Relation between the cloud radiative forcing and the aerosol optical depth

• Autores: M. Dolores Freile Aranda, José Luis Gómez-Amo, María Pilar Utrillas Esteban, José Antonio Martínez Lozano
• Localización: 2nd Iberian Meeting on Aerosol Science and Technology: Proceedings Book RICTA 2014 / coord. por Jordi Grifoll Taverna, Joan Rosell Llompart, 2014, ISBN 978-84-695-9978-5, págs. 95-99
• Idioma: inglés
• Enlaces
  • Texto Completo Libro
• Resumen

  • Clouds are one of the most important factors that regulate the Earth’s climate. They interact scattering and absorbing solar and thermal radiation. Because of this interaction, clouds modify the quantity of radiation that reaches the Earth’s surface. The cloud radiative forcing (CRF) accounts for the changes that clouds produce on net radiation and it is defined as the difference between the net radiation in all sky and clear sky conditions. Another important factor is the presence of aerosols, because they interact with the radiation too, but differently from clouds. They can directly scatter or absorb radiation, but also alter the microphysical properties of clouds, so the radiative effects of clouds will change.

    In this work we analyse the influence of aerosols on the cloud radiative forcing at surface and the top of the atmosphere (TOA), using the aerosol optical depth (AOD) and considering the shortwave and longwave spectral regions. This way, we have studied how the AOD affects the radiative properties of clouds at the Iberian Peninsula from March of 2000 to December of 2012.

    All the data employed in this work has been obtained from CERES. CERES (Clouds and Earths Radiant Energy System) is an instrument on board of the satellite Terra and Aqua which provides global estimations of the radiative fluxes of the atmosphere, clouds properties and other atmospheric characteristics. Some of these measurements are provided by the instrument MODIS (Moderate Resolution Imaging Spectrometer), located on Terra and Aqua too, as it happens with the aerosol information. To calculate the cloud radiative forcing we will use the shortwave and longwave fluxes given by CERES at surface, while the aerosol optical depth is provided by MODIS. The spatial resolution of the data used is of 1º longitude x 1º latitude, while the temporal resolution is daily.

    Results show us that the CRF does not suffer large changes when the AOD at 470nm increases when we consider the longwave radiation. On the contrary in the case of the shortwave radiation, the AOD can produce an increase of 60W/m2 on the CRF, what proves the impact of aerosols on the cloud radiative forcing.