25 January 2005 Lecture 1 Part 2 Dirmeyer CLIM 714 Land-Climate Interactions Introduction to...

25 January 2005 Lecture 1 Part 2Dirmeyer

CLIM 714Land-Climate Interactions

Introduction toLand-Climate Interactions

Part 2

Paul DirmeyerCenter for Ocean-Land-Atmosphere

Studies



Climate is different than weather

Weather• Time scale

Hours-Days (less than 2 weeks)

• Spatial scale Local-Regional

• Main Components Atmosphere (ocean and

land beyond a few days)

• Prediction Deterministic (evolution

and movement of specific events over time) Initial Value Problem

Climate• Time scale

Months-Years-Beyond (more than 2 weeks)

• Spatial scale Local-Regional-Global

• Main Components Atmosphere, Ocean,

Land… Humans

• Prediction Probabilistic (deviation

from averages, categorical) Boundary Value ProblemClimate is weather

averaged over time



Orbital parameters/Extraterrestrial Impacts

Geology/Volcanology

Human Impacts (LUCC/Industry)

Biochemistry/Biology

Aerosols/Chemistry

Ocean

What is the “Climate System”?

• Internal versus external

Land

Atmosphere



Ocean versus Land

Water• Flows (x,y: 1y; z: 102y)• High heat capacity (4.2×106 J m-3 K-1)• Moderate heat conductivity (0.6 J m-1K-1s-1)• Dark (α=0.05)• Evaporation at potential rate

Dry Soil• Stationary (essentially)• Low heat capacity (0.6-1.3×106 J m-3 K-1)• Low heat conductivity (0.08-0.2 J m-1K-1s-1)• Light (α=0.13-0.50)• No evaporation

Wet Soil• Water flows (x,y: 0-30d; z: 0-104y)• Moderate heat capacity (2.2-2.9×106 J m-3K-1)• High heat conductivity (0.8-1.7 J m-1K-1s-1)• Not as light (α=0.1-0.4)• Evaporation is a function of soil moisture

Vegetation• Varies with time (species, density, color, coverage)• Canopy creates microenvironment for radiation, heat exchange, interception of rain and snow• Generally Dark (α=0.08-0.25)• Transpiration controlled by photosynthesis, moisture stress



• Simple Version

VqEP

Fluxes at the land surface

Vertically through the atmosphere

Air near the surface

State of the land surface

EvapSensible HeatRadiation

Solar rad.Precip.TemperatureWinds

Soil waterVegetationSnow

HumidityTemperatureWinds Vq

AlbedoRoughness

Soil WetnessLocal circulation

Large-scale dynamics

20-30% 70-80%

Land-Climate Interaction



It’s all in the fluxes

• Momentum Orographic drag, surface roughness, turbulence

• Radiation Solar radiation absorbed, reflected (albedo); longwave

radiation

• Heat Sensible heat (conduction), Latent heat (evaporation), Heat

storage

• Moisture Precipitation, evaporation, transpiration

• Aerosols• Trace Gases

Basic notions of the land’s effects on climate (mean, diurnal cycle, seasonal cycle)

These fluxes are the means of communication between land and atmosphere



Impact of High Terrain

• Himalayas affect the entire depth of the troposphere Temperatures at 500mb (about

halfway up through the atmosphere) are considerably warmer because of the presence of the mountain range.

This “elevated heat source” is the main engine driving the Asian monsoon.

Impacts are even seen in the opposite hemisphere.



General Circulation in Low Latitudes

• Hadley Circulation Meridional (north-south) Rising air, convection, rainfall

in deep tropics. Subsidence, clear and dry in

subtropics.

• Walker Circulation Zonal (east-west) Rising air, convection, rainfall

over heat sources (continents, islands, warm SST)

Subsidence over cooler oceans.



Land determines the location of precipitation

1. Tropical convection clusters at 60W (Amazon), 30E (Africa), and 120E (Indonesia)

2. Mid-latitude storm tracks form on the eastern margins of continents.

3. Deserts form in the subtropics on the western sides of continents.

4. Mid-latitude rain forests form where oceanic westerlies hit the coast.



3. Deserts form in the subtropics on the western sides of continents.



1. Tropical convection clusters at 60W (Amazon), 30E (Africa), and 120E (Indonesia).



Monsoons

• Over land, monsoons characterized by rainy/dry seasons Summer wet / winter dry monsoons exist primarily in the

subtropical regions, but can extend into mid-latitudes. Winter monsoons (a.k.a. Mediterranean climates) exist in the

Northern Hemisphere (California, North Africa, Middle East)



Precipitation and the Upper Troposphere

• Position of major convection regions and deserts determines the large-scale divergence patterns at 200mb.



