Mineral Dust Altering Cloud Microphysics and Precipitation

Min, Q., State University of New York, Albany

Aerosol Properties

Aerosol

Min, Q.-L., R. Li, B. Lin, E. Joseph, Y. Hu, V. Morris, and S. Wang, Evidence of mineral dust altering cloud microphysics and precipitation, submitted to PNAS, 2007.


Contoured frequency by altitude diagram (CFAD) of Precipitation Radar (PR) attenuation corrected reflectivity for both convective and stratiform precipitation regions for both dusty (DS) and dust-free (DF) sectors and for divided sub-sectors (DF1 and DF2) in dust-free sector. Also PR estimated rain rate profiles with standard errors in dusty and dust-free sectors for both case and statistical studies.


Contoured frequency by altitude diagram (CFAD) of Precipitation Radar (PR) attenuation corrected reflectivity for both convective and stratiform precipitation regions for both dusty (DS) and dust-free (DF) sectors and for divided sub-sectors (DF1 and DF2) in dust-free sector. Also PR estimated rain rate profiles with standard errors in dusty and dust-free sectors for both case and statistical studies.

Multi-platform and multi-sensor observations are employed to investigate the impact of mineral dust on cloud and precipitation processes over the eastern Atlantic Ocean.

A significant impact of dust on hydrometeors in the convective and stratiform regions was observed. In the convective region more hydrometeors, mostly ice particles, were detected in the dust-free sector than in the dust sector. In contrast, in the stratiform region the situation was reversed with much more ice particles found in the dust sector than in the dust-free sector. Mineral dust transported upward by strong convective updrafts enhanced ice nuclei concentration in convective clouds. Some of these ice particles contributed to convective precipitation. Others were advected into neighboring stratiform regions and slowly settled downward in the upper layer of the cloud system until they reached the melting level. Dust modified the cloud microphysical processes such that rainfall distribution shifted from heavy rain to light rain—effectively suppressing rainfall. Dust also enhanced evaporation processes, which further reduced surface rainfall. Another pathway for dust induced impacts on precipitation was through alteration of thermodynamic processes in the system. Cloud microphysics phase changes in the dust environment altered the vertical gradient of latent heating in both convective and stratiform regions.

Dust modified the cloud microphysical processes such that rainfall distribution shifted from heavy rain to light rain—effectively suppressing rainfall. These changes resulted in a weaker but longer lasting cloud system with decreased stratiform precipitation fraction.