Atmosphere

1. Atmosphere Structure and Composition

2. Concepts to learn The general concepts found in this section are: • The earth's atmosphere is a very thin layer wrapped around a very large planet. • Based on temperature, the atmosphere is divided into four layers: the troposphere, stratosphere, mesosphere, and thermosphere. • Energy is transferred between the earth's surface and the atmosphere via conduction, convection, and radiation. • Ocean currents play a significant role in transferring this heatpoleward. Major currents, such as the northward flowing Gulf Stream, transport tremendous amounts of heat poleward and contribute to the development of many types of weather phenomena.

3. Atmospheric Properties • The thin envelope of air that surrounds our planet is a mixture of gases, each with its own physical properties. • Two elements, nitrogen and oxygen, make up 99% of the volume of air. • The other 1% is composed of "trace" gases, the most prevalent of which is the inert gaseous element argon. • The rest of the trace gases, although present in only minute amounts, are very important to life on earth. • Two in particular, carbon dioxide and ozone, can have a large impact on atmospheric processes.

4. Another gas, water vapor, also exists in small amounts. It varies in concen-tration from being almost non-existent over desert regions to about 4% over the oceans. Water vapor is important to weather production since it exists in gaseous, liquid, and solid phases and absorbs radiant energy from the earth.

5. Atmospheric • The atmosphere is divided vertically into four layers based on temperature: the troposphere, stratosphere, mesosphere, and thermosphere. • In this portion of the unit we'll focus primarily on the layer in which we live - the troposphere.

6. Troposphere • The word troposphere comes from tropein, meaning to turn or change. All of the earth's weather occurs in the troposphere. • It extends from the earth's surface to an average of 12 km (7 miles). • The pressure ranges from 1000 to 200 millibars(29.92 in. to 5.92 in.). • The temperature generally decreases with increasing height up to the tropopause (top of the troposphere); this is near 200 millibars or 36,000 ft. • The temperature averages 15°C (59°F) near the surface and -57°C (-71°F) at the tropopause. • The layer ends at the point where temperature no longer varies with height. This area, known as the tropopause, marks the transition to the stratosphere.

7. Troposphere • Winds increase with height up to the jet stream. • The moisture concentration decreases with height up to the tropopause. • The air is much drier above the tropopause, in the stratosphere. • The sun's heat that warms the earth's surface is transported upwards largely by convection and is mixed by updrafts and downdrafts. • The troposphere is 70% N2 and 21% O2. • The lower density of molecules higher up would not give us enough to survive

8. Interactions - Atmosphere and Ocean • Water is an essential part of the earth's system. • The oceans cover nearly three-quarters of the earth's surface and play an important role in exchanging and transporting heat and moisture in the atmosphere. • Most of the water vapor in the atmosphere comes from the oceans.Most of the precipitation falling over land finds its way back to oceans.About two-thirds returns to the atmosphere via the water cycle. • You may have figured out by now that the oceans and atmosphere interact extensively. Oceans not only act as an abundant moisture source for the atmosphere but also as a heat source and sink (storage).

9. Heat transfer • The exchange of heat and moisture has profound effects on atmospheric processes near and over the oceans. • Ocean currents play a significant role in transferring this heat poleward. • Major currents, such as the northward flowing Gulf Stream, transport tremendous amounts of heat poleward and contribute to the development of many types of weather phenomena. • They also warm the climate of nearby locations. Conversely, cold southward flowing currents, such as the California current, cool the climate of nearby locations.

10. Energy Heat Transfer • Practically all of the energy that reaches the earth comes from the sun. • Captured first by the atmosphere, a small part is directly absorbed, particularly by certain gases such as ozone and water vapor. • Some energy is also reflected back to space by clouds and the earth's surface.

11. Conduction vs. convection • Energy is transferred between the earth's surface and the atmosphere via conduction, convection, and radiation. • Conductionis the process by which heat energyis transmitted through contact with neighboring molecules. • Some solids, such as metals, are good conductors of heat while others, such as wood, are poor conductors. Air and water are relatively poor conductors. • Since air is a poor conductor, most energy transfer by conduction occurs right at the earth's surface. • At night, the ground cools and the cold ground conductsheat away from the adjacent air. • During the day, solar radiation heats the ground, which heats the air next to it by conduction.

12. Convections Convectiontransmits heat by transporting groups of molecules from place to place within a substance. Convection occurs in fluids such as water and air, which move freely. • In the atmosphere, convection includes large- and small-scale rising and sinking of air masses and smaller air parcels. • These vertical motions effectively distribute heat and moisture throughout the atmospheric column and contribute to cloud and storm development (where rising motion occurs) and dissipation (where sinking motion occurs).

13. Convection • To understand the convection cells that distribute heat over the whole earth, let's consider a simplified, smooth earth with no land/sea interactions and a slow rotation. • Under these conditions, the equator is warmed by the sun more than the poles. • The warm, light air at the equator rises and spreads northward and southward, and the cool dense air at the poles sinks and spreads toward the equator. • As a result, two convection cells are formed.

