# Assessment of CYGNSS Wind Speed Retrievals in Tropical Cyclones
## 2 Datasets and Methodology
### Hurricane Weather Research and Forecasting (HWRF) Model  
The Hurricane Weather Research and Forecasting (HWRF) Model is a high-resolution model run at NCEP/NWS used by agencies such as the National Hurricane Center (NHC) and the Joint Typhoon Warning Center (JTWC) for real-time tropical cyclone forecasting and forecast guidance ([[https://www.emc.ncep.noaa.gov/gc_wmb/vxt/HWRF/](https://www.emc.ncep.noaa.gov/gc_wmb/vxt/HWRF/)]([https://www.emc.ncep.noaa.gov/gc_wmb/vxt/HWRF/](https://www.emc.ncep.noaa.gov/gc_wmb/vxt/HWRF/)), accessed on 15 November 2021). For this study, we used the HWRF 0-h wind analyses produced every six hours (00Z, 6Z, 12Z, 18Z) for several tropical cyclones. Each 0-h analysis consists of three gridded domains: one parent domain and two smaller, nested domains. In this study, we used the innermost nested domain, which covers a 9\({}^{\circ}\)\(\times\) 9\({}^{\circ}\) grid box surrounding the storm center at a resolution of approximately 1.5 km. This domain was used as it allowed us to resample the HWRF data at coarser resolutions to make more direct comparisons  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**(a) CYGNSS L2** & **Start/End Date** & **Wind Products** & \begin{tabular}{c} **Track-Wise Bias Correction** \\ **(Dataset Used, Latency)** \\ \end{tabular} \\ \hline SDR V3.0 & Aug 2018–present & \begin{tabular}{c} Fully Developed Sea (FDS) \\ Young Sea Limited Fetch (YSLF) \\ \end{tabular} & \begin{tabular}{c} No \\ (\(\sim\)2 days) \\ Yes \\ \end{tabular} \\ CDR V1.0 & Mar 2017–Feb 2021 & \begin{tabular}{c} FDS \\ YSLF \\ \end{tabular} & \begin{tabular}{c} Yes \\ (MERRA2) \\ Yes \\ \end{tabular} \\ CDR V1.1 & Aug 2018–present & \begin{tabular}{c} FDS only \\ (MERRA2, \(\sim\)1 month) \\ \end{tabular} \\ NOAA V1.0 & 2017–2019 & Single wind algorithm, all winds & \
\begin{tabular}{c} Yes \\ (ECMWF) \\ \end{tabular} \\ NOAA V1.1 & May 2017–present & Single wind algorithm, all winds &
\begin{tabular}{c} Yes \\ (ECMWF, \(\sim\)6 days) \\ \end{tabular} \\ \hline
**(b) CYGNSS L3** & **Start/End Date** & **Wind products** & \
\begin{tabular}{c} **Track-Wise Bias Correction** \\ **(Dataset Used)** \\ \end{tabular} \\ \hline Storm-Centric & Aug 2018–Oct 2019 &
\begin{tabular}{c} Storm-centric, high winds only \\ N. Atlantic and E. Pacific basins \\ \end{tabular} & No \\ \hline \hline \end{tabular}
\end{table}
Table 1: (a) Level 2 (L2) CYGNSS datasets assessed in this manuscript, all available on PO.DAAC, with the exception of NOAA V1.0, a preliminary beta version. (b) Level 3 (L3) CYGNSS datasets assessed in this manuscript, available on PO.DAAC. Notice that some datasets start in 2018 because they are processed using the V3.0 L1 files, which begin in 2018. Others (NOAA V1.1 and CDR V1.0) start in 2017 because they use V2.1 of L1 files, which are available from 2017 onward.  
with the coarser resolution CYGNSS data. The 0-h analyses are initializations of the HWRF model, rather than a forecast, and represent the state of the storm at any given realization time. They contain a storm vortex which is constructed by assimilating data from the National Center for Environmental Prediction (NCEP) Global Data Assimilation (GDAS) 6-h forecasts along with conventional in situ data, satellite observations, and Doppler radar radial velocities when available [45]. It is worth mentioning that none of the other satellite datasets used in this study are assimilated into the HWRF 0-h analyses. Therefore, HWRF can be considered an independent comparison dataset.