Weather and Climate

 Weather is the short term (day to day) conditions of the atmosphere.

 Temperature  Precipitation  Humidity  Cloud cover  Wind  Air pressure

Climate

 Involves the key weather variables  Temperature  Moisture  Air pressure  But does so in terms of patterns over the course of decades.

Earth – Sun relationship

 The Earth is attracted to the sun as a result of the gravitational pull of the sun.

 The earth

revolves

around the sun once every year. (365.25 days)  The Earth is tilted at an angle of 23.5 degrees throughout its orbit.

 The Earth

rotates

24hrs.

on its own axis once each

Equinox

 Because of the earth’s tilt there are only 2 times during the year when the sun shines equally on both the Northern and Southern Hemispheres: late March (20-23 rd ) late September (20-23 rd )  These times of the year are called equinoxes

Solstices

     The times of the year when either the Northern or Southern Hemispheres receive the most sunlight are called solstices.

These occur during/around June 21(longest day of the year in NH) and December 22 (shortest day of the year in the NH) Observe seasonal changes in the amount of sunlight reaching locations on Earth.

Explore a model of Earth's yearly revolution around the sun.

Climate Controls: Latitude

Solar Radiation

Solar Radiation

Cloud Cover and Temperature

 During the day, the earth is heated by the sun. If skies are clear, more heat reaches the earth's surface (as in the diagram below). This leads to warmer temperatures.

Cloud Cover and Temperature

 However, if skies are cloudy, some of the sun's rays are reflected off the cloud droplets back into space. Therefore, less of the sun's energy is able to reach the earth's surface, which causes the earth to heat up more slowly. This leads to cooler temperatures.

Cloud Cover and Temperature

 At night cloud cover has the opposite effect. If skies are clear, heat emitted from the earth's surface freely escapes into space, resulting in colder temperatures.

Cloud Cover and Temperature

 However, if clouds are present, some of the heat emitted from the earth's surface is trapped by the clouds and reemitted back towards the earth. As a result, temperatures decrease more slowly than if the skies were clear. http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/fcst/tmps/cld.rxml