Impacts of long-range-transported Saharan dust layers on atmospheric stability and turbulence in the trades

Aeolian Saharan mineral dust particles can be transported over long distances. Great amounts of Saharan mineral dust particles are transported westwards over the Atlantic Ocean towards the Caribbean islands especially during the boreal summer months. During the transport they can either have a direct environmental effect by absorbing, emitting and scattering radiation or an indirect effect by changing cloud micro-physical properties and by modifying cloud lifetime or formation.

Our recent studies indicate that elevated transported Saharan dust layers, so-called Saharan Air Layers (SALs), come along with enhanced concentrations of water vapor compared to the surrounding atmosphere. Radiative transfer simulations reveal that not the dust particles inside the SALs but the enhanced concentrations of water vapor play the dominant role for atmospheric heating in dust-laden subtropical regions. In this way water vapor has the potential to impact both atmospheric stability and turbulent properties not only inside the SALs but also at lower atmospheric levels.  To study the effects of water vapor on atmospheric turbulence and stability in SAL-regions, we performed wavelet analyses as well as calculations of power spectra on the basis of airborne lidar backscatter and water vapor measurements by the DLR lidar system WALES during the NARVAL-II research campaign. For an in-depth investigation of SAL-properties, several research flights during NARVAL-II were designed to lead over dust-laden regions upstream the Caribbean island of Barbados. Our analysis shows that water vapor heating does not only have an effect on the stability and turbulence of SALs by maintaining their confining inversions and promoting vertical mixing in their interior, but also hinders the development of shallow marine convection below.

In our presentation we will give an overview of the performed measurements and radiative transfer simulations as well as of the conducted stability and turbulence analyses by means of calculated power spectra and wavelet analyses.