Climate & Climatic Variation (Chapter 2). CLIMATE = 1. Statistics of Weather Daily Precipitation -...

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Climate & Climatic VariationClimate & Climatic Variation

(Chapter 2)(Chapter 2)

CLIMATE =CLIMATE =

1. Statistics of Weather1. Statistics of Weather

Daily Precipitation - Iowa/Nebraska

CLIMATE =CLIMATE =

1. Statistics of Weather1. Statistics of Weather

2.2. The expected weather + The expected weather + departures from expected departures from expected weatherweather

CLIMATE CLIMATE

Reflects the geophysical processes active at Reflects the geophysical processes active at a location…a location…

Northeastern Siberia

Namibia

Amazon

Rainforest

CLIMATE =CLIMATE =

……and how they might change (e.g., seasonally)…and how they might change (e.g., seasonally)…

Winter Daily Precipitation - Iowa/Nebraska

CLIMATE =CLIMATE =

Summer Daily Precipitation - Iowa/Nebraska

……and how they might change (e.g., seasonally)…and how they might change (e.g., seasonally)…

… and in the future! (and of course the past)

CLIMATECLIMATE

1.1. Implies samples over a period of time. Implies samples over a period of time. How long? How frequent?How long? How frequent?

2. WMO standard: 30 years2. WMO standard: 30 years

- which 30?which 30?

- paleoclimate?paleoclimate?

3. There is no universal standard, but 3. There is no universal standard, but mustmust define the interval for the topic at handdefine the interval for the topic at hand

CLIMATECLIMATE

1.1. Has regular cycles …Has regular cycles …

CyclesCycles - Net Radiation

FSHFLH

- Net Radiation

Grassland

Dry Lake

Diurnal

CyclesCycles

Annual

Soil Temperature at depths marked

CLIMATECLIMATE

1.1. Has regular cycles …Has regular cycles …

2.2. … … with other types of variability with other types of variability superimposed …superimposed …

Climatic Variation and ChangeClimatic Variation and Change

(IPCC TAR, Ch. 2)

Note: Note: Trends, Abrupt Change, StationarityTrends, Abrupt Change, Stationarity

(IPCC TAR, Ch. 2)

Note: Note: Quasi-periodicQuasi-periodic

Increased range of variabilityIncreased range of variability

Additional FactorsAdditional Factors

1.1. Abrupt changeAbrupt change- external conditions (e.g., solar output)external conditions (e.g., solar output)

- internal feedbacksinternal feedbacks

- passing a threshold (e.g. ice caps passing a threshold (e.g. ice caps melting)melting)

2. Multiple climate states from the same 2. Multiple climate states from the same external conditionsexternal conditions

The Climate SystemThe Climate System

(IPCC TAR, Ch. 1)

Three important controling factors:Three important controling factors:

1.1. LatitudeLatitude

- insolation- insolation

2.2. ElevationElevation

- temp. decrease with height- temp. decrease with height

3.3. Closeness to oceansCloseness to oceans

- heat reservoir- heat reservoir

(Peixoto & Oort, 1992)

Water in the climate system:Water in the climate system:

Mean extreme temperatures and differences (˚C) :Mean extreme temperatures and differences (˚C) :

Northern Hemisphere

Southern Hemisphere

Globe 12.3

Thermal Inertia of OceansThermal Inertia of Oceans

Annual Temperature Range

(Wallace & Hobbs, 1979)

(Michael Pidwirny, DLESE, 2004)

The Climate SystemThe Climate SystemSubsystemsSubsystems

1.1. AtmosphereAtmosphere

- rapid changes- rapid changes

- links other subsystems- links other subsystems

- greenhouse gases - greenhouse gases

2.2. OceanOcean

- slow evolution (“memory”, “flywheel”)slow evolution (“memory”, “flywheel”)

- chemical role, esp. COchemical role, esp. CO22

3.3. LandLand

- range of time scales- range of time scales

- cryosphere & biosphere roles- cryosphere & biosphere roles

- location of continents- location of continents

CryosphereCryosphere

(106 km2)

Sea-lev. equiv. (m)

Max extent (%)

Min extent (%)

N.H.Land snow & ice 2.2

(Grnl: 1.7)

Sea ice 8.9

Total 11.0 24 % (Feb) 4 % (Aug)

S.H.Land snow & ice 13.0

(Antr: 13)

Sea ice 4.2

Total 17.2 13 % (Oct) 7 % (Feb)

Note: Note: Time scales, albedo effectsTime scales, albedo effects

BiosphereBiosphere

Note: albedo, evapotranspiration, surface roughness, gas exchanges (esp. CONote: albedo, evapotranspiration, surface roughness, gas exchanges (esp. CO22))

Feedbacks

Internal couplings through linking processes

Amplify or diminish initial induced climate change

Negative Feedback: Example

How does Earth’s temperature get established and maintained?

