Event Title

Trend and variability of Pineapple Express events and other synoptic-scale weather patterns: Impacts on Northern California precipitation

Location

Eccles Conference Center

Event Website

http://water.usu.edu

Start Date

4-1-2014 5:15 PM

End Date

4-1-2014 5:20 PM

Description

We investigate the climatology and variability of seven distinct synoptic scale weather patterns including the so-called Pineapple Express (PE), i.e. a type of atmospheric river event. We examine the relative contribution of these weather events to winter precipitation in northern California using a combination of six global reanalyses. These data were analyzed to determine whether the documented change in the winter precipitation over northern California is attributed to any change in the frequency, duration, and intensity of these storm types. Over a 31 year period from 1975 to 2005, a northerly shift in the moisture origin source and circulation extent of winter time precipitation occurred. This observed spatial shift is shown to coincide with a northward shift and weakening of the 200mb zonal wind (jet stream) over the central pacific. Next, an analysis of northern California precipitation from 1975 to 2005 was performed using three CMIP5 sets of ‘historical’ single-forcing experiments. These model experiments, driven by greenhouse gas, aerosol, and natural forcing show agreement between the phenomena of atmospheric warming, a northerly shift and weakening of the wintertime jet over north America, a decrease in the development of mid-latidude cyclones, and the resultant shift in winter time precipitation patterns. These phenomena together account for the observed shifts in the relative contributions to winter precipitation in northern California from PE and other synoptic circulation types.

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Apr 1st, 5:15 PM Apr 1st, 5:20 PM

Trend and variability of Pineapple Express events and other synoptic-scale weather patterns: Impacts on Northern California precipitation

Eccles Conference Center

We investigate the climatology and variability of seven distinct synoptic scale weather patterns including the so-called Pineapple Express (PE), i.e. a type of atmospheric river event. We examine the relative contribution of these weather events to winter precipitation in northern California using a combination of six global reanalyses. These data were analyzed to determine whether the documented change in the winter precipitation over northern California is attributed to any change in the frequency, duration, and intensity of these storm types. Over a 31 year period from 1975 to 2005, a northerly shift in the moisture origin source and circulation extent of winter time precipitation occurred. This observed spatial shift is shown to coincide with a northward shift and weakening of the 200mb zonal wind (jet stream) over the central pacific. Next, an analysis of northern California precipitation from 1975 to 2005 was performed using three CMIP5 sets of ‘historical’ single-forcing experiments. These model experiments, driven by greenhouse gas, aerosol, and natural forcing show agreement between the phenomena of atmospheric warming, a northerly shift and weakening of the wintertime jet over north America, a decrease in the development of mid-latidude cyclones, and the resultant shift in winter time precipitation patterns. These phenomena together account for the observed shifts in the relative contributions to winter precipitation in northern California from PE and other synoptic circulation types.

https://digitalcommons.usu.edu/runoff/2014/2014Posters/22