[Grad-postdoc-assn] ASP seminar on January 27th with Mike Alexander

Karen McKinnon mckinnon at ucar.edu
Tue Jan 12 17:51:52 MST 2016

Dear NCAR post-docs,

Our next ASP seminar will be on January 27th, when Mike Alexander
<http://www.esrl.noaa.gov/psd/people/michael.alexander/> will be visiting
us from NOAA. Mike's interests are broad-ranging, including air-sea-ice
interactions, ENSO and its teleconnections, heavy precipitation, and the
impact of climate change on marine ecosystems. The title of his talk
is *Moisture
Sources for Heavy Precipitation in the Western US During Winter*, and the
abstract is below.

Mike is able to be with us for the day, beginning at 10:30. We will have
lunch with him at 12:30, and his talk is at 2:00. A reminder that all ASPs
should attend the lunch and talk if they are in town.

If you'd like to chat with Mike one-on-one during his visit, send me an
email, including any time preferences for your meeting.



“Moisture Sources for Heavy Precipitation in the Western US During Winter”

It is not obvious how the large volume of water necessary to sustain
intense precipitation events in the intermountain west reach their
destination given the distance from the moisture source in the Pacific and
the complex topography that impedes the flow of moisture to that region.
Since flow over mountain causes air to cool and thus hold less moisture,
air parcels may take unique pathways to retain enough water to have intense
precipitation events in states such as Arizona, Colorado, Idaho and Utah.
In general, it would be useful for scientists and water mangers, to better
understand the synoptic and climatic processes that influence heavy
precipitation events in the US intermountain west (IMW).

We investigate extreme precipitation events during winter and their
relation to water vapor transport, in the US intermountain west (taken here
to be between the Sierra Nevada/Cascade Mountains and the Continental
Divide). We employ air-parcel trajectory analysis, empirical orthogonal
function (EOFs) and self organizing maps (SOMs) of integrated water vapor
transport (IVT) and synoptic analyses to determine the moisture pathways
and the broader set of processes that result in these intense precipitation

The results indicate that moisture originating from the Pacific that leads
to extreme precipitation in the IMW during winter take distinct pathways
and is influenced by gaps in the Cascade (Oregon-Washington), Sierra-Nevada
(California) and Peninsula Mountains (southern California through Baja
California). The moisture transported along these routes appears to be the
primary source for heavy precipitation for the mountain ranges in the IMW.
The synoptic conditions associated with the dominant IVT patterns include a
trough ridge couplet at 500 hPa, with the trough located northwest of the
ridge where the associated circulation funnels moisture from the
west-to-southwest through the mountain gaps and into the IMW.

We will also briefly examine how ENSO & climate change may impact moisture
transport into the western US.

Karen McKinnon
ASP post-doctoral fellow
National Center for Atmospheric Research
1850 Table Mesa Dr., Boulder, CO, 80305
(303) 497-1709
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