A Physical Initialization Method for the Economical Prognostic Arakawa-Schubert Scheme

Abstract

A physical initialization method for the economical prognostic Arakawa-Schubert scheme (EPAS) is developed to incorporate observed precipitation data into a numerical weather prediction model. The method adopted is a variational approach which minimizes the difference between the first guess and the initialized model variables, subject to strong constraints on precipitation areas and precipitation rates. The physical initialization method is divided into 2 parts:(1) Adjustment of the initial thermodynamic variables such that the model precipitation areas diagnosed from the adjusted variables become consistent with the observed precipitation areas at the initial time.(2) Adjustment of the initial cloud-base mass flux (Mb) in such a way that the model precipitation rates are equal to the observed precipitation rates.In order to examine the impact of the physical initialization method, forecast experiments for a case study of Typhoon WALT (T9407) were performed.The results of the forecast experiments indicate that the physical initialization method eliminated the spin-up error of precipitation forecast for the first one hour, and reduced the positional error of precipitation forecasts for the first few hours.The results suggest that the adjustment of the initial cloud base mass flux was essential for eliminating the spin-up error. It is also found that the adjustment of the initial cloud base mass flux contributed to reduce the positional error by strengthening the model convective precipitation around the observed heavy-rain area, and that the adjustment of the initial thermodynamic variables reduced the positional error by removing extreme moist-convective instability in the observed rain-free areas.

The JRA-25 Reanalysis

“…An excess energy proportional to the mixing length of the planetary boundary layer is added to the moist static energy at the cloud base in order to take the turbulence effect into account. Further details of the scheme are described in Aonashi, Kuma and Matsushita (1997). The scheme was updated by Nakagawa and Shimpo (2004) by considering the effect of detrainment due to downdraft instead of simply re-evaporating the precipitation.…”

“…A nonlinear normal mode initialization which includes all physical processes is performed in order to suppress high frequency gravitational oscillations. A physical initialization (Aonashi et al 1997) is not used.…”

Direct Assimilation of Multichannel Microwave Brightness Temperatures and Impact on Mesoscale Numerical Weather Prediction over the TOGA COARE Domain

“…Substituting dt=0 into Eq. (9) Similarly, we calculate Mb and the model convective precipitation rate, Prc, whose compensation as (c is balanced with aatc I Ls by using iteration method of Aonashi et al (1997).…”

Impacts of Diabatic Initialization and Cumulus Parameterization on Numerical Typhoon Prediction

“…One feature of this study is the use of "observed" precipitation rates estimated from hourly infrared (IR) measurements from the Geostationary Meteorological Satellite (GMS), as discussed in Section 3.3, for our physical initialization. The use of radiometric measurements from satellites as supplementary data to improve the prediction of TCs has been actively explored by many investigators in connection with the implementation of physical initialization (e.g., Davidson and Pun, 1992;Krishnamurti et al, 1993;Mathur, 1995;Peng and Chang, 1996;Aonashi et al, 1997).…”