Two-dimensional numerical analysis of a thermally generated mesoscale wind system observed in the MacKenzie Basin, New Zealand

Abstract

A mesoscale numerical model was used to perform two-dimensional numerical simulations of a thermally driven circulation, known as the Canterbury Plains Breeze, to examine the effect of key physical mechanisms that determine the intensity of this circulation. The mesoscale model has a 2.5 order turbulence closure scheme with a terrain following coordinate system, and has been previously used successfully for numerical studies in mountainous landscapes. The numerical results confirm observational data showing that during settled weather, the Canterbury Plains Breeze is a significant climatological feature of surface airflow in the Mackenzie Basin in the South Island of New Zealand. This circulation is generated because the elevated plateau creates a horizontal temperature gradient between the air inside and outside the basin at the same height. Other forcing factors, such as the gradient in soil moisture and the landsea discontinuity, only enhance the intensity of this mesoscale flow by modifying the horizontal temperature gradient.