Two-dimensional Pattern of Forecast Model Drift in the Amazon Basin
José
Antonio
Aravéquia, CPTEC / INPE, araveq@cptec.inpe.br
(Presenting)
Pedro
Leite
Silva Dias, IAG / USP, pldsdias@master.iag.usp.br
The precipitation forecast drift (bias) at several time intervals of the CPTEC and the NCEP global models were computed for the period of 1997-1999. The CPTEC model shows less precipitation than the observations in the Amazon Basin during the summer, indicating that the model is not able to sustain enough convective forcing. As a result of the precipitation negative bias it is shown that the upper air flow develops a cyclonic drift. The NCEP model tends to overestimates the precipitation in the northern portion of the basin and underestimate in the central and southern portions. This pattern is shown to be related to the precipitation bias in the Andes. The causes of the precipitation bias are partially related to the convective parameterization and numerical constraints associated with the numerical treatment of steep orography. Both models indicate that there is a significant intraseasonal (20-60 day) signal in the precipitation bias of the 120hr forecast in the Amazon region which is shown to be related to the Madden Julian oscillation. Thus, there are periods of higher predictability of the precipitation and periods of lower predictability with period of the order of 20-60 days.
Submetido por José Antonio Aravéquia em 25-MAR-2004