Post on 20-Jan-2016
Lecture 5
Weather Maps and Models
Chapters 5 and Chapter 6
Homework Due Friday, October 3, 2014
TYU Ch 6: 1,2,5,7,11,14,17,18,20; TYPSS Ch 6: 2
TYU Ch 7: 1,5,10,11,13,14,15,18,20; TYPSS Ch 7: 1
TYU Ch 8: 1,2,6,7,12,14,15,18,20; TYPSS Ch 8: 2
Weather Models• Deterministic Prediction: Bjerknes (1906), Richardson (1924): weather can be
predicted from Newtonian equations as an initial value problem.• Mathematical equations describe how:
– Conservation of momentum (Newton, ~ 1700 AD)• Newton’s 1st Law: Objects (or air parcel) in a state of uniform motion tends to
remain in motion unless acted upon by an external force…concept of inertia• Newton’s 2nd Law: The acceleration of an object (or air parcel) due to the
application of a force is proportional to and in the direction of the force applied and inversely proportional to the mass
– Conservation of mass (Lavoiser, 18th Century)• Air mass is conserved• Moisture is conserved
– Conservation of energy • 1st Law of Thermodynamics, principle of work , conservation of energy,
(Clausius, 1850)• 2nd Law of Thermodynamics, entropy (disorder), (Carnot, 1824)
– For any thermodynamic process, total entropy must increase or remain constant
– Chaos, predictability and probabilistic forecasting Lorenz (1963)
Two Basic types of Models
• Finite Difference Model– Solved on a grid– Taylor series approximations to continuous equations
• Spectral Model– Analysis of variables on a grid in real space is
transformed to a grid in wave space grid using a Fourier transform
– Equations moved forward in wave space analytically– Variables transformed back to real space
Examples of Horizontal Grids
Vertical Grid
Vertical grid may be :
•Height coordinate
•Pressure coordinate
•Sigma or terrain following coordinate
Map Projection
Various map projections are used to take into account the curved Earth surface. For instance:
1. Mercator projection
2. Polar Stereographic Grid
3. Lambert Conformal
4. Spherical Grid
Topography Representation
Ensemble Prediction
Key Prediction Models for this Class
• Global Forecasting System (GFS):– NOAA model run 4 times per day out to 20 days – Global model– ~ 30 km resolution, but spectral– comprehensive global data assimilation– No lateral boundaries
• North American Model (NAM)– NOAA model run 4 times per day out to 3.5 days– Limited area over North America– < 10 km resolution– 1 way nest in GFS for lateral boundaries
• Nonhydrostatic Modeling System NMS model– Run 4 times per day out to 48 hours– Tripoli (UW) locally run limited area model over North America– 60 km resolution– Separate runs nested in GFS or NAM