One visually striking feature of hurricane Rita that I will explore a bit below is known as the "stadium effect".

This effect is caused as a result of air parcels ascending in a spiral within the eye wall moving outwards from the core of the storm as they ascend. The motion of these causes the eye to become larger in diameter (or wider) as the altitude above the oceans surface increases. This widening of the eye with increasing altitude forms what looks like the "bowl" of a stadium hence the formation is sometimes called the stadium effect). The reasons for this effect are quite complex, but I will attempt to offer a simplified explanation below.

The reason the air parcels move outwards as they ascend is due in part to the decrease in friction as one ascends in the atmosphere. As a result of the decrease in friction, the wind speeds increase (studies have shown by about 1-4%) and therefore as a result of the increased wind speed the centrifugal and Coriolis forces also increase as the speed increases. Since a balance must be maintained between the inward pull of the pressure gradient of the storm (which observations have actually shown as decreasing with the increasing altitude), the parcels attempt to balance these forces by moving outward from the center of the storm as they ascend in atitude.

For a striking visual example of the stadium effect please look at the four photographs below taken by the MODIS Terra and Aqua satellites maintained by NASA. The images were taken between September 20-23, 2005. Note that the stadium appearance is not readily visible in these smaller images, but clicking on each image will display a large high resolution graphic (that takes some time appear due to the large size) that clearly shows this feature. To see it most apparently look in the area around the eye of the storm.

(Hurricane Rita between Florida and Cuba on September 20, 2005 at 1835Z (235pm EDT). Image taken by the Aqua Satellite)	(Hurricane Rita in the Gulf of Mexico on September 21, 2005 at 1610Z (1210pm EDT). Image taken by the Terra Satellite)
(Hurricane Rita in the Gulf of Mexico on September 22, 2005 at 1655Z (1255pm EDT). Image taken by the Terra Satellite)	(Hurricane Rita in the Gulf of Mexico on September 23, 2005 at 1910Z (310pm EDT). Image taken by the Aqua Satellite)

Now that you have seen an an example of the visually striking condition known as "the stadium effect" and have a basic understanding of its cause, please click here to move on to some reflections on this discussion and the course on tropical meteorology in general, or return to the main page to examine a different section.