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1 Climatic zones
The interaction of solar radiation with the atmosphere and the gravitational forces, together with the distribution of land and sea masses, produces an almost infinite variety of climates. However, certain zones and belts of approximately uniform climates can be distinguished.
The global classification of climatic zones is:
- cool zones
- temperate zones
- arid / sub- tropical zones
- tropical zones
Figure 1.1 Global distribu tio n of climatic zones [1]
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2 Climatic factors
The climate of a given place / region / area is the total composition of many factors defining the state of the atmosphere at that place.
Such factors include temperature, humidity (wetness / dryness), wind (speed, direction), atmospheric clarity (or dustiness) etc. Some of the major factors influencing climate on a global scale will be further explained below.
2.1 Solar radiation
The sun is the major factor influencing climates. Almost all of the energy reaching the earth comes from the sun in the form of radiation.
2.1.1 Mode of action of
2.1.1.1 Solar power
The solar constant I^0 is defined as the intensity of radiation reaching the upper surface of the atmosphere. It varies slightly due to variations of the output of the sun itself and due to changes in the earth- sun distance.
Regardless of these effects the “standard” solar constant at the top of the atmosphere is defined as I^0 = 1395 W/m².
The amount of radiation reaching the earth ´s surface depends (among other things) on the location and the time. For example in Germany the maximum is approximately 700 – 1000 W/m².
The resulting energy received per unit area is equally depending on location and time and averages for example in Dortmund, Germany, 1055 kWh/(m²a).
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2.1.2 Influences of the sun´s position on the
2.1.2.1 Intensity of radiation
The earth - sun- relationship described before affects the amount of radiation received at a particular point on the earth ´s surface three ways:
- The angle of incidence effects that the intensity measured on normal surfaces is distributed on a larger surface that is tilted. This is described by the “cosine law”, as shown below.
Figure 1.3 Angle of incidence of the sun [2]
- The longer the path of radiation through the atmosphere (due to lower solar altitudes caused by the earth - sun- relationship), the higher is the atmospheric depletion. Atmospheric depletion (i.e. absorption, dispersion and reflection) creates a reduction factor of 0.2 to 0.7, generated by the the absorption of radiation by ozone, vapours, smoke and dust particles in the atmosphere.
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Figure 1.4 Length of path through the atmosphere [2]
Figure 1.5 Passage of radiation through the atmosphere [2]
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2.1.2.3 Sky condition
As described before, the amount of solar radiation passing through the atmosphere depends significantly on the amount of water vapour it contains. The presence or absence of clouds in the atmosphere relative to the total size of visible atmospheric hemisphere is usually expressed as a percentage.
For example a cloudiness of 50% would indicate that half of the sky hemisphere is covered by clouds.
The following picture shows different sky conditions. With special cameras you can take such hemispherical pictures (imagine you lying on the ground, looking to the sky).
Figure 1.7 Sky condit ions ( 0%, ~80%, 100% cloudiness)
On the left picture, the hemisphere contains no clouds (0% cloudiness), on the right picture the cloudiness is 100 %. From the picture in the middle you can measure the sky´s and the clouds´ surfaces and thereby calculate the actual cloudiness factor.
2.2 Air temperature
Temperature is usually expressed in degrees Celsius ( °C ), but absolute temperature is usually expressed in Kelvin (K), which is a SI- Unit (SI: International System of Units). The Kelvin scale starts at - 273.15 °C and goes by the same steps as °C.
Therefore the freezing point of water (0 °C) is already 273.15 K.
This leads to the relation
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°C = K - 273,15 and K = °C + 273,15.
The differences between two temperatures is expressed in absolute values, i.e. Kelvin. For example: The difference between 10°C and 15 °C is 5 K, or the temperature is rising by 3 K from 15°C to 18 °C.
In some English- speaking countries usually temperature is measured on the Fahrenheit scale (°F) where the freezing point of water is 32 °F (0 °C).
The relation of the Fahrenheit scale to the SI- Unit Kelvin is described by
K = (°F + 459,67) / 1,8 and °F = K x 1,8 – 459,67.
