The variation of the vertical electric field (
$${{\varvec{E}}}_{\mathrm{z}}$$
E
z
) with height during dust storms and the effects of environmental variables on
“…The instantaneous fluctuations at some locations are sufficiently high to cause a reversal in the direction of the vertical electric field component. Such a change in the direction of the electric field has been observed in the field [12], and similarly observed in the saltation layer [20]. An incremental change in particle concentration boundary conditions tends to increase the electric field levels in the sandstorms.…”
supporting
confidence: 59%
“…For cases III, III-B and IV, the maximum magnitude of horizontal electric field exceeds 100kV/m, which is also observed in the field [5]. For the weak sandstorm case (Case I) the near wall average electric field (E z ) are close to the observed electric field, (E z ≈ −10KV/m) [12], while for Case II (moderate) E z ≈−30KV/m and Case III (strong sandstorm) observations E z ≈−80KV /m, agree with field measurements [2,12]. The RMS fluctuation of the near wall vertical electric field for the case II, Fig.…”
supporting
confidence: 57%
“…Comparison with Field Observations.-The time variation of E z is plotted in Fig. 2 wherein we superimpose our simulation results with field observations [2,12]. Since the time origin is somewhat arbitrary we align the minimum of E z (Fig.…”
Sandstorms are frequently accompanied by the generation of intense electric fields and lightning. In a very narrow region close to the ground level, sand particles undergo a charge exchange mechanism whereby larger (resp. smaller) sized sand grains become positively (resp. negatively) charged are then entrained by the turbulent fluid motion. Our central hypothesis is that differently sized sand particles get differentially transported by the turbulent flow resulting in a large-scale charge separation, and hence a large-scale electric field. We utilize our simulation framework, comprising of large-eddy simulation of the turbulent atmospheric boundary layer along with sand particle transport and an electrostatic Poisson solver, to investigate the physics of electric fields in sandstorms and thus, to confirm our hypothesis. We utilize the simulation framework to investigate electric fields in weak to strong sandstorms that are characterized by the number density of the sand particles. Our simulations reproduce observational measurements of both mean and RMS fluctuation values of the electric field. We propose a scaling law in which the electric field scales as the two-thirds power of the number density that holds for weak-to-medium sandstorms.
“…The instantaneous fluctuations at some locations are sufficiently high to cause a reversal in the direction of the vertical electric field component. Such a change in the direction of the electric field has been observed in the field [12], and similarly observed in the saltation layer [20]. An incremental change in particle concentration boundary conditions tends to increase the electric field levels in the sandstorms.…”
supporting
confidence: 59%
“…For cases III, III-B and IV, the maximum magnitude of horizontal electric field exceeds 100kV/m, which is also observed in the field [5]. For the weak sandstorm case (Case I) the near wall average electric field (E z ) are close to the observed electric field, (E z ≈ −10KV/m) [12], while for Case II (moderate) E z ≈−30KV/m and Case III (strong sandstorm) observations E z ≈−80KV /m, agree with field measurements [2,12]. The RMS fluctuation of the near wall vertical electric field for the case II, Fig.…”
supporting
confidence: 57%
“…Comparison with Field Observations.-The time variation of E z is plotted in Fig. 2 wherein we superimpose our simulation results with field observations [2,12]. Since the time origin is somewhat arbitrary we align the minimum of E z (Fig.…”
Sandstorms are frequently accompanied by the generation of intense electric fields and lightning. In a very narrow region close to the ground level, sand particles undergo a charge exchange mechanism whereby larger (resp. smaller) sized sand grains become positively (resp. negatively) charged are then entrained by the turbulent fluid motion. Our central hypothesis is that differently sized sand particles get differentially transported by the turbulent flow resulting in a large-scale charge separation, and hence a large-scale electric field. We utilize our simulation framework, comprising of large-eddy simulation of the turbulent atmospheric boundary layer along with sand particle transport and an electrostatic Poisson solver, to investigate the physics of electric fields in sandstorms and thus, to confirm our hypothesis. We utilize the simulation framework to investigate electric fields in weak to strong sandstorms that are characterized by the number density of the sand particles. Our simulations reproduce observational measurements of both mean and RMS fluctuation values of the electric field. We propose a scaling law in which the electric field scales as the two-thirds power of the number density that holds for weak-to-medium sandstorms.
“…Due to the canceling contributions of positive and negative particles, the volumetric charge density in lofted dust systems is expected to be very small, while the charge on each individual particle can still be large. Studies have shown that, to some extent, smaller and larger particles tend to charge with different polarities (Zhao et al, 2002;Forward et al, 2009;Bilici et al, 2014;Waitukaitis et al, 2014;Toth et al, 2017). This particle-size-dependent polarity of charge, combined with the separation of small and large particles in a gravitation field such that smaller particles are lofted higher, generates the electric fields in dust storms.…”
Abstract. Large amounts of dust are lofted into the atmosphere from arid
regions of the world before being transported up to thousands of kilometers.
This atmospheric dust interacts with solar radiation and causes changes in the climate, with larger-sized particles having a heating effect, and
smaller-sized particles having a cooling effect. Previous studies on the
long-range transport of dust have found larger particles than expected,
without a model to explain their transport. Here, we investigate the effect
of electric fields on lofted airborne dust by blowing sand through a
vertically oriented electric field, and characterizing the size distribution
as a function of height. We also model this system, considering the
gravitational, drag, and electrostatic forces on particles, to understand
the effects of the electric field. Our results indicate that electric fields
keep particles suspended at higher elevations and enrich the concentration
of larger particles at higher elevations. We extend our model from the
small-scale system to long-range atmospheric dust transport to develop
insights into the effects of electric fields on size distributions of lofted
dust in the atmosphere. We show that the presence of electric fields and the
resulting electrostatic force on charged particles can help explain the
transport of unexpectedly large particles and cause the size distribution to
become more uniform as a function of elevation. Thus, our experimental and
modeling results indicate that electrostatic forces may in some cases be
relevant regarding the effect of atmospheric dust on the climate.
“…values synthesised from various terrestrial sandstorm measurements by Zhang, Wang, Qu, and Yan (2004) (circles, Observ. 1) and Zhang, Li, and Bo (2018) (stars, Observ. 2).Figure 8.Wall-normal height-based variation in the ( a ) charge density fluctuations, ( b ) normalised r.m.s.…”
Martian dust storms in the planetary boundary layer share many qualitative similarities to terrestrial sandstorms. Both of these turbulence-driven, particle-laden boundary layer flows are known to generate electric fields due to the transport of differentially charged particles; this charge separation can be strong enough to lead to dielectric breakdown in the form of sparks or lightning. Using wall-modelled large-eddy simulations supplemented with conservation of equations for the charged particle transport, representative simulations of neutrally stable Martian and terrestrial particle-laden boundary layer flows are compared. The simulations, albeit canonical in nature, provide evidence to support previous observations of the less frequent occurrence of lightning on Mars but a higher occurrence of localised electric discharge events due to the much lower breakdown potential. The rarefied Martian atmosphere impedes charged particle transport, resulting in a weaker electric field than the equivalent terrestrial sandstorm. The lower drag force in the rarefied Martian atmosphere means that the electrostatic force plays a more significant role in the particle transport, which results in a self-regulation of the electric field. The strongest Martian dust storms show evidence of significant breakdown events and these discharge events only occur very close to the ground despite the very large boundary layer on Mars.
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