Amazon and Orinoco River Plumes and NBC Rings: Bystanders or Participants in Hurricane Events?

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Abstract
The Amazon and Orinoco River plumes and North Brazil Current (NBC) rings are investigated during the 1 June through 30 November Atlantic hurricane season to identify their impact on upper-ocean temperatures in the region and to draw attention to their potential role in hurricane maintenance and intensification. The analysis uses ocean temperature and salinity stratification data, infrared and microwave satellite-derived sea surface temperature (SST) data, and Atlantic tropical storm and hurricane tracks data. The Amazon–Orinoco River plume spreads into the western equatorial Atlantic Ocean forming an extensive (0°–20°N, 78°–33°W) 10–60-m-thick buoyant surface layer associated with the warmest surface temperatures (up to +3°C) in the region due to the freshwater barrier layer effect. At times the warm Amazon–Orinoco River plume is bisected by cool-surface NBC rings. For the 1960 to 2000 time period, 68% of all category 5 hurricanes passed directly over the historical region of the plume, revealing that most of the most destructive hurricanes may be influenced by ocean–atmosphere interaction with the warm plume just prior to reaching the Caribbean. Statistical analyses of tropical Atlantic SSTs and tropical cyclone wind speeds reveal a significant and unique relationship between warm (cool) SSTs in the Amazon–Orinoco River plume and stronger (weaker) tropical cyclone wind speeds between 35° and 55°W. This implies that warmer (cooler) plume SSTs due to increased (decreased) river discharge may directly contribute to a more (less) vigorous hurricane season.