Impact of Radio Occultation Data on the Prediction of Typhoon Haishen (2020) with WRFDA Hybrid Assimilation

Shu-Ya Chen,Ching-Yuang Huang,Thi-Chinh Nguyen

doi:10.3390/atmos12111397

Abstract

FORMOSAT-7/COSMIC-2 (FS7/C2) satellite was successfully launched in June 2019. The satellite provides about 5000 radio occultation (RO) soundings daily over the tropical and partial subtropical regions. Such plentiful RO soundings with high accuracy and vertical resolution could be used to improve model initial analysis for typhoon prediction. In this study, assimilation experiments with and without the RO data were conducted with the WRFDA hybrid system for the prediction of Typhoon Haishen (2020). The experimental results show a remarkable improvement in typhoon track prediction with RO data assimilation, especially when using a nonlocal refractivity operator. Results in cycling DA and forecast are analyzed and verified for the RO data impact. Diagnostics of potential vorticity (PV) tendency budget helps explain the typhoon translation induced by different physical processes in the budget. The typhoon translation is essentially dominated by horizontal PV advection, but the track deviation can increase due to the vertical PV advection with opposite effects in the absence of RO data. Sensitivity experiments for different model initial times, physics schemes, and RO observation amounts show positive RO data impacts on typhoon prediction, mainly contributed from FS7. Complementary, an improved forecast of Typhoon Hagupit (2020) is also illustrated for the RO data impact.

Highlights

The northwestern Pacific basin is one of the regions where tropical cyclones are ac‐tive, and the tropical cyclones or typhoons are usually accompanied by strong wind speeds and heavy precipitation, which could result in human life and economic damages
Results of the assessment of the FS7/C2 Radio Occultation (RO) data in the numerical weather predictions (NWP) system can be found in Healy [12], Shao et al [13], and Lien et al [14], and they showed generally positive to neutral impacts and a significant effect in the tropical region
Over most of the northwestern Pacific Ocean, the RO data assimilation tended to a warm at‐ mosphere at mid‐troposphere (Figure 4a,b) and colder at the lower troposphere (Figure 4c,d)

Summary

Introduction

The northwestern Pacific basin is one of the regions where tropical cyclones are ac‐tive, and the tropical cyclones or typhoons are usually accompanied by strong wind speeds and heavy precipitation, which could result in human life and economic damages. GNSS RO data have been operationally used in several weather prediction centers (e.g., [2,3,4,5,6]). About one year after the launch, the FS7/C2 RO data started to be used operationally in some official weather centers. The RO data were implemented in both European Centre for Medium‐Range Weather Fore‐ casts (ECMWF) and National Centers for Environmental Prediction (NCEP) starting in March and May 2020, respectively. Results of the assessment of the FS7/C2 RO data in the NWP system can be found in Healy [12], Shao et al [13], and Lien et al [14], and they showed generally positive to neutral impacts and a significant effect in the tropical region

Objectives

Results

Conclusion