Abstract
The westerly phase of the quasi-biennial oscillation (QBO) was unexpectedly disrupted by an anomalous easterly near 40 hPa (~23 km) in February 2016. At the same time, a very strong El Nino and a very low Arctic sea-ice concentration in the Barents and Kara Sea were present. Previous studies have shown that the disruption of the QBO was primarily caused by the momentum transport of the atmospheric waves in the Northern Hemisphere. Our results indicate that the tropical waves evident over the Atlantic, Africa, and the western Pacific were associated with extratropical disturbances. Moreover, we suggest that the El Nino and sea-ice anomalies in 2016 account for approximately half of the disturbances and waves based on multiple regression analysis of the observational/reanalysis data and large-ensemble experiments using an atmospheric global climate model.
Highlights
The quasi-biennial oscillation (QBO) is the dominant mode of stratospheric variability with a period of 22–36 months.[1]
We examine the recent reduction of the Arctic sea-ice, which is associated with significant atmospheric disturbances in the Northern Hemisphere.[9,10]
The waves are examined using the Eliassen–Palm (EP) flux[11] and the threedimensional wave activity flux (WAF),[12] which run parallel to the group velocity, identifying the propagation direction of the waves
Summary
The quasi-biennial oscillation (QBO) is the dominant mode of stratospheric variability with a period of 22–36 months.[1] The oscillation is characterized by alternating easterlies and westerlies descending from ~1 hPa (~50 km) to ~100 hPa (~16 km) and has been observed to occur in a very similar manner for several decades.[2,3] Due to its strong periodicity and its various influences on the atmosphere, the QBO is an important factor in the predictability of the seasonal forecasts.[4] in February 2016 the descent of the westerly phase of the QBO was unexpectedly disrupted by an easterly in the lower stratosphere near 40 hPa. As emphasized in previous studies, this disruption was completely unprecedented and not predicted by the forecast models.[5,6]. The primary cause of the easterly was the momentum transport from the planetary waves from the Northern Hemisphere converging near the equator.[6,7]. Previous studies mentioned that the El Nino in 2016 was a leading candidate for the source of the tropospheric waves that caused the QBO disruption.[5,7,8]. We examine the recent reduction of the Arctic sea-ice, which is associated with significant atmospheric disturbances in the Northern Hemisphere.[9,10] This study aims to understand why the unprecedented disruption occurred in 2016
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