An inviscid model study of sandstorm in unstably stratified atmospheric boundary layer

TL;DR

This study develops an inviscid model to understand the slumping phase of gravity currents in unstably stratified atmospheric boundary layers, revealing how stratification affects front speed and aligning with field observations of sandstorm fronts.

Contribution

The paper introduces an inviscid model that explains the influence of unstable stratification on gravity current dynamics, matching numerical simulations and field data.

Findings

Froude number decreases with unstable stratification.

Model predictions agree with numerical simulations.

Field velocity increments align with model evaluations.

Abstract

According to field observations, the atmospheric boundary layer is usually unstably stratified before a dust and sandstorm, the particle-laden turbulent gravity current with an extremely high Reynolds number. In this paper, an inviscid model is built to study the mechanism governing the slumping phase of gravity current, and it is shown that the dimensionless current front speed, the Froude number, decreases when the current fluid or the ambient medium or both fluids are unstably stratified. In spite of the density interface mixing, the relation between the front speed and the front height described by the inviscid model agrees with the numerical simulation results, where the lock-exchange gravity currents with different initial lock heights are calculated for different unstable stratification cases. Furthermore, the velocity increments obtained by field observations at the sandstorm fronts are satisfactorily consistent with the evaluations of the model, suggesting that the inviscid mechanism makes contribution to such high Reynolds number turbulent flows.