Impact of GNSS RO Data on the Prediction of Atmospheric River Events: A ROMEX Experiment

The assimilation of GNSS (Global Navigation Satellite Systems) radio occultation (RO) data has been shown to improve atmospheric river (AR) predictions. Building on previous research, this study leverages the ROMEX (Radio Occultation Modeling Experiment) dataset, which provides approximately 40,000 RO profiles daily from various operational and commercial missions, far exceeding the 12,000 profiles operationally available.

In this study, we utilize the WRFDA (Weather Research and Forecasting Data Assimilation) system to assimilate GNSS RO data for an AR event that occurred from November 3-5, 2022, affecting the U.S. West Coast. We aim to: (1) evaluate the effectiveness of the default RO observation error in WRFDA for ROMEX data, and (2) examine the impact of increased RO data on AR forecasting accuracy.

Preliminary results showed that the expanded RO data improved AR predictions in terms of moisture transport as well as the timing of AR landfall. The study also suggested that caution must be taken in assimilating RO data from different missions (which have different error characteristics, particularly in the lower tropical troposphere). These findings will be presented and discussed at the conference, providing insights into the design of future RO observing systems in support of numerical weather prediction.