Computer Models of the Earth s Climate

Transcription

1 Computer Models of the Earth s Climate DARGAN M. W. FRIERSON DEPARTMENT OF ATMOSPHERIC SCIENCES MATH DAY,

2 Climate Models

3 Climate Models

4 Climate Models Mathematical model: uses equations to describe a system (physical, biological, economic, etc) Climate model: simulating the Earth s climate with computers solving equations

5 About Me Home town: Wilmington, NC Wilmington, NC Hurricane Floyd, 1999

6 About Me Home town: Wilmington, NC Wilmington, NC Hurricane Fran, 1996

7 About Me Home town: Wilmington, NC Wilmington, NC Hurricane Diana, 1984

8 About Me Home town: Wilmington, NC Wilmington, NC Hurricane Bonnie, 1998

9 About Me Home town: Wilmington, NC Wilmington, NC Hurricane Bertha, 1996

10 About Me Undergraduate: North Carolina State, Raleigh, NC Raleigh, NC Total precipitation from Hurricane Fran, 1996 (my freshman year)

11 Undergraduate Majored in Math and Physics Freshman year took Astrophysics on a whim Discovered computational science: a relatively new field combining science, math, and computers

12 Undergraduate Research Did research for Prof. John Blondin Best college job ever! Published results in Blondin, Chevalier, and Frierson (Astrophysical Journal, 2001)

13 Graduate School Knew I wanted to do computational science, but wanted something more down to Earth Considered: Hydrology Coastal processes Oceanography Atmospheric Sciences Went to grad school at Princeton in Applied and Computational Mathematics (5 yrs) Focused on Atmospheric Modeling

14 After Grad School Postdoc (2 yrs) at University of Chicago Professor at UW in Atmospheric Science starting in 2007 Animation of precipitation from a climate model I wrote Latitude Longitude

15 The First Numerical Model of the Atmosphere Lewis Richardson made the first numerical weather prediction in 1922 Did the calculations completely by hand! Took over 1000 hours! Also had a dream of the future of weather prediction

16 Richardson s Dream: The Forecast Factory Filled with employees ( computers ) doing calculations Richardson s dream in 1922 of a global forecasting system He estimated 64,000 computers (people) would be necessary to forecast over the globe

17 Richardson s Experiment Used data from May 20, 1910 Surface pressure and temperature

18 Failure or Success? First prediction was for pressure to change by 145 mbar in 6 hours Hugely, hugely wrong. Richardson himself realized that noisy wind data was likely the problem He suggested 5 different filtering methods to fix this Obviously he couldn t try this experiment again But we can reproduce the results using today s computers

19 Computer Forecast w/ Richardson s Proposed Fix A good forecast!

20 Climate/Weather Model Components Equations of fluid motion on a rotating sphere Both the atmosphere and the ocean are just fluids Equations put basic physics principles in mathematical form: Mass is neither created nor destroyed Heating/cooling changes temperature Forces change momentum

21 Fluid Motion on the Sphere! The atmosphere looks like a fluid from the global perspective 6 weeks of satellite observations of water vapor

22 Climate Models Chop up the Earth into Grid Cells Spherical coordinates are used to represent fields Numerical analysis is the mathematical theory of putting equations into a form that computers can solve

23 Model Resolutions

24 Simple Fluid Dynamics Problems Mathematical techniques for solving the fluid equations are often tested on simple set-ups like this:

25 Climate Model Components Other main components of climate models: Heat sources Solar radiation and the greenhouse effect Condensation, convection & clouds Fluxes from the land and ocean Have to parameterize small-scale processes like clouds

26 Highest resolution models can capture more details of cloud structures This will be the resolution of the future Weather models will also improve, but weather prediction is fundamentally limited by chaos

27 Weather forecasting focuses on the exact location of these features Limited by The Butterfly Effect (when little changes make a big difference) Instead climate forecasts look at weather statistics

28 My Modeling Research I use computer models of all different complexity From climate models used for IPCC Report predictions To more simplified models to develop understanding of climate

29 Ocean-covered planets Take out land, mountains, etc Vary water vapor content over wide range Helps better understand how moisture affects atmospheric circulation

30 Atmospheric Models We only have one Earth With computer models, you can change parameters and make imaginary planets Different rotation rates Different solar heating, radius, gravity, take out clouds, etc

31 Usefulness of Simple Problems Then link the simplified modeling work to simulations of weather, climate, global warming, etc Helps improve the forecasts eventually as well!

32 Cloud Models Clouds are important for climate Both warm and cool

33 Our recent study on clouds Clouds far away affect tropical rainfall! Rainfall here is affected by clouds here!

34 UW Dept. of Atmospheric Sciences #1 ranked in the country Based on Thompson Scientific citation rankings and other metrics 18 faculty in weather, climate, and atmospheric chemistry Dedication to research and teaching Around 15 undergraduates per year 3 degree tracks: Climate, weather and air quality Many opportunities for undergraduate research I have three undergrads currently working with me