Thursday, November 17, 2011

Short Paper on Atmospheric Rivers

One of my students, Jon Rutz, is working to better understand the inland penetration and impacts of atmospheric rivers over the interior western United States.  Atmospheric rivers are corridors of moisture transport that contribute to a large fraction of the flooding events in California and appear to play a role in major precipitation events over the interior, as we have discussed in previous posts.

Mike Dettinger, Marty Ralph, Paul Neiman, and several compadres have done a great job illustrating the importance of atmospheric rivers in the weather and climate of the west coast.  In Dettinger et al. (2011) they present a fantastic analysis of the contribution of atmospheric rivers to the hydroclimate of the western United States.

Contribution of precipitation on the day of and day following
atmospheric river landfall on the west coast of the
United States to the wet season (Nov–Apr) precipitaiton.
From Dettinger et al. (2011).
Jon and I were both surprised that the precipitation on atmospheric river days was not higher over Arizona, which we believed was a result of their analysis not considering ARs crossing the west coast of the Baja Peninsula.

Thus, we have just submitted a short paper to Atmospheric Sciences Letters expanding the Dettinger et al. (2011) analysis to include those atmospheric rivers.  Indeed, this does result in a substantial increase in precipitation related to atmospheric rivers over the southwest especially southern Arizona.  Compare the results of our gridded analysis below to their analysis above based on station data (for details, see the paper).

Rutz and Steenburgh (2012) analysis including
atmospheric rivers making landfall on
the west coast of the Baja Peninsula.
An underlying issue in this work is that not all precipitation that falls on a day with an atmospheric river can be attributed to the moisture flux in that river.  This becomes more problematic as you extend the length of the coastline for the analysis.  We'll be looking into this in the future, along with issues related to atmospheric river penetration into the interior.


  1. Having been involved with forecasting related to water management in some of these high-impact areas, this was a very interesting paper to me. Do you have any data on freezing levels associated with the AR events? It seems like most have a high (8-10k foot)freezing level, so may contribute to snowmelt flooding as well as rain. Also, I am curious about the role of subtropical ("kona low") types of systems. These often establish a broad connection to deep tropical moisture near the ITCZ, which can later be entrained into a mid-latitude trough. Perhaps these subtropical systems are important in terms of forecasting the potential of an AR event. The 18-20 Dec 2010 event is a great example of this.

  2. Appreciate the comments. We will be looking at some of the issues you've noted above, and that December 2010 event is high on the list too!