This shows, that the difference between for example 20 °F and 21 °F equals only 0,56 K.
Herewith you can make a conversion between the °C and the °F scale using the formula
°C = (°F - 32) / 1,8 and °F = °C × 1.8 + 32.
2.2.1 Measured quantities
The most interesting measured quantities are air temperatures and surface temperatures. In the appraisal of climates the differences between minimum and maximum temperature in any day can also be helpful.
2.2.2 Essential quantities in solar influence
The air and surface temperatures of climates are particularly influenced by solar radiation (Intensity [W/m²] and Duration [h]) winds (velocity [m/s], duration [h] and direction) caused by global weather conditions local influences, especially at ground level.
2.2.3 Mechanisms of heating and cooling
In detail temperatures are influenced by the following mechanisms: Solar radiation heats the atmosphere (through absorption by water vapour, dust, CO^2 , etc) and the ground The energy absorbed by the ground and other surfaces is transformed into infra- red (IR) radiation The IR radiation emitted by the ground cools the ground. This effect diminishes with growing cloudiness. The IR radiation emitted can be absorbed by the atmosphere again. This heats the atmosphere and the ground.
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Trees act against prevailing temperature layering by mixing the air. Furthermore shading and evaporation by trees as well as from vegetation and crops have a cooling effect.
Dry pavements: The warming effect of different surfaces depends on their colour (reflection / absorption / emittance) and thermal storage capacity.
Water surfaces: Water surfaces reflect some radiation and water is evapourated at the surface, cooling the body of the water. At the same time water tores a lot of thermal energy due to its good thermal capacity. As a result, water bodies have a balancing influence on the climate of a locality and even larger areas when they act in conjunction with other factors (esp. wind).
Figure 1.9 Different urban surfaces (dry pavements, water surfaces) influencing the climate
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The Heat island effect: Due to different wind situations, surfaces, thermal storage of buildings, industrial and transport activities and other anthropogenic factors there is a significant difference between city- and rural temperatures.
Figure 1.10 Urban Heat - Island Profile
2.3 Winds
Air movement is another important part of climate, in local as well as in global dimensions. Through the action of winds the different climatic zones interact with each other..
2.3.1 Quantities of measurement
The first important vaeiable is the windspeed, usually measured in m/s. Free wind velocities are normally recorded in open flat country at a height of 10 m. Measurements in urban areas are often taken at a height between 10 and 20 m to avoid obstructions. Velocities near the ground are lower than the free wind speed.
The other important consideration is the wind direction. This is usually grouped into eight: the four cardinal (N., E., S. and W.) and four semi- cardinal compass points (NE., SE., SW. and NW.). Occassionally these 8 are further subdivided into 16 (e.g. NNW, WNW, NNE etc)
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Tropical or equatorial zones between the tropics of Cancer and Capricorn with strong thermal air movements, NE-winds north of the Equator and SE-winds south of the Equator. There is little seasonal and diurnal (daily) of temperatures in these areas, and humidities are often high.
The Inter- tropical convergence zone, with calms and unsteady wind directions. Within this zone the wind patterns shift seasonally from north to south and back again. Most arid (dry) areas are found in these latitudes and there tends to be a relatively large seasonal and diurnal temperature swing.
Mid- latitude westerlies between 30 ° and 60 ° N and S, where SW- winds (northern hemisphere) and NW- winds (southern hemisphere) dominate as a physical reaction (“Coriolis force”) to the tropic air movements.
Polar winds, thermally induced, from colder to warmer zones (NE- or SE-winds).
Figure 1.12 Seasonal shift of the inter - tropical convergence zone [2]
2.3.5 Local situations close to the ground
The topography and type of ground cover affects the wind speed gradient.
Near to the ground the wind speed is always less than higher up, but with an uneven ground cover the rate of increase in speed with height is much more than with an unbroken smooth surface, such as water.
Wind speed can be reduced after a long horizontal barrier for example by 50% at a distance of ten times the height and by 25 % at a distance of twenty times the height.
