Estimating Hourly Mixing Depths from Historical Meteorological Data

Abstract

The planetary boundary layer is defined as the layer of the lower atmosphere whose characteristics are directly influenced by the ground surface. In the atmosphere, turbulent mixing forms and maintains this layer; hence, the planetary boundary layer is also a mixing layer. Turbulent mixing can be either convectively or mechanically produced. A simple one-dimensional operational model is proposed to estimate reliable and realistic hourly mixing depths from routinely available upper air and surface data. The model inputs are 0000 and 1200 GMT temperature soundings from the nearest radiosonde station and the hourly surface wind speeds and temperatures from the nearest representative surface station. The model distinguishes between primarily convective and primarily mechanical mixing regimes. In a primarily mechanical regime, such as during nighttime hours or on cloudy or windy days, the mixing depth can be estimated from the surface wind speed and roughness length. During convective regimes, such as on sunny days, the mixing depth can be estimated from the surface temperature and the morning temperature sounding. The model adjusts the surface temperature for temperature advection. By statistical comparisons with available acoustic sounder and radiosonde data, it is shown that for one month of data at a central Illinois site the proposed model demonstrates more skill than a presently available operational scheme.