Solar ConstantSolar Constant

At photosphere surface, At photosphere surface, solar flux ~ 6.2solar flux ~ 6.2..101077 W-m W-m-2-2

Solar ConstantSolar Constant

At Earth’s orbit, solar flux ~ 1360 W-mAt Earth’s orbit, solar flux ~ 1360 W-m-2-2

At photosphere surface, At photosphere surface, solar flux ~ 6.2solar flux ~ 6.2..101077 W-m W-m-2-2

Planetary AlbedoPlanetary Albedo

Scattering: air molecules, aerosols Reflection: clouds

Surface albedo

What is Earth’s temperature?What is Earth’s temperature?

Balance: Radiation in = Radiation outBalance: Radiation in = Radiation out

Incoming = 1360 W-m-2 x (1-albedo) x (area facing sun) = 1360 x (1-0.3) x a2

= 1.2.10+17 W

Outgoing = T4 x (area emitting) ; i.e., black body = T4 x 4 a2

= 1.2.10+17 W

Balance implies T = {0.71360 W-m-2)/4}1/4 = 255 K = -18 oC

Outgoing = T4 x (area emitting) ; (i.e., black body) = T4 x 4 a2

Difference? Must account for atmosphere (greenhouse effect).

Balance implies T = -18 Balance implies T = -18 ooCCObserved surface T = +15 Observed surface T = +15 ooCC

What if temperature decreases?What if temperature decreases?

The same:Incoming = 1.2.10+17 WOutgoing = T4 x (area emitting) = T4 x 4 a2

What if temperature decreases?What if temperature decreases?

~ Negative Feedback ~~ Negative Feedback ~

These are the same:Incoming = 1.2.10+17 WOutgoing = T4 x (area emitting) = T4 x 4 a2

But for T < 255 K: imbalance Incoming solar exceeds outgoing IR net energy input T increases

Negative Feedback

1. Perturb climate system

2. Negative feedback moves climate back toward starting point

3. A stabilizing factor

Positive Feedback: Example

How does Earth’s temperature get established and maintained?

Greenhouse EffectGreenhouse Effect

IR radiation absorbed & re-emitted, partially toward surface

Solar radiation penetrates

IR radiation absorbed & re-emitted, partially toward surface

Emitted IR: ~200-500 W-mEmitted IR: ~200-500 W-m

Net IR: ~25-100 W-mNet IR: ~25-100 W-m

Cooler atmosphere: - Less water vapor - Less IR radiation absorbed & re-emitted

Cooler atmosphere: - thus less surface warming - cooler surface temperature

Positive Feedback

1. Perturb climate system

2. Positive feedback moves climate away from starting point

3. A destabilizing factor

Other examples (textbook):

- ice-albedo feedback

- CO2-ocean temperature feedback

Feedbacks

Distinguish between:

1. external forcing change

- e.g., insolation, volcanism

- often predictable

2. Internal feedback mechanisms

- nonlinear, coupled interactions

- generally less predictable (stochastic)

Black Body Curves

6,000 K 255 K

Wavelength []

(shortwave, visible)

Terrestrial

(longwave, infrared)

Radiation SpectrumRadiation Spectrum

Daily Daily Solar Solar

Radiation Radiation at Top of at Top of Atmos.Atmos.

[106 J-m-2]

Earth’s mean annual Earth’s mean annual radiation and energy balanceradiation and energy balance

Absorbed Solar RadiationAbsorbed Solar Radiation

Outgoing Terrestrial RadiationOutgoing Terrestrial Radiation

Key Energy Fluxes at SurfaceKey Energy Fluxes at Surface

Sensible Heat

FSH = Cp(wT)s

FSH ≈ - CpCH(Tair-Ts)

CH = CH(V, zo, d/dz)

Surface Sensible Heat FluxSurface Sensible Heat Flux

Latent Heat

FLH ~ - CpCW{eair-esat(Ts)}

CW = CW(V, zo, d/dz)

but also

CW = CW(physiology)

soil moisture

CW leaf temp.

sunlight

CO2 level

Key Key Energy Energy Fluxes at Fluxes at SurfaceSurface

Surface EvaporationSurface Evaporation

CyclesCycles - Net Radiation

FSHFLH

- Net Radiation

Grassland

Dry Lake

Diurnal

Less cooling by evaporation

Ts increases

FSH larger

Role of AlbedoRole of Albedo

Scattering: air molecules, aerosols Reflection: clouds

Surface albedo

Ocean 2-6%Snow 40-95%Crop 15-25%Forest 5-10%Cities 14-18%

Albedo changes with latitudeAlbedo changes with latitude- changing land surface- changing land surface- changes in incidence angle- changes in incidence angle

