The Role of Saharan Dust on Cloud Droplet and Ice particle Production: Observations

from NAMMA

by

Andrew Heymsfield, Aaron Bansemer and Cynthia Twohy

NCAR, Oregon State University

Collaborators: Simone Tanelli

Contributing Data: LASE, DLH, MMS, APR2

Overview• Does dust influence the spin up of tropical cyclones into hurricanes through its

effect on cloud microphysical and radiative properties and on the vertical profile of latent heating??

• Mineral dust is one of the main natural sources of atmospheric aerosol particles• Mineral dust particles (insoluble) are often coated with sulfate as well as with other

soluble substances [e.g., Fonner and Ganor, 1992] such as sea salt.• The soluble coating of the mineral dust particles could significantly change their

ability to serve as cloud condensation nuclei (CCN)• Dust particles are relatively good ice forming nuclei (IFN), and coating them with

soluble substances could enhance their ability to act as IFN.

• The connection between aged mineral aerosols and cloud microphysical properties has been modeled but rarefy observed, especially for maritime-based clouds

• This study will investigate the connection between enhanced dust aerosols below cloud base and cloud microphysical properties.

Dust particle collected during NAMMA project that is coated with soluble material. This makes it potentially active as both a cloud condensation nucleus and an ice nucleus. Length of central particle is about 0.2 microns.

CAS Optical Block

CAS ShroudedInlet

LWC Sensor

Pitot CIP

mc

Summary and Conclusions

• Dust aerosols size distributions are broad• High droplet concentrations, much above those expected for maritime

situations, are found in the dust layers, influencing drop coalescence• The liquid water zones within vigorous convection are substantially sub-

adiabatic, indicating unloading of the updrafts of the large drops• Nonetheless, high droplet concentrations are found in the strong

updrafts in mid-levels• Given the observed supersaturations, this would suggest that there is

new droplet activation in the updrafts• These results have substantial implications for the vertical distribution

of latent heating and radiative properties.• A statistical analysis of the data in regions where shattering of particles

on the CAS inlet is not an issue will be conducted• The results will dovetail with the aerosol residual studies underway with

the Twohy (CVI) and Anderson (SP2) studies and with APR2 efforts.