Climate

Climate versus Weather Weather is the short-term daily characteristics of the atmosphere in a given region. It includes wind, humidity, cloud cover, visibility, temperature, precipitation, and air pressure. Climate is the long term characteristics of the atmosphere in a region. Climate is like the average seasonal weather for a given region.

Climatic Controls Climatic Controls are the major and minor things that help to produce the climate of a region.

Latitude Generally the higher latitude a land region is, the cooler it will be because the sunlight at higher latitudes is spread out over a larger area which makes the sunlight per given area less which means that less warming will occur.

Altitude The greater the altitude, the lower the temperature and pressure. On average, air temperature drops by 6.4 o C for every 1000 m increase in altitude. This is called the environmental lapse rate. Since the atmosphere is less dense at higher altitudes, it can not store as much heat and does not heat up as much.

Mountains Mountains can act as barriers to air masses, blocking warm humid air from moving farther inland. Air that rises up a mountain expands, becomes less dense and cools. Dry air cools 10 o C per 1000 m of vertical rise. This is called the dry adiabatic lapse rate.

Orographic Precipitation Air rising up a mountain loses its ability to hold water and eventually reaches its condensation point (dew point) where it form dew, clouds, rain or snow. If the air continues to rise and cool it does so at the wet adiabatic lapse rate of 3 o C per 1000 m because condensing water releases heat so it doesn’t cool as quickly. Orographic precipitation is when moist air is lifted up a mountain range releasing rain on the windward side and sinking as dry, warmer air on the leeward side, here referred to as a chinook or foehn wind.

Pressure and Wind Systems Climates at various places are affected by the major wind and pressure systems on earth. See video, Atmospheric Circulation on you tube.

Seasonal Movement of Pressure Bands and Winds In the Northern Hemisphere’s Summer, the Pressure bands move northward as the hemisphere receives more radiation and in winter, the Northern Hemisphere’s pressure bands migrate southward.

Ocean Currents Ocean currents generally follow atmospheric winds in their circulation pattern. The Gulf stream has a major warming effect on Europe and Northeastern Russia. Regions where ocean currents flow counter to winds are often stormy regions (like the waters off Labrador and Cape Horn South America.

The Pattern of Water Bodies and Continents 1 Land locations near large water bodies generally experience wetter climates unless the water is a cold current, the land is at a high latitude (with cooler air - unable to hold water), or the land has offshore winds for much of the year.

The Pattern of Water Bodies and Continents 2 Land near large water bodies generally have cooler Summer temperatures and warmer Winter temperatures. This is because water has a much higher capacity to store heat (1 cal/gC o ) from the sun than land (.2 cal/gC o ). An amount of land will rise in temperature 5X more quickly and cool 5X as quickly as than the same amount of water. Thus in Summer, water remains cooler than land and heat moves from land to the adjacent water. In Winter, water drops its temperature less than land whose temperature is cooler so heat moves from the water to the adjacent land. In addition, water absorbs heat from the sun to great depths while land only absorbs heat for a few cm of its surface.

The Pattern of Water Bodies and Continents 3 Inland continental regions warm up faster in summer, which causes air expansion, rising currents and low pressure regions. Surface winds blow towards these low pressure regions. In winter, inland regions of continents cool more and accumulate cool, dense air masses of high pressure over them. These high pressure regions tend to have more sunny days and also cause winds to flow outward from them.

The Land Mass of Asia Asia is the largest land mass so it develops the lowest pressures in the Summer and the highest pressures in the winter. The winds flowing into the Asian continent in Summer from the Indian ocean bring Monsoon rains while winds flowing out from the Asian Continent in Winter bring a dry season and Monsoon rains to Northern Australia.

Local Factors Affecting Climate: Aspect direction a slope faces (in the northern hemisphere, a south facing aspect will get higher concentrations of sunlight) The aspect of a hill or mountain refers to the direction it faces. A north-facing aspect receives much less sunlight and is cooler than a south-facing aspect which will be warmer.

Local Factors Affecting Climate: Incline The angle or slope of a hill will affect the intensity of the sun’s rays The incline of a region of land is its slope compared to the horizontal. Inclined land that has a south-facing aspect will receive more sunlight. This is important for some crops like grapes which produce more sugar and mature faster when they are on a south-facing slope. In the Cowichan Valley, south-facing slopes are warmer.

Local Features Affecting Climate: Land/Sea or On/Offshore Breezes For land near a lake or ocean, in the morning the land heats up more which causes air over it to rise and cool air from the water moves in to replace the rising air. This produces a offshore breeze. At night the land cools more quickly and heavier cool air moves from land to the water while warmer air over the water moves up over the land, cooling and dropping.

Local Features Affecting Climate: Katabatic and Anabatic Winds On mountains at night, air at higher altitudes cools causing katabatic breezes down the mountain slope. On mountains during the day, warmer air from valleys, lakes or oceans rises up the mountain slopes, creating up-flowing breezes called anabatic breezes.

Local Features Affecting Climate: Urban Areas Urban areas tend to add particulate pollution to the air as well as heat so that cities become heat islands, especially at night compared to cooler country surroundings. Cities tend to heat up more since concrete and asphalt absorb shorter wavelengths of radiation and re-emit this as heat, especially at night time. The extra surface area of high rise buildings presents more area for reflecting and absorbing radiation. High city buildings catch, alter and channel winds, increasing their speed.

Albedo Albedo refers to the degree that a surface reflects sunlight radiation. Surfaces with high albedos include clouds, snow (.8-.9), ice and white concrete (.6-.8) and desert sand (.4). Surfaces with low albedos include oceans (.07-.1), tundra (.2), coniferous trees ( ), deciduous trees ( ), grassland (.25), asphalt (.1-.15).

Green Roofs and Gardens Constructing roofs with vegetation has the following benefits: 1.Roof vegetation provides insulation. 2.Roof vegetation reduces the heat island effect of cities. 3.Roof vegetation reduces water runoff from roofs. 4.Roof vegetation absorbs CO 2 5. Roof vegetation can provide food. VIU, Duncan BC

Local Features Affecting Climate: Large Lakes and Snow Belts In winter, cool air moving over a body of water may pick up moisture, especially if the water is warmer than the air. When this moisturized air then passes over colder land, it may cause condensation in the form of snow or sleet. Regions subject to extra snowfalls due to this effect are referred to as snow belts. Southern Ontario and Buffalo New York both receive extra snow as northwest winds pass over the great lakes in a southeasterly direction, dropping snow on the leeward side of the lake.

Climatographs A climatograph is a graph of the yearly temperatures and rainfall for a city or region. A line graph shows the temperatures while a bar graph shows the precipitation. Strong seasonal precipitation often indicates monsoon winds that alternate bringing dry and wet seasons. High and even temperatures indicate an equatorial climate.

Other Climatographs Unique climates produce distinctive climate graphs.

End of Presentation

A A