Public Abstract

DE-SC0021256: Understanding the Vertical Transport and Removal of Aerosols during Deep Convective Events

Award Status: Inactive

Institution: The Curators of the University of Missouri (Rolla) (Mo. Univ of Sci and Tech), Rolla, MO
UEI: Y6MGH342N169
DUNS: 804883767

Most Recent Award Date: 07/19/2021
Number of Support Periods: 2
PM: Stehr, Jeffrey

Current Budget Period: 09/01/2021 - 08/31/2022
Current Project Period: 09/01/2020 - 08/31/2023
PI: Wang, Yang

Supplement Budget Period: N/A

Public Abstract

Atmospheric aerosols affect the global energy budget by scattering and absorbing sunlight (direct effects) and by changing the microphysical structure, lifetime, and coverage of clouds (indirect effects). Globally, the free troposphere is a major source of nucleation- and Aitken-mode aerosols due to enhanced new particle formation rates at high altitudes. Recent studies have shown deep convective systems are capable of transporting these small aerosols from the free troposphere to the boundary layer by strong convective downdrafts and weaker downward motions in the stratiform regions associated with deep convection. These vertically transported aerosols can grow into cloud condensation nuclei (CCN) and play a significant role in global climate. During deep convective processes, existing accumulation-mode aerosols that act as coagulation sinks of smaller particles are also removed by wet scavenging. Compared to the vertical transport of these particles by entrainment mixing, which is slower but more prevalent, deep convective downdraft processes may be more rapid and efficient in the vertical transport of aerosols. However, most current climate models do not include this mechanism as a source of CCN, mainly because the frequency of deep convective events varies significantly with geographic location and thus their contributions to CCN are unpredictable. We plan to target this critical gap in understanding the vertical transport and removal of aerosols by deep convection. We propose to analyze a multi-year, multi-site measurement record available from the U.S. Department of Energy (DOE) ARM program, including observations from the 2014/15 Observations and Modeling of the Green Ocean Amazon (GoAmazon) field campaign, the 2018/19 Cloud, Aerosol, and Complex Terrain Interactions (CACTI) field campaign, and long-term measurements collected at the Southern Great Plains (SGP) atmospheric observatory, where deep convective clouds are frequently observed. This project is aimed at the following three objectives: (1) Gaining a detailed and quantitative understanding of the aerosols transported by a convective downdraft and their evolution in the atmosphere; (2) Examining the wet scavenging mechanisms and efficiencies of aerosols at altitudes of deep convective systems based on aircraft measurements; (3) Evaluating the contribution of deep convective systems to CCN as both a source and a sink of atmospheric aerosols and the seasonal variability of that contribution. To achieve our research objectives, we will perform the following tasks: (1) Identify deep convective events using ARM meteorological and cloud radar data to analyze the frequency and intensity of such events at study locations; (2) Study the correlation between the deep convective downdraft intensity and the properties of aerosols transported from the free troposphere; (3) Derive the size-dependent wet scavenging efficiency of aerosols using data collected from aircraft campaigns; (4) Estimate the overall and seasonal contributions of deep convective events to boundary layer aerosols; and (5) Synthesize long-term measurements of aerosol physical and chemical properties to better understand the climate impacts of aerosols associated with deep convective events. This study will address the influence of deep convection on aerosol microphysical and chemical properties and help improve the estimates of aerosol-climate effects in both pre-industrial and present-day atmosphere.

Atmospheric aerosols affect the global energy budget by scattering and absorbing sunlight (direct effects) and by changing the microphysical structure, lifetime, and coverage of clouds (indirect effects). Globally, the free troposphere is a major source of nucleation- and Aitken-mode aerosols due to enhanced new particle formation rates at high altitudes. Recent studies have shown deep convective systems are capable of transporting these small aerosols from the free troposphere to the boundary layer by strong convective downdrafts and weaker downward motions in the stratiform regions associated with deep convection. These vertically transported aerosols can grow into cloud condensation nuclei (CCN) and play a significant role in global climate. During deep convective processes, existing accumulation-mode aerosols that act as coagulation sinks of smaller particles are also removed by wet scavenging. Compared to the vertical transport of these particles by entrainment mixing, which is slower but more prevalent, deep convective downdraft processes may be more rapid and efficient in the vertical transport of aerosols. However, most current climate models do not include this mechanism as a source of CCN, mainly because the frequency of deep convective events varies significantly with geographic location and thus their contributions to CCN are unpredictable.

We plan to target this critical gap in understanding the vertical transport and removal of aerosols by deep convection. We propose to analyze a multi-year, multi-site measurement record available from the U.S. Department of Energy (DOE) ARM program, including observations from the 2014/15 Observations and Modeling of the Green Ocean Amazon (GoAmazon) field campaign, the 2018/19 Cloud, Aerosol, and Complex Terrain Interactions (CACTI) field campaign, and long-term measurements collected at the Southern Great Plains (SGP) atmospheric observatory, where deep convective clouds are frequently observed. This project is aimed at the following three objectives: (1) Gaining a detailed and quantitative understanding of the aerosols transported by a convective downdraft and their evolution in the atmosphere; (2) Examining the wet scavenging mechanisms and efficiencies of aerosols at altitudes of deep convective systems based on aircraft measurements; (3) Evaluating the contribution of deep convective systems to CCN as both a source and a sink of atmospheric aerosols and the seasonal variability of that contribution.

To achieve our research objectives, we will perform the following tasks: (1) Identify deep convective events using ARM meteorological and cloud radar data to analyze the frequency and intensity of such events at study locations; (2) Study the correlation between the deep convective downdraft intensity and the properties of aerosols transported from the free troposphere; (3) Derive the size-dependent wet scavenging efficiency of aerosols using data collected from aircraft campaigns; (4) Estimate the overall and seasonal contributions of deep convective events to boundary layer aerosols; and (5) Synthesize long-term measurements of aerosol physical and chemical properties to better understand the climate impacts of aerosols associated with deep convective events.

This study will address the influence of deep convection on aerosol microphysical and chemical properties and help improve the estimates of aerosol-climate effects in both pre-industrial and present-day atmosphere.