Abstract
Abstract. Dust and sand electrification, which is a ubiquitous phenomenon in dust events, has a potentially dramatic effect on dust and sand lifting and transport processes. However, the effect of such electrification is still largely unclear, mainly due to its complexity and sparse observations. Here, we conducted an extensive observational analysis involving mild and severe dust storms with minimum visibility, ranging from ∼0.09 to 0.93 km, to assess the electrical properties of airborne dust particles in dust storms. The space charge density has been estimated indirectly based on Gauss's law. Using the wavelet coherence analysis that is a method for evaluating the correlations between two non-stationary time series in the time–frequency domain, we found that the space charge density and dust concentration were significantly correlated over the 10 min timescales (on the order of the typical integral timescale of atmospheric turbulence). We further presented a simple linear regression (SLR) model to quantify such large timescale correlations and found that there was a significant linear relationship between space charge density and dust concentration at given ambient temperature and relative humidity (RH), suggesting that the estimated mean charge-to-mass ratio of dust particles was expected to remain constant (termed as the equilibrium value μ∗). In addition, the influences of ambient temperature and RH on μ∗ were evaluated by a multiple linear regression (MLR) model, showing that the μ∗ is nonlinearly related to environmental factors. The present study provides observational evidence for the environmental-dependent electrification equilibrium effects in dust storms. This finding may reduce challenges in future quantifications of dust electrification, as it is possible to exclude effects, such as the particles' collisional dynamics, on dust electrification.
Highlights
Granular materials in dust events such as blowing sand, dust devils and dust storms, are frequently brought into contact or collision with each other, accumulating large amounts of electrical charge on their surfaces (Kamra, 1972; Rudge, 1913; Schmidt et al, 1998)
We have successfully recorded 10 dust storms lasting a total of ∼ 66 h, which is sufficient to perform a series of reliable statistical analyses (Table 1)
The vibrating-reed electric field mill (VREFM) spacing is respectively ∼ 1.6, 5 and 10 m in the vertical, spanwise and streamwise directions owing to the rapid variation of electric field (E-field) along the vertical direction and slow variation along the spanwise and streamwise directions, in order to eliminate the disturbances from other VREFMs and the observation tower, and the calculated space charge density is a measure of the mean charge of dust particles in a multi-cubic meter volume
Summary
Granular materials in dust events such as blowing sand, dust devils and dust storms, are frequently brought into contact or collision with each other, accumulating large amounts of electrical charge on their surfaces (Kamra, 1972; Rudge, 1913; Schmidt et al, 1998). The strong electrostatic forces exerted on dust particles, which are comparable to gravitational force, could considerably affect the motion of particles and facilitate the lifting of particles from the ground (Esposito et al, 2016; Harper et al, 2017; Kok and Renno, 2008; Schmidt et al, 1998; Zheng et al, 2003). Recent observations have demonstrated that electrostatic forces can enhance dust concentration by up to a factor of 10 when the intensity of the electric field (E-field) exceeds a certain threshold value (Esposito et al, 2016). Aizawa et al (2016) and Zhang et al (2017) have documented that the substantial enhancement in the inten-
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