Diabatic Digital-Filtering Initialization: Application to the HIRLAM Model

Abstract

A digital-filtering initialization scheme, which includes the effects of diabatic processes, has been formulated. This scheme gives a lower noise level in the forecast and a better organized initial pressure-tendency field than for the corresponding adiabatic initialization. The implementation of the scheme is very easy, requiring only the calculation of the filter coefficients and minor adjustments to the model code. The computational expense of the digital-filtering initialization is directly proportional to the length of the time span over which the filter is applied. By a careful choice of filter weights, based on optimal filter theory, the span of the filter can be reduced by a factor of 2 or 3, with a corresponding increase in efficiency.