This document defines and describes several key atmospheric variables: - Air temperature is measured with a thermometer in degrees Celsius, Fahrenheit, or Kelvin and shown on weather maps with isotherms. Solar radiation is the main source of heat for the atmosphere. - Air pressure is measured with a barometer in units like millibars and shown on maps with isobars. Pressure is affected by altitude, temperature, and moisture and influences wind speed. - Moisture in the air is measured with instruments like a hygrometer and shown as dew point temperature or relative humidity on station models. Dew point is the temperature at which air becomes saturated.

1. Atmospheric VariablesAtmospheric Variables
08/22/1308/22/13

2. Air TemperatureAir Temperature
 Instrument used toInstrument used to
measure:measure:
 ThermometerThermometer
 Units:Units:
 °C, °F, °K°C, °F, °K
 How it is shown on aHow it is shown on a
weather map:weather map:
 IsothermsIsotherms
Important Information:Important Information:
 Solar radiation is theSolar radiation is the
main source of heatmain source of heat
energy for theenergy for the
atmosphere.atmosphere.
 The amount of solarThe amount of solar
radiation is affected by:radiation is affected by:
 Hours of sunlight/dayHours of sunlight/day
 Reflection, refraction, andReflection, refraction, and
absorbtionabsorbtion

4. IsothermsIsotherms

5. Air PressureAir Pressure
 Instrument used to measure:Instrument used to measure:
 BarometerBarometer
 UnitsUnits
 cm, inches, millibarscm, inches, millibars
 How it is shown on aHow it is shown on a
weather map:weather map:
 Isobars, H and L pressureIsobars, H and L pressure
Important Information:Important Information:
 Affected by altitude,Affected by altitude,
temperature, and moisturetemperature, and moisture
content.content.
 Warm air = less dense = lowWarm air = less dense = low
pressurepressure
 Cold air = more dense = highCold air = more dense = high
pressurepressure
 Dry air = high pressureDry air = high pressure
 Moist air = low pressureMoist air = low pressure
 High altitude = low pressureHigh altitude = low pressure
 Pressure differences affects windPressure differences affects wind
speedspeed

9. Moisture in the AirMoisture in the Air
 Instrument used to measure:Instrument used to measure:
 Hygrometer, psychrometerHygrometer, psychrometer
 UnitsUnits
 % relative humidity% relative humidity
 °C, °F Dew point temperature°C, °F Dew point temperature
 How it is shown on aHow it is shown on a
weather map:weather map:
 Dew point temperature isDew point temperature is
shown on a station modelshown on a station model
Important Information:Important Information:
 Dew point temperature is theDew point temperature is the
temperature at which air istemperature at which air is
saturated.saturated.
 Relative Humidity is the ratio ofRelative Humidity is the ratio of
the amount of water vapor inthe amount of water vapor in
the air to the maximum amountthe air to the maximum amount
that it can hold at thatthat it can hold at that
temperature.temperature.
 Absolute humidity is the numberAbsolute humidity is the number
of grams of water vapor in oneof grams of water vapor in one
cubic meter of air.cubic meter of air.

10. Air MovementAir Movement
 Instrument used to measure:Instrument used to measure:
 Anemometer (speed)Anemometer (speed)
 Wind Vane (direction)Wind Vane (direction)
 UnitsUnits
 Km/h, mi/h, knotsKm/h, mi/h, knots
 N, E, S, WN, E, S, W
 How it is shown on aHow it is shown on a
weather map:weather map:
 Isotachs or on a station modelIsotachs or on a station model
Important Information:Important Information:
 Wind ALWAYS blows from highWind ALWAYS blows from high
pressure to low pressure and ispressure to low pressure and is
influenced by the Coriolis Effect.influenced by the Coriolis Effect.
 In High pressure (anticyclone)In High pressure (anticyclone)
winds blow out from the centerwinds blow out from the center
and clockwise.and clockwise.
 In Low pressure (cyclone) windsIn Low pressure (cyclone) winds
blow toward the center andblow toward the center and
counterclockwise.counterclockwise.

11. Air TransparencyAir Transparency
 How it is shown on aHow it is shown on a
weather map:weather map:
 a station modela station model
 Visibility:Visibility:
 Horizontal distance theHorizontal distance the
eye can see (mi)eye can see (mi)
 Cloud Cover:Cloud Cover:
 Fraction/percentage ofFraction/percentage of
the sky that is obscuredthe sky that is obscured
(covered) by clouds(covered) by clouds
 Cloud Ceiling:Cloud Ceiling:
 The base height (bottom)The base height (bottom)
of the cloud layers.of the cloud layers.
 Measure with a ceilometerMeasure with a ceilometer
which uses light pulseswhich uses light pulses
and photoelectricand photoelectric
telescope.telescope.
Base
height