## Frequently Asked Questions

### What is numerical modeling?

Excerpted from *Lectures on Numerical Meteorology* by Roger K. Smith and Wolfgang Ulrich (1998):

The story goes that Wilhelm Bjerknes in 1904 was the first to point out in that the future state of the atmosphere could be predicted by integrating the partial differential equations that govern the behaviour of the atmosphere, using as initial fields the observed state of the atmosphere at a particular time. However, the equations are too complicated for analytic solutions to be found and one must resort to numerical methods. We refer now to such integrations as *numerical weather prediction*, commonly abbreviated NWP. When numerical integrations of the equations are carried out with fictitious initial fields, they are referred to as *numerical simulations*.

### When did numerical modeling begin?

Excerpted from *Lectures on Numerical Meteorology* by Roger K. Smith and Wolfgang Ulrich (1998):

The first attempt at NWP was carried out by Lewis Frey Richardson during the First World War. At this time the calculations had to be performed by hand and were very tedious and time-consuming. The result was a spectacular failure, but the details were published in what has become one of the most famous books in meteorology* (Richardson, 1922).

* *Weather Prediction by Numerical Process*

### What types of numerical models exist?

Numerical models applied in the atmosphere can be divided into three categories: 1) General Circulation Models (GCM) cover the entire atmosphere; regional models (or mesoscale models) cover a particular area (for example, the United States, Asia, or Hawaii); and small scale cloud models and large eddy simulation models study clouds, convection, or turbulence.

### Who uses numerical modeling?

Numerical models have been used in weather prediction for the last several decades. They are also applied in many fields in sciences and engineering—for example, computational fluid dynamics models are used to study the motion of flow under various conditions. Numerical models are also used to study the stress of a construction, the motion of stars and satellites, the environmental response to the change of trace gases, and even the climate of prehistorical times. Because we can change the initial and boundary conditions to study the results and mechanisms involved in different conditions, numerical models are extremely versatile, and we can simulate experiments on the computer that would be impossible to set up in the real world.

### Other FAQ about numerical modeling

Pete’s Potpourri: Numerical Weather Prediction in FAQ. “Because of their academic backgrounds in the study of fluid dynamics, the Bergen School scientists understood that air as a fluid obeys the fundamental physical laws for fluids, called the hydrodynamic equations. These include the equations of motion, the thermodynamic energy equation, the hydrostatic equation, the equation of mass conservation, and the Boyle-Charles equation of state.” Read more.

British Meteorological Office: Numerical Modeling. “Numerical modelling is the process of obtaining an objective forecast of the future state of the atmosphere by solving a set of equations that describe the evolution of variables (temperature, wind speed, humidity, pressure) that define the state of the atmosphere.” Read more.