20C-L02-Climate

Biology 20C - Fall 1998

ECOLOGY AND EVOLUTIONARY BIOLOGY

Lecture 2 - Abiotic Environment: Climate, Weather, Micro-environment

Prevailing regimes of heat and water are usually the major determinants of the abiotic environment. On different spatial and temporal scales, they are expressed as climate, weather and micro-environment. Other physical and chemical factors may modify the basic patterns, or act in addition. We will concentrate on processes responsible for climatic patterns, but analogous processes, acting on smaller temporal and spatial scales, modify the larger-scale climatic patterns to produce local weather and micro-environments.

		_________Scale of Variation__________
	_Scale_	___Ecological___	_Spatial_	_Temporal__
Climate	Regional	Community-Ecosystem	10³ - 10⁴ km	10¹ - >10⁴ years
Weather	Local	Population-Community	10¹ - 10² km	10^-1 - 10¹ days
Micro-environment	Individual	Individual-Population	10^-3 - 10¹ m	10^-2 - 10¹ hours

Climate can be thought of as being the long-term outcome of a variety of processes involving the Gain, Storage, Transport and Loss of heat and water by the medium (gas, liquid or solid) that supports and/or surrounds the organisms. It is useful to emphasize flows of heat and cycles of water driven by physical processes:

	Gain è	Storage è	Transport è	Loss
HEAT	Radiation è (from sun)	Absorption è	Conduction, è Convection, Radiation	Radiation (to space)

WATER	Precipitation è	Oceans, è Lakes, Ice, Rock, Soil	Streams, è Currents, Atmosphere	Evaporation

MODELS

Models are tools that scientists use to help them explore and understand natural systems. While there are many kinds of models, four kinds commonly used by scientists are:

	Conceptual	= Verbal
	Visual	= Graphs, diagrams, drawings, flowcharts, etc.
	Physical	= Machines, scale replicas, etc.
	Mathematical	= Equations, simulations, graphical, etc.

Models are constructed and used for many different purposes, that are limited mainly by human imagination. Models cannot be used to recreate the "real world": while they all simulate some aspects of reality, they must not be confused with "reality". Common uses of models include:

*	Simplify; reduce complexity
*	Study a few parts of the system in isolation
*	Seek generalizations
*	Explore and test logic
*	Make projections of logical consequences of a specified situation
*	Make predictions of "real" situations in the future
*	Distinguish essential from non-essential parts of the system
*	Generate testable hypotheses
*	Test hypotheses
*	Explore "limiting cases" or "boundary conditions"

MODEL OF GLOBAL CLIMATES

The following conceptual/physical model answers the question: What are the minimal, essential components, processes and properties required to generate the regional patterns of climate observed on the surface of the Earth?

This model should also be studied as an example of how models are constructed, tested, modified and improved. The process is based on the standard "scientific method":

	1.	Pose a simple hypothesis based on a few assumptions
	2.	Project the long-term equilibrium outcome
	3.	Test the assumption by comparing the outcome with observations
	4.	Modify the hypothesis and/or assumptions to minimize deviations
	5.	Repeat the process (go back to step 2)

The model is presented as a sequence of 10 steps. At each step, several assumptions are made about what materials are present, and about how they may be moving:

	Prior = assumptions continuing unchanged from the previous step
	New = assumptions being made for the first time, or being changed in this step

	Climate = logical projections from those assumptions in a system at equilibrium, and assuming that nothing else is involved

STEP 0: The simplest possible climate!
Assume:	Materials_______________	Motions_____________________
Prior	Nothing	None

New	+ Nothing	+ No motion

Climate	It has no climate	And nothing is moving

STEP 1:	We have a planet!
Assume:	Materials__________________	Motions____________________
Prior	Nothing	No motion

New	+ Space + Ball of Rock

Climate	Eternally Cold - near 0^oK (-273^oC) Eternally Dark Nothing ever moves

STEP 2: Let there be light! [Fig. 46.4}
Assume:	Materials_________________	Motions______________________
Prior	Space; Rock	No motions

New	+ Star (radiation, heat)	Positions fixed

Climate	Eternal Day/Night hemispheres Eternal, intense temperature gradients: Day/Night Equator/Pole

STEP 3: Pre-Galilean universe
Assume:	Materials_________________		Motions______________________
Prior	Space; Rock; Star		No motions

New			+ Star Orbits Rock (24 hours)

Climate		24 hr Day/Night Less extreme temperature gradients Especially at equator Slight moderation at poles Diurnal temperature fluctuations Daily cycle - constant amplitude Amplitude varies with latitude (max. at equator; none at poles) Moderated average temperatures

STEP 4: Let there be mighty winds, etc.[Fig. 46.6]
Assume:	Materials__________________	Motions______________________
Prior	Space; Rock; Star	Star orbits rock

