Unit 4 Weather Dynamics Chapters 13 16 Weather

Unit 4: Weather Dynamics Chapters 13 -16

Weather Dynamics Weather dynamics is the study of how the motion of water and air causes weather patterns. n The main components of Earth that affects weather are the atmosphere, the land forms, and water in the forms (solid, liquid, and vapor). n

Web sites to know and love! n Environment Canada ¨ http: //weatheroffice. ec. gc. ca/canada_e. html

Weather vs. Climate n Weather - is the set of environmental conditions encountered from one day to the next. ¨ “Today n is …. ” Climate - is the set of environmental conditions averaged over many years. ¨ What is the climate of central Labrador? ¨ How does our climate compare to the Avalon Peninsula?

EARTH’S ENERGY BALANCE (p. 504 - 507) n n n The sun is our primary energy source and this energy is transferred to air, land water Particles that make up the air, land water absorb the energy and this effects their movement which in turn determines weather patterns Thus the sun is the ultimate cause of changing weather systems on a global scale

Kinetic Molecular Theory 1. 2. All matter is made up of particles that are in constant motion because they possess kinetic energy (energy of motion) The physical state of the substance is determined by the speed at which the particles of a substance move as well as the distance between the particles

3. Temperature is a measure of the average kinetic energy of the particles of a substance or how “hot” or “cold” something is ¨ 4. The greater the temperature, the greater the average kinetic energy and thus the faster the particles move Heat (a. k. a. thermal Energy) is the total kinetic energy of all particles of a substance. n It is transferred from a warm object to a cooler one due to a difference in temperature

Methods of heat transfer (these methods distribute energy around the Earth) 1. Radiation the transfer of energy by waves. ¨ does not require a physical medium ¨ Example: n visible light ¨ reaches us from the sun via empty space

2. Conduction n transfer of energy through the collision of particles n Some materials are better conductors of heat than others ¨ Metals are generally better conductors than some materials such as rock, sand, etc.

3. Convection n transfer of energy vertically by movement of particles in a fluid (particles that flow), including liquids (eg. water) and gases (eg. air) 4. Advection n the transfer of energy horizontally by movement of particles in a fluid ( water or atmosphere).

Reflection and Absorption of Radiant Energy n Not all of the solar energy reaching the Earth’s atmosphere actually reaches the land water. ¨ See n p. 506 Fig. 4 of your text. Some solar radiation gets reflected back into space. How much radiation that is reflected at any given time is dependent upon the surface features.

n albedo ¨ percentage of light reflected by an object ¨ this determines how much radiation is reflected by an object ¨ Examples: n Clean snow has a high albedo whereas black soil has a low albedo.

n heat sink ¨ Any material that absorbs energy and becomes warmer ¨ Examples: n The oceans are good heat sinks whereas soil and rock are poor heat sinks. ¨ The heat capacity of a substance will indicate whether a substance is a good heat sink or not. (Table 5, p. 506)

Specific Heat Capacity the measure of how much heat a substance requires to increase it’s temperature one degree. ( Or how much energy it releases as it’s temperature decreases. ) n P. 506 Figure 5 in your text shows the heat capacity of some common substances. n

Types of Heat n Latent heat of fusion (melting) ¨ The amount of heat needed to change a unit mass of a substance from a solid to a liquid. n Latent heat of vaporization ¨ The amount of heat needed to change a unit mass of a substance from a liquid to a gas.

n ‘Latent’ means ‘hidden’. When a substance changes state, the substance either absorbs or releases energy without changing temperature. n A substance will have its own latent heats of Fusion and Vaporization constants. Vaporization requires more energy than Fusion. ¨ Water has latent heat of fusion of 3. 3 x 105 J/kg and a latent heat of vaporization of 2. 3 x 106 J/kg

The Atmosphere n The atmosphere consists of air and moisture that surrounds the Earth. The common atmospheric gases are oxygen, nitrogen, carbon dioxide, and water vapor. n The density of the atmosphere varies with height above sea level (most dense at sea level).

n Altitude is the height (m or km) above sea level. n The atmosphere is thicker above the equator than it is above the poles. Warmer air takes up more space because warmer air expands.

