Photo courtesy of NOAA.
Ocean and Atmosphere: Linked Fluids in Motion
The atmosphere and the ocean are both dynamic fluids, ever circulating as they are driven by the uneven heating of the earth and the earth's rotation on its axis. While we often think of the atmosphere and ocean as two separate systems - with weather and wind moving the air, currents and tides affecting the sea - in reality they are two sides of a single air-sea system. The ocean and atmosphere influence and interact with each other in very complex ways. Reflecting this linkage between air and ocean, researchers in the fields of meteorology and oceanography often work together.
We can investigate basic atmosphere-ocean interactions using some of modern oceanography's most valuable tools, satellites. From their orbits high above the earth, ocean observing systems provide global and regional perspectives that reveal the effects that atmosphere and ocean have on one another. Thanks to advancing technology, satellites now collect all sorts of data: ocean temperature; water color (indicating sediment load or phytoplankton density, for example); wind speed and direction; the roughness of the ocean's surface; and more. And we can access this information, plus data from buoys, ships and coastal observing stations, using the internet. In this series of activities, we'll use ocean observing systems to study the formation and impacts of coastal storms.
Coastal Storms
But, first, let's introduce our subjects, coastal storms. Here in Virginia, we get two main types of severe coastal storms: Hurricanes and Nor'easters. They differ in their region of origin, season, and duration of impact.
Hurricanes develop over tropics in late summer and fall. These powerful coastal storms are characterized by high winds, waves and storm surge and heavy rain that results in flooding. They usually migrate quickly, at speeds of 10 to 25 miles/hour.
In contrast, Northeasters, or Nor'easters, are not of tropical origin. They can form right off the North American coast any time during the fall, winter or early spring. They also generate high winds, waves and flooding, but they don't always move very quickly. Although Nor'easter winds are not as intense as those of many hurricanes, they make up for it in duration. Nor'easters may be held in place for days by arctic (Canadian) high pressure systems. As a result, the seas have time to develop to maximum wave size, pounding the coast for prolonged periods.
Data Activities
To investigate these two types of storms, we'll take one step at a time, learning about meteorology and oceanography as we work through five activities.
- What Starts a Coastal Storm? Water Temperature Highs Fuel Air Pressure Lows
- Thar She Blows!
- And the Lows Go Round and Round
- Surf's Up!
- The Gulf Stream: Storm-Maker
Extensions
Tracking the factors that fuel coastal storms
- SST in a record hurricane year. To see how tropical sea surface temperature varied through the seasons of 2005, sample SST at 25ºN latitude and between 60-65ºW longitude on or about the 15th of each month (bracket several days to be sure there's at least one day with SST readings for that site). Record the SST and plot this as a line graph with month on the X-axis and SST on the Y-axis. Does this help you understand why NOAA Weather Service defines Hurricane Season as June to November of each year? Why does Hurricane Season extend so far into the autumn months? What special property of water holds the key? How do temperatures at this location compare with surrounding waters?
- A year of SST on the Gulf Stream. To see how Gulf Stream temperature varies through the seasons, we'll sample the SST off Cape Hatteras at approximately 35ºN latitude, 75ºW longitude on or about the 15th of each month (bracket several days to be sure there's at least one day with SST readings for that site). Record the SST and plot this as a line graph with month on the X-axis and SST on the Y-axis. Does this help you see how the Gulf Stream can fuel storms even in the cooler winter months? How do Gulf Stream temperatures normally compare with surrounding waters?
- What made the Perfect Storm? One of the most notorious Nor'easters is "The Perfect Storm" of October 31, 1991, which caused damage from the Carolinas to Maine. It has been immortalized in books, movies and TV specials. You can read more about the formation of Nor'easters at the NASA-sponsored Storm-E Weather Simulation web page, and about the Perfect Storm. In this famous example, you'll see that a failed late-season hurricane actually contributed to the unusual severity of this Nor'easter!
If you have questions about this Data Tip or have suggestions for a future data tip, contact Chris Petrone.
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