Weather

Weather is the condition of Earth’s atmosphere at a particular time and place. – Short-term: Hours and days – Localized: Town, Region or State Rain showers Snow storm Tornado Hurricane

Causes of Weather 1.Uneven distribution of thermal energy, heat, in Earth’s atmosphere. – The sun’s energy, by radiation. 2.The Earth’s tilt and revolution Described by: – Density – Air pressure – Temperature – Wind – Water

Density Air consists of atoms and molecules that have mass and occupy space, volume = density. – Colder air: Particle Speed = slower molecule speed Volume = lower volume Density = increased density – Cold air sinks! – Warmer air: Particle Speed = faster molecule speed Volume = increased volume Density = decreased density. – Hot air rises! Convection

Air Pressure Air pressure – the result of the weight of a column of air pushing down on an area. – The closer to Earth’s surface the higher the air pressure. Sea level = greatest air pressure – The farther away from Earth’s surface, altitude or elevation, the lower the air pressure. On top of a mountain = lowest air pressure.

Factors Affecting Air Pressure 1.Altitude is greatest at point: 2.Air pressure is greatest at point: 3.Density of the air is least at point: A B A ElevationAir PressureDensity High Low High

Measuring Air Pressure 1.Mercury BarometerMercury Barometer a.Mercury adjusts to the amount of pressure pushing down on it. As air pressure increases, the mercury in the tube rises/high. – Sunny and Clear As air pressure decreases, the mercury in the tube falls/low. – Cloudy and Rainy

Measuring Air Pressure 2. Aneroid Barometer a.Aneroid = “without liquid” When air pressure increases, the walls push in, higher readings – Fair to Dry conditions When air pressure decreases, the walls bulge out, lower readings – Stormy and Rainy Low High

Temperature Air temperatures vary over time due to the thermal energy content of the atmosphere. – About half of the sun’s energy is absorbed and converted to heat by Earth’s surface. – The other half is either absorbed by the atmosphere or reflected back into space.

Factors Affecting Temperature 1.Earth’s rotation – Earth rotates, spins, once in 24 hours. Half of earth is facing the sun – Warmer temperatures Half of earth is facing away from the sun. – Cooler temperatures Night Day

Factors Affecting Temperature 2.Earth’s tilt and Revolution – Earth’s axis is tilted at 23.5 off perpendicular. – Earth orbits once around the sun in 365 days (1 year) Causes different amounts of sunlight to be absorbed or scattered during different seasons.

Factors Affecting Temperature 3. Clouds – Thicker clouds reflect more solar radiation 4. Surface Color – Lighter colors reflect more solar radiation Snow and sand – Darker colors absorb more solar radiation Forests 5. Surface Texture – The rougher the surface the more solar radiation gets trapped and is absorbed.

Solar Radiation Reflection Which two surfaces absorb the greatest amount of the sun’s energy? Which two factors reflect the most solar radiation? On a winter day, where would you be warmer – a sandy beach or a grassy field? Forests and water – reflect the least amount of solar radiation Thick clouds and snow = 75-90% Grassy field = absorbs more sunlight

Charting Air Pressure & Temp Isobars – similar air pressure recordings connected by a solid line. Low Pressure: Cold Wet and Stormy High Pressure: Hot Warm and Humid Close Lines: Windy Farther Apart Isobars: Calm Air Pressures move from regions of High to regions of Low Isobars L H

Each isobar differs from the next isobar by ______ millibars. The lowest air pressure reading on the map is _____ millibars. What weather conditions would they most likely be experiencing? The highest air pressure reading on the map is ______ millibars. What weather conditions would they most likely be experiencing? What pressure range is New York City located in? Stormy 1016 Change Low High

Reading Isotherms Isotherms – Similar temperature recordings connected by a solid line. NYC 1.Pittsburgh, Cincinnati and Indianapolis are all at this temperature: 2. Name one city that is currently at The farther South you travel, the temperature gets: 40 NYC, DC, Richmond Roanoke warmer South

Where Does Weather Occur? Weather takes place in the atmosphere. – The layer of gases that surround planet Earth. Importance of the Atmosphere: 1.Make conditions on Earth suitable for living things. 2.Contains oxygen (O)and other gases. 3.Keeps Earth warm enough for liquid water to exist. 4.Protects organisms from radiation from the sun and meteoroids.

Composition of the Atmosphere Made up of a mixture of gases: – Nitrogen – 78% The most abundant gas – Oxygen – 21% – Argon -.93% – Carbon Dioxide -.036% Nitrogen – 78% Oxygen – 21% Argon & Carbon Dioxide – 1%

Layers of the Atmosphere The atmosphere is divided into 4 main layers based on temperature and air pressure changes. 1.Troposphere 2.Stratosphere 3.Mesosphere 4.Thermosphere

The Troposphere Closest to Earth’s surface. – Earth’s weather occurs here! 0-16 km above sea level Contains almost all the mass of the atmosphere As altitude increases, temperature decreases – 1 km increase = 6.5C cooling. At -60C it levels off.

The Stratosphere Extends from 16-50km above the earth’s surface Increases in temperature as altitude increases due to the ozone layer. – Protective layer that absorbs the sun’s energy and converts it to heat.

The Mesosphere As altitude increases, temperature decreases. – The coldest layer at -90C 50-80km above the Earth‘s surface. Protective layer where most meteoroids burn up.

The Thermosphere Extends from 80km to infinity – has no outer limit. – Divided into two different sections: 1.Ionosphere – aurora borealis 2.Exosphere – satellites orbit Earth. The hottest layer at 1800C – due to heat coming in.

Aurora Borealis A natural light display caused by the collision of energetic charged particles with atoms in the high altitude atmosphere