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BASIC CONCEPTS ON CLIMATE

ARC 810: BUILDING CLIMATOLOGY DEPARTMENT OF ARCHITECTURE FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE. BASIC CONCEPTS ON CLIMATE. 1.1 Movement of the earth around the sun 1.2 Solar time 1.3 Solar radiation 1.4 Global wind pattern 1.5 Spatial systems of climate 1.6 Design with climate.

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BASIC CONCEPTS ON CLIMATE

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  1. ARC 810: BUILDING CLIMATOLOGY DEPARTMENT OF ARCHITECTURE FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE BASIC CONCEPTS ON CLIMATE

  2. 1.1 Movement of the earth around the sun 1.2 Solar time 1.3 Solar radiation 1.4 Global wind pattern 1.5 Spatial systems of climate 1.6 Design with climate SUB - TOPICS

  3. 1. INTRODUCTION To understand some basic concepts in Building Climatology, some preliminary knowledge of science is needed. Therefore, this course aims to unify students’ different backgrounds and perceptions of basic concepts especially on global climate.

  4. INTRODUCTION (cont’d) • The following will be discussed: • The motion of the earth and how it gives rise to various seasons. • Various ways of measuring time. • How the distribution of solar radiation affects climate.

  5. INTRODUCTION (cont’d) • The genesis of the global wind pattern. • The spatial and time scales used to delineate categories of climate. • Design with climate.

  6. 1.1 MOVEMENT OF THE EARTH AROUND THE SUN The earth makes one rotation along its north - south axis in 24 hours which leads to day and night and it makes one revolution in 365 days, 5 hours, 48 minutes and 46 seconds.

  7. 1.1 MOVEMENT OF THE EARTH AROUND THE SUN (cont’d) The earth's north-south axis inclination to the plane of orbit at 23 degrees and 27 minutes leads to different seasons.

  8. 1.1 MOVEMENT OF THE EARTH AROUND THE SUN (cont’d) The movement of the Sun can be said to be between the tropic of cancer (23.5 degrees North) and the tropic of capricon (23.5 degrees South).

  9. 1.1 MOVEMENT OF THE EARTH AROUND THE SUN (cont’d) • Summer solstice: This happens in June when the Earth is tilted towards the sun and the tropic of cancer receives maximum intensity of solar radiation. Summer is experienced in the Northern hemisphere.

  10. 1.1 MOVEMENT OF THE EARTH AROUND THE SUN (cont’d) • Winter solstice: When the Earth is tilted towards the sun and the tropic of capricon receives maximum intensity of solar radiation. Winter is experienced in the Northern hemisphere.

  11. 1.1 MOVEMENT OF THE EARTH AROUND THE SUN (cont’d) • Vernal equinox and Autumnal equinox: When the day and the night have equal length for all places on Earth. It happens in March and September when the sun crosses the equator.

  12. 1.1 MOVEMENT OF THE EARTH AROUND THE SUN (cont’d) The day is longer than the night during the summer with the reverse in winter. A section through the sun, the ecliptic plane and the earth in two directions.

  13. 1.2 SOLAR TIME (cont’d) The following four terms are usually used in discussing solar time: ‑ clock time ‑ mean solar time ‑ true solar time ‑ local apparent time (LAT)

  14. 1.2 SOLAR TIME (cont’d) • CLOCK TIME • Time shown by a time piece. The world is divided into time zones. Each of the 24 hours of the day has a time zone. All part of each time zone has the same clock time irrespective of the longitude.

  15. 1.2 SOLAR TIME (cont’d) MEAN SOLAR TIME A uniform time indicated by a clock which does not take the equation of time into consideration. In a particular time zone, the mean solar time and the clock time are the same on the reference longitude.

  16. 1.2 SOLAR TIME (cont’d) MEAN SOLAR TIME Location Mean Solar Time Correction Factor on the reference longitude West Earlier 4 minutes to be added East Later 4 minutes to be subtracted

  17. 1.2 SOLAR TIME (cont’d) MEAN SOLAR TIME Worked Example Determine the mean solar time for Lagos (3:24 degrees East), the reference longitude for Nigeria is 15 degrees East, given a clock time of 12noon and a reference longitude of 15 degrees East.

