Search Results

You are looking at 1 - 3 of 3 items for

  • Author or Editor: Amy Ffield x
  • Refine by Access: All Content x
Clear All Modify Search
Amy Ffield

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.

Full access
Amy Ffield and Arnold L. Gordon

Abstract

Western Pacific central and tropical waters characterized by a subsurface salinity maximum spread into the Indonesian seas as part of the Indonesian throughflow. Within the Indonesian seas this salinity maximum is attenuated and, in some places, completely removed. A simple advection-diffusion model verifies the importance of vertical mixing in the transformation of Western Pacific waters to Indonesian thermocline water. The profiles indicate a predominant North Pacific presence in most of the seas, although some South Pacific water is present in the eastern ses of Halmahera, Seram, and Banda. The main interocean route is through the western seas of Sulawesi, Makassar, and Flores, while the flow pathway in the eastern seas is less certain. The Banda Sea can be renewed from either the northern passages (Halmahera and Maluku) or from the south via the Flores Sea. Using representative basin property profiles derived from the archieved data allows determination of a range of vertical diffusivities and residence times that best reproduce the transformation of Pacific waters into Indonesian water. In the Makassar thermocline a lower limit of 1 × 10−4 m2 s−1 for vertical diffusivity is inferred from the model results with reasonable throughflow and precipitation values. This estimate is roughly an order of magnitude greater than those deduced for the interior oceanic thermocline in an environment not conductive to salt fingers. In the Banda Sea a Kz of 1 × 10−4 m2 s−1 implies a predominant North Pacific source. If Kz is higher, then a larger South Pacific presence is possible.

Full access
Amy Ffield and Arnold L. Gordon

Abstract

Expressions of low-frequency tidal periods are found throughout the Indonesian Seas' temperature field, supporting the hypothesis that vertical mixing is enhanced within the Indonesian Seas by the tides. The thermal signatures of tidal mixing vary mostly at the fortnightly and monthly tidal periods due to nonlinear dynamics redistributing tidal energy into these periods. Away from the coasts, the largest tidal mixing signatures are observed in sea surface temperature within the Scram and Banda Seas. Most of the Indonesian Throughflow passes through the Banda Sea where strong vertical mixing modifies the thermocline by transferring surface heat and freshwater to deeper layers before the upper water column is exported to the Indian Ocean. Modulation of vertical eddy fluxes within the Indonesian Seas by fortnightly and monthly tides may act to regulate ocean-atmosphere fluxes.

Full access