Weather Weather Measurements Measurements

and Instrumentsand Instruments

Thermometers measure air Thermometers measure air temperatures. (The average temperatures. (The average kinetic energy of air kinetic energy of air molecules).molecules).

Thermometers work because Thermometers work because matter expands when matter expands when heated. Most thermometers heated. Most thermometers are closed glass tubes are closed glass tubes containing liquids such as containing liquids such as alcohol.alcohol.

Data is recorded in degrees Data is recorded in degrees Celsius(°C) or degrees Celsius(°C) or degrees Farenheig (°F)Farenheig (°F)

ThermometerThermometer

A barometer measures A barometer measures air pressure.air pressure.

There are two types of There are two types of Barometers: Barometers: Mercury Mercury Barometer and Barometer and Aneroid Barometer.Aneroid Barometer.

Aneroid Barometers Aneroid Barometers give data in give data in Hectopascals (Hp—Hectopascals (Hp—same as millibars mb. same as millibars mb. Standard pressure is Standard pressure is 1013.25 Hp)1013.25 Hp)

BarometerBarometer

A Mercury Barometer A Mercury Barometer consists of a glass tube consists of a glass tube inserted into a dish of inserted into a dish of mercury or colored mercury or colored denatured alcohol.denatured alcohol.

*(If you build your own, *(If you build your own, don’t use mercury—it is don’t use mercury—it is poisonous) poisonous)

Barometer: How it worksBarometer: How it works

The surrounding air The surrounding air presses down on the presses down on the mercury in the dish and mercury in the dish and forces some of the forces some of the mercury up into the mercury up into the tube. The height to which tube. The height to which the mercury rises in the the mercury rises in the tube is directly tube is directly proportional to the proportional to the atmospheric pressure.atmospheric pressure.

Data is given in mm or in Data is given in mm or in of Hg (760 mm or 29.92 of Hg (760 mm or 29.92 in. is standard pressure)in. is standard pressure)

Barometer: How it worksBarometer: How it works

A psychrometer A psychrometer measures the measures the humidity of the air. humidity of the air. One of the two One of the two thermometers has a thermometers has a wick (cloth cover) wick (cloth cover) which is dipped in which is dipped in distilled water.distilled water.

PsychrometerPsychrometer

Evaporation of water Evaporation of water from the wick on the wet from the wick on the wet bulb thermometer leads bulb thermometer leads to cooling. to cooling.

Using a Using a Relative Relative Humidity TableHumidity Table, the , the temperature difference temperature difference between the two between the two thermometers gives the thermometers gives the relative humidity of the relative humidity of the air (in percent).air (in percent).

Psychrometer: How it Psychrometer: How it worksworks

This is an This is an example example of the of the type of type of table you table you would would use. use.

Relative Humidity Table:

One such One such psychrometer psychrometer is a is a Sling Sling Psychrometer.Psychrometer.

Measurements are taken by whirling the psychrometer with the handle.

An Anemometer An Anemometer measures the measures the wind speed. The wind speed. The cups catch the cups catch the winds, turning a winds, turning a dial attached to dial attached to the instrument.the instrument.

AnemometerAnemometer

Wind Vane or Weather VaneWind Vane or Weather Vane* It is a tool for * It is a tool for

measuring wind measuring wind direction (N, S, E, direction (N, S, E, W)W)

It spins on a rod It spins on a rod and points in the and points in the direction from direction from which the wind which the wind comes. comes.

Weather map Weather map symbol: blows from symbol: blows from flag to ballflag to ball

Rain GaugeRain Gauge Type of instrument Type of instrument

used by used by meteorologistsmeteorologists

Used to gather and Used to gather and measure the amount measure the amount of liquid precipitation of liquid precipitation over a set period of over a set period of timetime

Most rain gauges Most rain gauges generally measure generally measure the precipitation in the precipitation in millimetersmillimeters