  18. 1.2 SOLAR TIME (cont’d) MEAN SOLAR TIME Worked Example The correction factor: = 4 (15 - 3:24) minutes. = 4 x 11:36 minutes. = 46:24 minutes. Lagos is to the West of the reference longitude, therefore mean solar time: = 12:00 - 00:46:24 = 11:13:36.

  19. 1.2 SOLAR TIME (cont’d) • TRUE SOLAR TIME The time in which noon occurs when the sun is due South, as shown by a sundial. Equation of time: This is the correction applied to the mean solar time to obtain the true solar time. It may be positive or negative.

  20. 1.2 SOLAR TIME (cont’d) • TRUE SOLAR TIME • Worked Example Obtain the true solar time for Maiduguri (13:05 degrees East) on January 15th given a clock time of 12 noon. To obtain the mean solar time, time difference: = 4 (15 - 13:05) minutes. = 4 (1:55). = 7:40 minutes.

  21. 1.2 SOLAR TIME (cont’d) • TRUE SOLAR TIME • Worked Example To obtain the mean solar time, time difference: = 4 (15 - 13:05) minutes. = 4 (1:55). = 7:40 minutes. Mean solar time: = 12:00 - 00:07:40. = 11:52:20.

  22. 1.2 SOLAR TIME (cont’d) • TRUE SOLAR TIME • Worked Example Mean solar time: = 12:00 - 00:07:40. = 11:52:20. The equation of time on January 15 is +9 minutes: True solar time is therefore: The equation of time on January 15 is +9 Mins

  23. 1.2 SOLAR TIME (cont’d) • TRUE SOLAR TIME • Worked Example True solar time is therefore: = 11:52:20 + 00:09:00 = 12:01:20. = 11:52:20 + 00:09:00 = 12:01:20.

  24. 1.2 SOLAR TIME (cont’d) • LOCAL APPARENT TIME This term is used in astronomical and nautical calculations and is equivalent to the true solar time.

  25. 1.3 SOLAR RADIATION (cont’d) Earth’s main source of energy comes from the Sun and comes in form of electromagnetic radiation. Heat flow rate is measured in Watts (W), in Joules per second (J/S). The speed of light (c) = frequency (v) X wavelength (Lambda)

  26. 1.3 SOLAR RADIATION (cont’d)

  27. 1.3 SOLAR RADIATION (cont’d) Frequency = No. of oscillations per second, measured in Hertz. Wavelength = Distance between identical points of two succeeding oscillations, measured in unit length.

  28. 1.3 SOLAR RADIATION (cont’d) • SPECTRUM OF SOLAR RADIATION • This can be broadly divided into 3 sections with wavelength extending from 290 to 2300 nanometres: • i. Ultraviolet radiation (290-380 nm) • ii. Visible light (380-700 nm) • iii. Infra-red radiation (700-2300 nm)

  29. 1.3 SOLAR RADIATION (cont’d) • THE SOLAR CONSTANT The intensity of solar radiation reaching the upper surface of the atmosphere. It has a value of 1395 W/m . Slight variations may occur in this value due to changes in the sun and distance between the earth and the sun.

  30. 1.3 SOLAR RADIATION (cont’d) • THE SOLAR CONSTANT Atmospheric depletion of solar radiation The absorption of solar radiation by ozone, vapours and dust particles in the atmosphere. Not all the solar radiation reaching the upper surface of the atmosphere get to the earth's surface as a result of this.

  31. 1.3SOLAR RADIATION (cont’d) • THE SOLAR CONSTANT Atmospheric depletion of solar radiation The absorption of solar radiation by ozone, vapours and dust particles in the atmosphere. Not all the solar radiation reaching the upper surface of the atmosphere get to the earth's surface as a result of this.

  32. 1.3 SOLAR RADIATION (cont’d) ATMOSPEHRIC DEPLETION OF SOLAR RADIATION

  33. 1.3 SOLAR RADIATION (cont’d) • THE SOLAR CONSTANT The purity of the atmosphere affects the amount of radiation absorbed. The greater the quantity of ozone, dust, smoke, vapours, etc. in the atmosphere, the less radiation reaches the surface of the Earth.

