Surface Weather Observations (Worldwide, every 3 Hours GMT starting at 00:00) Current and past state of the weather e.g. Rain, Fog, etc. Air temperature Dry bulb temperature (Wet bulb temperature) Maximum, minimum temperatures

Surface Observations (continued) Relative humidity Amount and type of clouds Wind speed and direction Pressure, pressure tendency Precipitation

Psychrometers – Hygrometers Measure humidity and/or dew point Sling psychrometers use wet and dry bulb thermometers.

Other instruments (many)

Earth

Clouds Aid in weather forecasting Trace atmospheric motions (e.g. satellite imagery) Produce precipitation Reflect sunlight away from Earth Absorb/emit heat radiation Absorb or rainout air pollution

Luke Howard (1772-1864) In 1803 introduced terminology for clouds based on their appearance, i.e. altitude, size, shape, and texture.

High-Level (> 20 kft) Ice crystals Cirrus (Ci) Cirrocumulus (Cc) Cirrostratus (Cs)

Mid-Level (6.5 to 20 kft) Mixed phase (i.e. water drops and ice crystals) Altocumulus (Ac) Altostratus (As)

Low-Level (up to 6500 ft) Water drops Cumulus (Cu) Stratocumulus (Sc) Stratus (St)

“Nimbo-” or “-nimbus” means cloud is producing precipitation. e.g. Cumulonimbus, Cb (thunderstorm) Nimbostratus, Ns (rain or snow)

Tower of the winds in Athens, Greece (drawn in 1762)

(18th Century reconstruction, original c 48 B.C.)

Wind Vane or Weather Vane Measures direction wind is blowing FROM

Artistic wind vanes

Wind vane on George Washington’s home at Mount Vernon

“Dove of Peace” by Joseph Rakestraw (1787)

Thomas Jefferson’s wind vane at Monticello.

Robinson cup anemometer (1795) Munro (1870)

Windmill anemometer measures wind speed and direction

Sonic anemometer Laser anemometer

Magdeburg hemispheres used to illustrate force produced by air pressure.

Water barometers Berti (1639) in Rome Guericke (c1654) in Magdeburg

In 1644, Torricelli wrote in a letter: "We live submerged at the bottom of an ocean of air."

Height of mercury is independent of shape of tube

Fortin (Mercury) Barometer

Weather glass or Thunder glass Used to measure CHANGES in atmospheric pressure (or temperature) "decreasing pressure predicts stormy weather"

Aneroid barometer – sealed metal case expands or contracts in response to variations in atmospheric pressure. High Low Levers magnify these changes, causing a pointer to move on a dial, or numbers to change on a digital read-out device.

Aneroid microbarograph

Rain gauges measure depth of precipitation that occurred. over a Rain gauges measure depth of precipitation that occurred over a (known) area, or volume of rain per unit area Basic Gauge Tipping bucket and recorder gives time