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Arti Jadav

Postdoctoral fellow

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Improved Cloud Parameterization in Global Climate Model : Aerosol effects and secondary ice production mechanisms

Author

  • Arti Jadav

Summary, in English

The response of clouds to the changes in climate is uncertain, and the representation of the cloud-climate feedback is a key challenge in the global circulation models (GCM) for future climate projections. Factors contributing to this uncertainty include processes that involve particles of various sizes and phases, as well as the interactions between these particles and the surrounding atmosphere. The deep convective and stratiform cloud parameterizations in the Community Earth System Model (CESM) were improved and validated against the observations from the field campaign. These parameterizations explicitly resolve all known modes of heterogeneous cloud droplet activation, ice nucleation, secondary ice production (SIP) mechanisms, and growth processes, including collision/coagulation. The focus of the thesis is to improve the aerosols-cloud interaction and include the overlooked SIP mechanisms. A new detrainment scheme from a recent formulation based on high-resolution cloud modelling provides a better linkage between the convective and stratiform clouds. The mesoscale convective system (MCS) observed over Oklahoma, USA, during the Midlatitude Continental Convective Cloud Experiment (MC3E) was simulated with a single-column model, version 6 (SCAM6). The results are validated with ground measurements and in-situ aircraft observations. The analysis shows that the new microphysical parameterization provides a good representation of the ice initiation processes by including the empirically quantified primary ice processes and SIP mechanisms. Furthermore, the addition of SIP mechanisms has significantly improved the ice number concentrations in the mixed-phase
regions of simulated MCS. Sensitivity experiments show that breakup in ice-ice collisions is predicted to be the most significant SIP mechanism in the simulations. Increasing the soluble aerosols resulted in reduced cloud particle sizes, inhibiting the growth of droplets, and thus enhancing the homogeneous cloud droplet
freezing.

Department/s

  • Dept of Physical Geography and Ecosystem Science
  • MERGE: ModElling the Regional and Global Earth system

Publishing year

2024-03-15

Language

English

Document type

Dissertation

Publisher

Lund University

Topic

  • Meteorology and Atmospheric Sciences

Keywords

  • Cloud
  • Coud parameterization
  • Primary ice mechanisms
  • Secondary ice production
  • Global climate model

Status

Published

Supervisor

  • Vaughan Phillips
  • Paul Miller

ISBN/ISSN/Other

  • ISBN: 978-91-89187-38-2
  • ISBN: 978-91-89187-37-5

Defence date

12 April 2024

Defence time

13:00

Defence place

Världen, Geocentrum 1, Sölvegatan 10, Lund.

Opponent

  • Andrew Gettelman (Doctor)