric effects become noticeable during atmospheric reentry of spacecraft. The Karman line, at 100 km (62 mi), also is often regarded as the boundary between atmosphere and outer space.

Weather Forecasts:
National Oceanic and Atmospheric Administration (NOAA) - National Weather Service - Western Regional Headquarters (WRH) (wrh.noaa.gov)

Natl Weather Svc (NWS) Northern California at wrh.noaa.gov/sto/
Truckee forecast at NWS forecast.weather.gov
Hydrometeorological Prediction Center (HPC)
  at (The National Centers for Environmental Prediction) hpc.ncep.noaa.gov
  HPC Quantitative Precipitation Forecasts
  5-day precipitation forecast image  
Northern California at the National Weather Service by the U. Utah
Current Tahoe Conditions from the Forest Service

The Weather Channel
Weather Central
Pacific Coast Satellite

Other California
Weather West
Tahoe Weather Links

Temperature Indexes (wind chill, heat index)
Average Relative Humidity and Heat Index (HI) for large cities
Frostbite and Hypothermia:
Heat Related Conditions:

El Niño-Southern Oscillation (ENSO) is a quasi periodic climate pattern that occurs across the tropical Pacific with a roughly 5 year cycle. It is composed of an oceanic component, called El Niño (or La Niña), which is characterized by warming or cooling of surface waters in the tropical eastern Pacific Ocean.

ENSO Alert System: El Niño Advisory


See National Weather Service Glossary 
12z - 12:00 zulu (UTC) - Time of day a weather model is run
   A model is typically run at 4 cycles per day (i.e., 00Z, 06Z, 12Z, and 18Z).
CICS - Cooperative Institute for Climatic Studies
CPC - Climate Prediction Center 
CTB - Climate Test Bed 
COLA - Center for Ocean-Land-Atmosphere Studies 
ENSO - El Niño-Southern Oscillation 
El Niño - A warming of the ocean current along the coasts of Peru and Ecuador
   that is  associated with dramatic changes in the weather patterns of the region.
ESRL - Earth System Research Laboratory 
ESSIC - Earth Systems Science & Interdisciplinary Center 
GFS - Global Forecast System - One of the  forecast models run at NCEP
GRAD - Gradient- A rate of change with respect to distance of a variable quantity,
    as temperature or pressure, in the direction of maximum change. 
GrADS -  Grid Analysis and Display System
HPC - Hydrometeorological Prediction Center at NCEP
kt - Knot- Unit of speed used in navigation, 1 kt =  1.15 MPH 
La Niña - Weather caused by nusually cool temperatures in the equatorial Pacific.
MESO - Mesocyclone- A storm-scale region of rotation
Mesoscale - The middle of three scales used to describe the size range of atmospheric processes.
    The mesoscale covers the range from a few kilometres to a few tens of kilometres.
MOS - Model Output Statistics - a technique used to objectively interpret numerical model output. 
NAM - The operational North American Meso-scale forcasting system (formerly Eta)
  Study of atmospheric phenomena on a large scale
NCEP - National Centers for Environmental Prediction at NOAA
NOAA - National Oceanic and Atmospheric Administration
NOMADS - National Operational Model Archive And Distribution System at NOAA
NWS - National Weather Service at NOAA
OSDPD - Office of Satellite Data Processing and Distribution at NOAA
PPT - precipitation
SST - Sea Surface Temperature
UTC - Universal Time Coordinated
WRH - Western Regional Headquarters of the National Weather Service
Z time - Zulu time same as UTC
Satellites and the International Space Station
Atmosphere at TheOzoneHole.com
Oxygen in the Atmosphere
Atmosphere of Earth at Wikipedia
Orbits at NASA.gov
Hurricanes | Tornadoes
Global Warming/Climate Change
Earth's atmosphere protects life on Earth by absorbing ultraviolet solar radiation - From the New Universe
Greenhouse Gases
Satellite - Software: Satellite tracking
X XM & Sirius in Orbit

last updated 1 Jul 2011