A new look at the influence of mineral dust on cirrus cloud formation by combining global-scale measurements, global modeling, and detailed microphysical simulations

Abstract:

Mineral dust aerosol particles act as effective cloud seeds for cirrus in the upper troposphere. However, our ability to assess the impact of dust on the climate system and predict the effects of future changes to dust emissions is most hampered by a lack of dust aerosol abundance measurements in the cirrus-forming regions of the atmosphere.

We report global-scale, in situ measurements of mineral dust aerosol performed during the NASA ATom (Atmospheric Tomography) campaign, an airborne mapping survey that spanned 165 degrees of latitude, two ocean basins, and four seasons. These highly sensitive measurements represent a new standard for evaluating global models that simulate dust transport and abundance.

We then combine this new dust data set with global modeling and detailed cloud freezing simulations to provide a quantitative assessment of mineral dust’s influence on cirrus formation in the background atmosphere. The large majority of non-convective cirrus clouds throughout the northern hemisphere were initially seeded by dust particles. In the southern hemisphere dust-induced cirrus were less common, and their frequency did not follow seasonal variations in surface emissions. This study confirms that convectively lofted mineral dust particles are often abundant enough to initiate cirrus formation throughout the extra-tropics, including the southern hemisphere.