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SUMMARY:Why did the 2010 Eyjafjallajökull volcanic eruption cloud last so
  long? - Mark Jellinek\, Department of Earth\, Ocean and Atmospheric Scien
 ces University of British Columbia
DTSTART:20130509T103000Z
DTEND:20130509T113000Z
UID:TALK44824@talks.cam.ac.uk
CONTACT:Catherine Pearson
DESCRIPTION:The global economic consequences of the relatively small Eyjaf
 jallajo ̈kull eruption in the spring of 2010 caught the world off guard. 
 That the eruption cloud lasted for several months rather than weeks\, effi
 ciently disrupting air travel and the holiday plans of thousands of Northe
 rn Europeans\, drew arguably more attention and a certainly garnered a hig
 hly emotional response. The unexpected longevity of this eruption cloud wa
 s touted to be the consequence of unusual "perfect-storm-like" weather pat
 terns that also conspired to produce the very dry conditions leading to th
 e massive Russian fires later that summer.  It was called "an anomaly". Ho
 wever\, this anomaly nearly repeated itself the following year in the form
  of the 2011 Grimsvo ̈tn eruption cloud. Indeed\, in the geological recor
 d\, possibly 45% of explosive eruptions produced long-lasting clouds simil
 ar to the 2010 Eyjafjallajo ̈kull event\, which is clearly not so unusual
 .  \nA major reason that the behavior of the 2010 Eyjafjallajo ̈kul erupt
 ion cloud was surprising is that "standard" models for how ash sedimentati
 on works (i.e.\, heavy particles fall out of the cloud faster than light p
 articles) are incomplete with significant consequences not just for assess
 ing hazards to air traffic\, but also for understanding\, for example\, th
 e effect of volcanism on climate. Observations of the 2010 Eyjafjallajo ̈
 kull and 2011 Grimsvo ̈tn umbrella clouds\, as well as the structure of a
 tmospheric aerosol clouds from the 1991 Mt Pinatubo event\, suggest that a
 n additional key process in addition to particle settling is the productio
 n of internal layering. I will use analog experiments on turbulent particl
 e-laden umbrella clouds understood with simple models to show that this la
 yering occurs where natural convection driven by particle sedimentation an
 d the differential diffusion of primarily heat and fine particles give ris
 e to a large scale instability leading to this layering. This “particle 
 diffusive convection” strongly influences cloud longevity where volcanic
  umbrella clouds are enriched in fine ash. More generally\, however\, volc
 anic cloud residence times will depend on ash fluxes related to both indiv
 idual particle settling and diffusive convection. I will discuss a new sed
 imentation model that includes both sedimentation processes captures real-
 time measurements of the rate of change of particle concentration in the 1
 982 El Chichon\, 1991 Mt Pinatubo and 1992 Mt Spurr ash-clouds. Finally\, 
 although we have made progress to understanding how volcanic ash clouds ul
 timately work\, there remain some fundamental problems that I will discuss
 \, depending on time.  
LOCATION:Open Plan Area\, BP Institute\, Madingley Rise CB3 0EZ
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