© crown copyright met office essentials of climate modelling and intro to precis rcm data analysis...

© Crown copyright Met Office

Essentials of Climate Modelling and Intro to PRECISRCM Data Analysis and postprocessing workshop

Malaysian Met. Department, Nov 2012


Essentials of Climate Modelling

The goal of this session is a brief introduction to:

• the PRECIS regional climate model

• the climate system

• climate variability

• modelling of the climate system

• climate of the past

• projection of future climate


PRECIS


What is PRECIS?

Providing REgional Climates for Impact Studies

It can be applied to any area of the globe

Used to generate detailed projections of future climate

A simple user interface to set up and run an RCM

Runs of the freely available Linux operating system

PRECIS also provides utilities for users to manipulate RCM output


The PRECIS user interface


The components of PRECIS

The RCM

User interface to design and configure RCM experiments

Display and data processing software

Lateral boundary conditions

Training course and materials

Technical and Scientific Support web forum

Website (http://www.metoffice.gov.uk/precis)

http://www.metoffice.gov.uk/precis


Why was PRECIS developed?

* UNFCCC requirement for all countries to assess their national vulnerability and plans for adaptation.

* RCMs resolve local details and provide realistic extreme events for impact studies which can contribute to this assessment.

* This meets the need for countries more vulnerable to climate change to generate their own national scenarios of climate change for use in impact studies.

* Additionally, the PC version of PRECIS addresses the UNFCCC requirement on the UK to assist in capacity building and technology transfer.


What is a Regional Climate Model?

Mathematical model of the atmosphere and land surface (and sometimes the ocean)

‘High’ resolution: Produces data in

grid cells < 50km in size

Spans a limited area (region) of the globe

Contains representations of many of the important physical processes within the climate system

Cloud

Radiation

Rainfall

Atmospheric aerosols

Soil hydrology

Etc.


Boundary conditions

• Limited area regional models require meteorological information at their edges (lateral boundaries)

• These data provide the interface between the regional model’s domain and the rest of the world• The climate of a region is always

strongly influenced by the global situation

• These data are necessarily provided by global general circulation models (GCMs) • or from observed datasets with global

coverage (re-analysis experiments)


Future developments

* Continuously upgraded to new processors/new Linux

* PRECIS version 2.0 – the HadRM3P RCM driven by CMIP5/AR5 GCMs

* PRECIS version 3.0 – the HadGEM3-RA RCM (derived from the HadGEM3 GCM) driven by CMIP5/AR5 GCMs


The Climate System


Weather and climate

Weather:

the fluctuating state of the atmosphere around us

Climate:

the averages, variations and extremes of weather in a region over long periods of time


The climate system


Planetary energy balance

A planetary object intercepts a circle (of radius R) of incoming solar energy S as

SR2

A (for Albedo) of which is reflected

Energy absorbed is balanced by radiation to space. Hence,

SR2 (1-A) = 4R22T44

therefore

T = (S(1-A)/4)1/4

T = Temperature = Stefan-Boltzmann constant

See the “Stefan-Boltzmann Law” for more information


Planetary energy balance

For the Earth, S is 1365 Wm-2 and A is 0.3, predicts

255 K (~ -18˚ C)

In fact, the mean surface temperature of the Earth is

287 K (~ +14˚ C)

What accounts for the difference of ~33K?


The Greenhouse Effect

1.Sunlight passes through the atmosphere

2. It warms the Earth

3. Infrared radiation (IR) is given off by the Earth

5....but some IR is trapped by gases in the air, thus reducing the cooling effect

1.

2.3.

4.

5.

