GY205 Weather and GY205 Weather and ClimateClimate

Lecture 2Lecture 2

(Please turn in homework on the table.)(Please turn in homework on the table.)

Solar Radiation InteractingSolar Radiation Interactingwith the Atmospherewith the Atmosphere

• Absorption – some solar energy is absorbed, heating the atmosphere directly

• Reflection – solar energy is redirected, not absorbed

• Most natural surfaces are diffuse reflectors, scattering energy

Reflection and ScatteringReflection and Scattering

Rayleigh ScatteringRayleigh Scattering• Caused by gas molecules• Energy scattered in all directions• Mostly scatters shorter wavelengths

MythbusterMythbuster

• The sky is blue because air molecules scatter the blue wavelength of incoming visible light, NOT because the sky is reflecting the ocean.

Mie ScatteringMie Scattering• Caused by aerosols• Most energy scattered forward• Scatters all wavelengths• Causes gray and hazy skies

Nonselective ScatteringNonselective Scattering• Caused by water droplets in clouds• Scatters all wavelengths about equally• Makes clouds white

AlbedoAlbedo• Percentage of visible light reflected• Earth’s albedo is 30%

Atmosphere Energy Atmosphere Energy Balance Balance

Earth’s Energy BudgetEarth’s Energy Budget•The amount of energy entering the atmosphere equals the amount of energy leaving

Global Warming Global Warming

The Greenhouse EffectThe Greenhouse Effect

The Greenhouse EffectThe Greenhouse Effect

• Shortwave radiation from the sun passes through the atmosphere and is absorbed by the surface, warming it

• The earth emits longwave radiation which is partially absorbed by “greenhouse gases” warming the atmosphere

• The atmosphere is mostly heated from below

MythbusterMythbuster

• The greenhouse effect is GOOD, without it earth would be freezing cold

• Increasing “greenhouse gases” is bad since more energy is absorbed in the atmosphere, and the result is global warming

HeatHeat• Sensible heat – heat that you can sense• Latent heat – heat stored and released during

phase changes

Water Phase Changes Water Phase Changes

TemperatureTemperature

• Not the same as heat

• Measure of average kinetic energy of molecules in a substance

• A cup of coffee may have a higher temperature than the ocean, but the ocean contains much more heat

Influences on TemperatureInfluences on Temperature• Latitude• Altitude• Cloud cover• Large bodies of water• Ocean currents• Slope aspect• Vegetation• Time of day

Temperature GradientsTemperature Gradients• Changes in temperature with distance• Isotherms – lines of equal temperature

ThermometersThermometers

• Mercury or alcohol• Bimetallic strip• Thermistors

Wind Chill Temperature IndexWind Chill Temperature Index

PressurePressure

• Air has mass and weight

• Gas molecules are in motion

• Pressure is the force these molecules exert on a surface

• Sea level pressure is 14.7 psi, 29.92”Hg, or 1013.2 mb

Temperature and PressureTemperature and Pressure

Cooler Warmer

Mass of Air and PressureMass of Air and Pressure

Pressure Decreases with AltitudePressure Decreases with Altitude

BarometersBarometers• Used to measure pressure• Mercury or aneroid type

Horizontal Pressure GradientHorizontal Pressure Gradient• Changes in pressure with distance• Caused by uneven heating of earth’s surface• Isobars – lines of equal pressure

WindWind• Differences in pressure result in the

pressure gradient force

• The PGF starts the wind blowing

• Wind blows away from areas of higher pressure and toward areas of lower pressure

The Coriolis EffectThe Coriolis Effect• An object traveling in a straight line across a

rotating surface appears to curve relative to the surface

Coriolis Force Coriolis Force

MythbusterMythbuster

• The Coriolis effect does NOT cause the water to flow down a drain one way or the other.

Frictional ForceFrictional Force

• Force that opposes motion between objects that are touching

• Stronger nearer the surface

• Lowers wind speed

• Reduces Coriolis effect

• Affected by surface roughness

Wind Pattern Wind Pattern Development Development

Pressure Systems and WindPressure Systems and Wind• Cyclones are low-pressure systems

• Anticyclones are high-pressure systems

Cyclones and Cyclones and Anticyclones Anticyclones

Troughs and RidgesTroughs and Ridges• Troughs form around low-pressure systems• Ridges form around high-pressure systems

Measuring the WindMeasuring the Wind• Wind direction is always given as the direction the

wind is blowing from • Wind vane – points into the wind• Anemometer – measures wind speed• Aerovane – measures both

GY205 Weather and GY205 Weather and ClimateClimate

End of Lecture 2