Land surface processesLand surface processes

Review of last lectureReview of last lecture• Global distribution of shallow and deep convection• Vertical structure of trade wind cumulus (shallow

convection)• Vertical structure of deep convection. Four

components: convective updraft, convective downdraft, mesoscale updraft, mesoscale downdraft

• Differences between shallow convection and deep convection: change of T, q and h in the boundary layer

• Self-suppression processes in deep convection: Overly stabilized state after deep convection

• Problems in current global climate models: lack of self-suppression processes

Effects of different surface typesEffects of different surface types

Deeper heat reservoir (smaller T change) Deeper water reservoir (Wetter surface) Bowen ratio decreases (More LH contribution)

BL depth decreases Convective instability increases

Effects of vegetationEffects of vegetation• Makes water/heat reservoir deeper (transport deep water out of soil) • Enhances evaporation (leafs increase evaporation area)• Dependent on vegetation type

Global distribution of different Global distribution of different vegetation typesvegetation types

(From Bonon et al. 2002)

Vegetation feedbackVegetation feedbackVegetation in turn is affected by environmental Vegetation in turn is affected by environmental

conditions (e.g. seasons, droughts, global warming)conditions (e.g. seasons, droughts, global warming)

Effects of human activitiesEffects of human activitiesHuman beings are living in the BL and affect the BL in three

different ways:• Change land cover (deforestation and afforestation)• Release or cleanse pollutants (aerosols)• Release or cleanse greenhouse gases

The heat island effectThe heat island effect

• Nighttime: City warmer than surrounding rural area• Daytime: City has same air temperature as rural area

Causes of the heat island effectCauses of the heat island effect• Increased SW absorption caused

by canyon geometry (increased area and multiple reflection)

• Decreased LW loss caused by canyon geometry

• Increased greenhouse effect caused by air pollution

• Anthropogenic heat source• Increased sensible heat storage

caused by construction materials• Decreased latent heat flux caused

by change of surface type• Decrease sensible and latent heat

fluxes caused by canyon geometry (reduction of wind speed)

“Canyons” between buildings

Mitigation of heat island effectMitigation of heat island effect

• Greening the city (streets and roof top)

• Change construction materials

• Reduce anthropogenic heat sources

Land Surface Processes in Land Surface Processes in Global Climate Models Global Climate Models

Coupler .

Land (CLM)

Sea Ice (CSIM)

Atmosphere (CAM)

Ocean (POP)

Framework of National Center for Atmospheric Research Framework of National Center for Atmospheric Research (NCAR) Community Climate System Model (CCSM)(NCAR) Community Climate System Model (CCSM)

Framework of National Center for Atmospheric Research Framework of National Center for Atmospheric Research (NCAR) Community Climate System Model (CCSM)(NCAR) Community Climate System Model (CCSM)

Community Land Model (CLM) Community Land Model (CLM) ComponentsComponents

• Biogeophysics • Hydrologic cycle• Biogeochemistry • Dynamic vegetation

CLM Model Components: BiogeophysicsCLM Model Components: Biogeophysics

CLM Model Components: Hydrological Cycle ICLM Model Components: Hydrological Cycle I

CLM Model Components: Hydrological Cycle IICLM Model Components: Hydrological Cycle II

CLM Water balanceCLM Water balance

River Systems Simulated by CLMRiver Systems Simulated by CLM

Dai, Qian, Trenberth and Milliman (2009), J. Climate

CLM Model Components: Biogeochemistry CLM Model Components: Biogeochemistry

CLM Model Components: Dynamic VegetationCLM Model Components: Dynamic Vegetation

DGVM Vegetation biogeography vs. SatelliteDGVM Vegetation biogeography vs. Satellite

SummarySummary

• Effects of different surface types: desert, city, grassland, forest, sea. Deeper heat/water reservoir, decreased Bowen ratio, thinner BL and enhanced convective instability.

• Effects of vegetation: (1) makes heat/water reservoir deeper, (2) enhance evaporation, (3) grows and dies in response to environmental conditions

• Heat island effect. 7 causes• Community land model (CLM). 4 components:

biogeophysics, hydrological cycle, biogeochemistry, dynamical vegetation