Identifying the seeding signature in cloud particles from hydrometeor residuals
Abstract. Cloud seeding experiments for modifying cloud and precipitation have been underway for nearly a century; yet practically all the attempts to link precipitation enhancement or suppression to the presence of seeding materials remained inclusive. In 2019, the Cloud-Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) implemented a novel method to detect seeded clouds during its operations in Solapur, India. In this experiment, residuals of cloud hydrometeors in seeded and non-seeded clouds were analyzed with an airborne mini-Aerosol Mass Spectrometer (mAMS). The mAMS instrument was utilized in conjunction with a counterflow virtual impactor (CVI) inlet, which had a cutoff diameter size of approximately 7 µm. Upon traversing the CVI inlet, the cloud droplets underwent a drying process, enabling the subsequent examination of cloud residuals through the mAMS instrument to identify potential seeding signatures. The Chlorine (Cl) associated with hygroscopic materials, i.e., Calcium Chloride (CaCl2) and potassium (K), which serve as the oxidizing agents in the flares, is found in relatively higher concentrations in the seeded clouds compared to the non-seeded clouds. After seeding, small-size cloud droplet concentrations increased in the convective and stratus clouds. In the convective clouds, flare particles propagated to higher cloud depths (≈ 2.25 km, vertical distance from cloud base) and modulate cloud microphysical properties to initiate warm rain. This new technique help to trace activated flare particles in seeded clouds and identify the post-seeding chain of cloud microphysical processes.
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