Special radars on satellites, known as scatterometers, use the relationship between the conditions on the ocean surface and surface wind speed and direction to provide a view of the surface winds in and around tropical cyclones (hurricanes in the Atlantic and east Pacific oceans). This manuscript is an initial study of the tropical cyclone surface wind using a large, global set of scatterometer data. The surface wind speeds are first compared to trustworthy aircraft measurements from stepped frequency microwave radiometers (SFMRs), which also use the roughness of the ocean to determine the wind speed. After this successful comparison, average surface wind speed fields are created for different tropical cyclone basins around the world and for different tropical-cyclone intensities, such as tropical storms, hurricanes (Category 1-2 on the Saffir Simpson wind scale), and major hurricanes (Category 3-5 of the Saffir Simpson wind scale). These average wind fields indicate important differences around the world that are, in general, related to the most common strength of tropical cyclones for those regions.
- Average wind fields, in general, support previous studies that showed that the highest wind speeds in the northern hemisphere tend to occur on the right side of the two-dimensional surface wind field when viewed with respect to the direction the tropical cyclone is moving.
- Vertical wind shear, the difference in the wind speed and direction between two levels of the atmosphere, affects where the maximum surface wind speed occurs. The average fields for each region indicate that the strongest winds are located on the left side of the storm when viewed with respect to the vertical wind shear direction after taking away the forward motion effect.
- Global analyses (all regions combined) separated by tropical cyclone strength show that the location of the strongest winds in weaker cyclones (tropical storms) occurs on the left side of the wind field when viewed with respect to the vertical wind shear direction after taking away the forward motion effect. However, as the storm strength increases, the location of these winds turns clockwise from mostly to the left of the wind shear direction to mostly in the same direction as the wind shear. This conclusion provides initial evidence that vertical wind shear may affect the surface wind field differently depending on the strength of the tropical cyclone.
This will allow for a more detailed study with scatterometer data of the surface winds and their relation to changes in the vertical wind shear and forward movement of a tropical cyclone.
Read the article at http://onlinelibrary.wiley.com/doi/10.1002/2016GL071066/full.