Vertical Distributions of Aerosol and Cloud Microphysical Properties and the Aerosol Impact on a Continental Cumulus Cloud Based on Aircraft Measurements From the Loess Plateau of China

Abstract

Based on aircraft measurements of aerosols and continental cumulus clouds made over the Loess Plateau of China (Xinzhou, Shanxi Province) on 30 July 2020, this study focuses on the vertical profiles of microphysical properties of aerosols and cumulus clouds, and use them to study aerosol-cloud interactions. During the study period, the boundary layer was stable with a height ∼1,500 m above sea level. Aerosols in the boundary layer mainly came from local emissions, while aerosols above this layer were mostly dust aerosols transported over long distances. Vertical profiles of aerosols and cloud condensation nuclei were obtained, and aerosol activation ratios at different supersaturation (SS) levels ranged from 0.16 to 0.32 at 0.2% SS and 0.70 to 0.85 at 0.8% SS. A thick cumulus cloud in the development stage was observed from the bottom to the top with the horizontal dimension of 10 km by 7 km, the cloud-base height of 2,450 m (15.8°C), and the cloud-top height of 5,400 m (−3°C). The maximum updraft velocity near the cloud top was 13.45 m s−1, and the maximum downdraft velocity occuring in the upper-middle part of the cloud was 4.44 ms−1. The temperature inside the cloud was higher than the outside, with their difference being positively correlated with the cloud water content. The temperature lapse rate inside the cloud was about −6.5°C km−1. The liquid water content and droplet effective radius (Re) increased with increasing height. The cloud droplet number concentration (Nc) increased first then decreased, peaking in the middle and lower part of the cloud, the average values of Nc and Re were 767.9 cm−3 and 5.17 μm, respectively. The cloud droplet spectrum had a multi-peak distribution, with the first appearing at ∼4.5 μm. SS in the cloud first increased then decreased with height. The maximum SS is ∼0.7% appearing at ∼3,800 m. The conversion rate of intra-cloud aerosols to cloud droplets was between 0.2 and 0.54, with the ratio increasing gradually with increasing height. The cloud droplet spectral dispersion and Nc were positively correlated. The aerosol indirect effect (AIE) was estimated to be 0.245 and 0.16, based on Nc and Re, respectively. The cloud droplet dispersion mainly attenuated the AIE, up to ∼34.7%.

Diverse Dispersion Effects and Parameterization of Relative Dispersion in Urban Fog in Eastern China

“…Owing to the positive correlation between β and ε (Figure S2 in Supporting Information ), the influence of the dispersion effect on the Twomey effect has mostly been assessed through the correlation between ε and N f in previous studies (e.g., Cai et al., 2022; Liu & Daum, 2002; Ma et al., 2010; Martin et al., 1994; Pontikis & Hicks, 1992; Zhao et al., 2006). Figures 1a and 1b show the relationship between ε and N f under different LWC conditions for all fog cases combined and each fog case, respectively.…”

“…Furthermore, the ε varies nonlinearly with these factors. For instance, most studies (Cai et al., 2022; Liu & Daum, 2002; Liu et al., 2008; Martin et al., 1994; Wang, Zhao, et al., 2021) have shown positive correlations between ε and aerosol amount, whereas others have found negative correlations (Hudson et al., 2012; Ma et al., 2010) and no correlation (Zhao et al., 2006). The diverse correlations indicate that whether the dispersion effect enhances or weakens the Twomey effect is an outcome that is supposed to be region‐specific.…”