GEO1010 tirsdag 31.08.2010 Jørn Kristiansen; jornk@met.no I dag: Først litt repetisjon Stråling (kap. 4) Atmosfærens sirkulasjon (kap. 6)
Latitudinal Geographic Zones Figure 1.12
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Temperature Profile Figure 3.6
Temperature Inversion Figure 3.10
Latitude and Temperature Figure 5.4
Altitude Normal lapse rate Thinner atmosphere with height => greater diurnal temperature range Figure 5.5
Land Water Heating Differences and locally Figure 5.7
Marine and Continental Climates: Trondheim vs. Verkhoyansk Figure 5.16
Global Temperature Ranges Figure 5.19
Solar and Terrestrial Energy Figure 2.7
Figure 2.9
Reasons for Seasons Revolution Rotation Tilt of Earth s axis Axial parallelism Sphericity
Annual March of the Seasons Figure 2.15
Atmosphere and Surface Energy Balances
Earth Atmosphere Energy Balance Figure 4.12
Short-Wave Essentials Insolation at TOA and surface Scattering (diffuse radiation) Albedo and reflection Absorption
Insolation at Top of Atmosphere Figure 2.10
Insolation at Earth s Surface Figure 4.2
Scattering and absorption
About scattering and absorption Atmospheric gases and particulates (clouds and aerosols) interact with insolation (scattering and absorption) Absorption Assimilation of energy by molecules of matter (air, vapour, solid); raises temperature Reemitted as longwave radiation or converted to chemical energy by plants Scattering Redirects radiation without changing the wavelength Direct to diffuse radiation Rayleigh scattering (air molecules): The shorter the wavelength, the greater the scattering (and vice versa) Blue skies (but haze appears almost white) Red sun (direct minus diffuse radiation)
Earth Atmosphere Energy Balance Figure 4.12
Albedo Solar radiation reflected by the Earth- Atmosphere system back to space (backscattering) Reflective fraction = albedo Gases + Aerosols (7%), Clouds (21%) and Surfaces (3%) reflect radiation
Figure 4.5 Albedo
July and January Albedos Figure 4.6
Non-solar Heat Transfer Conduction Molecule-to-molecule transfer Convection Energy transferred vertically by movement (fluids) Advection Horizontally dominant movement (fluids) Radiation Energy traveling through air or space
Energy Balance in the Troposphere The Earth-atmosphere system is in radiative equilibrium at TOA
The Greenhouse Effect and Atmospheric Warming Atmosphere absorbs heat energy Re-emits to space and Earth s surface at lower temperatures; warms the troposphere Atmosphere delays transfer of heat from Earth into space until air-surface temperatures are increased to compensate for the increased absorption
Clouds and Forcing Figure 4.10
Earth Atmosphere Energy Balance Summary Figure 4.12
Energy Budget by Latitude Figure 4.13
Energy Balance at Earth s Surface
Insolation at Earth s Surface Figure 4.2
Diurnal insolation at surface Figure 4.14
Simplified Surface Energy Balance NET R = +SW (insolation) SW (reflection) +LW (infrared) LW (infrared) Midlatitude, summer day over land Figure 4.16
Global NET R mean annual Figure 4.17
Net radiation is expended through three pathways LE latent heat of evaporation (dominant expenditure of NET R) H sensible heat; conduction and convection (20% of NET R) G ground heating and cooling; 1) conduction within the soil or conduction and motion within water (annual mean is 0); 2) snow and ice melt
Global Latent Heat Figure 4.18
Global Sensible Heat Figure 4.19
Atmospheric and Oceanic Wind Essentials Circulations Driving Forces within the Atmosphere Atmospheric Patterns of Motion Oceanic Currents
Wind Horizontal gradients (differences) in pressure (the pressure force) produce wind Winds direction is defined along longitude (u) and latitude (v) where positive values are westerly (wind from the west blowing eastward) and southerly (wind from the south blowing northward) Figure 6.4
Local (small-scale) winds
Land-Sea Breezes See slide on Land-water heating differences Figure 6.18
Mountain-Valley Breezes Mountain lower density air results in greater night time cooling (and day time warming) Valley heating pot during daytime when solar energy input is effectively captured by the geometry of the valley Figure 6.19
Katabatic winds Larger scale and more intense than mountain and valley breezes Radiative cooling of a plateau Most commonly found blowing out from the large and elevated ice sheets of Antarctica and Greenland
Monsoonal Winds Figure 6.20
Large-scale wind patterns
Driving Forces within the Atmosphere Gravity vertical; uniform worldwide Pressure Gradient Force vertical and horizontal Coriolis Force - horizontal Friction Force - horizontal
Coriolis Force Increases with increasing speed and latitude Figure 6.9
Pressure Gradient km Figure 6.7
Horizontal balance of forces in the lower troposphere Figure 6.8
Horizontal balance of forces in the upper troposphere Geostrophic winds Figure 6.8
Primary High-Pressure and Low-Pressure Areas Equatorial low-pressure trough (ITCZ) Polar high-pressure cells Subtropical high-pressure cells Subpolar low-pressure cells
Climatological Mean Surface Pressure Figure 6.10
Climatological Mean Surface Pressure Figure 6.10
General Atmospheric Circulation Figure 6.12
General Atmospheric Circulation Hadley cell Figure 6.12
Equatorial Low-Pressure Trough Intertropical convergence zone (ITCZ) Convergence of wind along a narrow band Constant high Sun altitude and consistent daylenght => large amounts of energy available throughout the year Warm, moist air ascends Deep clouds (often to tropopause) with heavy precipitation Trade winds (calm)
June July ITCZ Figure 6.11
Wind Portrait of the Pacific Ocean -from satellite -inferred from observation of ocean waves Figure 6.6
Subtropical high-pressure cells Descending branch of the Hadley cell Between 20 and 35 degrees N/S (depending on season) Hot, dry dessert air Cloudless skies Mid-latitude surface westerlies
General Atmospheric Circulation Figure 6.12
General Atmospheric Circulation Figure 6.12
Subpolar low-pressure cells Over the oceans around 60N Aleutian Low Icelandic Low Weaken or disappear in summer Polar front
Climatological Mean Surface Pressure Figure 6.10
Upper Atmospheric Circulation In the Extra-tropics 500 hpa and above (i.e. from about 5 to 12 km) Part of large-scale weather systems that extends vertically from the surface to the tropopause and horizontally over several 1000 km.
Rossby Waves Figure 6.16
Jet Streams Figure 6.17
Oceanic Currents Surface Currents Deep Currents
Major Ocean Currents Figure 6.21
Deep-Ocean Thermohaline Circulation Figure 6.22