WEATHER DYNAMICS Science 10 – May 2013

Weather - Meterology Video

WHAT YOU SHOULD RECALL : ABOUT WEATHER

What is weather??  Weather is the physical conditions of the atmosphere at a specific time and place.  Weather can include: temperature, precipitation (rain/snow), humidity, atmospheric (air) pressure, sky cover and wind speed and direction.

What is weather??  The Sun’s energy or solar energy is very important in weather.  Solar energy is absorbed by the land, oceans and atmosphere.

What is weather??  Solar energy is absorbed by land and oceans, it also warms the air above them.  Land and water cool at different rates which causes a temperature difference that can affect weather conditions.

Precipitation  Evaporation is the result when water absorbs the Sun’s energy and is absorbed into the air.  When this moist air cools, it condenses and falls as precipitation (rain/snow)  These steps continue in a cycle. This cycle is referred to as the water cycle.

Clouds  Clouds are composed of water droplets or ice crystals that are suspended in the atmosphere.  There are 10 different types of clouds that are classified by their shapes and by their height above the Earth’s surface (altitude) where they form.

Cloud types  Cirrus  Cirrostratus  Cirrocumulus  Cumulonimbus  Altocumulus  Altostratus  Cumulus  Stratus  Nimbostratus  Stratocumulus

Types of Clouds  Cirrus : generally characterized by thin, wispy strands  Cirrostratus : cloud is a high, thin, generally uniform stratiform genus-type, composed of ice-crystals.  Cirrocumulus : cirrocumulus includes a small amount of liquid water droplets, although these are in a supercooled state.  Cumulonimbus : is a dense towering vertical cloud associated with thunderstorms and atmospheric instability, forming from water vapour carried by powerful upward air currents. Cumulonimbus may form alone, in clusters, or along cold front squall lines.  Altocumulus : characterized by globular masses or rolls in layers or patches, the individual elements being larger and darker than those of cirrocumulus and smaller than those of stratocumulus.

Types of Clouds  Altostratus : characterized by a generally uniform gray to bluish-gray sheet or layer, lighter in color than nimbostratus and darker than high cirrostratus. The sun can be seen through thin altostratus, but thicker layers can be quite opaque.  Cumulus : are a type of low-level cloud that can have noticeable vertical development and clearly defined edges.  Stratus : the term stratus is used to describe flat, hazy, featureless clouds of low altitude varying in color from dark gray to nearly white. Stratus clouds may produce a light drizzle or snow  Nimbostratus : is characterized by a formless cloud layer that is almost uniformly dark grey  Stratocumulus : A stratocumulus cloud belongs to a class of clouds characterized by large dark, rounded masses, usually in groups, lines, or waves, the individual elements being larger than those in altocumuli.

WHAT YOU SHOULD RECALL: ABOUT THERMAL ENERGY AND HEAT

Thermal energy and heat  All matter is made up of extremely small particles.  These particles are constantly in motion and which produces a type of energy referred to as kinetic energy.  Thermal energy is the total kinetic energy of all particles in a substance.

Thermal Energy and Heat  All particles do not all have the same amount of kinetic energy.  The temperature of a substance is a measure of the average kinetic energy of its particles.  When particles are the same size, the faster-moving particles have more kinetic energy than the slower-moving particles.

Thermal Energy and Heat  The particles of any solid substance move more slowly and have less kinetic energy than those of a liquid or gaseous substance.  Gaining or losing thermal energy causes a substance to change state. Thermal energy can be transferred in three ways: radiation, convection and conduction.

Thermal Energy and Heat  Radiation: is thermal energy transfer in which atoms or molecules give off energy as electromagnetic waves.  Convection: is a thermal energy transfer by the movement of heated material from one place to another.  Conduction: is the thermal energy transfer between two objects or substances that are in direct contact.

Thermal Energy and Heat

WHAT YOU SHOULD RECALL: ABOUT FLUIDS, DENSITY AND PRESSURE

Fluids, Density and Pressure  Fluids take on the shape of the containers that hold them.  Density is a measurement of mass per volume.  Density also refers to how closely particles are packed together in a substance.  The density of a fluid changes with temperature.  When a fluid is heated, it has more thermal energy and its particles move faster.  These particles collide more and spread out to fill a greater volume. = a decrease in density

Fluids, Density and Pressure  Pressure is a force that is applied to a given area.  The density of a fluid changes with pressure.  Since the same numbers of particles are in the fluid, it is more dense.

Humidity “Humidity is the experience of looking for air and finding water”  Humidity is the amount of water vapour present in the air. **Warm air can hold more water vapour than cold air.

Humidity  Relative humidity is the amount of water vapour in the air expressed as a percentage of the amount of vapour that the air would have if saturated.

Relative Humidity

Humidity  Absolute humidity is the actual quantity of water in the air, in grams of water vapour per kilogram of air.  Saturated air is when there is as much water vapour in the air as the air can hold.

Absolute Humidity

Saturated Air  A : Condensation  B : Evaporation  C : Saturated Air

Measuring Humidity  Relative humidity is usually measured with a hygrometer of which there are several types.  Sling psychrometer  Analog hygrometer  Digital hygrometer

Humidity and the Humidex Scale  The Humidex scale was created by Environment Canada.  This scale takes into account both the temperature and the relative humidity of the air.  The Humidex value indicates how warm a given temperature will feel to the average person when relative humidity is taken into account.

Humidity and the Humidex Scale  On a summer day when the relative humidity is high, you feel much hotter than when the temperature is the same but it is less humid.  A weather forecast may indicate that the temperature is 35 degrees Celsius, but that it feels like 40 degrees Celsius on the Humidex Scale.  Why do you experience the air around you as warmer?

Humidex from Temperature and Relative Humidity Readings