Tropospheric aerosol forcing of climate: a case study for the greater area of Greece

Although greenhouse gas forcing has global significance, the aerosol forcing is regional and seasonal, associated with the much shorter aerosol residence times in the atmosphere, and could become dominant on a regional scale. Several studies indicate that aerosol radiative forcing is among the highest in the world over the Mediterranean in the summer. In this study, the aerosol impact (forcing) on the short-wave and long-wave fluxes, as well as the radiative heating rate due to aerosols for different altitudes in the atmosphere over Athens, Greece, was estimated using satellite data and SBDART (Santa Barbara DISORT Atmospheric Radiative Transfer) model. The short-wave aerosols radiative forcing at the surface in cloud-free conditions during the period 2000-2001 ranged from 10.8 to 20.1Wm(-2) in the winter and from 15.2 to 16.6Wm(-2) in the summer. The radiative heating rates near the surface due to aerosols were found to be in the range of 0.2-0.5Kday(-1) during the winter period and 0.4 K day(-1) during the summer period simultaneous with enhanced heating in the lower troposphere (below 5km). The long-wave radiative forcing (clear sky) at the top of the atmosphere induced by aerosols during night-time was estimated to be only 0.02-0.04Wm(-2) and 0.04-0.05Wm(-2) for the winter and summer months, respectively.