4. Most IR escapes to outer space and cools the Earth…

Greenhouse gases

Various trace gases and aerosols intercept reflected longwave radiation and re-emit in all directions

• Water vapour is the biggest contributor (~30 of ~33 K)

• Other important gases are CO2 (~2 K), CH4 and N2O (total ~1 K)

• Aerosols (including cloud droplets) do similar

H2O

CH4

CO2

N2O


Indicators of the human influence on the atmosphere during the industrial era


Climate variability


• Radiative forcing is a simple measure of the effect of a climate change mechanism

• There are various mechanisms that cause the climate to change

Radiative forcing

• Natural climate drivers

• External

• Internal

• Anthropogenic climate drivers

• The enhanced greenhouse effect

• The effect of anthropogenic aerosol

+


Natural variabilityof climate

External radiative forcings

Solar radiation changes

Volcanic eruptions

Internal climate variability

ENSO (El Niño Southern Oscillation)

NAO (North Atlantic Oscillation)

MJO (Madden-Julian Oscillation)


The effect of the Mt. Pinatubo eruption (June 1991) on global temperature


• The enhanced greenhouse effect

• The effect of anthropogenic aerosols

• direct effect (scattering of incoming solar radiation)

• indirect effect (affecting the radiative properties of clouds)

• Land-use change (agriculture, deforestation, reforestation, afforestation, urbanisation, traffic, …)

Human-induced climate variations

The direct effect of aerosol

• Effect climate directly via their interaction with solar radiation and indirectly via their effect on clouds.

• The scattering of radiation causes atmospheric cooling, whereas absorption can cause atmospheric warming

• Aerosols are particles suspended in the atmosphere

• For example; dust, soot, sea salt, pollen, sulphates

Somesunlightreflected

More sunlightreflected–

cooling effect

Brighter clouds‘Normal clouds’

Relatively cleanlower atmosphere

Pollutedlower atmosphere

The indirect effect of aerosol

Additional warming if all anthropogenic emissions of sulphur dioxide are cleaned up

Emission policies: unexpected consequences

Reducing pollution can lead to more rapid warming with large regional consequences

Pollution from anthropogenic aerosols over China

© Crown copyright Met Office© Crown copyright Met Office

Climate feedbacks

• Feedbacks occur when a change in our climate has an impact which changes our climate further

• They either amplify the effect of the initial forcing (a positive feedback) or reduce it (a negative feedback)

• Examples:• Water vapour (+)

• Albedo (+)

• Methane hydrates (+)

• Permafrost methane (+)

• Clouds (+ and –)

…and possibly other feedbacks we don’t know about yet

How do we quantify the response of the climate?

• The response of the climate system to radiative forcings is complicated by:

• feedbacks

• the non-linearity of many processes

• different response times of the different components to a given perturbation

• We can use numerical models of the climate system as a means to calculate the climate response


Climate models


Climate models

• A global climate model (GCM) is a model of the climate system.

• The advective (relating to motion) and thermodynamical (relating to heat) evolution of atmospheric pressure, winds, temperature and moisture (prognostic variables) are simulated, while including the effects of many other physical processes.

• Other useful meteorological quantities (diagnostic variables) are derived consistently within the model from the prognostic variables, such as precipitation, evaporation, soil moisture, cloud cover and many more.


Main components of globalclimate models

• Atmosphere and ocean dynamics

• Model grid

• Physical parameterizations

• Initial conditions of the model

• Boundary conditions (e.g. land sea mask, orographic height, vegetation and soil characteristics)

The three dimensional model grid


Vertical exchange between layersof momentum, heat and moisture

Horizontal exchangebetween columnsof momentum, heat and moisture

Vertical exchangebetween layersof momentum, heat and saltsby diffusion, convectionand upwelling

Orography, vegetation and surface characteristics included at each grid box surface

Vertical exchange between layersby diffusion and advection


Parameterization of physical processes

• Important processes occur in the atmosphere on scales smaller than those which are resolved by the grid of the dynamical part of the model.

• The effects of these unresolved (sub-grid scale) processes are deduced from the large scale state variables predicted by the model (wind, pressure, temperature, moisture).

• This procedure is called parameterization.

Initial and boundary conditions

• All climate models require information about the initial state of the atmosphere at the beginning of the climate model experiment. These are the initial conditions of the model experiment.