Six layers of the Atmosphere n 1. Troposphere - the layer closest to the Earth’s surface. Altitude of 8 km at the poles and up to 16 km at the equator. Most of our weather occurs in this layer. The upper part of this layer is colder than the lower part. n 2. Tropopause – the transition layer between the troposphere and stratosphere n 3. Stratosphere - a dry layer located between 12 km and 50 km above the Earth’s surface. This layer contains high concentrations of ozone. Ozone protects the Earth from harmful doses of ultraviolet given off by the sun. The ozone also cause the stratosphere to be warmer.

Atmosphere (continued) n 4. Mesosphere - the middle layer extends from 50 km to 80 km. This layer has low concentrations of gases and low temperatures. n 5. Thermosphere - extends from 80 km to 500 km. It is in this layer that X-rays (from the sun) are absorbed. This absorption by the few air molecules in this layer gives the molecules energy producing higher temperatures. The sun’s radiation cause the particles in this layer to become electrically charged to produce the northern and southern lights. n 6. Exosphere - the thin outer part of our atmosphere. There are very few particles (mainly hydrogen) in this layer.

Gradients n Temperature Gradient ¨ The change in temperature over a distance. ¨ Example: The troposphere has a temperature gradient of n -6° C per 1000 m (vertical distance) n

n Pressure Gradient ¨a measure of the amount the atmosphere pressure changes across a set distance. ¨ can be vertical or horizontal. A line graph or closed lines on a map can indicate a pressure gradient. n To show a high pressure, lines are bunched together. To show low pressure, lines are spaced further apart. (See p. 512 for illustrations) n

The Hydrosphere n The hydrosphere is made up of both fresh and salt water found on Earth. n Approximately 70% of the Earth’s surface is water. ¨ Only 2. 5 % of all water is fresh. ¨ Of this 2. 5 % , most of the fresh water on Earth is frozen in glaciers and in the ice caps.

The Water Cycle (p. 523) Radiant energy from the sun causes water to evaporate or ice to sublimate. n Transpiration in plants adds to the formation of water vapor. n The water vapor rises , cools, and condenses into fog, mist, and clouds. n This precipitation falls to the Earth and the process repeats. n

n Water is found on Earth in: ¨ oceans (most of the hydrosphere) ¨ lakes ¨ rivers ¨ ground water (water underground) ¨ ice (glaciers and snow) ¨ water vapor (clouds)

Phase Changes of Water n Evaporation - process of changing a liquid to a vapor. (l → g) n Sublimation - process of changing a solid to a vapor (s → g) n Condensation - process of changing a vapor to a liquid. (g → l)

Types of Precipitation 1. drizzle n fairly steady, light precipitation n drop size: smaller than rain (0. 5 mm diameter)

2. Rain n separate drops of water fall to the Earth's surface from clouds

3. freezing rain n begins as snow, falling from a cloud towards earth and melts completely on its way down through a layer of relatively warm (above freezing) air. n As it falls toward the earth's surface, it encounters a layer at lower level of colder air and becomes supercooled n This water will freeze on impact with any object it then encounters. n The ice can accumulate to a thickness of several centimetres

4. Snow n Crystallized water (ice) n Consists of snowflakes that fall from clouds

5. Hail n consists of balls or irregular lumps of ice (hailstones) n 5 mm– 50 mm in diameter on average n much larger hailstones result from severe thunderstorms

6. Dew n In the evening, surfaces will cool by radiating its heat n Atmospheric moisture will condense at a rate greater than that of which it can evaporate n Water droplets then form on surfaces

7. Frost n Ice crystals that grow on a cold surface n Results from water vapour in the air coming in contact with that cold surface

Clouds and Fog Solar energy heats up water causing evaporation. n This mixture of water vapor and heated air rises in the atmosphere. n As the moist air rises, air pressure and temperature lowers, causing condensation to occur. n If the temperature drops low enough ice crystals will form. n

Three categories of Clouds 1. Convective Clouds n formed when air near the ground absorbs energy from heated surfaces and rises in the atmosphere. n The water vapor cools, condenses, forming clouds.