New	+ Atmosphere

Climate	Much less extreme temperature gradients (buffered) Transport, insulation Hemispheric convection cells in Troposphere (7 - 25 km) 3 cells (Hadley, Ferrel , Polar ) Driven mainly by equatorial heating; aided by polar cooling North/South winds - top and bottom of each cell move in opposite directions 3 hemispheric bands Hurricane force Extreme diurnal changes in strength Latitudinal pressure zones bound cells: Alternating pressure from Equatorial Low to Polar High Calm zones (little wind) between wind belts Equatorial "doldrums" (5^o N - 5^o S) Mid-latitude "horse latitudes" (30^o - 40^o N and S) No seasons - only constant amplitudes of diurnal and latitudinal variation in wind strength and temperature

STEP 5: Let the earth move!
Assume:	Materials__________________	Motions______________________
Prior	Space; Rock; Star; Atmosphere	Star orbits rock; Winds

New		+ Rock Rotates on Axis (to east; 24hr)

Climate	Coriolis "Force" ( = inertia, not a physical force) Deflects equatorward winds to west (NE and SE Tradewinds; Polar Easterlies) Deflects poleward winds to east (high latitude Westerlies; "Roaring Forties") No seasons - only constant amplitudes of diurnal and latitudinal variation in wind strength and temperature N.B. Winds are named for the direction FROM which they are coming.

STEP 6: The "Leaning Tower"! [Fig. 46.5]
Assume:	Materials__________________	Motions_______________________
Prior	Space; Rock; Star; Atmosphere	Star orbits rock; Axial rotation; Winds

New		+ Axial Tilt (23.5^o from vertical to "plane of the elliptic")

Climate	Eternal Seasons - half of each hemisphere always summer; half always winter

STEP 7: Annual seasons! [Fig. 46.5]
Assume:	Materials__________________	Motions______________________
Prior	Space, Rock, Star, Atmosphere	Axial rotation; Axial tilt Winds

Delete		- Star Orbits Rock
New		+ Rock Orbits Star (1 year)

Climate	Annual seasons

STEP 8: Water, water, everywhere! [Fig. 46.6]
Assume:	Materials_________________		Motions_______________________
Prior	Space; Rock; Star; Atmosphere		Rock orbits star; Axial rotation; Axial tilt Winds

New	+ Water layer (No Land)

limate		Thermal capacity of oceans buffers temperature gradients, latitudinal gradients, wind velocities. Atmospheric water and clouds further buffer extremes. Conditions approach those observed on earth. Climatic bands parallel equator Rain belts in low pressure convergences Doldrums = Inter Tropical Convergence Zone (ITCZ) (Amazon, Congo) Sub-polar convergences (Pacific Northwest; northern Europe) Arid belts in high pressure divergences Horse latitudes (California; Middle East; Gobi; Kalahari) Polar deserts (Antarctica) Circum-global currents Equatorial Currents, driven by tradewinds Sub-polar West Wind Drift N.B. Currents are named for the direction TOWARDS which they go.

STEP 9: Let there be land!
Assume:	Materials_________________	Motions______________________
Prior	Space; Rock; Star; Atmosphere; Oceans	Rock orbits star; Axial rotation; Axial tilt Winds; Currents

New	+ Continents

Climate	Gyral oceanic currents in each hemisphere Deflected N or S by land Intensified by Coriolis Force adding E or W deflections to N or S currents Intensified further by wind-driven Ekman Transport Causes upwelling along coastlines where currents flow towards equator (eastern sides of ocean basins) leading to vertical circulation of oceans Modified latitudinal widths of climatic bands; bands no longer exactly parallel equator on continents Expand moist climates on east of continents Expand dry climates on west of continents

STEP 10: Home, Sweet Home. (Messy but Comfortable)! [Fig. 46.7]
Assume:		Materials_________________	Motions_______________________
Prior		Space; Rock; Star; Atmosphere; Oceans; Continents	Rock orbits star; Axial rotation; Axial tilt Winds; Currents

New		+ Mountain Ranges

Climate	Interrupt latitudinal climatic bands Alter course of latitudinal winds N/S ranges block or deflect winds (Rockies, Andes) E/W ranges channel latitudinal winds (Atlas, Alps, Himalayas) Create orographic rains to windward Create rain shadows to leeward Intensify and direct monsoons Responsible for El Nino?

Development of this model illustrates that climate is a consequence of :

Essential Interactions between land, sea, air (and "space")

Flows of heat; and Cycling of water

Essential Interactions between regimes of heat and water.

Dynamic processes.

Buffering of thermal gradients and transport systems in space and time

Modification of temperature and water regimes by other factors

Global climates are expressed as characteristic regional patterns of:

TEMPERATURE

RAINFALL

SOILS

TERRESTRIAL VEGETATION (= BIOMES)