Meteorology

1. Meteorology Geography Department East China Normal UniversityShu Jiong

2. The Earth’s Global Energy Balance ◆Solar radiation is the driving power source for wind, waves, weather, rivers, and ocean currents. ◆ The earth’s energy balance, which includes land and ocean surfaces and the atmosphere, controls the seasonal and daily changes in the earth’s surface temperature.

3. Electromagnetic Radiation ◆ Wavelengthdescribes the distance separating one wave crest from the next crest. ◆ The unit to measure wavelength is the micrometer. ◆ Radiant energy can exist at any wavelength.

4. Radiation and Temperature ◆There is an inverse relationship between the radiation that an object emits and the temperature of the object. ◆ Hot objects radiate more energy, and at shorter wavelengths, than cooler objects.

5. Solar radiation ◆ The Sun is a ball of constantly churning gases that are heated by continuous nuclear reactions. It has a surface temperature of about 6000oC. Like all objects, it emits energy in the form of electromagnetic radiation.

6. electromagnetic spectrum Shortwave radiation ◆ Ultraviolet radiation(0.2 to 0.4 μm) ◆ Visible lightradiation(0.4 to 0.7μm) ◆ Shortwave infrared radiation(0.7 to 3μm) Longwave radiation ◆ Thermal infrared wavelengths(>3μm)

7. Characteristics of solar energy ◆The sun does not emit all wavelengths of radiation equally ◆The intensity of solar energy is strongest in visible wavelengths

8. Longwave radiation from the Earth ◆The earth’s surface and atmosphere are much colder than the sun’s surface,so the energy from the Earth has longer wavelength

9. The global radiation balance ◆ The earth constantly absorbs solar shortwave radiation and emits longwave radiation. ◆ The sun provides a nearly constant flow of shortwave radiation toward earth. ◆ The atmosphere, land, and ocean also emit energy in the form of longwave radiation.

10. Figure 1 Global Energy Balance

11. Insolation over the Globe ◆ Insolation(incoming solar radiation) depends on the angle of the sun above the horizon.

12. The Path of the Sun in the Sky The sun’s path in the sky changes greatly in position and height above horizon from summer to winter. ◆ At equinox, the sun rises directly to the east and sets directly to the west. ◆ The noon sun is positioned at an angle of 50o above the horizon in the southern sky.

13. ◆ The sun is above the horizon for exactly 12 hours. ◆ At noon it will be 73.5o above the horizon. ◆ The sun is above the horizon for about 15 hour

14. Daily Insolation Through the Year ◆Daily insolation depends on two factors: ◆the angle at which the sun’s rays strike the earth ◆the length of time of exposure to the rays ◆the equator has two periods of maximum daily insolation, these periods occur near the equinoxes.

15. ◆ There are also two minimum periods near the solstices, when the subsolar point moves farthest north and south from the equator. All latitudes between the tropic of cancer 23.5oN and the tropic of Capricorn 23.5oS have two maximum and minimum values . ◆ Seasonal pattern of daily insolation is directly related to latitude.

16. Annual Insolation by Latitude ◆ Annual insolation varies smoothly from the equator to the pole ◆ The annual insolation value at the pole is about 40% of the value at the equator. ◆ The tilting of the earth’s axis redistributes a significant portion of the earth’s insolation from the equatorial regions toward the poles.

17. World Latitude Zones ◆ The equatorial zone encompasses the equator and covers the latitude belt roughly 10oN to 10oS ◆ Spanning the tropics of cancer and Capricorn are thetropical zones, ranging from latitudes 10o to 25o north and south

18. ◆ Moving toward the poles from each of the tropical zones are transitional regions called the subtropical zones, ranging from latitudes 25o to 35o north and south ◆ The midlatitude zones lie between 35o and 55o latitudes in the northern and southern hemispheres

19. ◆ Bordering the midlatitude zones on the poleward side are the subarctic zone and subantarctic zone, 55o to 60o north and south latitudes ◆ Astride the arctic and Antarctic circles from latitudes 60o to 75o N and S lie the arctic and Antarctic zones ◆ The polar zones, north and south, are circular areas between about 75o latitude and the poles

20. Composition of the Atmosphere ◆The earth’s atmosphere consists of air-a mixture of various gases surrounding the earth to a height of many kilometers. ◆ Almost all the atmosphere 97% lies within 30km of the earth’s surface.

21. The upper limit of the atmosphere is at a height of approximately 10,000km above the earth’s surface, a distance approaching the diameter of the earth itself.

22. ◆ Pure, dry air consists largely of nitrogen, about 78% by volume, and oxygen, about 21%. Other gases account for the remaining 1% ◆ Water vapor is an important component of the atmosphere that varies in concentration from place to place and time to time

23. Ozone in the Upper Atmosphere ◆ Ozone (O3) is found mostly in the upper part of the atmosphere, in a layer termed the stratosphere. Ozone in the stratosphere absorbs ultraviolet radiation from the sun as this radiation passes through the atmosphere

24. At both polar regions, climate and chemistry combine to deplete ozone during spring months. Dark blue indicates lowest ozone amounts. Arctic total ozone amounts seen by TOMS in March 2003 (above, left) were among the lowest ever observed in the northern hemisphere. The Antarctic ozone hole of 2003 (above, right) was the second largest ever observed.

