WEATHER AND CLIMATE

Weather Patterns

High-pressure system – large body of circulating air with high pressure at its center and lower pressure outside the system; brings sunshine and good weather Low-pressure system – large body of circulating air with low pressure at its center and higher pressure outside the system; brings clouds and precipitation

Air mass – large bodies of air that have uniform temperature, humidity and pressure Air masses are classified by temperature and moisture – those formed over water are called maritime, those formed over land are called continental; warm masses are tropical and cold are polar

In the continental United States, air masses are commonly moved by prevailing westerlies and jet streams.

Colliding air masses can form four types of fronts: cold fronts – cold air moves under warm air forcing warm air up warm front – move slowly and bring warm, humid air stationary front – forms when a cold mass meets a warm mass but neither have enough force to move the other occluded front – warm air mass is caught between two cold air masses

Storm – violent disturbance in the atmosphere called severe weather thunderstorms – small storm accompanied by thunder and lightning formed from large cumulonimbus clouds tornado – rapidly, whirling, funnel-shaped cloud that reaches down from a storm cloud and touches the Earth’s surface formed when thunderstorm updrafts begin to rotate

Storm cont. hurricane – intense tropical storm with winds exceeding 119 km/hr formed over warm ocean water as a low-pressure area blizzard – violent winter storm characterized by freezing temperatures, strong winds and blowing snow

Weather Forecasts

Meteorologist – scientist who study the causes of weather and try to predict it; use maps, charts and computers to analyze data to prepare weather forecasts Surface report – description of a set of weather measurements made on Earth’s surface Upper-air report – describes wind, temperatures, and humidity conditions above Earth’s surface

Doppler radar – specialized type of radar that can detect precipitation as well as the movement of small particles, which can be used to approximate wind speed

Station models – diagram that displays data from many different weather measurements for a particular location:

Isobars – lines joining places on a map that have the same air pressure Isotherms – lines joining places that have the same temperature

Climates of Earth

Scientists classify climates using a system developed by Wladimir Köppen around 1900 that uses two major factors: temperature and precipitation. The system identifies six broad climate regions: Tropical Climate tropical wet – year-round heat and heavy rainfall; dense forests called rainforests tropical wet-and-dry – have less rainfall and distinct dry and rainy seasons; savannas or tropical grasslands found here

Dry Climate arid regions – also called deserts get less than 25 cm of rain every year semiarid regions – also called steppes, are usually located on the edges of deserts, enough rainfall for short grasses to grow

Temperate Marine Climate – humid with mild winters marine west coast – humid air brings cool, rainy summers and mild, rainy winters humid subtropical – climates are wet and warm, but not as hot as tropics Mediterranean – summers are drier and warmer, winters are cool and rainy

Temperate Continental Climate – only in Northern Hemisphere humid continental – constantly changing weather subarctic – line north of humid continental; summers are short winters are long and bitterly cold

Polar Climate ice caps – covered with ice and snow and always at or below freezing tundra – short, cool summers followed by bitterly cold winters Highlands – temperature falls as altitude increases, so highland regions are colder than regions that surround them

Factors that Influence Climate

Climate – the long-term average weather conditions that occur in a particular region; determined by two main factors: temperature and precipitation Microclimate – small areas with climate conditions that differ from those around them

Main factors that influence temperature: Latitude – Earth’s surface is divided into three temperature zones based on latitude Tropical zone (23.5ᵒN – 23.5ᵒS latitude) – area near the equator that has warm climate since it receives direct sunlight all year Polar zone (66.5ᵒ-90ᵒN lat to 66.5ᵒ-90ᵒS lat) – cold climates because sun strikes ground at lower angle

Temperate zones (23. 5ᵒ-66. 5ᵒN to 23. 5ᵒ-66 Temperate zones (23.5ᵒ-66.5ᵒN to 23.5ᵒ-66.5ᵒS lat) – between the polar and tropical zones with weather that ranges from warm in summer to cold in winter. Altitude – climate factor because air temperature decreases as altitude increases Distance from oceans and lakes – large bodies of water influence temperatures because water heats up and cools down more slowly than land

Marine climates – relatively warm winters and cool summers Continental climates – occur in inland areas and are often characterized by cold winters and warm or hot summers. Ocean currents – currents cool or warm air above them, bringing warm or cooled air to the land it touches.

Main factors that affect precipitation: Prevailing winds – winds carry warm, moist air or cool air over land Presence of mountains – a mountain range in the path of prevailing winds influences where precipitation falls Rain shadows – areas of low rainfall on a downward, or leeward side of the mountain Seasons – sea and land breezes over a large region that change direction with the seasons are called monsoons

Climate Cycles & Recent Climate Change

Earth experiences many climate changes in its history Earth experiences many climate changes in its history. Scientists use evidence from ice cores, or ice drilled from layers in glaciers, fossilized pollen, ocean sediments and growth rings of trees to gain information on past climates. Long-Term Cycles Ice ages – long cold periods lasting from hundreds to millions of years when glaciers cover much of Earth Interglacials – long warm periods that occur between ice ages

Short Term Cycles Seasons – short periods of climate change due to amount of solar energy an area receives during different times of the year El Niño – an occasional climatic event (occurs every 3-8 years) in which the trade winds weaken, reversing the normal pattern of high and low pressures across the Pacific Ocean monsoon – a wind circulation pattern that changes directions with the seasons

Recent Climate Change Average temperature on Earth has been increasing for the past 100 years, which is often referred to as global warming greenhouse gases – gases in the atmosphere that absorb Earth’s outgoing infrared radiation; higher levels of greenhouse gases which include carbon dioxide (CO2) create greater greenhouse effect

Humans have impacted climate change: burning of fossil fuels increases amount of carbon dioxide deforestation – the large-scale cutting and/or burning of forests which also increases carbon dioxide aerosols – tiny liquid or solid particles released from burning of fossil fuels which prevent Sun’s energy from reaching Earth