Answer to Question 1
Answer: The three phases include analysis, prediction, and postprocessing. First is the analysis phase, in which observations are used to supply values corresponding to the starting (current) state of the atmosphere for all the variables carried in the model. Prediction phase: Fundamentally, the job of a numerical model is to solve the basic equations describing atmospheric behavior. Beginning with values delivered by the analysis phase, the model uses physical equations to obtain new values a few minutes into the future. The process is then repeated, using the output from the first step as input for the next set of calculations. This procedure is performed over and over as many times as necessary to reach the end of the forecast period (24 hours, 48 hours, or whatever). This is called the prediction phase of the model run. This involves many billions of calculations for each time step, despite the fact that there are just a handful of fundamental atmospheric variables (temperature, pressure, wind velocity vector, density, and moisture). Postprocessing phase: The conditions forecast by the model at regular intervals (for example, every 12 hours) are represented on a grid for mapping and other display purposes.
Answer to Question 2
Answer: D
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