Estimating Aerosol Mass Loading from Intense Pyroconvection in the Upper-Troposphere and Lower-Stratosphere

Intense fire-triggered thunderstorms, known as pyrocumulonimbus (or pyroCb), are known for injecting a significant quantity of aerosol mass into the upper-troposphere and lower-stratosphere (UTLS).  Ground and spaceborne lidar are commonly employed to estimate the altitude of the injection.  These lidar observations are most advantageous when applied to pyroCb smoke plumes confirmed by passive sensors.  The Naval Research Laboratory (NRL) has developed the first automated near-real-time pyroCb detection algorithm using a constellation of geostationary satellite sensors covering North America, Eastern Asia, and Australia.  Application of this algorithm to 88 intense wildfires observed during the 2013 fire season in western North America produced an inventory of 26 intense pyroCb events.  The CALIOP vertical feature mask and depolarization ratio confirm that the majority of these pyroCb injected a layer of smoke particles within the UTLS, occasionally extending several kilometers into the stratosphere.  The mass of each injection is estimated with CALIOP Level 1 backscatter.  This estimation is sensitive to aerosol physical and optical properties, requiring assumed values of backscatter-extinction ratio (lidar ratio), as well as particle mass extinction efficiency. Geometric properties of the plume are constrained using a combination of passive and active satellite observations, which also introduce significant uncertainty.  A mass injection rate is then calculated by integrating over the lifetime of the pyroCb event, estimated from frequent geostationary observations.  Applying this methodology to several well-observed cases from the 2013 inventory results in UTLS aerosol mass injection estimates between 3.08x10⁶ and 9.02x10⁶ kg for each individual pyroCb event.  Meteorological conditions observed during these events suggest that pyroCb and ensuing UTLS smoke injection are likely a significant and endemic feature of summer climate in temperate and boreal latitudes.