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PyroCb vs. VolcanoCb: Stratospheric Pollution Revisited

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Monday, October 5, 2009, 4 pm

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This is a past event.

Mike Fromm
Naval Research Laboratory
Washington, DC

Wildfire is becoming the focus of increasing attention with heightened concerns related to climate change, global warming, and safety in the urban-wildland interface. One aspect of wildfire blowup has been totally overlooked until recently—the role of pyrocumulonimbus (pyroCb for short) in both firestorm dynamics and atmospheric impact. PyroCb are fire-started or -augmented thunderstorms that in their most extreme manifestation inject huge abundances of smoke and other biomass burning emissions into the lower stratosphere. The observed hemispheric spread of smoke and other biomass burning emissions could have important climate consequences. Such an extreme injection by thunderstorms was previously judged to be impossible because the extratopical tropopause is considered to be an effective lid on convection.

Two recurring themes have developed as pyroCb research unfolds. First, some “mystery layer” events—puzzling stratospheric aerosol layer observations—and volcanic aerosol layers can now be explained in terms of pyroconvection as the “smoking gun.” Secondly, pyroCb events occur with surprising frequency, and they are likely a relevant aspect of several historic wildfires. Here we will show that pyroCbs offer an alternative explanation for previously assumed volcanic aerosols in 1989-1991. In addition we will explore more recent pyroCb and volcano events to illustrate the challenge we have understanding stratospheric pollution from these eruptions. Finally we take one fire season, 2002, and go deeply into how frequently pyroCb storms occur.

Suggested Reading Material

Latitudinal distribution of stratospheric aerosols during the EASOE winter 1991/92

Polarization Lidar and Synoptic Analyses of an Unusual Volcanic Aerosol Cloud

SAGE II Observations of a Previously Unreported Stratospheric Volcanic Aerosol Cloud in the Northern Polar Summer of 1990

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