Meteorology Lecture 1

Weather and Climate Review

What drives our weather?

• The sun

• Insolation – solar energy reaching the Earth

• Remember the sun’s output can vary, which impacts weather on Earth– e.g. The Little Ice Age

Folklore: Sirius – The Dog Star

• Thought to produce heat at the end of summer

• Worshipped by numerous civilizations

• The “Dog Days of Summer”

Sirius

Sun

What about the Moon?

• Does it warm the Earth?

• Why does it glow?Albedo – % of insolation an object reflects

High – light surfacesLow – dark surfaces

Solar Radiation and Earth’s Surface

Why do we have seasons?

Sun conditions at the Solstices and Equinoxes

Solar declination: latitudinal change ofatitudinal change of subsolar pointssubsolar points

Energy Pathways

Figure 4.1

Heat Transfer

• Heat – energy produced by the motion of molecules and atoms in a substance

• 4 ways to transfer heat:

1. Radiation – electromagnetic waves (sunlight)

2. Conduction – energy moved from high to low

3. Convection – vertical movement of energy

4. Advection – horizontal movement of energy

Earth’s Modern Atmosphere

• The atmosphere is absolutely essential for life on Earth

• Earth’s atmosphere exists in a series of spheres or layers that grade into one another  

• Layers: Composition, temperature, and function  

Protective Atmosphere

Figure 3.6

Energy Balance in the Troposphere  • Greenhouse Effect – where gases

(carbon dioxide, water vapor, methane, nitrous oxide, and CFCs) absorb insolation and reradiate it back to Earth in longer wavelengths thereby warming the lower troposphere

• The Greenhouse Effect and Atmospheric Warming– Atmosphere absorbs heat energy– Atmosphere delays transfer of heat from

Earth into space

Local Factors Influencing Air Temperature

• Urban Effect– Urban Heat Island

• Darker surfaces – less reflection• Less forest cover• Less water on surface• Heat from human energy use

The Urban Environment

Figure 4.21

Urban Heat Island

Figure 4.22

Global NET R

• Surfaces lose heat in one of 3 ways:– Latent heat of evaporation – energy released

as water changes state; can’t feel it– Sensible heat – heat you can feel and

measure; convection and conduction– Ground heating and cooling – energy stored

during warm periods and released during cool periods

Radiation Budgets

Figure 4.20

El Mirage, CA

Pitt Meadows,BC

Principal Temperature Controls

• Latitude

• Altitude

• Cloud Cover

• Land-Water Heating Differences

Latitude and Temperature

Figure 5.4

• Latitude  – Affects insolation– Sun angles– Daylength

Altitude

Figure 5.5

• Altitude  – High altitude has greater daily range– High altitude has lower annual average

Cloud Cover

Land–Water Heating Differences 

• Evaporation (= latent heat)

• Transparency (= penetration of insolation)

• Specific heat (differs among objects)

• Movement (= vertical mixing)

• Ocean currents and sea surface temperatures(= spread of energy spatially)

All this leads to this important concept:Marine vs. continental effects

Land–Water Heating Differences  

Figure 5.7

Global Temperature Ranges

Figure 5.17

Atmospheric Pressure Systems

High-pressure system-also called anticyclone-circulating body of air-descending air-clockwise circulation innorthern hemisphere

Low-pressure system-also called cyclone-circulating body of air-rising air-counterclockwise circ. in northern hemisphere

Atmospheric Pressure Map

Isobars – lines of equal air pressure on a map

Wind DirectionWinds are named according to the direction FROM which they are blowing

Direction of Air Flow• Unequal heating of land surfaces

• Pressure gradient force – air flows from high to low

• Coriolis force – deflection or change in direction caused by Earth’s rotation

• Frictional forces – places a drag on that air flow

Pressure Gradient Force

Fluctuations in the Pressure Gradient

High pressure to low pressure, perpendicular to isobars

Coriolis Force•Due to Earth’s rotation

•Pulls wind to right in northern hemisphere

•Pulls wind to left in southern hemisphere

•Strongest at poles

•None at equatorCoriolis Force

Frictional Forces

• Near surface, friction (f) works against pressure gradient force (pgf), so resulting wind direction is between pressure gradient force and coriolis force (cf)

pgf

f

cf – northern hemisphere

WIND

Three Forces Combined

Rossby Waves

Figure 6.17

Strong boundaries often

occur between warm and cold

air. In the mid-latitudes, the

polar front marks this thermal

discontinuity at the surface.

The Polar Front and Jet Streams

Relative Humidity• Relative humidity is the indication of how

close the air is to saturation and when condensation will begin

• Dew-point temperature not really a temperature, but a measure of moisture content

• When air temperature tries to decrease below the dew point, surplus water vapor is removed from the air by condensation

Relative Humidity

Figure 7.8

Cooling

Warming

Actualwater vapor

Hydrologic Cycle