Variation characteristics of different atmospheric blocking and its influence on temperature over Northern Hemisphere
Wednesday, 17 December 2014
By using the blocking index of Lupo, the variation characteristics of different atmospheric blocking intensity and duration and its influence on surface temperature were analysed during 1968-2010 in the three regions of Northern Hemisphere (NH) where blocking highs occur frequently (Atlantic, Pacific and eastern Europe-Asia regions). The results show that the blocking frequency of Atlantic was the highest in the three regions of NH, while that of the eastern Europe-Asia was the lowest. From the aspect of blocking intensity, it is revealed that the strong blocking all exhibited decreased trend over the three regions, especially in the Atlantic, where weak blocking increased slightly. The increased trend for long duration (≥13 days) NH blocking were insignificant from 1968-2000. However, long duration NH blocking presented remarkable increase since 2000. A decrease of short duration blocking frequency was only found in Atlantic region. In addition, long duration blocking contributed 25% for the strong blocking in Atlantic region, whilst 14% for Pacific blocking region. It was found that the increased probability was accompanied by the enhanced intensity of blocking. Different blocking intensity and duration yielded a significant difference on temperature. Negative anomaly of the temperature difference between the more long duration blocking years and the fewer long duration blocking years were mainly in the mid-low latitude regions, while it showed positive anomaly temperature in high latitudes. Comparison with strong blocking, the influence of long duration blocking on temperature were more remarkable over the Atlantic and Pacific regions.