25. Sensible Heat and Latent Heat Transfer ◆ Sensible Heat-the quantity of heat held by an object that can be sensed by touching or feeling ◆ When two objects of unlike temperature contact each other, heat energy moves by conduction from the warmer to the cooler. This type of heat flow is referred to as sensible heat transfer

26. The Global Energy System ◆Insolation losses in the Atmosphere ◆ Albedo ◆ Counterradiation and the Greenhouse Effect ◆ Global Energy Budget of the Atmosphere and Surface ◆ Net Radiation, Latitude, and the Energy Balance

27. Winds and the Pressure Gradient Force ◆ Wind is air motion with respect to the earth’s surface, and it is dominantly horizontal. ◆Barometric pressure falls with increasing altitude above the earth’s surface.

28. ◆The change in barometric pressure across the horizontal surface of a map constitutes a pressure gradient. The gradient is in the direction from higher pressure to lower pressure.

29. ◆Where a pressure gradient exists, air molecules tend to drift in the same direction as that gradient. This tendency for mass movement of the air is referred to as the pressure gradient force.

30. Sea and Land Breezes ◆During the daytime, more rapid heating of the lower air layer over the land than over the ocean causes a pressure gradient from sea to land. Air moving landward in response to this gradient from higher to lower pressure constitutes the sea breeze.

31. At higher levels, a reverse flow sets in. Together with weak rising and sinking air motions, a complete flow circuit is formed.

32. ◆During the night, when radiational cooling of the land is rapid, the lower air becomes colder over the land than over the water. Higher pressure now develops over land and the barometric gradient is reversed. Air now moves from land to sea as aland breeze.

33. Figure 2 Sea breeze and land breeze

34. Cyclones and Anticyclones ◆A center of low pressure is called a cyclone; a center of high pressure is an anticyclone. ◆Winds in a cyclone in the northern hemisphere show an anticlockwise inspiral. In an anticyclone, there is a clockwise outspiral.

35. ◆ The surface winds spiral inward on the center of the cyclone, so the air is converging on the center and must also rise to be disposed of at higher levels.

36. ◆ For the anticyclone, by contrast, surface winds spiral out from the center. This motion represents a diverging of airflow and must be accompanied by a sinking of air in the center of the anticyclone to replace the outmoving air.

37. Figure 3 Surface winds in cyclones and anticyclones

38. Global Distribution of Surface Pressure Systems ◆ Over the equatorial zone is a belt of somewhat lower than normal pressure, between 1011 and 1008 mb, which is known as the equatorial trough.

39. ◆ Lower pressure is conspicuous by contrast with belts of higher pressure lying to the north and south and centered at about lat.30°N and S. These are the subtropical belts of high pressure, in which pressure exceed 1020mb.

40. ◆ In the southern hemisphere, south of the subtropical high-pressure belt, is a broad belt of low pressure, extending from the midlatitude zone to the arctic zone. The axis of low pressure is centered at about lat.65S. This pressure trough is called thesubantactic low-pressure belt.

41. ◆ Lying over the continuous expanse of Southern Ocean, this trough has average pressure as low as 984mb. Over the continent of Antarctica is a permanent center of high pressure known as thepolar high.

42. The Global Pattern of Surface Winds ◆ From the two subtropical high-pressure belts the pressure gradient is equatorward, leading down to the equatorial trough of low pressure. Air moving from high to low pressure is deflected by the Coriolis effect. As a result, two belts oftrade windsare produced.

43. ◆ Meeting of the trades takes place within a narrow zone called the intertropical convergence zone. ◆ Along parts of the equatorial trough of low pressure at certain times of year, the trades do not come together in convergence. Instead, a belt of calms and varible winds, called the doldrums, forms.

44. ◆ Between lat.35 and 60N and S is the belt of prevailing westerly winds, or westerlies. ◆ A wind system called the polar easterlies is characteristic of the arctic and polar zones.

45. Figure 4 Surface winds

46. Monsoon Winds of Southeast Asia ◆ In summer southern Asia develops a cyclone into which there is strong flow of air. From the Indian Ocean and the southwestern Pacific, warm, humid air moves northward and northwestward into Asia. This airflow constitutes the summer monsoon and is accompanied by heavy rainfall in southeastern Asia.

47. ◆ In winter, Asia is dominated by a strong center of high pressure from which there is an outward flow of air reversing that of the summer monsoon. Blowing southward and southeastward toward the equatorial oceans, this airflow constitutes the winter monsoon and brings dry weather for a period of several months.

48. Mountain winds and valley winds ◆ During the daylight hours the air along the slopes of the mountains is heated more intensely than the air at the same elevation over the valley floor. This warm air glides up along the slope and generates avalley wind.

49. ◆ After sunset the pattern is reversed. Rapid radiation heat loss along the mountain slopes results in cool air drainage into the valley below and causes the mountain wind.

50. Global Circulation ◆ The Hadley Cell Circulation In the zone between the equator and roughly 30° latitude, the surface flow is equatorward while the flow aloft is poleward. Near the equator the warm rising air that releases latent heat during the formation of cumulus towers is believed to provide the energy to drive this cell