Earth Science Chapter 8 Climates

Climates Climate - an average of weather conditions over a long-term period of time. Driven by interaction of solar energy with Earth’s surface and atmosphere. Based on conditions of temp. and humidity. Determined by ratio of amount of moisture in the air to potential for evapotranspiration.

Water Cycle and Climates Some latitude zones have a surplus of precipitation over evaporation or vice-versa. Precipitation excess occurs at the equatorial and two middle latitude zones (40o to 70o). Precipitation deficit occurs between 10o and 40o in each hemisphere. A belt of convection currents moves the moisture from places of high humidity to places of low humidity.

Water Cycle and Climates

Water Cycle and Climates A land and sea moisture exchange takes place because continents have more precipitation than evaporation. Moisture from evaporated sea water is transported to continents by winds. The water cycle is a closed system Water that evaporates in one place usually precipitates hundreds to thousands of miles away.

Insolation and Earth’s Surface Insolation (INcoming SOLar radiATION) is the major source of energy for Earth. About half of the insolation received by Earth is short-wave radiation, which we see as light. The rest is long-wave radiation (heat). Most of the short-wave radiation absorbed by Earth is re-radiated from Earth’s surface as long-wave infrared energy. Angle and duration of insolation influence climate

Factors Affecting Insolation Angle of insolation The angle at which the sun’s rays strike Earth. Because Earth’s surface is curved, the Sun’s rays strike at angles from 0o to 90o.

Factors Affecting Insolation Rays that strike Earth’s surface at a 90o angle are called direct. As the angle of insolation decreases from 90o, the suns rays become less direct and more spread out over a larger area. Direct rays provide the greatest intensity of insolation, because the insolation is spread over the smallest possible area. Locations receiving direct rays will have higher temperatures.

Factors Affecting Insolation At any location on Earth’s surface, the angle and intensity of insolation vary with time of day. Greatest at solar noon Lowest at sunrise and sunset

Factors Affecting Insolation The intensity of insolation varies with the seasons of the year. Seasonal changes are NOT related to the Earth’s varying distance from the sun. Seasonal changes are caused by: Tilt of Earth’s axis Parallelism of Earth’s axis Revolution around the sun

Factors Affecting Insolation

Factors Affecting Insolation Because Earth is spherical every degree of latitude has a different angle of insolation. As Earth orbits the sun direct rays are received from 23.5oN (summer solstice) and 23.5oS (winter solstice) due to Earth’s tilt. At any given latitude the angle of the sun varies throughout the year.

Factors Affecting Insolation Example for 43oN (Westmoreland): On 3/21 & 9/23 the Sun is directly overhead at 0o. On 3/21 & 9/23 the Sun’s altitude at 43oN is 47o. On 12/22 the Sun is directly overhead at 23oS. On 12/22 the Sun’s altitude at 43oN is 23.5o. Lowest angle and intensity of year On 6/21 the Sun is directly overhead at 23oN. On 6/21 the Sun’s altitude at 43oN is 70.5o. Highest angle and intensity of year

Factors Affecting Insolation

Factors Affecting Insolation Duration of Insolation The number of daylight hours at a given location. Daylight hours vary with latitude and time of year There is a direct correlation between the angle and intensity of insolation and duration. When angle and intensity are greatest, duration is greatest.

Factors Affecting Insolation

Factors Affecting Insolation The longer the duration of insulation, the higher the temperatures. Earth is in radiative balance. As the amount of insolation received by Earth increases, the amount of infrared energy radiated from Earth also usually increases.

Factors Affecting Insolation Hottest time of day Occurs some hours after solar noon Insolation received is greatest at solar noon, but temp. continues to rise after solar noon because the incoming radiant energy exceeds the outgoing radiant energy. Temp. rises until mid-afternoon when Earth is in radiatiave balance, then decrease until sunrise the next day when cycle starts again. Coldest time of day?

Factors Affecting Insolation Hottest time of year in Northern Hemisphere Occurs in August Insolation received is greatest at June 21, but temp. continues to rise for many days after June 21 because the incoming radiant energy exceeds the outgoing radiant energy. Temp. rises until August when Earth is in radiatiave balance, then begins to decrease. Coldest time of year?

Greenhouse Effect Water vapor and carbon dioxide are present in the atmosphere Let short-wave energy in from the Sun Absorb long-wave infrared energy radiated from the Earth’s surface. Results in raising of temperature in lower atmosphere. Example: Inside of car gets hot in the summer

Greenhouse Effect

The Water Budget A monthly account of what happens to the water in an area over the course of a year is the water budget. The “income” of a water budget is precipitation. The “expenses” of a water budget is potential evapotranspiration. The amount of water that would evaporate if the water were available.

The Water Budget The primary source of evapotranspiration is the Sun, so potential evapotranspiration is greatest in the summer and lowest in the winter. If the total annual precipitation is less than the potential evapotranspiration the climate is arid. If the total annual precipitation is greater than the potential evapotranspiration the climate is humid.

Factors Affecting Climate Patterns The moisture and temperature conditions that affect a location depend on: Latitude Elevation Proximity to large bodies of water Ocean currents Prevailing winds Mountain ranges Storm tracks

Factors Affecting Climate Patterns Latitude Most important factor affecting climate At lower latitudes the temperatures remain fairly constant since the angle and duration of insolation remain fairly constant. At higher latitudes, there is high variation in insolation resulting in high variation in temp. As latitude increases, the average yearly temperature decreases, although the seasonal range of temperatures increases.

Factors Affecting Climate Patterns Elevation As elevation increases the temp. decreases and relative humidity increases. At a given latitude places with higher elevation have more precipitation and a wider range of weather conditions than do places at lower elevation. Changes in elevation have similar effects on temperature as changes in latitude.

Factors Affecting Climate Patterns Large bodies of water Water takes longer than land to absorb and radiate energy. Temperatures at locations along the shore have a much smaller annual range than those at inland regions at the same latitude. Areas regulated by water have a marine climate. Inland areas with large temperature ranges have a continental climate.

Factors Affecting Climate Patterns Ocean Currents Warm ocean currents bring warm water from the equator to higher, colder latitudes, warming the air above them. Cold ocean currents from the polar regions help cool the air over the southern regions.

Factors Affecting Climate Patterns Prevailing winds Air that originates over water may be carried over land, causing it to be very moist. Air that originates over continental areas bring dry winds. Low pressure belts (equator and 60o) consist of rising air which results in high humidity. High pressure belts (30o and poles) produce dry conditions due to descending air.

Factors Affecting Climate Patterns Mountains The windward side of mountains are colder and have more precipitation than the warm, dry leeward side. Storm tracks Low pressure systems, which affect temperature and moisture, follow somewhat predictable paths.

Seasonal Wind Patterns Monsoons Large-scale seasonal changes in winds. Due to differences in heating and cooling of land and water. Similar to the smaller scale local daily land and sea breezes. Bring heavy summer rains.

Seasonal Wind Patterns El Niño Occurs every 3 to 5 years. Lasts 1 to 2 years. Caused by shifts in winds and movements of warm equatorial waters. Warmer waters occur along the equator and the west coast of South America causing the wind patterns to shift from west to east. Impacts weather patterns in North America.