WEATHER & THE ATMOSPHERE

Used to measure the 5 major parts of weather observation Weather Instruments Used to measure the 5 major parts of weather observation 1. Atmospheric pressure 2. Humidity 3. Precipitation 4. Wind 5. Temperature

Tools: Atmospheric Pressure Barometer: Measures air pressure, millibars or inches of mercury

Tools: Humidity Hair Hygrometer: (Sling) Psychrometer: Uses hair to measure humidity, hair expands and contracts in response to water vapor content in the air. (Sling) Psychrometer: Difference between wet bulb and dry bulb used to determine relative humidity.

Tools: Precipitation Rain Gauge: Simple funnel with marks

Tools: Wind Anemometer – Wind Speed Wind Vane – Wind Direction km per hour mi per hour Wind Vane – Wind Direction Cardinal units or numerical

Measuring Upper-Atmospheric Conditions Radiosonde: Carried aloft by a helium balloon. Measures upper-atmospheric. conditions: Relative humidity, air pressure, air temperature. Information sent back to scientists via radio… waves.

Not weather satellites, but still cool Carry cameras Upper level Cloud speed, direct. Hurricane observation Infrared reading of cloud tops Not weather satellites, but still cool

The study of weather = METEROLOGY Weather is the condition of the atmosphere at any given time or place Much of weather forecasting and prediction can be accomplished by direct observation To predict weather, you must make observations of the clouds, wind, temperature, humidity, air pressure and precipitation

ATMOSPHERIC VARIABLES things that can be measured and change from moment to moment Temperature Air Pressure Wind Speed and Direction Water Content & Humidity Cloud Cover Precipitation Others (dust, transparency, pollen, etc)

TEMPERATURE Measures the average kinetic energy of molecules. Heat enters the atmosphere from the sun as solar radiation (Insolation) is an average of all of the kinetic energies- hence Average Kinetic Energy

3 ways to Measure temperature: Fahrenheit Water freezes at 32° Water boils at 212° Celsius AKA Centigrade (100 levels) Water freezes at 0° Water boils at 100° Makes more sense and is easier to make a thermometer Kelvin Same scale as Celsius but 0 means zero energy No degrees mark for Kelvin 0K means that all atomic vibrations stop.

Air Pressure the weight of the air in a certain area Sinking air pushes down more- cold air is dense air and brings high pressure Hot air is less dense air and brings low pressure Air pressure is measured using an instrument called a barometer It is measured in inches (height of the mercury column in the barometer), or with the metric units called millibars

Air pressure drops with increasing altitude (less air) Weather maps show sea level air pressure It ranges from 960mb – 1050mb

Air in the Atmosphere Relationships Air Temperature Density Air Pressure Evaporation Molecular reaction Warm Less Dense Low Pressure High evaporation Loose molecule particles Moving fast Cold More Dense High Pressure Low evaporation Tightly packed molecules

Changes in Air Pressure Temperature- warm air is lighter than cold air! Humidity- humid (moist) air is lighter than dry air!! Water vapor (H2O) weighs less than the N and O gases that it pushed out Winds are caused by the unequal heating of the atmosphere (remember that temperature causes changes in air pressure)

Water Vapor in the Air The amount of water vapor in the air depends on the air temperature The warmer the air, the more water vapor it can hold (think of those hot, humid summer days)

Relative Humidity the amount of water vapor in the air, compared to how much water vapor it could hold at that temperature Relative humidity is a percent measurement Air with 100% humidity is said to be saturated Precipitation will occur

Finding Relative Humidity use an instrument called a hygrometer One particular type of hygrometer is called a sling psychrometer This instrument is made of two thermometers attached two a handle One thermometer has a piece of gauze which is the soaked with water - This is called the WET BULB The other thermometer is called the DRY BULB These thermometers are swung in the air for a few minutes, and then the temperatures are recorded (take the wet bulb temperature first) The wet bulb thermometer should have a lower temperature, since it removes heat from the thermometer as water evaporates from it

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Condensation and Dew remember that air’s ability to hold moisture decreases as the temperature decreases As the air cools, its relative humidity increases When the relative humidity reaches 100% (saturated), the water comes out of the air as liquid droplets The temperature at which this will occur is called the dew point

Condensation and Dew Condensation can only occur if the water has something to condense on Tiny particles in the air on which water condenses is called condensation nuclei This can be dust, salts, chemicals from burning fuel, etc. * Water vapor that condenses on the ground is called dew (think of walking across wet grass in the morning) If the dew freezes on the ground, it is called frost Water vapor condensing in the air forms clouds If the cloud forms close to the ground, it is called fog