EGU24-2702, updated on 08 Mar 2024
https://doi.org/10.5194/egusphere-egu24-2702
EGU General Assembly 2024
© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.

Exploring the Influence of Turbulence on Droplet Size Growth and Precipitation in Warm Clouds

Shri Vignesh1,2, Ambedkar Sanket1,2, Arya Narayanan Unni1,2, Srikrishna Sahu3, Sachin S. Gunthe4,5, Swetaprovo Chaudhuri6, Rama Govindarajan7, and Raman I. Sujith1,2
Shri Vignesh et al.
  • 1Department of Aerospace Engineering, Indian Institute of Technology Madras, Chennai - 600 036, India (kshrivignesh1995@gmail.com)
  • 2Centre of Excellence for studying Critical Transitions in Complex Systems, Indian Institute of Technology Madras, Chennai - 600 036, India
  • 3Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai - 600 036, India
  • 4Department of Civil Engineering, Indian Institute of Technology Madras, Chennai - 600 036, India
  • 5Center for Atmospheric and Climate Sciences, Indian Institute of Technology Madras, Chennai - 600 036, India
  • 6Institute for Aerospace Studies, University of Toronto, Toronto, Ontario M3H 5T6, Canada
  • 7International Centre for Theoretical Sciences, TIFR, Bangalore 560089, India

There has been significant progress in comprehending the role of characteristic properties of aerosol in cloud droplet formation over the past decade [1]; however, the growth of cloud droplets into rain droplets, initiating precipitation in warm clouds, is still not well understood [2]. Collision and coalescence among droplets are assumed to be responsible for the rapid growth of cloud droplets to rain droplets. Turbulence is believed to play a significant role in the growth of cloud droplets [2]. 

The influence of turbulence on droplet dynamics is nominally characterized by the Stokes number, which decides if the droplet either follows the streamlines or decorrelates from it. Due to their deviation from the streamlines, droplets can form clusters and caustics, thereby increasing the chance of collisions [3]. Thus, the size distribution of droplets can determine the influence of turbulence on droplet collisions. The cloud droplet size distribution depends on several parameters, such as the initial aerosol number concentration, aerosol properties, and the in-cloud supersaturation. Thus, investigating the influence of turbulence on a given droplet size distribution can facilitate a better scientific understanding of the onset of precipitation. 

In the present study, we experimentally investigated the influence of turbulence on different cloud droplet size distributions. We generated homogeneous isotropic turbulence of various intensities in a closed chamber and seeded it with droplets relevant to that observed in clouds originating under different environmental conditions. Using Phase Doppler particle analyzer (PDPA), we measured the droplet size distributions and analyzed the changes with turbulence intensity. Our experiments show significant growth for cloud droplet size distributions with a higher degree of polydispersity than slender droplet size distributions. We attribute this enhancement in collisions to the induced relative velocity between droplets of different Stokes numbers. We observed a positive trend between clustering and droplet size growth, thus indicating the role of clustering in enhancing collisions.

Acknowledgments: We thank Dr. Amit Kumar Patra and Dr. T. Narayana Rao for their valuable suggestions. We acknowledge the ISRO-IITM cell (No. SP/21-22/1197/AE/ISRO/002696) and  IoE initiative (SP22231222CPETWOCTSHOC) for funding this work. 

References:

[1] Gunthe, S.S., King, S.M., Rose, D., Chen, Q., Roldin, P., Farmer, D.K., Jimenez, J.L., Artaxo, P., Andreae, M.O., Martin, S.T. and Pöschl, U., 2009. Cloud condensation nuclei in pristine tropical rainforest air of Amazonia: size-resolved measurements and modeling of atmospheric aerosol composition and CCN activity. Atmospheric Chemistry and Physics, 9(19), pp.7551-7575.

[2] Devenish, B.J., Bartello, P., Brenguier, J.L., Collins, L.R., Grabowski, W.W., IJzermans, R.H.A., Malinowski, S.P., Reeks, M.W., Vassilicos, J.C., Wang, L.P. and Warhaft, Z., 2012. Droplet growth in warm turbulent clouds. Quarterly Journal of the Royal Meteorological Society, 138(667), pp.1401-1429.

[3] Ravichandran, S. and Govindarajan, R., 2015. Caustics and clustering in the vicinity of a vortex. Physics of Fluids, 27(3).

How to cite: Vignesh, S., Sanket, A., Narayanan Unni, A., Sahu, S., S. Gunthe, S., Chaudhuri, S., Govindarajan, R., and I. Sujith, R.: Exploring the Influence of Turbulence on Droplet Size Growth and Precipitation in Warm Clouds, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2702, https://doi.org/10.5194/egusphere-egu24-2702, 2024.