Archive for the ‘Tides and Currents’ Category

What is a Rossby wave?

This item was filled under Basics, Facts, Ocean Observations, Tides and Currents


Oceanic and atmospheric Rossby waves — also known as planetary waves — naturally occur largely due to the Earth's rotation. These waves affect the planet's weather and climate. Waves in the ocean come in many different shapes and sizes. Slow-moving oceanic Rossby waves are are fundamentally different from ocean surface waves. Unlike waves that break along the shore, Rossby waves are huge, undulating movements of the ocean that stretch horizontally across the planet for hundreds of kilometers in a westward direction. They are so large and massive that they can change Earth's climate conditions. Along with rising sea levels, King Tides, and the effects of El Ni?o, oceanic Rossby waves contribute to high tides and coastal flooding in some regions of the world.

About this image: Rossby waves naturally occur in rotating fluids. Within the Earth's ocean and atmosphere, these planetary waves play a significant role in shaping weather. This animation from NASA's Goddard Space Flight Center shows both long and short atmospheric waves as indicated by the jet stream. The colors represent the speed of the wind ranging from slowest (light blue colors) to fastest (dark red).

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What are the Totten Beacons?



In 1513, Spanish explorer Ponce de León sailed into the strong currents of the Florida Straits. Little did he know that within a few years, these uncharted waters, which fed into the Gulf Stream, would become a major international shipping route to and from Europe and the New World.

As Europeans explored and colonized the Americas, they took advantage of the Florida Straits' winds and currents. The winds changed direction often, however, easily pounding countless vessels against miles of treacherous submerged coral reefs off the southern Florida coast.

By 1852, Lieutenant James B. Totten, the U.S. Army's assistant to the Coast Survey, had installed 15 wooden signal poles in the reefs to create more accurate charts of the Florida Keys. Local mariners quickly recognized that the poles themselves helped them safely navigate the reefs, and by 1855, Totten and his team installed a second generation of 16 poles using a more permanent material—iron. The "beacons" each displayed a letter, starting with "A" and ending with "P." Today, remnants of Totten Beacons are protected as historical resources by the Florida Keys National Marine Sanctuary (FKNMS).

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What is a tide gauge?

This item was filled under Basics, Facts, Ocean Observations, Tides and Currents


A tide gauge, which is one component of a modern water level monitoring station, is fitted with sensors that continuously record the height of the surrounding water level. This data is critical for many coastal activities, including safe navigation, sound engineering, and habitat restoration and preservation.

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What is a catcher beach?



Not to be confused with a dumping ground or heavily trashed public beach, a catcher beach typically receives its accumulations of debris due to its shape and location in combination with high-energy waves, storms, or winds. Awareness and common knowledge of these types of areas vary significantly by state, although many states have a good understanding of where catcher beaches are located. In many cases, catcher beaches are found in remote areas that are difficult to access and can be challenging in terms of debris cleanup and removal.

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What is a King Tide?



A King Tide is a non-scientific term people often use to describe exceptionally high tides. Tides are long-period waves that roll around the planet as the ocean is "pulled" back and forth by the gravitational pull of the moon and the sun as these bodies interact with the Earth in their monthly and yearly orbits. Higher than normal tides typically occur during a new or full moon and when the Earth is at its perigee, or during specific seasons around the country

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What is the difference between local sea level and global sea level?

This item was filled under Basics, Facts, Ocean Observations, Tides and Currents


Global sea level trends and relative sea level trends are different measurements. Just as the surface of the Earth is not flat, the surface of the ocean is also not flat — in other words, the sea surface is not changing at the same rate at all points around the globe. Sea level rise at specific locations may be more or less than the global average due to many local factors: subsidence, ocean currents, variations in land height, and whether the land is still rebounding from the compressive weight of Ice Age glaciers.

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Where do I get real-time and forecast coastal conditions?



NOAA's nowCOAST is a GIS-based webmap service that provides frequently updated ocean observations along with coastal and marine weather forecasts 24 hours a day. The free online map offers point-and-click access to 60 NOAA data products and services all in one place. With nowCOAST, you can get a one-stop-shop look at coastal conditions — real-time and forecast — before you do or plan anything on the water.

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What are the Roaring Forties?



During the Age of Sail (circa 15th to 19th centuries), these strong prevailing winds propelled ships across the Pacific, often at breakneck speed. Nevertheless, sailing west into heavy seas and strong headwinds could take weeks, especially around Cape Horn at the southern tip of South America, making it one of the most treacherous sailing passages in the world. The Roaring Forties take shape as warm air near the equator rises and moves toward the poles. Warm air moving poleward (on both sides of the equator) is the result of nature trying to reduce the temperature difference between the equator and at the poles created by uneven heating from the sun.

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What are the doldrums?



Known to sailors around the world as the doldrums, the Inter-Tropical Convergence Zone, (ITCZ, pronounced and sometimes referred to as the “itch”), is a belt around the Earth extending approximately five degrees north and south of the equator. Here, the prevailing trade winds of the northern hemisphere blow to the southwest and collide with the southern hemisphere’s driving northeast trade winds.

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What is a NOAA tide table?


A tide table provides daily high and low tide predictions. NOAA tide tables are available for more than 3,000 locations around the nation. NOAA’s Center for Operational Oceanographic Products and Services and predecessor agencies have produced tide tables for more than 150 years.

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