D27    Report on MM5 GPSPW nudging

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This report is part of work-package 4200, the purpose of which is

* Development of GPS ZTD assimilation software for the 3DVar assimilation system for the mesoscale NWP model MM5.
* Investigate the impact of assimilation of GPS PW into the MM5 at high resolution using different assimilation techniques: nudging and 3DVAR.

Methodology/Work Description: Recent work showed the impact of the assimilation of GPS precipitable water (PW) into high resolution weather forecasts (Faccani et al., in preparation)  for a few cases using the nudging technique. It is desirable to test this technique operationally and compare it with a more accurate assimilation technique such as 3DVAR. Therefore, during the first period the GPS PW will be assimilated through nudging, in the mean time the 3DVAR system will be implemented and the assimilation will be carried out using the 3DVAR only. A comparison with the nudging will be performed for a few selected cases. The GPS ZTD assimilation technique will be developed for fully operational use.

The results of the MM5 GPSPW nudging experiments are available in an article: Near real-time data assimilation of GPS ZTD and PW into a non-hydrostatic model