Radiative Effects of Dust - Mineral Dust: A Key Player in the Earth System - page 277

Fig. 11.6 Two-dimensional graphic depiction of RGB rendering showing colours as functions
of the difference in brightness temperature between the 12 and 10.8 m channel ( T B120 T B108
( T BR )) and a similar difference between the 10.8 and 8.7 m channels ( T B108 T B087 ( T BG ))
with simulations using varying aerosol optical properties ( symbols ) for specific atmospheric
conditions ( colours ). The different colours represent three different sets of land surface and
atmospheric conditions, whilst the different symbols represent different refractive indices being
used in the retrieval (Reproduced from Figure 6b of Brindley et al. 2012 )

11.5 Dust and Visibility

Up to this point, we have considered the radiative effect of dust in scattering
radiation in the framework of the Earth's energy balance. However, another way
in which the interaction of dust and radiation manifests itself in the Earth's system
is through the substantial reduction of visibility at ground level. Not only does
this have impact on activities at the surface, but monitoring of visibility provides
an alternative measurement of dust. However, although there are links between
the column AOD measured from the ground or space and visibility, Mahowald
et al. ( 2007 ) showed that AERONET AOD and visibility data are only moderately
correlated in dusty regions. If the dust is elevated, a high AOD does not always mean
low visibility at the ground. Conversely, we can imagine a case where there is very
localised surface dust event that significantly reduces visibility on the ground, but
does not give a substantial AOD.