## 4 Results and Discussion
### Effects of Background Winds on Scatterometer Retrievals  
A critical component of the ambiguity removal process is the input of background winds, which are typically provided by a weather model. It has been shown that national weather prediction (NWP) model biases are due to mesoscale processes, e.g., convection, which are resolved by the scatterometers but not by models [71]. [PERSON] et al. [53] investigated the rain effects on ASCAT-retrieved winds and found that the ECMWF winds did not resolve well high-wind-variability cases, such as downdraft-like wind patterns, due to the coarse spatial resolution. In the same study, the inability of the ECMWF to resolve wind variability under rainy conditions was also observed. A distinctive signature of a well-organized MCS is the cold pool [1] that develops near the surface as radially expanding winds, producing gusty winds [72]. At the overpass of ASCAT-A ECMWF (Figure 7a) indicated southeasterly flow with constant wind speed over the domain. A similar response to the winds was also captured by MERRA-2 (Figure 7b). Buoys near the coast measured winds coming from variable directions, indicating that there was at least some wind variability present. More specifically, buoy 42035, located within the precipitation area, measured northwesterly direction. Considering the inability of the ECMWF to wind variability under rainy conditions [PERSON] et al. [53] and the buoy measurements, it is evident that both models failed to capture surface wind features associated with the presence of the MCS. On the contrary, the RAP model (Figure 7c) clearly captured wind speed and direction changes in front and within the system itself. In front of the MCS, over the western side, wind speed magnitude was decreased substantially, which could be attributed to opposing winds over the convergence zone. Variable wind direction was observed by the model at the eastern side of the domain, near the buoys EINL1 and AMRL1. Surprisingly, the low wind speed magnitude observed by the buoys was also captured by the models. Around an area centered at 28.7\({}^{\circ}\)N 95.5\({}^{\circ}\)W the wind direction shifted to northwesterly with increased speed capturing the RJI that was also observed by the radar analysis wind field (Figure 1b). Around 29\({}^{\circ}\)N 91.6\({}^{\circ}\)W, the RAP winds were variable in direction and speed magnitude. Importantly, the UHR-wind gradient magnitude was elevated over the same area (Figure 6e), which was also included in the gradient feature, providing evidence that the UHR is able to identify wind features not related to convective systems. At the overpass of ASCAT-B, wind direction retrieved by ECMWF (Figure 7d) and MERRA-2 (Figure 7e) remained southeasterly throughout the domain at the same wind speed. At the western side of the system, the decreased wind speed area had expanded along the precipitation boundary, as well as towards the open ocean probably denoting a vigorous outflow boundary. Behind the system wind direction was southeasterly in contrast with the radar-derived wind analysis field (Figure 1e). Buoy station CAPL1 measured northerly wind with high speed magnitude, whereas RAP captured easterly direction with moderate speed, which was higher than at the overpass of ASCAT-A (Figure 1c). Near buoy station AMRL1, wind speed magnitude and direction was variable, which was also indicated by a nearby station (EINL1) that measured northerly direction and high speed magnitude. Not surprisingly, UHR-wind gradient magnitude was elevated and enclosed in a gradient feature over the same area (Figure 6f). In order to examine the response of the UHR retrievals to the background wind field, Figure 8 was created, which depicts the divergence field calculated from the UHR wind retrievals as a result of the ambiguity removal process from the MERRA-2 and RAP models. ECMWF and MERRA-2 wind field had nearly-identical wind direction (southeasterly) over the domain, therefore only MERRA-2 winds were used in the ambiguity removal process.