Weather: Chapter 14 Sec 14.1 Meteorology Meteorologist The study of atmospheres and weather Meteorologist Someone who studies atmospheres and weather.

Sec 14.2:Weather Systems Weather systems Set of temperatures, wind pressures, moisture conditions for a region that moves as a unit for a period of days. In N. America they are pushed west to east by mid-latitude westerlies.

Four main air masses of N. America Large body of air in which the temperature and moisture content at a specific altitude are fairly uniform. Air mass stays stationary for a period of time Can be small 100Km or large 1000Km Four main air masses of N. America Maritime polar Continental polar Maritime tropical Continental tropical

Continental air masses Maritime air masses Formed over water Are moist, bring rain Continental air masses Formed over land Are dry Polar Formed at poles Are cold Tropical Formed around equator Are warm

Fronts: Warm Front: Leading edge of a moving air mass. Warm air moves into/over a cold air mass and carries moisture . Creates nimbostratus clouds. Direction of air mass movement is indicated by the direction of the “bumps”

Cold front Cold air moves into/under a warm air mass. Creates cumulus clouds, heavy precipitation.

Stationary Front Boundary between warm air mass and cold air mass remains still for some time. Appears on weather maps as:

Occluded front A cut-off or closed front. As a storm grows,one front rotates around the storm and catches another. This forms an occluded front, which is the boundary that separates the new air mass (to the west) from the older air mass already in place.

Fronts and Systems:

Regional Weather General weather conditions of a region such as temperature, humidity, precipitation, and winds

Convection Current When a temperature difference occurs in a fluid (water or atmosphere). Hot fluid rises and cold fluids sink which create a current or movement in the fluid

Sec 14.4 Regional Weather 1. Thermals The uneven heating of the Earth’s surface from radiation Are created when; sun heats land, energy absorbed by the land heats the air air warms, expands and rises.

Sea Breeze: day time A cool breeze flowing over the land from the sea that occurs during the day when land warms because a convection current is created when: Warm air over land rises Sea breeze moves inland replacing the air Upper cool air cools and sinks

Land breeze A cool breeze blowing towards the sea at night because land cools faster at night and the waters are warmer Warm air over water rises Cool air over land sinks Land breeze moves out over water to replace warm air

Precipitation Water which can change form in the atmosphere. Solid or liquid form (depends on ground and air temperatures). Found in cumulus clouds. Made via condensation, freezing and sublimation.

Dew Created when moisture in air contains condenses on a cool surface near the ground. Frost sublimation on a very cold surface. Drizzle Fine water droplets Less than 0.5 mm in diameter.

Hail Forms in troposphere (in thunder clouds) Ice pellets move up and down in troposphere. Each rise upward passes them through cold water droplets. They grow larger as the freezing water droplets form more and more ice layers (~ 20 layers).

Ice pellets/sleet Rain Freezing rain Small hard pieces of ice. Formed as Snow falls through layer of warm air and melts a little. It them passes through cold air and re-freezes. Rain Falling water droplets Up to 5mm in diameter. Freezing rain Rain that hits a very cold surface and freezes immediately.

Snow Forms when air temp is below 0 degrees Celsius. Water vapour crystallize on dust or other particles. Ice crystals combine and form snow flakes. (may turn into sleet/ ice pellets) if it passes through warm air then cold again.

Meteorological data is collect using: Thermometers: temperatures Hydrometer/psychrometer: humidity Aneroid barometer: barometric/air pressure Anemometer: wind speed, direction Rain gauge: level of precipiatation