2. Frontal Clouds n form where the leading edge, or front, of a large moving mass of air meets another mass of air at a different temperature. n Warm air contains more water vapor and will be pushed up by a cold air mass. n The rising warm air will cool and water vapor condenses to form clouds.

3. Orographic Clouds n form when air moves up a mountain, expands at the lower pressure, and cools. n Clouds are formed when water vapor in this air cools and condenses.

Cloud Classification Two General Shapes 1. Cumulus clouds n these clouds have a rounded billowing shape. n They tend to grow vertically, usually indicating unstable weather.

n formed as a result of: ¨ convection currents ¨ orographic lifting ¨ when a cold air front moves into a warm air mass. ¨ They look fluffy, like cotton balls

n 2. Stratus clouds ¨ these clouds have a stretched- out, flattened shape. ¨ They tend to grow horizontally and usually indicate stable conditions. ¨ They usually form where the front of a warm air mass overruns a cold air mass. ¨ They look stretched like cotton candy

Further classification n According to height: ¨ alto - medium height clouds ¨ cirrus - high-level clouds n Also: nimbus - rain-holding cloud.

Fog n Fog is actually a cloud at ground level. Air near the ground cools (especially on clear nights ) and water vapor condenses into fog.

n Fog is produced when: ¨ 1. On clear nights, energy from the Earth’s surface radiates upward but is not reflected back to Earth by clouds. The air near the ground cools, allowing water vapor to condense into fog. ¨ 2. When warm air passes over a snow-covered ground or moist sea air drifts over a cold current (or seashore), fog forms. ¨ 3. When warm air rises up the sides of a mountains during orographic lifting.

Global Geography n n n Longitude - the angle measured east or west from the 0° line, which passes through Greenwich, England. Latitude - the angle measured south or north of the equator. Equatorial Region - region located between the Tropic of Cancer (23. 5 N)and the Tropic of Capricorn (23. 5 S). Polar Regions - Region north of the Arctic Circle (67. 5 N) and the region south of the Antarctic Circle (67. 5 S). Mid-latitude Regions - Regions between the tropics and the polar regions.

Prevailing Winds A wind is a movement of air in the atmosphere. n Prevailing winds are winds that affect large areas/weather around the world. n Winds are affected by the Earth’s rotation. n The apparent change in direction of a moving mass in a rotating system is called the Coriolis Effect. n

Major Prevailing Winds 1. Polar Easterlies ¨ near the poles , the air is cold and dense. ¨ This air sinks and moves toward the equator. ¨ The Earth’s rotation cause this air mass to twist to the right in the northern hemisphere (left in South) causing the easterlies.

2. Mid-latitude Westerlies n At 30° latitude, some of the warm air from the equatorial convection current meets the cold polar air and a low pressure forms around 60 ° latitude. n The surface air moving north twists to the right in the northern hemisphere (left in Southern hemisphere) to form the mid latitude westerlies.

3. The Trade Winds n the sun heats up everything at the equator. n Hot air rises leaving behind a low pressure. n This rising air moves northward, cools and becomes more dense and falls around 30 ° latitude. n This air moves back towards the equator (low pressure area) producing the trade winds. n This air movement twist to the right in the northern hemisphere to form the northeast trade winds (they twist left in the southern hemisphere - southeast trade winds)

4. Jet Streams n high speed winds in the upper troposphere near the middle latitudes. n This is due to the different thickness of the troposphere. ¨ Where the troposphere is thicker (equator) the atmospheric pressure is greater. n The higher pressure air at the equator will move northward while twisting.