Articles | Volume 16, issue 6
Atmos. Chem. Phys., 16, 4005–4022, 2016
Atmos. Chem. Phys., 16, 4005–4022, 2016

Research article 29 Mar 2016

Research article | 29 Mar 2016

Environmental controls on pyrocumulus and pyrocumulonimbus initiation and development

Neil P. Lareau and Craig B. Clements Neil P. Lareau and Craig B. Clements
  • Fire Weather Research Laboratory, Department of Meteorology and Climate Science, San José State University, San Jose, California, USA

Abstract. In this paper we present the first direct observational evidence that the condensation level in pyrocumulus and pyrocumulonimbus clouds can be significantly higher than the ambient lifted condensation level. In addition, we show that the environmental thermodynamic profile, day-to-day variations in humidity, and ambient wind shear all exert significant influence over the onset and development of pyroconvective clouds. These findings are established using a scanning Doppler lidar and mobile radiosonde system during two large wildfires in northern California, the Bald Fire and the Rocky Fire. The lidar is used to distinguish liquid water from smoke backscatter during the plume rise, and thus provides a direct detection of plume condensations levels. Plume tops are subsequently determined from both the lidar and nearby radar observations. The radiosonde data, obtained adjacent to the fires, contextualize the lidar and radar observations, and enable estimates of the plume ascent, convective available potential energy, and equilibrium level. A noteworthy finding is that in these cases, the convective condensation level, not the lifted condensation level, provides the best estimate of the pyrocumulus initiation height.

Short summary
Lidar, radar, and radiosonde observations obtained during large wildfires shed new light on the initiation and development of pyrocumulus and pyrocumulonimbus clouds. Lidar data show, for example, that the condensation level in these towering convective plumes can be significantly higher than the condensation level in the ambient environment. Above the condensation level the subsequent cloud development is shown to be sensitive to wind shear and dry air entrainment, which limit vertical growth.
Final-revised paper