Revealing how different parts of mixed convective-stratiform clouds distinctly respond to cloud seeding

Cloud seeding is a method of placing condensation nuclei into clouds that induce rain or snowfall. Seeding is a complex process, and its effectiveness depends on the target cloud type. To better understand the mechanisms behind seeding, in a recent study, scientists showed how a connected mixture of both convective and stratiform clouds responds to cloud seeding.

Using data from Ka-band cloud profiling radar (KPR) measurements onboard aircraft, along with the remote sensing observations from SNPP and Himawari-8 satellites, members of the Hubei Weather Modification innovation team (HBWM), under the guidance of Prof. Chuanfeng ZHAO from Beijing Normal University (Currently at Peking University), published their findings in Advances in Atmospheric Sciences.

“A mixed convective-stratiform cloud is one type of precipitating cloud with complex structure, composed of both cumulus clouds and stratiform clouds.” said the study’s first author, Dejun LI, Chief Expert on Weather Modification in Hubei Province.

LI elaborated that the successful launch of NPP in 2011, Himawari-8 in 2014, and the new high-resolution instrument components of KPR developed by satellite scientists at the University of Wyoming in 2014, all make observing the fine structure of cloud properties possible. This study measures the properties of mixed convective-stratiform clouds using KPR onboard aircraft in China for the first time.

Based on the KPR measurements before and after seeding, along with multi-source data including satellite observations, researchers now have the ability to analyze the characteristics of icing seeding tracks within the stratiform region and cloud seeding mechanisms in the convective region. This wealth of data gives important clues that help determine the differences in the cloud’s macro- and micro-physical properties.

“Few researchers have carried out studies regarding the characteristics and mechanisms of cloud responses to seeding at different parts of clouds.” said Dr. LI. “This is mainly due to the scarcity of observation instruments for cloud macro- and micro- physical properties, the insufficiency of confidence from single source of cloud observations, and so on.”

According to corresponding author Prof. ZHAO, the distinct seeding responses of stratiform and convective regions within a stratocumulus cloud are quite different. In the convective region, the cloud top is higher, which is associated with more released heat and stronger convection due to water-ice conversion. This results in both a greater number of and larger precipitation particles.

Within the stratiform region, the radar echo becomes weaker near cloud tops, indicating that liquid droplets are converting to ice crystals faster than in the convective region, causing icing seeding tracks to occur.

“Now that we have discovered how these mechanisms between the convective and stratiform regions respond to cloud seeding, future studies should further investigate application into mesoscale weather model simulations.” adds Prof. ZHAO.