25 January 2005 Lecture 1 Part 2

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Introduction toLand-Climate InteractionsPart 2

• Paul Dirmeyer
• Center for Ocean-Land-Atmosphere Studies

2
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 Problem

Climate is weather averaged over time
3
What is the Climate System?

• Internal versus external

Orbital parameters/Extraterrestrial Impacts
Geology/Volcanology
Human Impacts (LUCC/Industry)
Biochemistry/Biology
Aerosols/Chemistry
Ocean
Land
Atmosphere
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Ocean versus Land

• Water
• Flows (x,y 1y z 102y)
• High heat capacity (4.2106 J m-3 K-1)
• Moderate heat conductivity (0.6 J m-1K-1s-1)
• Dark (a0.05)
• Evaporation at potential rate

• Dry Soil
• Stationary (essentially)
• Low heat capacity (0.6-1.3106 J m-3 K-1)
• Low heat conductivity (0.08-0.2 J m-1K-1s-1)
• Light (a0.13-0.50)
• No evaporation

• Wet Soil
• Water flows (x,y 0-30d z 0-104y)
• Moderate heat capacity (2.2-2.9106 J m-3K-1)
• High heat conductivity (0.8-1.7 J m-1K-1s-1)
• Not as light (a0.1-0.4)
• 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 (a0.08-0.25)
• Transpiration controlled by photosynthesis,
  moisture stress

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Land-Climate Interaction
Evap Sensible Heat Radiation
Fluxes at the land surface

• Simple Version

State of the land surface
20-30
70-80
Soil water Vegetation Snow
Albedo Roughness Soil Wetness
Local circulation Large-scale dynamics
Air near the surface
Solar rad. Precip. Temperature Winds
Vertically through the atmosphere
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Its all in the fluxes
Basic notions of the lands effects on climate
(mean, diurnal cycle, seasonal cycle)

• 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

These fluxes are the means of communication
between land and atmosphere
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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.

8
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.

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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.

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.

1. Tropical convection clusters at 60W (Amazon), 30E
   (Africa), and 120E (Indonesia)
2. Mid-latitude storm tracks form on the eastern
   margins of continents.

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

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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)

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Precipitation and the Upper Troposphere

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

12
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

13
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.

14
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)
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Energy Balance Over Land
Absorbed energy raises the surface temperature
heat radiated from the surface increases
The sun is the ultimate source of all energy
If there is moisture available, most of the
remaining energy will go towards evaporating it.

• Shortwave Longwave
  Evapotranspiration Sensible
• Heat

Ta
Water has a high heat, capacity, so retards
warming. Dry soil will warm quickly, increasing
sensible heat flux.
Energy which reaches the ground and is not
reflected is absorbed
sTa4
sTs4
Ts
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Only about 45 of the Suns energy is visible
Plants mostly make use of visible light for
photo-synthesis
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The rest is in infrared (43) and UV (12)
The ozone layer blocks most of the UV from
reaching the surface
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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.

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Land Surface Time Scales
Relevant to seasonal-interannual studies
L(t) A A D D

• 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)

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Land Surface Time Scales
Relevant to decadal-centennial studies
L(t) T A A D D

• 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)

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Continental vs. Maritime Climate

• Atlanta shows a large annual temperature cycle
  (gt25C). Land has small heat capacity, and
  Atlanta is inland.

22
Continental vs. Maritime Climate

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

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So isnt this simple then?
Understanding land-climate interaction is not a
piece of cake.

• 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)

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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 Dirmeyer dirmeyer_at_cola.iges.org 301-902-1254
Randy Koster randal.koster_at_gsfc.nasa.gov
301-614-5781
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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.