Downscaling is used to
Answer: A
Dynamical downscaling nests a fine grid regional model inside the global one, and statistical downscaling uses fitted relationships instead. Neither adds information the global model did not contain. Two distinct approaches exist.
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Consider the following statements about downscaling.
1. Dynamical downscaling runs a regional model within the global one.
2. Statistical downscaling uses relationships fitted to observations.
3. Downscaling adds information that the global model did not have.
Answer: B
The first two are correct and describe the two approaches. The third is a common misunderstanding, since downscaling redistributes the global signal in space rather than creating new information. Detail is not the same as skill.
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Arrange the stages of a climate modelling experiment in order.
1. run the forced experiment alongside it
2. spin the coupled model up to a stable state
3. compare the two and assess significance
4. run a control integration with fixed forcing
Answer: C
The control run is what the forced run is compared against, and without it drift and variability cannot be separated from the response. Significance testing is the last step. The control run is the essential comparison.
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State whether the following is true or false.
A climate model must be able to forecast the weather to be useful for climate projection.
Answer: D
The two are different problems, since a projection concerns the statistics of the climate rather than the state on a particular day. A model may simulate the climate well while having no skill at all beyond a fortnight.
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Assertion (A): A climate model can be useful without having any weather forecasting skill beyond a fortnight.
Reason (R): Projection concerns the statistics of the climate rather than the state on a particular day.
Answer: A
Both are true and the reason gives the distinction, and confusing the two is behind the common objection that models cannot even forecast next week. The two problems differ in what is being asked as much as in the timescale.
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If a model is run at twice the horizontal resolution in both directions and the time step is halved, the computational cost rises by roughly a factor of
Answer: B
Twice as many points in each of two horizontal directions gives four times the work, and halving the time step doubles it again. Adding vertical refinement as well would make it sixteen times. Cost rises very steeply with resolution.
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Consider the following statements about model resolution.
1. Increasing resolution raises computational cost sharply.
2. Higher resolution allows some processes to be resolved rather than parametrised.
3. Higher resolution automatically gives a better simulation.
Answer: C
Correct answer: 1 and 2 only
Statements 1 and 2 are correct: halving the grid spacing multiplies the cost by roughly sixteen, because the three space dimensions and the time step all refine together, and finer grids allow processes such as deep convection to be resolved rather than parametrised. Statement 3 is too strong - a model whose parametrisations were tuned at coarse resolution can perform *worse* when refined, until they are retuned or replaced.
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Tuning a climate model refers to
Answer: D
Correct answer: adjusting parameters within plausible ranges
Tuning sets the parameters that a parametrisation leaves undetermined - a cloud droplet fall speed, an entrainment rate - to values within their physically plausible range, so that the model reproduces broad observed quantities such as the top of atmosphere radiation balance. It is a necessary step, not a fiddle, and it is properly reported: the equations are not altered, no runs are discarded, and no process is dropped.
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