Introduction to Atmospheric Climate Modeling (CAM within CCSM) Phil Rasch

What is CCSM? Coupler (CPL6) Atmosphere (CAM3) Ocean (POP) Sea Ice (CSIM5) Land (CLM3) Aerosols Trop Chem Aerosols Strat Chem WACCM Isotopes (H,C,O ) Isotopes (H,C,O ) Dynamic Vegetation Isotopes (H,C,O ) Bio Geochemistry

Some comments on CCSM configurations All components can be interactive All components can be replaced with “data models” –Information about that component is prescribed --- read in from an external dataset CAM can be run with –Full interaction –As a Chemical Transport Model (acts as a processor and conduit for exchange between other model components)

Implementation Details in the atmosphere of possible interest to the class Model performs sequential applications of a number of physical processes –State variables (temperature, winds, density, water substances, trace constituents) are updated after each process representation is applied We typically divide processes into two classes –“Dynamics” (the equations of motion = Navier Stokes equations simplified to assume hydrostatic balance in the vertical) Dynamics = dynamical core = instantaneous solution requires information in latitude, longitude, and height! –“Physics” (diabatic processes such as radiative transfer, processes involving water phase change, chemistry, etc) Physics = parameterizations = solutions generally only require information in height = work on a column by column basis –“Transport” (sometimes)

Time Loop Dynamics Shallow Convection Moist Deep Convection Dry Adiabatic Lapse Rate Adjustment Boundary Layer Processes Coupling to land/ocean/ice Chemistry Radiation Stratiform Clouds, Wet Chemistry, Aerosols

CAM dynamical configurations available for use Spectral dynamics, semi-Lagrangian transport (SLT) for tracers --- Traditional –Spherical harmonic discretization in horizontal –Low order finite differences in vertical –Inconsistent, Non-conservative -> fixers required for tracers Semi-Lagrangian Dynamics, semi-Lagrangian Transport for tracers –Polynomial representation of evolution of “mixing ratios” for all fields –Inconsistent, Non-conservative -> fixers required for tracers Finite Volume (FV) using “flux form semi- Lagrangian” framework of Lin and Rood –Semi-consistent, fully conservative

Standard Resolutions Spectral and Semi-Lagrangian dynamics –(~2.8x2.8 degree) –26 layers from surface to 35km –(optional ~4x4 resolution (T31!) through ~0.5x0.5) Finite Volume –(2x2.5 degree) –26 layers from surface to 35km –(optional 4x5 resolution through 1x1.25) –(optional WACCM surface to 150km) –Half Atmosphere version (to 70km)

Examples of Global Model Resolution Typical Climate Application Next Generation Climate Applications

Vertical resolution Resolution near sfc 100m Resolution near tropopause is > 1000m

High-Resolution Global Modeling Courtesy, NASA Goddard Space Flight Center Scientific Visualization Studio Reference Panel Still a Need to Treat Subgrid-Scale Processes zoom T42 Grid Galapagos Islands Panama ~ 130 km

What can you do with these models/tools? Use them as our most comprehensive statement of the earth’s climate system to explore the behavior of the system, E.g.: –IPCC Assessments –Interpreting & understanding the climate record Attempt to improve the representation of component processes within this tool –Leads to a better understanding of the component processes –Leads to a better understanding of the interactions between processes

Some examples of Exploration of component processes and their interactions Sensitivity of transport processes to numerical representations How our formulation of convection influences the climate system How component models, numerics and physics interact to influence our ability to represent the climate system

Tracer Experiments – –Co-authors: D. B. Coleman, N. Mahowald, D. L. Williamson, S. J. Lin, B. A. Boville and P. Hess Passive Tracers (short 30 day runs) Radon SF6/Age of Air Ozone Biosphere Carbon Source

Initial Conditions Passive Tracer Tests Mixing ratio = 1 (single layer) = 0 (elsewhere)

Mixing in Mid-latitude UTLS Descent in sub-tropics, subtropical barrier Mixing into Free Troosphere and PBL

Simple Ozone Studies Source in Stratosphere –Fixed concentration (Pseudo-Ozone) –Fixed emissions (SYNOZ) Sink near surface Pseudo-Ozone test case

SYNOZ test case Spectral solutionFV solution

Ratio of POZONE/SYNOZ Spectral solution FV solution More rapid exchange

Coupled Models allow biases to grow CAMCCSM

Revised/DiluteStandard/Undilute JJA FV 2x Modifications to CAM Convection by Neale & Mapes Observationally based

Dilute Undilute

Sea Ice Distribution in coupled simulation after 200yrs Finite Volume Spectral

Low ViscosityControl Low Viscosity minus ControlControl minus HadiSST

The end

Nino 3 evaluation from years of FV run Dilute parcel modification

Current formulations and changes on the horizon Boundary Layer formulation No knowledge of moist physics No knowledge of entrainment due to cloud/radiation interaction New Shallow and PBL from Bretherton and Colleagues

Cloud Fraction –Current formulation uses RH and stability following Sundqvist, J. Slingo, Klein/Hartmann –New formulation uses a PDF based approach followingTompkins, Johnson Ties fraction, condensate, and physical processes together much more tightly Cloud Condensate –Bulk formulation, mass only, (number prescribed or function of aerosols mass (Boucher and Lohmann) (liquid and ice drops, snow and rain) Condensate advected and sediments –Next generation will predict mass and number, better representation of exchange between liquid and ice –New formulation will have more realistic characterization of ice crystal size, shape, partitioning of mass/number relationships

Scavenging –Current formulation tied directly to production of condensate, production and evaporation of rain in stratiform clouds –Formulation for convection a bit hokey. Have separated transport processes from microphysics in attempt to avoid too tight coupling of scavenging to a particular convective parameterization –Time scale for mixing between cloud and environment = model physics timestep (30-60 minutes) New Scavenging formulation???? –Increase connection and consistency between other processes.

Convection –A variety of schemes are under consideration Modified closure for Zhang/McFarlane scheme Donner (vertical velocity spectra, meso-scale circulations) Emanuel (bouyancy sorting formulation) Kain Fritsch? Super-parameterizations –Neural net 3 or 4 other possibilities

Aerosols –Current formulations are all bulk forms for mass only Externally mixed BC, OC, Sulfate are assumed submicron Sea Salt Dust have 4 bins, with range up to about 10 microns Hydrophobic  Hydrophilic on 1.5 day timescale Quite old inventories (except sulfate) –Next generation Better inventories Tied to CLM much more closely (fire, VOC, N, C) Aerosol number? Internal mixtures? Tied to cloud microphysics more closely