Climate Feedback

• Does the cycle between land and atmosphere lead to amplification or damping of climate anomalies?

• Climate attractors (potential) can be a useful way to visualize this

time

Negative feedback

Positive feedback

Neutral

Stable (negative feedback)

Unstable (positive feedback)



Precipitation and Soil Moisture

• Lack of precipitation leads to dry soil (drought).

• Does dry soil lead to lack of precipitation?

• This is an example of positive feedback between land and atmosphere.



Tropical land and teleconnections

• Heating of the atmosphere over the tropical convective areas can induce “wavetrains” that arc into the mid-latitudes. These wavetrains may provide a teleconnective link between changes to the land surface in the tropics, and climate in the mid-latitudes

Nigam (1988)



Energy Balance Over Land

Storage

The sun is the ultimate source of

all energy

Energy which reaches the

ground and is not reflected is

absorbed

Absorbed energy raises the surface

temperature; heat radiated

from the surface

increases

If there is moisture available, most of the

remaining energy will go towards evaporating it.

Water has a high heat, capacity, so retards warming. Dry soil will warm quickly, increasing sensible heat flux.

σTa4

σTs4

Ta

Ts

Shortwave Longwave Evapotranspiration SensibleHeat



Only about 45% of the Sun’s energy is visible

Plants mostly make use of visible

light for photo-

synthesis



The rest is in infrared (43%) and UV (12%)

The ozone layer

blocks most of the UV

from reachin

g the surface



Vegetation distribution

• Much of the variety at the land surface is in the vegetation. The distributions of major types are determined by: climate, soils, and human activity.



Land Surface Time Scales

• L(t) Time-varying land surface quantity

• A Mean annual cycle (climatology)

• A’ Perturbation on mean annual cycle (climate anomaly)

• D Mean diurnal cycle

• D’ Perturbation on mean diurnal cycle (synoptic variations; weather)

Relevant to seasonal-interannual studies

L(t) = A + A’ + D + D’



Land Surface Time Scales

• L(t) Time-varying land surface quantity

• T Trend (climate change)

• A Mean annual cycle (climatology)

• A’ Perturbation on mean annual cycle (climate anomaly)

• D Mean diurnal cycle

• D’ Perturbation on mean diurnal cycle (synoptic variations; weather)

Relevant to decadal-centennial studies

L(t) = T + A + A’ + D + D’



Continental vs. Maritime Climate

• Atlanta shows a large annual temperature cycle (>25C). Land has small heat capacity, and Atlanta is inland.



Continental vs. Maritime Climate

• San Diego has a small annual cycle (10C), as its climate is strongly influenced by SST from the adjacent ocean.



So isn’t this simple then?

• Reality is but one “realization.” We cannot do controlled sensitivity studies with the “real world” to understand it better.

• So we construct and use models. But models are imperfect Assumptions Simplifications Parameterizations Errors

• The climate system is non-linear Utterly sensitive to initial conditions Instabilities exist that make prediction difficult

• The system is not closed (as we simulate it)

Understanding land-climate interaction is not a “piece of cake”.



Class Notes on the Web

• www.iges.org/lci/ (Land-Climate Interactions)• Syllabus• Status of assignments• PowerPoint files of lectures • References and pointers to supplementary

material on the web.

Paul [email protected]

Randy [email protected] 301-614-5781

http://www.iges.org/lci/

mailto:[email protected]





References

• Gibson, R. K., P. Kallberg, S. Uppala, A. hernandez, A. Nomura, and E. Serrano, 1997: ECMWF Re-analysis (ERA) Description. ERA Technical Report No. 1, ECMWF, Reading, UK.

• Hahn, D. G., and S. Manabe, 1975: The role of mountains in the South Asian monsoon circulation. J. Atmos. Sci., 32, 1515-1541.

• Nigam, S., I. M. Held, and S. W. Lyons, 1988: Linear simulation of stationary eddies in a general circulation model. Part II: The mountain model. J. Atmos. Sci., 45, 1433-1452.

• Xie, P., and P. A. Arkin, 1997: Global precipitation: A 17-year monthly analysis based on gauge observations, satellite estimates, and numerical model outputs. Bull. Amer. Meteor. Soc., 78, 2539-2558.

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25 January 2005 Lecture 1 Part 2 Dirmeyer CLIM 714 Land-Climate Interactions Introduction to...

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