Characteristics of Texas Coastal Current from 2018 to 2019 from HF Radar Observations

The Texas HF Radar network consists of five radars (operational since 2016) distributed along the Texas Coast and covers most of the Texas Coastal Current (TCC) region. Based on this HF-Radar system dataset from 2018.10 to 2019.8, the TCC shows a significant seasonal difference between summertime and non-summer time. This has been revealed by the previous research that the low-frequency (>40hr) variations of the TCC are dominated by the local wind stress, and this summertime change of the TCC is due to the reverse of the summer wind. Since the wind shifted from down-coast to up-coast in July, the TCC also reversed to up-coast. The area of the TCC region is not only controlled by the strength of local wind, but it is also affected by passing sub-mesoscale eddies and density-driven currents related to freshwater input from local and remote rivers. The Empirical Orthogonal Function (EOF) analyzed results of the 40-hour low-passed stream function showed that roughly 74% of the total variance of the TCC is dominated by the variation of the local wind, and about 13% is impacted by the passing eddies and ocean stratification. The impact of local wind is more dominant in the nearshore shallow water region, and the effect of passing eddies mainly focuses on the relatively offshore area. Cyclonic eddies show a similar effect as the down-coast wind stress, it could intensify the down-coast TCC and make it wider, but the intensity of the TCC in the nearshore region will be rarely impacted by the passing eddies. When the anticyclonic eddies passed, the down-coast TCC would be countered partially in the offshore area so that the down-coast (up-coast) TCC would become relatively narrower (wider). The third EOF mode (5%) seems related to the geopotential anomaly, which is caused by the terrestrial input freshwater that could generate strong stratification. The high-frequency (<40hr) part of TCC shows correlations to the high-frequency variations of the local wind.