Class Outline, Class #8, 9 February ) Review 2) Today s topics - Climate and Weather forecast models - Dynamical Downscaling 3) Project

Transcription

1 Class Outline, Class #8, 9 February ) Review 2) Today s topics - Climate and Weather forecast models - Dynamical Downscaling 3) Project Discussion

2 Review Given a column of air, what processes determine its heat budget? Given the poleward heat transport processes (sensible, latent, geopoten;al, kine;c), which one is the largest? What are an atmospheric reanalysis?

3 What is a Model? Simplifica;on of what happens in Nature. Range of applicability of the model must be understood. Quotes "All models are wrong but some are useful." George E.P. Box "Make your theory as simple as possible, but no simpler." A. Einstein "For every complex ques;on there is a simple and wrong solu;on." A. Einstein.

4 Prehistory of Climate Models Vilhelm Bjerknes ( ) 1904 paper proposed numerical weather predic;on. Not feasible at the ;me due to lack of computers. 7 equa;ons to predict large atmospheric scale mo;on solved by graphical methods on weather maps. He considered weather forecasmng the principal objecmve of meteorology research. Adequate observa;ons and computer facili;es would emerge in the future. hpp://www-groups.dcs.st-and.ac.uk/~history/pictdisplay/bjerknes_vilhelm.html 4

5 Basic Dynamical Equa;ons Conserva;on of momentum (Newton s 2nd law) Conserva;on of mass Conserva;on of energy Ideal gas law Hydrosta;c equa;on Unknowns==> air Velocity, Density, Pressure, Temperature and Humidity

6 Richardson s Forecast Factory WW1 Medic first NWP system ( 09) Reality 1940 s

7 ENIAC Electronic Numerical Integrator And Computer - When ENIAC was announced in 1946 it was heralded in the press as a "Giant Brain" It had a speed of one thousand Mmes that of electro-mechanical machines. (Wikipedia)

8 Post-War and Numerical Weather Predic;on J. Von Neumann (Princeton) an early pioneer simula;ng nuclear weapons and saw applica;on to weather. In 1946, soon ajer ENIAC was opera;onal, he pushed for weather predic;on. He was an anm-communist and hoped modeling would lead to control of weather resulmng in poor Soviet Harvests & the end of communism. Began a group of theore;cal meteorologists at Princeton s Ins;tute for Advanced Study and recruited Jule Charney (of Charney Report 1979). First computerized forecast in 1950 on ENIAC. Covered North America with 270 points and 700km resolu;on. Good enough to warrant further work. Swedish Air Force first to run regular forecasts, star;ng in 1954 In 1952, Von Neumann & Charney convinced US Weather Bureau to establish Joint Numerical Weather Predic;on (JNWP) Unit in Suitland MD. They began roumne forecasmng in May more years to beat humans. 8

9 Model Development Global Climate Models 1960s Weather Forecast Models of 1950s Simpler model development (Example) By early 1980 s GCMs eclipsed simple models By late 1980 s simpler models in again! (Hierarchical modeling)

10 MODEL GRID Numerical models break up globe into a grid on which the equa;ons are solved.

11 Some processes occur in column and others exchange info horizontally Companion website:

12 Processes in a single column are shown in right panel Processes in a single column Companion website:

13 Processes Evaluated in Global Climate Model Companion website:

14 Coupling: ocean and atmosphere Atmospheric GCM info traded SST/sea ice Sea Ice Model wind stress, P-E Net heat flux info traded Ocean GCM

15 Climate Model VerMcal Coordinates Sigma coordinates help deal with the terrain and are called Terrain Following Coordinates [Washington & Parkinson, 1986] 15

16 Resolu;on in Models Computa;on goes up rapidly as resolu;on increases. [Washington & Parkinson, 1986] 16

17 Impact of Resolu;on on Model Fields Features that are resolved look quite different depending on resolu;on [Washington & Parkinson, 1986] 17

18 Model ResoluMon gets higher and currents are beber simulated Companion website:

19 Model ResoluMon increases and mountains are beber represented Companion website:

20 What is a parameterizamon? Physical processes that are too small to be exactly represented on model grid size. Examples: cumulus clouds solar radia;on Terrestrial radia;on (Longwave)

21 Validate Model Climate models do a remarkable job reproducing the climate, but are s;ll dicey for predic;ng climate (tunable parameters) They have improved immensely over the last 40 years Need more Valida;on and Verifica;on to increase our confidence in their results. ValidaMon - "Are you building the right thing?" Verifica;on - "Are you building the thing right?" Long-term goals Reduce tuning of parameters

22 Validate model data with observed data Model Observations M minus O 22 [NCAR]

23 Sea ice declining faster than projected Julienne Stroeve, NSIDC Challenging us to determine WHY????

24 Circulation during Last Glacial Maximum LGM- 21k BP Monsoon Experiments By Kutzbach [Kutzbach and Guetter, 1986]

25 IPCC, 2007: projected hydrologic changes, : In Arc;c: Precip., Evap., Runoff (10-30%), Soil moisture IPCC 2007, slide from J.E. Walsh

26 Projected change in winter sea level pressure: lower pressure more storms? Plausible SLP Anomalies [J.E. Walsh]

27 Shipping in the Arc;c Lawson Brigham Projec;on of shipping season length based on IPCC climate model output.

28 In 1979, the National Academy of Sciences was asked by the Director of the Office of Science and Technology Policy to prepare a report to assess the scientific basis for projection of possible future climate changes resulting from anthropogenic carbon dioxide emissions. The Academy convened an ad hoc study group, headed by Jule Charney, to write the report. This report became influential for both policy makers and scientists, and is frequently cited as "the Charney report." It is especially useful as an outline of the state of climate models in the late 1970s, including some discussion of the largest unknowns in climate modeling. Charney Report 1977 Report linked to class web page

29 Reading Assignment NaMonal Academies of Sciences, Engineering, and Medicine Next GeneraMon Earth System PredicMon: Strategies for Subseasonal to Seasonal Forecasts. Washington, DC: The NaMonal Academies Press. doi: / Read pages 1-15 for Feb 16, 2017