Evaluating the impact of the COSMIC-RO bending angle data on predicting the heavy precipitation episode during SoWMEX-IOP8

Local operators for simulating the radio occultation bending angle and refractivity are implemented in the assimilation framework of the WRF-Local Ensemble Transform Kalman system. The impact of the COSMIC data are evaluated for predicting a heavy precipitation episode during the 2008 SoWMEX-IOP8. Results show that both the COSMIC refractivity and bending angle are able to contribute positive influence for predicting the location and intensity of the heavy rainfall event.

The advantage of assimilating the bending angle is identified in the lower troposphere in the moisture and wind fields. The convergence near surface is better sustained near the offshore to coastal region of southwestern Taiwan. Therefore, the analysis is able to lead to forecast precipitation characterized by the coastal rainfall, in comparison to the excessive rainfall in the mountainous region in the control forecast without incorporating any COSMIC data.