  34. 1.3 SOLAR RADIATION (cont’d) • THE SOLAR CONSTANT Cosine Law of Solar Radiation The intensity of solar radiation on a tilted surface equals the normal intensity times the cosine of the angle of incidence.

  35. 1.3 SOLAR RADIATION (cont’d) • THE SOLAR CONSTANT To maintain the thermal balance of the Earth, the equivalent amount of the radiation absorbed is lost back to outer space. Without this regulatory system the temperature of the Earth would constantly be on the increase.

  36. 1.3 SOLAR RADIATION (cont’d) • THE SOLAR CONSTANT Incoming Radiation If the total amount of solar radiation reaching the outer surface of the earth is 100%, 20% is reflected from clouds 25% is absorbed in the atmosphere 5% is reflected from the ground 50% of the total radiation is absorbed by the Earth's surface.

  37. 1.3 SOLAR RADIATION (cont’d) • THE SOLAR CONSTANT Incoming Radiation 23% of the 50% being in the form of diffuse radiation and the remaining 27% as direct solar radiation. This energy is absorbed by the hydrosphere to raise water temperature, by the bare soil and by land and marine vegetation.

  38. 1.3 SOLAR RADIATION (cont’d) • THE SOLAR CONSTANT Incoming Radiation

  39. 1.3 SOLAR RADIATION (cont’d) • THE SOLAR CONSTANT Outgoing Radiation The Earth loses the heat absorbed through Longwave radiation (40%) Evaporation (40%) Convection (20%)

  40. 1.4 GLOBAL WIND PATTERN • The global wind pattern is the result of 3 • basic forces. • Thermal force • Coriolis force • Force explained by law of conservation of angular momentum

  41. 1.4 GLOBAL WIND PATTERN (cont’d) • Thermal Force • Is a result of the differential radiation balance on the surface of the earth. The difference in temperature between the equator and the poles gives rise to convection currents.

  42. 1.4 GLOBAL WIND PATTERN (cont’d) Inter-Tropical Convergence Zone (ITCZ) The area where the hot air rises, between the tropics of Cancer Capricon. This is where the northerly and southerly winds meet, forming the Tropical Front.

  43. 1.4 GLOBAL WIND PATTERN (cont’d) • The Corollis Force • The Coriolis force is caused by the apparent higher speed of rotation of the equator than the poles.

  44. 1.4 GLOBAL WIND PATTERN (cont’d) The Coriolis force and the thermal force create a resultant force in the form of a wind. This is the North-East trade wind in the Northern Hemisphere and the South-East trade wind in the southern hemisphere

  45. 1.4 GLOBAL WIND PATTERN (cont’d) Westerly Winds They are strong winds blowing between latitudes 30 and 60 degrees. But unlike the trade-winds, they blow in the same direction as that of the earth's rotation.

  46. 1.4 GLOBAL WIND PATTERN (cont’d) The Polar Winds They are created by thermal forces and the lag of air behind the rotating earth. These forces create easterly winds known as the north- easterly and south-easterly polar winds.

  47. 1.4 GLOBAL WIND PATTERN (cont’d) Origin of the North East and South East trade winds.

  48. 1.5 SPATIAL SYSTEMS OF CLIMATE • The concept of scale is very important in building climatology. • There are 4 generally recognised categories of climate based on spatial and time scales: • - The global climate. • - The regional macroclimate. • - The (local) topoclimate. • The microclimate.

  49. 1.5 SPATIAL SYSTEMS OF CLIMATE (cont’d) • The concept of scale is very important in building climatology. • There are 4 generally recognised categories of climate based on spatial and time scales: • - The global climate. • - The regional macroclimate. • - The (local) topoclimate. • The microclimate.

  50. 1.5 SPATIAL SYSTEMS OF CLIMATE (cont’d) • The Global Climate • This is a result of the movement of air masses due to temperature and pressure changes. This climate is largely independent of surface topography.

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