Term Definitions Systems (Earth Systems)

System

An entity composed of diverse but interrelated parts that function as a complex whole

Component

Individual parts of a system can be a reservoir, an attribute of a system, or a subsystem

Negative Couplings

Links between system components that are negative (a change in one component stimulates a change of the opposite direction in the linked component)

Positive Couplings

Links between system components that are positive (a change in one component causes a change in the same direction in the linked component)

State

A set of attributes that characterize the system at a particular time

Flux

The rate of matter or energy movement (amount per unit). Synonyms: Input/Output, Flow, Transfer, and Converter

Reservoir

A place where matter or energy resides, Synonyms: Stock, Pool, and Storage

Cycle

Constant movement of material from one reservoir

Sink

If the flux of matter or energy into a reservoir is greater than the flux out

Source

If the flux of matter or energy out of a reservoir is greater than the flux in

Feedback

A self-perpetuating mechanism of change and response to that change

Negative feedback loop

Diminishes the effect of disturbances. Synonym: Balancing

Positive feedback loop

Amplifies the effect of disturbances. Synonyms: Reinforcing

Response Time

The length of time for a system to return to steady state after being perturbed

Residence Time

The length of time a substance remains in a given reservoir

Threshold

The level or value at which a rapid change in the system state, often from one equilibrium state to another, occurs. Synonyms: Tipping point

Perturbation

A temporary disturbance of a system

Forcing

A persistent disturbance of a system. Synonyms: Driver and Cause

Response

Change in a system as a result of perturbation or forcing. Synonym: Effect

Equilibrium State

Describes whether a system is stable or unstable

Stable System

Disturbances from equilibrium will be followed by system responses that return the system to its equilibrium state; results from negative feedback. Synonyms: Homeostasis or dynamic equilibrium

Unstable System

Disturbances from equilibrium will be followed by system responses that lead the system further from equilibrium; results from positive feedbacks

Steady State

No change in a component or source//sink in a system as a function of time, although the system may not be at equilibrium

System Diagram

A graphical representation of a system, showing system components and coupling

Box Model

A graphical and quantitative representation of a system, where reservoirs and fluxes are given values and followed through time. Synonyms: Dynamic systems model

Open System

Describes when matter and/or energy is lost from a system

Closed System

Describes when matter and/or energy is contained within a system