Albedo changes with timeAlbedo changes with time- land changes (e.g., ice sheets)- land changes (e.g., ice sheets)- cloud cover- cloud cover

Albedo changes with latitudeAlbedo changes with latitude

Role of Greenhouse GasesRole of Greenhouse Gases

Primary gases: Primary gases: water vapor,water vapor, CO CO22, methane (CH, methane (CH44), nitrous oxide (N), nitrous oxide (N22O), ozone (OO), ozone (O33))

Time Scales of Climatic VariationTime Scales of Climatic Variation

(IPCC TAR, Ch. 2)Note: Note: Magnitude of changesMagnitude of changes

Reduced “detectability” farther back in timeReduced “detectability” farther back in time

(IPCC TAR, Ch. 2)

Different size of changesDifferent size of changes

Time Scales of Climatic VariationTime Scales of Climatic Variation

Earth’s Orbital ParametersEarth’s Orbital Parameters

Perihelion(~ Jan 3)

Vernal Equinox (~ March 21)

Aphelion(~ July 5)

Eccentricity = SQRT(a2 - b2)/a ; for circle, = 0

Longitude of perihelion (one choice: angle from NH vernal equinox)

Tilt of rotation axis (obliquity)

Variability of Earth’s Orbital ParametersVariability of Earth’s Orbital Parameters

Periodic variations

Current Range ~ Period (yr.)

Eccentricity: ~ 0.02 [0.0 - 0.05] 95,800

Longitude of perihelion ~ 270˚ [0˚ - 360˚] 21,700

Obliquity 23.4˚ [21.8˚ - 24.4˚] 41,000

Seasonal efffect of variations (little annual effect)

Eccentricity: intensity of seasons

Longitude of perihelion NH-SH differences in summer insolation

Obliquity extratropical summer-winter differences

Changes in Earth’s OrbitChanges in Earth’s Orbit

Some paleo-records can resolve different Some paleo-records can resolve different frequencies in an orbital element’s variability frequencies in an orbital element’s variability (e.g., 19,000 and 23,000 yr periods in (e.g., 19,000 and 23,000 yr periods in precession).precession).

Some can detect “beat” frequencies.Some can detect “beat” frequencies.

Relative importance of frequencies changes Relative importance of frequencies changes with time - and may not correspond to dominant with time - and may not correspond to dominant frequencies in climatic response.frequencies in climatic response.

Shorter, lower amplitude frequencies might be Shorter, lower amplitude frequencies might be important for decadal-millenial climate changes.important for decadal-millenial climate changes.

Changes in Earth’s orbit affect Changes in Earth’s orbit affect - annual insolation cycle- annual insolation cycle- past glacial-interglacial variability- past glacial-interglacial variability

Croll (late 1800s)Croll (late 1800s)

Milankovitch (1941)Milankovitch (1941)

Berger (1970s)Berger (1970s)

Changes in Earth’s orbit affect Changes in Earth’s orbit affect - annual insolation cycle- annual insolation cycle- past glacial-interglacial variability- past glacial-interglacial variability

Optimum conditions: Optimum conditions: minimum obliquity, high minimum obliquity, high eccentricity, aphelion during NH summereccentricity, aphelion during NH summer

- allow snow to persist through summer- allow snow to persist through summer- allow relatively warm winter (increased - allow relatively warm winter (increased subtropical evap. & increased snowfall)subtropical evap. & increased snowfall)- transition seasons may also be important - transition seasons may also be important for snow-cover expansionfor snow-cover expansion

Milankovitch TheoryMilankovitch Theory

GlobalRegional Regional Regional Regional

Microscale Microscale Microscale Microscale Microscale Microscale Microscale Microscale Microscale

Crop BCrop A

Air-TransportedPathogen A

Field Field Field Field Field Field Field Field Field Field

Regional Regional Regional Regional

Continental

Hydrology, Soil Microbiology, Soil Biochemistry

Soil AH2O, temperature,

nutrients, microbes, soil carbon, trace chemicals

Soil AH2O, temperature,

Soil BH2O, temperature,

Soil CH2O, temperature,

Scales of Climate

Scales of Landforms

Air-TransportedPathogen B

Human Influences

Management Management

Detritus

Particulate D

eposition, Precipitation, S

olar Radiation, IR

Microclimate A

Microclimate CMicroclimate B

ChemicalsChem

Climate & Climatic VariationClimate & Climatic Variation

(Chapter 2)(Chapter 2)

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Climate & Climatic Variation (Chapter 2). CLIMATE = 1. Statistics of Weather Daily Precipitation -...

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