Recurrent Rossby wave packets and their effect on dry and wet spells

Abstract:

Synoptic-scale Rossby wave packets are well-known to affect surface weather (e.g; warm or cold temperatures, precipitation). The persistence of such surface weather pattern can also lead to extremes. Rossby waves are found to have a recurrent pattern during several episodes of persistent surface weather which is termed as “recurrent Rossby wave pattern" (RRWP). RRWPs arise due to multiple transient synoptic-scale wave packets amplifying in the same geographical region in a short period. RRWPs are statistically significant for lengthening summer-hot and winter-cold spells over large areas of the Northern Hemisphere mid-latitudes. However, their effect on the persistence of dry and wet spells haven’t been studied so far. In this study, we find out that RRWPs can also significantly lengthen and shorten dry and wet spells over large areas of both Northern and Southern Hemisphere. The effect of RRWPs on the Northern Hemisphere dry and wet spells has some seasonality associated with it; there are clear regional zones for preferred wave-phasing. However, in the Southern hemisphere, their effect is more zonally symmetrical and has less seasonality. Our results demonstrate that RRWPs can lead to persistent high-impact surface weather; RRWPs should be considered as an important feature for understanding and predicting sub-seasonal weather patterns.