solar escalator: observational evidence of the self-lifting of smoke and aerosols by absorption of solar radiation in the February 2009 Australian Black Saturday plume

We present an analysis of the evolution of the smoke plume caused by the Black Saturday Bushfires on 7 February 2009 in the Australian state of Victoria.

Within three days this smoke plume was located at altitudes between 15-20 km thousands of kilometers away from its source region. Analysis of the vertical temperature profile at the time of the fires, forward trajectory calculations as well as a host of satellite observations strongly suggest that the original plume height after the fires did not and could not have exceeded 10 km altitude.

We postulate that the subsequent rise beyond 10 km altitude during the first three days after the fires started was caused by absorption of shortwave solar radiation in the plume. Observations indicate that the plume was highly absorptive and optically very thick. One-dimensional plume height radiative transfer calculations with realistic assumptions about the optical properties of the smoke show that the plume could rise to 16-18 km after 5 days and up to 20 km after 10 days. The plume rise exhibits a characteristic step-like time evolution tracking the variation in diurnal insolation resembling an escalator. This is the first time that this mechanism, known as “self-lifting”, has been observed on such a large scale. Potential consequences of the existence of such a process are briefly discussed.