• The three dimensional grid of a GCM has no lateral (North-South, East-West) boundaries. The upper boundary is the end of the atmosphere where it contacts outer space. The lower boundary is either the surface of the land or the bottom of the ocean.

• As such the GCM requires information about the topography of the Earth’s surface, called surface boundary conditions.


The World in Global Climate Models

SampleHadley Centre Global Climate Model FORTRAN program code

CALL SUBROUTINE LSP_FOCWWIL! Purpose: Calculate from temperature the Fraction Of Cloud Water Which! Is Liquid. Operates within range 0 to -9 deg.C based upon! MRF observational analysis.

*CALL C_0_DG_CREAL& TSTART ! Temperature at which ROCWWIL reaches 1.&,TRANGE ! Temperature range over which 0 < ROCWWIL < 1.PARAMETER(TSTART=TM, TRANGE=9.0)DO I = 1, POINTS

TFOC = T(I)! Calculate fraction cloud water which is liquid (FL)as in eq. P26.50.

IF (TFOC .LE. (TSTART - TRANGE)) THEN! Low temperatures, cloud water all frozen------------------------

ROCWWIL(I) = 0.0ELSE IF (TFOC .LT. TSTART) THEN

! Intermediate temperatures---------------------------------------ROCWWIL(I) = (TFOC - TSTART + TRANGE) / TRANGE

ELSE! High temperatures, cloud water all liquid-----------------------

ROCWWIL(I) = 1.0END IF

END DO ! Loop over points RETURNEND

*ENDIF


20th Century climate

Variations of the Earth’s surface temperature for the past 160 years

El Nino 1876-77

© Crown copyright Met Office© Crown copyright Met Office

1999 La Nina

1998 El Nino

2010

Met Office – CRU

Global average surface temperatures

Variations of the Earth’s surface temperature for the past 1000 years

+


Natural influence alone

+


Human and natural influence combined

+


Predicting climate change

Predicting Climate Change

Emissions

Atmospheric Concentrations CO2, methane, sulphates, etc

Global Climate ChangeTemperature, rainfall, sea level etc

Regional DetailMountain effects, islands, extreme weather etc

Scenarios from population, energy, economics models and mitigation

Regional climate models or statistical downscaling

Coupled global climate models

Carbon cycle and chemistry models

Impacts models

Preparing climate scenarios from model projections

Methods of applying global or regional model output

The climate scenario

ImpactsFlooding, agricultural yields etc

Range of emissions

Range of global

warming

Range of regional climate change

Range of

impacts

Range of concentrations

The classic “cascade of uncertainty”

Impact that we wish to avoid

Regional climate

change that may cause this impact

Global climate change that may cause this range

of regional climate change

GHG concentrations that may cause

this range of climate change

Emissions that may lead to this

range in concentrations

Upper bound: very likely to lead to this impact

Lower bound: very unlikely to lead to this impact


Temperature increases by 2100

Global average 5.5 ºCGlobal average 1.9 ºC

Land areas are projected to warm more than the oceans with the greatest warming at high latitudes


Precipitation changes by 2100

Some areas are projected to become wetter, others drier with an overall increase projected

... And in conclusion

This presentation is intended as a brief overview of the climate system and climate modelling.

For more in-depth training, consider registering for the free online course in the science of climate change and modelling at

http://www.climateeducation.net

This is a joint effort of the University of Oxford Continuing Education Department and the Met Office Hadley Centre consisting of 8 interactive online units intended for an educated (but non-scientist) audience.

This presentation is intended as a brief overview of the climate system and climate modelling.

For more in-depth training, consider registering for the free online course in the science of climate change and modelling at

http://www.climateeducation.net

This is a joint effort of the University of Oxford Continuing Education Department and the Met Office Hadley Centre consisting of 8 interactive online units intended for an educated (but non-scientist) audience.


Questions

© crown copyright met office essentials of climate modelling and intro to precis rcm data analysis...

Documents