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The Sugar-to-Flower Shallow Cumulus Transition Under the Influences of Diurnal Cycle and Free-Tropospheric Mineral Dust
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  • Pornampai Narenpitak,
  • Jan Kazil,
  • Takanobu Yamaguchi,
  • Patricia K. Quinn,
  • Graham Feingold
Pornampai Narenpitak
National Electronics and Computer Technology Center

Corresponding Author:pornampai.nar@nectec.or.th

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Jan Kazil
Cooperative Institute for Research in Environmental Sciences, University of Colorado and Chemical Sciences Division, NOAA ESRL
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Takanobu Yamaguchi
NOAA Earth System Research Laboratory
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Patricia K. Quinn
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Graham Feingold
CSD, ESRL, NOAA, Boulder
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A transition from sugar to flower shallow cumuli occurred under a layer of mineral dust on February 2, 2020, during the multinational ATOMIC and EUREC4A campaign. Lagrangian large eddy simulations following an airmass trajectory along the trade winds are used to explore radiative impacts of the diurnal cycle and mineral dust on the sugar-to-flower (S2F) cloud transition. The large-scale meteorological forcing is derived from the European Center for Medium-Range Weather Forecasts Reanalysis 5th Generation and based on in-situ measurements during the field campaign. A 12-hour delay in the diurnal cycle accelerates the S2F transition, leading to more cloud liquid water and precipitation at night. The aggregated clouds generate more, and stronger cold pools, which alter the original mechanism responsible for the organization. Although there is still mesoscale moisture convergence in the cloud layer, the near-surface divergence associated with cold pools transports the subcloud moisture to the drier surrounding regions. New convection forms along the cold pool edges, resulting in the next generation of flower clouds. The amount of cloud water, rain, and cold pools reduce after sunrise. The modulation of the surface radiative budget by free-tropospheric mineral dust poses a less dramatic effect on the S2F transition. Mineral dust absorbs shortwave radiation during the day, cooling the boundary layer temperature, enabling stronger turbulence, strengthening the mesoscale organization, and enlarging the aggregate areas. At night, the longwave heating effects of the mineral dust and more cloud liquid water warms the boundary layer, reducing the cloud amount and weakening the organization.