PAFOG—a new efficient forecast model of radiation fog and low-level stratiform clouds

Abstract The new one-dimensional forecast model PAFOG for radiation fogs and low-level stratiform clouds will be presented. The aim of the model is to improve the local visibility forecast on airports and other traffic locations where fog and low-level stratus frequently occur. PAFOG has been developed on the basis of the microphysical fog model MIFOG of Bott et al. [J. Atmos. Sci. 47 (1990) 2153]. To obtain a numerically efficient model, the detailed spectral cloud microphysics of MIFOG has been replaced by the parameterization scheme of Chaumerliac et al. [J. Geophys. Res. 92 (1987) 3114]. Furthermore, according to Siebert et al. [Beitr. Phys. Atmos. 65 (1992a) 93], a model for low vegetation is included in PAFOG so that now fog evolution as influenced by different types of vegetation can also be accounted for. The performance of PAFOG has been tested by comparing the model results with routine observations of the German Weather Service. Nine different weather periods comprising a total of 45 days have been investigated. In 41 cases, PAFOG yields agreement with the observations in terms of occurrence or nonoccurrence of fog or stratiform clouds. During radiation fogs, the calculated and observed visibilities are quite similar. However, in the model simulations the formation of dense fogs tends to be somewhat delayed. From the case studies with stratiform clouds, it is seen that cloud evolution in time and space strongly depends on the value of the large-scale subsidence. Since this quantity is not available from measurements, it must be provided by means of a numerical weather forecast model.

[1]  E. Richard,et al.  The Numerical Simulation of Clouds, Rains and Airflow over the Vosges and Black Forest Mountains: A Meso-β Model with Parameterized Microphysics , 1986 .

[2]  U. Sievers,et al.  A one-dimensional simulation of the interaction between land surface processes and the atmosphere , 1992 .

[3]  G. Mellor,et al.  A Hierarchy of Turbulence Closure Models for Planetary Boundary Layers. , 1974 .

[4]  R. Glasow,et al.  Interaction of radiation fog with tall vegetation , 1999 .

[5]  H. Sakakibara.  A Scheme for Stable Numerical Computation of the Condensation Process with a Large Time Step , 1979 .

[6]  Andreas Bott,et al.  A Radiation Fog Model with a Detailed Treatment of the Interaction between Radiative Transfer and Fog Microphysics , 1990 .

[7]  T. Trautmann,et al.  A numerical model of the cloud‐topped planetary boundary‐layer: Radiation, turbulence and spectral microphysics in marine stratus , 1996 .

[8]  P. Duynkerke,et al.  Current problems in the stratocumulus-topped atmospheric boundary layer , 1989 .

[9]  G. Mellor,et al.  Development of a turbulence closure model for geophysical fluid problems , 1982 .

[10]  Edwin L. Fisher,et al.  An Experiment in Numerical Prediction of Fog and Stratus , 1963 .

[11]  N. Chaumerliac,et al.  Sulfur scavenging in a mesoscale model with quasi‐spectral microphysics: Two‐dimensional results for continental and maritime clouds , 1987 .

[12]  R. Pielke.  Mesoscale Meteorological Modeling , 1984 .