An Observational Study on Cloud Spectral Width in North China

Abstract

Cloud droplet size distribution (CDSD) is a critical characteristic for a number of processes related to clouds, considering that cloud droplets are formed in different sizes above the cloud-base. This paper analyzes the in-situ aircraft measurements of CDSDs and aerosol concentration ( N a ) performed in stratiform clouds in Hebei, China, in 2015 to reveal the characteristics of cloud spectral width, commonly known as relative dispersion ( ε , ratio of standard deviation (σ) to mean radius (r) of the CDSD). A new algorithm is developed to calculate the contributions of droplets of different sizes to ε . It is found that small droplets with the size range of 1 to 5.5 μm and medium droplets with the size range of 5.5 to 10 μm are the major contributors to ε, and the medium droplets generally dominate the change of ε. The variation of ε with N a can be well explained by comparing the normalized changes of σ and r ( k σ / σ and k r / r ), rather than k σ and k r only ( k σ is Δσ/Δ N a and k r is Δr/Δ N a ). From the perspective of external factors affecting ε change, the effects of N a and condensation are examined. It is found that ε increases initially and decreases afterward as N a increases, and “condensational broadening” occurs up to 1 km above cloud-base, potentially providing observational evidence for recent numerical simulations in the literature.

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

“…. Similar to previous studies (Feingold, 2003b;Zhao C. et al, 2018;Wang et al, 2019), the aerosol first AIE, or Twomey effect, with respect to N c and R e , i.e., A IEn and A IEs , respectively, can be expressed as…”

Variations of aerosol and cloud vertical characteristics based on aircraft measurements in upstream of Shanghai during the 2020 China international import expo

“…Relative dispersion rate (ε), defined as the ratio of the standard deviation of cloud droplet size spectrum and average radius of cloud droplets, is used to illustrate the relative spectral width of cloud droplet spectrum. It is usually linked with the physical and chemical properties of aerosols, related activation process and hygroscopic growth (Ma et al, 2010;Wang et al, 2019), the development stage of clouds, atmospheric temperature, humidity, entrainment process, and turbulence (Lu et al, 2013). A positive correlation was found between the relative dispersion rate and D c (Figures 5H,I, r = 0.78).…”

Effects of Cloud Liquid‐Phase Microphysical Processes in Mixed‐Phase Cumuli Over the Tibetan Plateau

“… P 0 and T are the rate function and threshold function, respectively; x c is the normalized critical mass and can be written as a function of N c and q c (Liu, 2005). Based on observational studies of Wang, Niu, Lu, et al (2019) and Zhao et al (2006), ε is set to 0.4.…”