BIRA-IASB has long experience in the characterisation of stratospheric aerosols from satellite data. BIRA-IASB researchers have published several reference data sets for various radiative and microphysical parameters of aerosols in the upper troposphere and stratosphere, derived from various Belgian (ORA), European (GOMOS) and American (SAGE II, POAM III) satellite experiments.
These climatologies cover extremely diverse situations in terms of volcanic activity (the primary source of aerosols in the stratosphere) and aerosol load over nearly 3 decades.
New sources of aerosols of different composition
Long time series are important for studying the evolution of aerosols as a function of volcanic activity but also of human activity. We know, for example, that the anticyclone linked to the Asian monsoons allows the formation of a layer of pollution at the tropopause and provides a pathway for the pollution to the stratosphere.
Moreover, forest and bush fires are becoming more and more widespread with climate change and are also a source of aerosols in the stratosphere: the intense heat produces pyrocumulus, a kind of bubble that rises quickly enough to cross the otherwise hardly penetrable layer of the tropopause.
These new sources of aerosols of different composition change the situation and require characterisation algorithms to be developed, particularly to determine the size properties of the particles.
The challenge of processing of satellite measurements
BIRA-IASB has played a pioneering role in the derivation of particle sizes from occultation instruments. Recently, other research groups have been investing in this field using other types of satellite instruments using limb measurements.
A challenge that has emerged relatively recently is that the processing of satellite measurements leads to different particle sizes for the two types of instruments. The exact cause of this difference is not yet elucidated, although it is clear that it is due partly to the different configuration of the instruments, partly to the inversion methods used.
Nevertheless, it forces researchers to put the problem of inversion of satellite data back on the trade. This problem is of major importance because the size of aerosol particles influences their chemical and radiative impact. A poor estimate can therefore affect the quality of the predictions provided by the models.