Initialization Schemes for HIRLAM based on Recursive Digital Filters

Peter Lynch


Xiang-Yu Huang

HIRLAM Technical Report Number 12.

October, 1993.


A number of initialization schemes based on recursive filters are formulated and tested with a numerical weather prediction model, HIRLAM. These have an advantage over schemes which use nonrecursive filters in that they derive the initialized values from a diabatic trajectory passing through the original analysis. The changes to the analysed fields are comparable in size to typical observational errors. A non-recursive implementation of the recursive filters makes the new initialization schemes as easy to use as the original non-recursive filter schemes. It also allows use of higher order filters without added cost. An initialization method using sixth-order filter is compared to a scheme based on an non-recursive optimal filter, and is found to produce similar results for less than half the computational cost. If the sole aim is noise suppression, a filter whose output validates later than the initial time may be used. The advantage of this is that computation time is further reduced and phase error completely eliminated.

Back to Publications List