14. Coriolis effect • Meanwhile, the slow rotation of the earth toward the east causes the air to be deflected toward the right in the northern hemisphere and toward the left in the southern hemisphere. • This deflection of the wind by the earth's rotation is known as theCoriolis effect.

15. Radiation • Radiation is the transfer of heat energy without the involvement of a physical substance in the transmission. • Energy travels from the sun to the earth by means of electromagnetic waves. • Most of the sun's radiant energy is concentrated in the visible and near-visible portions of the spectrum. Shorter-than-visible wavelengths account for a small percentage of the total but are extremely important because they have much higher energy. These are known as ultraviolet wavelengths. ________________

16. PART I – SUN’S RADIATION AND HEATING OF THE ATMOSPHERE , Pre-Lab • How is the surface of • Solar radiation is energy that is released by the sun in the form of particles or electromagnetic waves, and there is no need of a substance for transport.  • All forms of radiation coming out from the sun can be seen on the electromagnetic spectrum. 

17. Electromagnetic spectrum • Visible light energy coming from the sun is the only solar radiation wave that we can see naturally, and is made up of all colors (Red, Orange, Yellow, Green, Blue, Indigo, and Violet or ROYGBIV).  • 43% of the solar radiation output is visible light, 49% is infrared radiation, and 7% is ultraviolet radiation.  The remaining 1% is in the form of x-rays, gamma rays, and radio waves.  • radiation is absorbed by the ozone layer.  Some of the infrared radiation gets absorbed by the clouds and other atmospheric gases.  • Therefore most of the energy that reaches the Earth’s surface is in the visible part of the electromagnetic spectrum. 

18. Electromagnetic • The Earth’s surface absorbs the radiation, and then re-emits the radiation in the form of long-wave infrared.  The infrared radiation that the earth emits is a longer wavelength of infrared than what the sun emits.  • So the earth emits long-wave radiation (long-wave infrared) and the sun emits short-wave radiation (ultraviolet, visible, and short-wave infrared).

19. Electromagnetic • The radiation emitted by the earth, can then be absorbed by clouds and other atmospheric gases.  • The two primary gases that absorb long-wave radiation in the lower atmosphere are water vapor andcarbon dioxide.  • Methane, ozone, and chlorofluorocarbons can also absorb some of the long-wave radiation.  • The gases can then re-emit the energy again and send the energy back down towards the Earth’s surface.  • The emitting long-wave radiation from the earth and gases heats our planet from the surface up into the atmosphere.  • The sun’s short-wave energy DOES NOT directly heat up the atmosphere.  If that were the case, then outer space would be very warm and not extremely cold.  

20. PART II – ALBEDO • Reflection is when energy (radiation) is bounced off of an object at the same angle and intensity.  • Albedo is the percent of radiation that is reflected by a surface.  • Surfaces that reflect a lot of energy have a high albedo. 

21. Albedo • Energy that is reflected does not get absorbed by the surface and is not changed into the long-wave infrared radiation.  • Therefore, the gases in the atmosphere can’t absorb it and the temperature remains cool.  • Surfaces that absorb a lot of energy have a low albedo.  • The energy is re-emitted as long-wave infrared radiation which heats the atmosphere

22. Albedo Albedo = % incident energy reflected by a body • Fresh snow: 75 – 95% • Old snow: 40 – 60% • Desert: 25 – 30% • Deciduous forest, grassland: 15 – 20% • Conifer forest: 5 – 15% • Camera light meters set to 18%

23. Global Albedo

24. Albedo • Albedo is calculated as the amount of energy reflected from a surface divided by the total amount of incoming energy to the surface, multiplied by 100 to get a percentage. Albedo (%)  =   Reflected energy   x 100                                       Incoming energy • For example: if the amount of energy hitting a surface is 645 units and the amount of energy being reflected by that surface is 135 units, then the albedo of that surface would be: 135 units  x 100    or   0.209 x 100 =  20.9% 645 units • This means that 20.9% of the energy that is hitting the surface is getting reflected back into the atmosphere, while 79.1% (100-20.9%) of the energy is being absorbed by the surface.  The earth’s surface heats up, emits the long-wave infrared radiation which the gases absorb and radiate energy back to us.  This surface will have a warm air temperature over it. • EXERCISE 1:  Calculate the albedo of the surfaces listed on the worksheet.  Rank the surfaces from 1 to 3, with 1 being the surface with the warmest air temperature above it and 3 being the surface with the coolest air temperature above it.  Write your answers on the pre-lab worksheet.

25. PART III – DAILY MEAN TEMPERATURE AND THE DAILY RANGE • you will be asked to calculate the daily mean temperature and the daily temperature range.  The daily mean temperature or average temperature is calculated by averaging the 24 hour readings from each hour of the day or by averaging the high and low temperature throughout the day.  Maximum Temp. + Minimum Temp.        =   Daily Temperature Mean                           2 •  The daily temperature range is simply the difference between the high and low temperatures.  Under normal conditions, the smaller the temperature range the more humid an observing station is.  The greater the temperature range, the less humid an observing station is.

