Event Title

Extreme spring precipitation events in Intermountain West influenced by quasi-biennial oscillation

Presenter Information

Jason Phelps
Simon Wang

Location

Eccles Conference Center

Event Website

http://water.usu.edu

Start Date

1-4-2014 3:00 PM

End Date

1-4-2014 3:20 PM

Description

An analysis of abnormally wet spring seasons in the Intermountain West has linked to a phenomenon of upper atmospheric zonal wind alternation known as the Quasi-Biennial Oscillation (QBO). Strong westerlies associated with this pattern during October-January often result in abnormally wet conditions in the following spring over the Intermountain West. A time series of the QBO was constructed for zonal averages of the 30mb zonal winds near the equator. Using this time series, the QBO was split into different phases according to the wind direction: westerly (positive), easterly (negative), and transitions. Composites of winter and spring precipitation anomalies based on different QBO phasing were then constructed. The results show that during the October-January season prior to most extreme spring precipitation events, the QBO was oriented in a positive and maximum phase. Drier springs tended to occur in the minimum phases of the QBO in the preceding fall. The dynamic processes leading the QBO to affect rainfall in the Intermountain West will be discussed. These findings are crucial for the Intermountain West because extreme wet springs triggered by the QBO could lead to flood events, such as the spring 1983 and 2011 floods, and also impact the amount of water available from spring runoff. Based on the apparent positive QBO phase during the 2013-14 winter, the spring of 2014 will likely be a wet one.

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Apr 1st, 3:00 PM Apr 1st, 3:20 PM

Extreme spring precipitation events in Intermountain West influenced by quasi-biennial oscillation

Eccles Conference Center

An analysis of abnormally wet spring seasons in the Intermountain West has linked to a phenomenon of upper atmospheric zonal wind alternation known as the Quasi-Biennial Oscillation (QBO). Strong westerlies associated with this pattern during October-January often result in abnormally wet conditions in the following spring over the Intermountain West. A time series of the QBO was constructed for zonal averages of the 30mb zonal winds near the equator. Using this time series, the QBO was split into different phases according to the wind direction: westerly (positive), easterly (negative), and transitions. Composites of winter and spring precipitation anomalies based on different QBO phasing were then constructed. The results show that during the October-January season prior to most extreme spring precipitation events, the QBO was oriented in a positive and maximum phase. Drier springs tended to occur in the minimum phases of the QBO in the preceding fall. The dynamic processes leading the QBO to affect rainfall in the Intermountain West will be discussed. These findings are crucial for the Intermountain West because extreme wet springs triggered by the QBO could lead to flood events, such as the spring 1983 and 2011 floods, and also impact the amount of water available from spring runoff. Based on the apparent positive QBO phase during the 2013-14 winter, the spring of 2014 will likely be a wet one.

http://digitalcommons.usu.edu/runoff/2014/2014Abstracts/11