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Abstract Aerosol deep-convective cloud (DCC) interactions remain highly uncertain in the study of water cycles, energy budgets, climate projections, and air quality, partly because it is difficult to disentangle aerosol impacts from the impacts of meteorology in observational studies. Prior studies have shown that increased aerosol ingestion by DCC updrafts can influence their microphysical characteristics through the mixed-phase and condensational aerosol invigoration effects. However, other studies claim that increased aerosol loading produces different microphysical responses that are not consistent with invigoration. This study thus examines the impact of aerosol regimes on DCC microphysics by analyzing ∼1300 DCCs tracked from the Houston–Galveston WSR-88D. Fields from the fifth major global reanalysis produced by ECMWF and Modern-Era Retrospective Analysis for Research and Applications, version 2, are used to estimate meteorological and aerosol conditions near DCCs. DCC tracking was completed using the Multicell Identification and Tracking algorithm applied to radar data. Composite difference contoured frequency by altitude diagrams show statistically significant bulk differences in the vertical structure of dual-polarization radar data that are consistent with previous studies. The probabilistic differences in radar variables were typically 1%–6% above the freezing level and <4% below the freezing level. Microphysical fingerprint distributions showed that DCCs under high aerosol loading exhibit decreased warm rain, increased freezing rates, and increased vapor deposition onto ice. These signatures together are found to be consistent with increased aerosol loading leading to less warm rain, more evaporation under high tropospheric moisture conditions leading to less cold rain, and increased riming/accretion in environments with large instability leading to more cold rain.
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Aerosol interactions with deep convective clouds
Deep convective clouds (DCCs) are associated with the vertical ascent of air from the lower to the upper atmosphere. They appear in various forms such as thunderstorms, supercells, and squall lines. These convective systems play important roles in the hydrological cycle, Earth’s radiative budget, and the general circulation of the atmosphere. Changes in aerosol (both cloud condensation nuclei and ice-nucleating particles) affect cloud microphysics and dynamics, and thereby influence convective intensity, precipitation, and the radiative effects of deep clouds and their cirrus anvils. However, the very complex dynamics and cloud microphysics of DCCs means that many of these processes are not yet accurately quantified in observations and models. This chapter outlines the main ways in which changes in aerosol affect the microphysical, dynamical, and radiative properties of DCCs. Aerosol interactions with DCCs depend on aerosol properties, storm dynamics, and meteorological conditions. When aerosol particles are light-absorbing, such as soot from industry or biomass burning, the aerosol radiative effects can alter the meteorological conditions under which DCCs form. These radiative effects modify temperature profiles and planetary boundary layer heights, thus changing atmospheric stability and circulation, and affecting the onset and development of DCCs. These large-scale effects, such as the effect of anthropogenic aerosol on the East and South Asian monsoons, can be simulated in coarse-resolution models. These processes are described in Chapter 13. This chapter is concerned with aerosol interactions with DCC systems ranging from individual clouds to mesoscale convective systems. Increases in cloud condensation nuclei (CCN) can enhance cloud droplet number concentrations and decrease droplet sizes, thereby narrowing the droplet size spectrum. For DCCs, a narrowed droplet size spectrum suppresses warm rain formation (rain derived from non-ice-phase processes), allowing the transport of more, smaller droplets to altitudes below 0°C. This may result in (i) freezing of more supercooled water, thereby enhancing latent heating from icerelated microphysical processes and invigorating storms (ice-phase invigoration); (ii) modification of ice-related microphysical processes, which changes cold pools, precipitation rates, and hailstone frequency and size; (iii) expansion of the mixed-phase zone and decreases in the cloud glaciation temperature; and (iv) slowing down of cloud dissipation, resulting in larger cloud cover and cloud depth in the stratiform and anvil regions due to numerous smaller ice particles. The increased cloud cover and cloud depth constitute an influence of aerosol on the cloud radiative effect. Reduced diurnal temperature variation has been observed and simulated as a result of enhanced daytime cooling and nighttime warming by expanded anvil cloud area in polluted environments. However, the global radiative effect of aerosol interactions with DCCs remains to be quantified.
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- Award ID(s):
- 2126098
- PAR ID:
- 10629554
- Publisher / Repository:
- Elsevier
- Date Published:
- ISBN:
- 9780128197660
- Page Range / eLocation ID:
- 571 to 617
- Subject(s) / Keyword(s):
- Aerosol Cloud
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Book Chapter:
- https://doi.org/10.1016/B978-0-12-819766-0.00001-8
