Alan Robock Department of Environmental Sciences Rutgers University, New Brunswick, New Jersey USA

1. Lecture 15, 10/28/13 Climate Dynamics11:670:461 Alan Robock Department of Environmental Sciences Rutgers University, New Brunswick, New Jersey USA robock@envsci.rutgers.edu http://envsci.rutgers.edu/~robock

4. Evolution of processes included in state-of-the-art climate models FAR: First IPCC Assessment Report SAR: Second Report TAR: Third Report AR4: Fourth Report IPCC AR4, Chapter 1

6. IPCC AR4, Chapter 1

9. General Circulation Models (GCMs) 1 Basic Physical Laws: Conservation of energy (First law of thermodynamics) Conservation of momentum (Newton’s second law of motion) Conservation of mass (Continuity equation) Conservation of moisture Hydrostatic equilibrium Gas law

10. General Circulation Models (GCMs) 2 • Physical Processes That Must or Can Be Included: Wind Sea ice Radiation Snow Precipitation Glaciers Soil moisture Vegetation Ground water Ocean biota Aerosols Clouds, convective and large-scale Air-sea exchanges of moisture, energy, and momentum Air-land exchanges of moisture, energy, and momentum Chemistry, particularly O3 and CO2 Ocean temperature, salinity, and currents

11. Real World vs. Model World

12. Theory of Climate Model Development Actual Climate Model Development How to Construct a Climate Model Sparse and infrequent observations Preconceived Incorrect interpretation notions of observations Theoretical Programmatic Management misunderstanding objectives directives Sophisticated computer model Code Unrealistic errors assumptions Confusion Further Further refinement of misunderstanding unimportant details Coincidental agreement between theory and observations Publication

13. Typical grid spacing of a GCM is now 1° x 1° latitude-longitude by 1 km in the vertical. Each time the horizontal resolution is increased by a factor of 2, the time needed to run the model goes up by a factor of 8. When the vertical resolution is doubled the time required doubles in general, but can go up by more, if winds become faster.

14. To include all the processes in a climate model which are of a scale smaller than is resolved by the model, they must be “parameterized.” One of the most important and difficult climate elements to parameterize is cloudiness. Clouds have a much smaller spatial and temporal scale than a typical GCM grid box. Usually, we consider separately 2 types of clouds, layer clouds and convective clouds. There is no fundamental prognostic equation for clouds (no conservation of clouds principle); rather they form when condensation takes place and dissipate due to precipitation and evaporation.

15. Rows and flows of angel hair And ice cream castles in the air And feather canyons everywhere; I’ve looked at clouds that way. But now they only block the sun. They rain and they snow on everyone. So many things I would have done But clouds got in my way. I’ve looked at clouds from both sides now. From up and down, and still somehow It’s cloud illusions I recall. I really don't know clouds at all. — Joni Mitchell Both Sides Now, 1967