Modelling sea salt aerosol and its direct and indirect effects on climate

A size-dependent sea salt aerosol parameterization was developed based on the piecewise log-normal approximation (PLA) for aerosol size distributions. Results of this parameterization from simulations with a global climate model produce good agreement with observations at the surface and for vertically-integrated volume size distributions. The global and annual mean of the sea salt burden is 10.1 mg m−2. The direct radiative forcing is calculated to be−1.52 and−0.60 W m−2 for clear sky and all sky, respectively. The first indirect radiative forcing is about twice as large as the direct forcing for all-sky (−1.34 W m−2). The results also show that the total indirect forcing of sea salt is −2.9 W m−2 if climatic feedbacks are taken into account. The sensitivity of the forcings to changes in the burdens and sizes of sea salt particles was also investigated based on additional simulations with a different sea salt source function.