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Figure 1.13 Wind velocity gradients for dif ferent topographies [2]
2.4 Humidity
In addition to temperatures and winds, humidity is the third important parameter in climate. It appears as vapour and rainfall. Rainfall is measured in mm/a
2.4.1 Rainfall quantities
Depending on the climatic zone and regional influences the periodical rainfall quantities vary a lot. The mean global rainfall is about 860 mm /a.
The minima in warm- dry zones are < 250 mm/a.
The maxima appear in warm - humid zones. They may reach or exceed 2000 mm /a.
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If the air (20 °C, 50 % RH) is heated to 30 °C, the AH stays the same (7. g/kg), but the RH reduces to approx. 28 %, because saturation of 30 °C- warm air is at 27.5 g/kg. These correlations are non- linear!
Humidity can be absorbed until the saturation for the actual air temperature is reached.
During the day (especially in the morning), as the lowest layer of air is being heated by the ground surface, evaporation increases, the vapour can be assimilated by the warm air. Winds even out the differences in air temperature and humidity between lower and higher air layers.
As long as temperature is rising and the absolute humidity keeps its level, the relative humidity decreases.
In the evening and during the night, the situation is reversed. Especially on a clear night with still air, as the lowest layer cools, its relative humidity increases, the point of saturation is soon reached and with further cooling the excess moisture condenses out in the form of dew.
When the air reaches the dewpoint temperature fog will start to form, and if there is no further rapid cooling and no air movement, a thick layer of fog can develop near to the ground.
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Figure 1.15 Example of daily course of relative humidi ty in January and July [3]
3 CONTEXT
3.1 ENVIRONNENTAL CONSCIOUS DESIGN
An awakening to environmental problems began at the end of the twentieth century, both on the part of the public and private decision makers, and from the general public. In particular concerns arose about: the destruction of the ozone layer, climate change caused by greenhouse gas emissions, management of waste, pollution of water resources, storage of the radioactive products, decrease in natural resources, attacks against bio- diversity, etc...
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Figure 1.16 greenouse gas emissions by sector (Ademe / PNICC) Though the greenhouse effect is one aspect of the environmental impact of human activities. It is not obviously the only one to be considered within the field of "sustainable development".
3.2.1 mechanism
The greenhouse effect is a natural mechanism caused by the presence of various gaseous compounds in the Earth's atmosphere.
A large part of solar energy, mainly short wave infra- red and visible radiation, arrives on the ground through the atmosphere (weak reflexion and weak absorption). A fraction of this radiation is reflected by the ground and goes back in space, the remaining part is absorbed by the ground, which leads to its heating and that of the very low layers of the atmosphere (Fig. 1.17).
Figure 1.17 Radiation exchanges in the atmosphere (Manchester university) Then, the heated ground emits long wave energy by radiation. This radiation passes through the atmosphere, where some gases are not very transparent to long infra- red radiation. Thus a part of the radiation from the ground is absorbed or returned towards the ground instead of disappearing in space.
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This phenomenon is similar to that of a greenhouse, the glazed cover acting in the same way: letting though the visible radiation from the sun and absorbing the infra- red radiation from the ground.
There is a lot of greenhouse effect gases, but in the Earth's atmosphere, the more important are the water vapor (content 3 to 4%) and carbon dioxide (content 0.03 - 0.04%).
Gas Greenhouse contribution H^2 O water vapor 55% CO^2 carbon dioxide 39% CH^4 methane 2% N^2 O nitrous oxide 2% O^3 ozone 2% Table 1.1 Greenhouse contribut ions
The contribution of water vapor is considered separately, because human activity does not have a quantifiable influence on it. However carbon dioxide plays an essential role in causing the greenhouse effect (Fig 1.18).
Figure 1.18 contribut ions to dif ferent greenhousse gases by source (Ademe / CITEPA)
3.2.2 Temperature on the ground
The average temperature of the Earth on the ground level is directly related to the energy balance between the absorbed solar radiation and the infra- red radiation emited by the ground (Fig 1.19).
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