Uso de filtro digital para iniciar um modelo de area limitada / A digital filter applied to initialize a limited area numerical model

AUTOR(ES)
DATA DE PUBLICAÇÃO

1999

RESUMO

A Digital Filter Initialization (IFD) technique was used in a limited area model to suppress spurious high frequency oscillations caused by an unbalance between initial mass and wind fields. A linearized model supporting only gravity wave modes was used to test the performance of the IFD. The results showed that the IFD was highly efficient in attenuating, in the average, up to 50% of the amplitudes of the large-amplitude high frequency modes, and removing practically all those with smaller amplitude. Subsequently, the IFD was applied to a limited area model (LAM) designed originally at the Japan Meteorological Agency (JMA). The input fields were prepared from a global analysis of the National Centers for Environmental Prediction (NCEP) for 1200 UTC 31 December 1979 by interpolating them to the sigma levels and to the resolution of the LAM. This analysis was chosen because it contained already a cyclone over the southern Atlantic Ocean that would intensify in the next hours. The LAM was then integrated for 12 hours, with the IFD technique incorporated with four cutoff periods (1, 2, 3 and 4 hours) to generate a new initial condition at 18 UTC 31 December 1979. Starting off from this initial state, the LAM was integrated for the next 24 hours, and it was possible to find out that for that 12 hour series, the best cutoff period to filter the unwanted oscillations was that of 3 hours. A set of three 48 hour runs was carried out to study the impact of the filtering technique on the performance of the model basing on two subjective criteria proposed by Lynch (1992). These numerical experiments included one case of no initialization procedure, one with a dynamic initialization in which the integration started six hours before actual comparison began and, finally, one using the IFD. The third case showed that the IFD technique succeeded in removing the high frequency oscillations, with a slight increase in the integration time (15 minutes to 18 minutes for a 48 hour forecast). It is worthy mentioning that this technique is non-recursive, thus avoiding unnecessary efforts to store the data series to be filtered.

ASSUNTO(S)

filtros digitais baixa pressao estudos do tempo e clima modelos atmosfericos fronteiras iniciacao ciclone

ACESSO AO ARTIGO

Documentos Relacionados