Quantifying the large-scale electrification equilibrium effects in dust storms using field observations at Qingtu Lake Observatory

Abstract

Dust/sand electrification, which is a ubiquitous phenomenon in dust events, has a potentially dramatic effect on dust/sand lifting and transport processes. However, the 15 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 20 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 that is on the order of the typical integral time scale of atmospheric turbulence. We further presented a simple linear regression (SLR) model to quantify such large timescale correlations and 25 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 * ). nn addition, the influences of ambient temperature and RH on * were evaluated by a multiple linear regression (MLR) model,

Reconstructing the electrical structure of dust storms from locally observed electric field data

“…18-19. A constant charge-to-mass (PM 10 ) ratio at each point suggests that, on average (over the scales of 2 9 s), the dust particles have acquired a dynamic charge equilibrium passing through each measured point, which was previously reported but only at one height [25][26][27]57,58 .…”

“…isperse two-phase flows, a huge number of discrete particles or droplets embedded in the turbulent flows, are widespread in nature, industry, and even on other planets [1][2][3][4][5][6][7][8] . There are many examples of interest in disperse twophase flows, such as sand saltation [9][10][11][12][13][14] , dust devils 15,16 , dust and sand storms [17][18][19][20][21][22][23][24][25][26][27] , blowing snows 28,29 , thunderstorms 30 , volcanic eruptions [31][32][33] , fluidization beds 8,34 , as well as dusty plasmas 2,35 . In these systems, very intense electric field (E-field) and even lightning have been frequently observed due to particle electrification.…”

“…It is worth noting that such monopole and bipolar charge structures have also been inferred in volcanic plumes based on three-dimensional (3D) lightning data 32,33 . However, recent 3D E-field measurements in dust storms using an atmospheric surface layer observation array have questioned these simple charge structures 26,27 . The direction of each component of the 3D E-field was found to vary with spatial location 27 , which cannot be explained by the monopole or dipole structure.…”

“…The reconstructed electrical structures can be used to quantify the essential properties of dust storms. For example, previous studies 27 found that, at given ambient temperature (T) and relative humidity (RH), there were significant linear relationships between the dust concentrations and space-charge densities over the timescales of 10 min, suggesting a constant charge-to-mass ratio of dust particles (termed large-scale charge equilibrium phenomenon). This phenomenon has been previously verified at only one measurement point 25,27 and can be examined at multiple points based on the inversion results.…”

“…To further verify our inversion method, we compare the reconstructed densities ρ inv with the GLA-based densities 27 ρ GLA at point p9 (see Methods). As shown in Fig.…”