期刊
QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY
卷 142, 期 694, 页码 196-210出版社
WILEY-BLACKWELL
DOI: 10.1002/qj.2645
关键词
systematic forecast error; Rossby waves; warm conveyor belt; potential temperature; potential vorticity; diabatic processes; tracers
资金
- United Kingdom's Natural Environment Research Council (NERC) through NCAS
- DIAMET project [NE/I005234/1]
- Natural Environment Research Council [NE/I005196/1, NE/I005234/1, ncas10003] Funding Source: researchfish
- NERC [NE/I005234/1, ncas10003, NE/I005196/1] Funding Source: UKRI
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 320 K 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 the ECMWF Ensemble Prediction System and the Met Office 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.
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