A practical understanding of dynamic adjustment

Special advanced subtopic:
Assimilation of high-resolution observations in high-resolution models

Consider two models of different resolution using the exact same analysis system:

each model has its own assimilation cycle
each model has its own analysis
the correlation lengths and other aspects of the analysis method are identical for the analyses for both models
the correlation lengths and other aspects of the analysis method are more appropriate for the scale of the coarser-resolution model.

Please use the drop-down box to answer True or False for each of the following statements. Click "DONE" after each one for its individual answer and explanation. You may read the answer to the parts you finish first before trying another statement.

a) High-resolution observations will contribute to more detail in the analysis in the higher-resolution model
FALSE because the analyses for both models use the same correlation lengths, meaning the information from each observation will be smeared around out to the same distance in both analyses. The finer-resolution model will have more detail in its analysis due to having more detail in the first guess forecast, but it will not be able to take full advantage of the high-resolution observations unless its correlation lengths are reduced and other aspects of the analysis suitably tuned.

b) If both models produce the same number of spurious features in their forecasts, the higher resolution model will have more spurious features in its analysis
TRUE for two reasons: The finer-resolution model makes smaller-scale spurious features in the short-term forecasts serving as the first guess fields. These smaller features can more easily slip between observations, thus showing up uncorrected in the analysis. Even if there are observations to correct a small spurious feature, this analysis applies smooth corrections that cannot cancel out the high-amplitude details in the spurious feature. A dense observation network could eliminate the first problem and a scale-appropriate analysis system for the high-resolution model could eliminate the second problem.

d) If the higher resolution model produces better fits to the observations during the first few hours of the forecast, it will have less run-to-run forecast variability
TRUE because the changes to the forecast come from the model's response to the analysis increments (corrections to the first guess). The analysis increments will be smaller if the fit to observations in the first guess forecast is better. The run-to-run forecast changes can be interpreted as adjustments to the analysis increments. The smaller analysis increments are like having the adjustment process act on a weaker disturbance, meaning the associated forecast changes will usually be smaller.

e) If the higher resolution model gets a new analysis system with shorter correlation lengths and it makes good use of high-density observations to create analyses with accurate small-scale details, then this will all result in large improvements in 36-hour forecasts.
FALSE because the small-scale features improved are mostly much smaller than the Rossby radius, so they disperse during the first 12-18 hours, leaving virtually no forecast improvement after roughly 24 hours. On rare occasions when a small-scale change triggers upscale development, a large improvement may result, but usually the 36-hour forecasts will have the same accuracy and the same characteristics as without the inclusion of these analysis improvements.

c) The sea-breeze convergence boundary will have better placement and strength in the initial analysis of the higher resolution model
TRUE because, as taught in the COMET module Understanding Data Assimilation, the analysis is the first guess plus corrections to the first guess. The higher-resolution model will have a better first guess forecast amplitude and placement for the sea breeze.

A practical understanding of dynamic adjustment

Special advanced subtopic: Assimilation of high-resolution observations in high-resolution models

Special advanced subtopic:
Assimilation of high-resolution observations in high-resolution models