Numerical simulation of observed submesoscale plume meandering under nocturnal drainage flow

Bimodal plume shapes are occasionally observed in the series of tracer release experiments conducted at Hanford known as Hanford 67. These particular cases have not been studied so far. A possible reason for the bimodal shape could be the nocturnal submesoscale meandering of wind over the valley terrain. This study investigates the ability of state of art nested numerical model (WRF-ARW) to dynamically down scale up to submesoscale range (10 km in space and less than one hour in time) to simulate the meandering wind flow. The simulated wind field is used to drive a Lagrangian particle dispersion model, FLEXPART-WRF for plume simulation. From the study it is confirmed that the reason for this bimodal plume pattern is the wind meandering with periodicity of the order of ∼30 min having physical origin in the nocturnal drainage flow. Further, it is observed that the above submesoscale motion could be simulated using WRF model by reducing the grid size to 1 km in the horizontal plane.