Shown are our MIT-MSEAS forecasts of forward float flow maps for three EM-APEX floats in the Gulf region during the period July 4-19, 2025.
We first compute the 3D forward float flow maps for different time windows (spanning July 4-19) for the whole Gulf domain. Float forward flow maps link the initial location of a float to its final position as it is advected over a specified time window by the currents and its vertical profiling motions. To mimic these motions of EM-APEX floats, the vertical velocity from the MIT MSEAS PE is replaced with an analytic float behavior model that either has the float parked at 1500 m or makes a profile from 1500 m to 0 m and back down to 1500 m over an 8.5 hour period.
In the table of panels below, we show float flow map forecasts for two types of EM-APEX behaviors, first for floats doing one profile per day and then for floats doing two profiles per day. For each type, two floats aim to start in LC frontal eddies (LCFEs) and remain in these LCFEs, while a third float aims to start and remain in the main LC. In all cases, forecasts start on July 4, 2025.
We selected the initial float regions (two floats in LCFEs and one float in the main LC lobe) based on watermass analyses (T, S, σT) at several depths, velocity and vorticity fields at several depths, and Lagrangian feature analysis (coherent structures, FTLE, etc.). Once these initial regions are defined, we then highlight the forward float flow maps at the initial time and color their forecast positions at the different intermediate times of the forward float flow map in two different ways. The first coloring scheme is a solid color for each region surrounding each float - 1 (dark blue), 2 (green), and 3 (maroon). This scheme simply highlights where the material in the region is going over time. The second scheme colors floats in each region by their initial distance from the centroid of the region. This scheme highlights how each region is being distorted, especially how its edges can be affected by shear and turbulence.
Floats starting in the northern Loop Current (LC) Frontal Eddy (FE) region (green) on July 4 are forecast to advect southward along the LC. These floats pass to the west of the Tortugas LCFE by July 14. By July 19 the are sheared east/west in the region of the neck of the LC.
Floats from the eastern Tortugas LCFE region (maroon) mostly remain coherent and within the region they started until July 9. Later, the float locations that started at the edges of the initial region are strained into filaments forming from the edges of the LCFE by July 19, see solid and distance color maps.
Floats starting in the LC core region (dark blue) are forecast to mostly remain inside the LC but are advected both to the west and to the southeast, see solid and distance color maps.
The results for the twice-a-day sampling for the floats in the LC core region (dark blue) are over all similar to the once-a-day sampling (e.g. compare for example once-a-day to twice-a-day on July 19). Floats that start in the northern LCFE are more likely to cross the neck of the LC and get caught up in the western branch of the LC with twice-a-day sampling. Floats that start in the Tortugas LCFE region (maroon) and sample twice-a-day retain a more coherent region in the Tortugas LCFE but a significant portion of the floats that shear into filaments can get caught up in the LC outflow.
| Initial position | July 4 to July 5 | July 4 to July 6 | July 4 to July 7 | July 4 to July 8 | July 4 to July 9 | July 4 to July 10 | July 4 to July 11 | July 4 to July 12 | July 4 to July 13 | July 4 to July 14 | July 4 to July 15 | July 4 to July 16 | July 4 to July 17 | July 4 to July 18 | July 4 to July 19 |
| Sampling once per day | |||||||||||||||
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| Sampling twice per day | |||||||||||||||
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