Energy & Energy Transfer
Readings
A&B: Ch 2. (p.
31-36)
www: 3. Energy
& Energy
Transfer
Lab 5
Topics
1. Energy - physical
definition
2. Energy
Conversion and
Transfer Modes:
a. Radiation
b. Conduction
c. Convection
3. Conservation of
Energy
G109: Weather and Climate
Energy - A Physical Definition
•
Energy:
ƒ
ƒ SI unit of energy: joule [J = kg m2 s-2]
•
Power: Energy per time
ƒ Rate at which energy is released, transferred or
received
ƒ SI unit: Watt [W = J s-1 = kg m2 s-3]
•
Energy Flux: Energy transfer per time per unit
area
ƒ SI unit: [W m-2]
1st Law of Thermodynamics:
ƒ
G109: Weather and Climate
3: Energy & Energy Transfer
Forms of Energy
•
Kinetic energy:
ƒ Motion of e.g. raindrops, water, dust
ƒ Electrical energy: Motion of ions
ƒ Heat energy: Microscopic motion of molecules
and atoms
• Temperature: measure of average speed of
atoms and molecules
•
Potential energy:
ƒ Gravitation potential energy
• e.g., water behind a dam, cloud droplets high in
atmosphere
ƒ Chemical energy
• e.g., battery, food, wood
G109: Weather and Climate
3: Energy & Energy Transfer
Forms of Energy
G109: Weather and Climate
3: Energy & Energy Transfer
Energy Conversion and Transfer
•
•
Energy can be converted from one form to
another
Energy can be transported from one place to
another:
ƒ Conduction:
•
ƒ Convection:
•
ƒ Radiation:
•
G109: Weather and Climate
3: Energy & Energy Transfer
Conservation of Energy
•
First Law of Thermodynamics
ƒ Energy can be neither created nor destroyed
ƒ One of the most fundamental laws of nature
 Energy is conserved 
•
Systems Approach to Conservation Principle
Input
shortwave
solar radiation
G109: Weather and Climate
System:
transformation
storage
Earth/Atmosphere
System
Output
longwave
terrestrial radiation
3: Energy & Energy Transfer
Conservation of Energy: Two Possibilities
i.
Input = Output
ƒ
ƒ
ƒ
No change of energy status of the system
The system is
Output energy is not necessarily in the same
form as the input energy (but same amount)
ii. Input = Output + Storage Change
ƒ
ƒ
ƒ
The system has gained/lost energy from/to its
environment
The system is
Energy transformations take place
Input
System:
transformation
storage
Output
G109: Weather and Climate
3: Energy & Energy Transfer
Conservation of Energy:
Thermal Consequences
i.
Equilibrium (Input = Output)
ƒ
ƒ
No temperature change
In Earth/Atmosphere-system: occurs over
• Medium time scales →
• Good approximation over
• Good approximation over
ii. Non-equilibrium (Input =Output +Storage ∆)
→
ƒ In Earth/Atmosphere-system: occurs over
• Short time scales →
• Very long time scales →
• Small spatial scales
G109: Weather and Climate
3: Energy & Energy Transfer