Atmospheric temperature

Review of last lecture Earth’s energy balance at the top of the atmosphere and at the surface. What percentage of solar energy is absorbed by the surface? Atmospheric influences on radiation (3 ways) What cause the greenhouse effect? What are the major greenhouse gases? Why is methane important? The three types of atmospheric scattering. What causes the blue sky? Why causes the reddish-orange sunsets? Sensible heat flux (dry flux from warm to cold regions) and latent heat flux (wet flux from wet to dry regions). Both proportional to surface wind speed

Atmospheric Thickness No defined top to the atmosphere The atmosphere is very shallow—and is less than 2% of the Earth’s thickness Over 90% of atmosphere in the lowest 16km & is where nearly all weather occurs

Temperature Basics Temperature – measure of average kinetic energy (motion) of individual molecules in matter Three temperature scales (units): Kelvin (K), Celsius (C), Fahrenheit (F) All scales are relative degrees F = 9⁄5 degrees C + 32 degrees K = degrees C + 273.15

Temperature Layers Due to Solar winds, Cosmic rays Due to ozone absorption of sunlight Decreasing rate w/ height (Lapse rate): 6.5 oC/km Due to surface heating (Longwave, Latent heat, Sensible heat)

Sub-layers in troposphere Definition of the boundary layer: "that part of the troposphere that is directly influenced by the presence of the earth's surface and responds to surface forcings (friction and heating) with a time scale of about an hour or less.” About 1 km deep. Often associated with turbulence.

Space shuttle Endeavour straddles mesosphere and stratosphere

An artist’s view

Video Weather: Wind

Horizontal distribution of temperature Isotherms – maps, connect lines of equal temperature

Seasonal variation of surface air temperature

Principal Controls on Temperature Latitudinal variations in net radiation Land-Water Contrasts Atmospheric Circulation Ocean Currents Altitude Local Effects

Controls on temperature 1. Latitudinal Variations in Net Radiation tropic-to-tropic – energy surplus poles – energy deficits ~ 38o N/S – balance imbalance of net radiation at surface  Equator/Tropics vs. high latitudes drives global circulation agents: wind, ocean currents, weather systems

Daily/Seasonal Radiation Patterns insolation peak vs. temperature daily lag seasonal lag Lag is function of type of surface, wetness, wind, etc

Seasonal variation of surface radiation

Seasonal variation of surface energy budget Storage change = net radiation - latent heat flux - sensible heat flux

Seasonal Temp Distributions T decreases poleward larger T gradient in winter isotherms shift seasonally NH steeper T gradient T over land > water in summer

Controls on temperature 2. Land-water contrasts Surface influences heating: Heat Capacity – water > land… (water takes longer heat/cool) Mixing – fluids can be physically mixed Transparency – greater penetration (distributed over greater volume) Evaporation – consumes large amount of energy – big over water

Temperature Ranges (Summer minus Winter) Large over land, small over ocean

Controls on temperature 3. Atmospheric circulation large scale circulation patterns resulted from pressure differences (gradients) generates winds  move warm/cold air around  affects temperature influences cloud cover

Controls on temperature 4. Ocean currents

Infrared Satellite image of the Gulf Stream Red/orange = 25-29oC Yellow/green = 17-24oC Blue = 10-16oC Purple = 2-9oC

Controls on temperature 5. Altitude Temperature decreases with increasing altitude  ground acts as heat source

Controls on temperature 6. Local effects slope orientation: North vs South-facing slopes  temperature/moisture regimes  vegetation forested vs open fields

Summary Thickness of the atmosphere: less than 2% of Earth’s thickness Definition of temperature. 3 units. Vertical distribution of temperature: 4 layers, what separate them? Horizontal distribution of temperature. 6 factors. Latitudinal variations in net radiation Land-Water Contrasts Atmospheric Circulation Ocean Currents Altitude Local Effects