## 4 Results and Discussion
### Impact of Different Scatterometer Product Resolutions
In front of the MCS's precipitation boundary (Figure 6c, blue line), wind vectors associated with the expanding outflow boundary shifted from southeast to east. Wind gradient magnitude increased over the same area to a maximum of 0.5 \(\times\) 10\({}^{-3}\) s\({}^{-1}\). Within the system, elevated values of wind gradient were locally confined near intense precipitation. A unique GF was identified that encompassed part of the precipitating system as well as the associated outflow boundary (Figure 6c, black solid line). The primary and secondary thresholds used in the GF algorithm were \(6.8\times 10^{-5}\) s\({}^{-1}\) and \(1.2\times 10^{-4}\) s\({}^{-1}\), respectively. [PERSON] et al. [23] evaluated the GF method using thresholds determined by a model simulation. Based on statistical indices--i.e., critical success index, false alarm and bias ratio--the authors obtained a value of \(6.8\times 10^{-5}\) s\({}^{-1}\) and \(1.2\times 10^{-4}\) s\({}^{-1}\) for the primary and secondary thresholds, respectively. The same sensitivity test performed on the ASCAT-A wind gradient process had similar results to the coarser wind product. [PERSON] and [PERSON] [26] hypothesized that ASCAT wind retrievals at 25-km spatial resolution failed to detect convective-scale gust fronts because the product's resolution is too coarse to resolve such phenomena. At the overpass of ASCAT-B (Figure 6d) the wind direction shifted to easterly in front of the border of the precipitation (Figure 6d, blue line). Wind direction within the system was northerly, according to the suggested solution. The wind gradient increased from near zero at the open ocean to 0.62 \(\times\) 10\({}^{-3}\) s\({}^{-1}\) towards the boundary of the precipitation. On the eastern side of the MCS (Figure 6d, R1), elevated values of wind gradient were associated with variable wind direction and speed on the contrary with the uniform wind field depicted by ASCAT-A. Single-Doppler analysis winds (Figure 1e) over the same area indicated a shift in the wind for distances longer than 150 km from the radar location; although at such distances the wind vectors didn't correspond to a low-level field, they might be representative of a deep gust front layer. The unique GF (Figure 6d, black solid line) extended further east near the coastline and included the shift in the wind  
Figure 5: Same configuration as Figure 3, but for the UHR product (7-km spatial resolution) on 28 May 2016 at 02:51 UTC and 03:42 UTC for ASCAT-A and -B, respectively. Wind solution 3 is excluded as rain effects were prevalent and did not provide any valid solution. vectors induced by the outflow boundary, thus supporting the utility of this method for the detection of such phenomena. The primary and secondary threshold values used in the GF algorithm were 2.2 \(\times\) 10\({}^{-4}\) s\({}^{-1}\) and 1.8 \(\times\) 10\({}^{-4}\) s\({}^{-1}\), respectively. The sensitivity test on the thresholds used in the GF algorithm affected only the size of the feature and not the population. UHR adjusted wind retrievals at the overpass of ASCAT-A (Figure 6e) were available as close as 10 km from the coast. Offshore Houston winds were characterized by northwesterly flow with high wind speeds reaching a maximum of 30 m s\({}^{-1}\). A buoy located at 29.3\({}^{\circ}\)N 94.4\({}^{\circ}\)W (Figure 6a, 42035) indicated northerly direction (350\({}^{\circ}\)N) at the closest time to the ASCAT-A overpass, in accordance with the UHR retrievals near the coast. However, some wind retrievals were suspect due to land contamination and/or precipitation. Rain-afflicted wind vector were aligned perpendicular to the MetOp-A track (ascending, towards northwest) near the center of the domain. In the eastern side of the domain (Figure 6a, R1) the wind was southerly (Figure 6e), over an area not affected by precipitation. However, at about 29\({}^{\circ}\)N 92\({}^{\circ}\)W, a wind shift to southwesterly winds was observed, which was characterized by elevated wind gradient values (2.7 \(\times\) 10\({}^{-3}\) s\({}^{-1}\)).