Observed and Simulated Persistence of the 500mb Height Anomalies

Abstract

Persistence of the extratropical planetary-scale circulations is examined by the use of pattern correlations between daily 500mb height anomalies. The dataset consists of the observation for the period from 1980 to 1987 and a 12-year simulation of the Meteorological Research Institute general circulation model (MRI.GCM) with climatological sea surface temperatures. Using 5-day lag correlations, a comparison is made between the Northern and the Southern Hemispheres, between the Pacific and the Atlantic sectors and between the observation and the simulation.
The observed anomalies in the Northern Hemisphere are more persistent than those in the Southern Hemisphere. There is no obvious distinction of the persistence between the Pacific and the Atlantic sectors in the Northern Hemisphere. However the distinction is evident between the two sectors in the Southern Hemisphere; the persistence in the Pacific sector is higher than that in the Atlantic. A contrast between the Northern and the Southern Hemispheres is small in the Pacific sector, while it islarge in the Atlantic. Seasonal variation of the persistence in the Southern Hemisphere is parallel with that in the Northern Hemisphere; both are high in late boreal winter and low in late boreal summer. This parallelism is distinct in the Atlantic sector. Year-to-year variation of the yearly mean 5-day lag correlations shows a tendency that when the Northern Hemisphere persistence is high, the Southern Hemisphere persistence is also high. This relationship is higher in boreal summer.
The simulated persistence is generally smaller and its standard deviation is larger than the observation. Less persistence in the GCM is distinct in the Pacific sector. Model's systematic errors such as stronger westerlies and less variance of height fields should have affected the difference of persistence between the GCM and the observation. However, the effects of the interannual variation of sea surface temperatures in regulating the atmospheric persistence should also be investigated.