26. Exercise 2 • EXERCISE 2 – Calculate the daily mean temperature and the daily range for each of the three cities listed on the worksheet.  Rank the three cities from 1 to 3, with 1 being the most humid and 3 being the least humid.  Write your answers on the pre-lab worksheet.

27. Temperature Controls  Cloud Cover and Albedo • remember that Albedois the fraction of total radiation that is reflected by any surface. • Many clouds have a highalbedo and therefore reflect back to space a significant portion of the sunlight that strikes them.

28. Clouds Reflect and Absorb Radiation

29. Clouds Reflect and Absorb Radiation • Clouds • On Earth, water naturally occurs in all 3 phases or states of matter (gas, liquid, solid) • Clouds are composed of tiny liquid waterdroplets or tiny ice crystals. • Clouds are not made of water vapor (Otherwise, we wouldn’t be able to see them!) • In nature, clouds form when the temperature of air is lowered to its dewpoint temperature.

30. Local Temperature Variations Equator The angle of sunlight varies with latitude. Atmosphere VOCABULARY The intensity of insolation (measure of solar radiation) depends upon the angle at which sunlight strikes Earth’s surface. The intensity is greatest at low latitudes, during the summer, and around noon. isotherm A contour line drawn on a weather map through places having the same atmospheric temperature at a given time.

31. Tilt of Earth’s Axis Insolation: The solar (energy) radiation that reaches Earth. reaches Earth. **The Axial Tilt of the Earth is the cause of the seasons.

32. Tilt of Earth’s Axis Altitude of sun affects amount of energy received at surface because lower angle -> more spread out and less intense radiation (as for flashlight beam). lower angle -> more of atmosphere to pass through, and hence more chance to be absorbed or reflected (can look at sun at sunset).

33. New Orleans New Orleans SUN’S RAYS Equator Equator June 21 Dec. 21 During the summer, the Northern Hemisphere is tiltedtowards the Sun. Here, locations receive the Sun’s most direct rays, and have longer periods of daylight hours. During the winter, the Northern Hemisphere is tiltedaway from the Sun. Periods of daylight are shorter, and the Sun’s rays are less direct.

34. Solstices and Equinoxes During the vernal (spring) and autumnal (fall) equinoxes, neither hemisphere is tilted towards or away from the Sun. On these dates, every location on Earth receives 12 hours of daylight and 12 hours of darkness.

35. Atmosphere Characteristics  Solstices and Equinoxes • The summer solsticeis the solstice that occurs on June 21 or 22 in the Northern Hemisphere and is the “official” first day of summer. • Thewinter solsticeis the solstice that occurs on December 21 or 22 in the Northern Hemisphere and is the “official” first day of winter.

36. Atmosphere Characteristics  Solstices and Equinoxes • The autumnal equinox is the equinox that occurs on September 22 or 23 in the Northern Hemisphere. • The spring equinox is the equinox that occurs on March 21 or 22 in the Northern Hemisphere.

37. Temperature Controls  Earth’s Motions • Earth has two principal motions—rotation and revolution. Rotation = 24 hours Revolution = 365 days  Earth’s Orientation • Seasonalchanges occur because Earth’sposition relative to the sun continually changes as it travels along its orbit.

38. Temperature Controls  Factors other than latitude that exert a strong influence on temperature include heating of land and water, altitude, geographic position, cloud cover, and ocean currents. • Geographic Position • The geographic setting can greatly influencetemperatures experienced at a specific location. • Land and Water • Land heats more rapidly and to higher temperatures than water. Land also cools more rapidly and to lower temperatures than water.

39. Temperature Controls What determines temperature? • Latitude: locations at lower latitudes typically experience highertemps year-round than higher latitude locations, because the lower latitudes receive moresolar energy • Proximity to water: locations near water, especially a coolocean current, have smaller annual tempranges than landlocked locations • Elevation: locations at higherelevations (altitude) usually have cooler conditions than locations at lower elevations

40. Observing the Atmosphere • Air Pressure: force per area exerted by the mass of air above a point • Measured in: • Inches of mercury (in. Hg) • Millibars (mb) • Average sea-level pressure = 1013.25 mb or 29.92 in. Hg • Air pressure is Measured using a barometer

41. Mercury Barometer Barometer - apparatus used to measure pressure;  is derived from the Greek "baros" meaning "weight"  Aneroid Barometers: (without liquid)

42. Air Pressure • By lucky coincidence, earth’s atmospheric pressure is approximately neat round numbers in metric terms • 14.7 pounds per square inch, PSI (1 kg/cm2) • Pressure of ten meters of water • Approximately one bar or 100 kPa • Weather reports use millibars (mb) • One mb = pressure of one cm water

43. The Effect of the Ocean on Annual Temperature

44. Dew Point • The dew point is the temperaturebelow which the water vapor in a volume of humid air at a constant barometric pressure will condense into liquid water. • Condensed water is called dew when it forms on a solid surface. • The dew point is a water-to-air saturationtemperature.