How do gyres affect hurricanes

The path of the Loop Current, and eddies from the Loop Current, can bring warmer than typical water into the Gulf of Mexico. Hurricane Science. Surface Ocean Circulation. Map showing the major ocean surface currents and subtropical gyres. American Meteorological Society. This movie shows sea-surface height in the Gulf of Mexico beginning in January through The red regions are "high" relative to the surroundings; below the figure is a height scale, in cm; the flow is clockwise around a high, counter-clockwise around a low.

In the open ocean, satellite-derived sea-surface height can be used to identify areas where the warm layer in the upper ocean is thick high sea-surface height and areas where this warm layer is thin low sea-surface height. A thicker warm layer is more favorable for developing and supporting intense hurricanes than a thinner warm layer.

Chlorophyll contributes to the ocean's color. In the study, to be published in an upcoming issue of Geophysical Research Letters , a journal of the American Geophysical Union, Gnanadesikan's team describes how a drop in chlorophyll concentration, and the corresponding reduction in ocean color, could cause a decrease in the formation of hurricanes in the color-depleted zone.

Although the study looks at the effects of a simulated drop in the phytoplankton population and therefore in the ocean's green tint , recently-published research argued that global phytoplankton populations have been steadily declining over the last century.

Gnanadesikan compared hurricane formation rates in a computer model under two scenarios. For the first, he modeled real conditions using chlorophyll concentrations in the North Pacific observed by satellites. He then compared that to a scenario where the chlorophyll concentration in parts ofthe North Pacific Subtropical Gyre -- a large, clockwise-circulation pattern encompassing most of the North Pacific -- was set to zero.

In the latter scenario, the absence of chlorophyll in the subtropical gyre affected hurricane formation by modifying air circulation and heat distribution patterns both within and beyond the gyre. In fact, along the equator, those new patterns outside the gyre led to an increase in hurricane formation of about 20 percent. Yet, this rise was more than made up for by the 70 percent decrease in storms further north, over and near the gyre. The model showed that more hurricanes would hit the Philippines and Vietnam, but fewer would make landfall in South China and Japan.

In the no-chlorophyll scenario, sunlight is able to penetrate deeper into the ocean, leaving the surface water cooler. The drop in the surface temperature in the model affects hurricane formation in three main ways: cold water provides less energy; air circulation patterns change, leading to more dry air aloft which makes it hard for hurricanes to grow.

The changes in air circulation trigger strong winds aloft, which tend to prevent thunderstorms from developing the necessary superstructure that allows them to grow into hurricanes. A decrease in hurricanes in the North Pacific is just one example of how changing chlorophyll concentrations can have far-reaching, previously unconsidered, effects.

The specific outcomes over different patches of the ocean will vary based on local currents and ocean conditions, said Gnanadesikan. It only determines the direction in which they spiral. Air spirals into the center of a hurricane or any low pressure center because it is deflected sideways when it collides with other air in the center.

Any imbalance in the forces on the air will produce a net rotation around the low pressure center. This is precisely what the Coriolis force provides. In the northern hemisphere it deflects moving objects to their right, so any air mass approaching the hurricane will be deflected to the right. Earth rotates such that the Sun rises in the east and sets in the west left. Therefore, the northern hemisphere rotates counter-clockwise top right and the southern hemisphere rotates clockwise bottom right.

Hurricanes: Always a Relevant Example. It is believed by an alarmingly large number of people, that the Coriolis force affects the water being flushed from your toilet in the same way it affects hurricanes - by determining the spiral direction. Of course the Coriolis force does act on the water in your toilet when you flush it, but the strength of the force is extremely small on the order of 0.

Thus, it is negligible compared to other factors such as the shape of the toilet bowl and any initial disturbances in the water. Simply walking into the bathroom will send vibrations through the water in your toilet.

This seemingly small disturbance can result in forces that are orders of magnitude larger than the Coriolis force would be. Satellite Image of Hurricane Sandy. This photo was taken on October 28, and shows Hurricane Sandy off the east coast of the United States. You can clearly see the hurricane is rotating CCW. Image: theverge. On its own the Coriols force tends to produce circular motion, because it always points perpendicular to an objects velocity.

This is similar to the Lorentz force on a charged particle as it moves through a magnetic field orthogonally to the field lines. However, the Coriolis force in the atmosphere rarely results in perfect circles because other forces are present. Instead it results in curved motion. Air that is approaching a hurricane is influenced by the pressure gradient force due to the low pressure of the hurricane and the Coriolis force, so its trajectory exhibits the presence of both forces.

Shown below are the Coriolis and pressure gradient force for a unit air mass on its trajectory toward the hurricane. The Coriolis force always acts to add curvature to the linear motion produced by the pressure gradient. It starts by deflecting the air to the right.

Closer to the hurricane its pull is stronger, because the pressure gradient is steeper.