| Autor: |
Martinez-Alvarado O. E. Madonna S. L. Gray and H. Joos |
| Rok vydání: |
2016 |
| Zdroj: |
Quart. J. Roy. Meteorol. Soc. |
| DOI: |
10.1002/qj.2645 |
| Popis: |
Recent work has shown that both the amplitude of upper level Rossby waves and the tropopause sharpness decrease with forecast lead time for several days in some operational weather forecast systems. In this contribution the evolution of error growth in a case study of this forecast error type is diagnosed through analysis of operational forecasts and hindcast simulations. Potential vorticity (PV) on the 320K isentropic surface is used to diagnose Rossby waves. The Rossby wave forecast error in the operational ECMWF high resolution forecast is shown to be associated with errors in the forecast of a warm conveyor belt (WCB) through trajectory analysis and an error metric for WCB outflows. The WCB forecast error is characterised by an overestimation of WCB amplitude a location of the WCB outflow regions that is too far to the southeast and a resulting underestimation of the magnitude of the negative PV anomaly in the outflow. Essentially the same forecast error development also occurred in all members of theECMWFEnsemble Prediction System and the MetOffice MOGREPS 15 suggesting that in this case model error made an important contribution to the development of forecast error in addition to initial condition error. Exploiting this forecast error robustness a comparison was performed between the realised flow evolution proxied by a sequence of short range simulations and a contemporaneous forecast. Both the proxy to the realised flow and the contemporaneous forecast were produced with the Met Office Unified Model enhanced with tracers of diabatic processes modifying potential temperature and PV. Clear differences between proxy and forecast were found in the way potential temperature and PV are modified in the WCB. These results demonstrate that differences in potential temperature and PV modification in the WCB can be responsible for forecast errors in Rossby waves. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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