An image showing internal and surface waves on the Indian Ocean near the Andaman islands has been published by NASA’s Earth Observatory website.
“When tides drag the ocean over a shallow barrier such as a ridge on the ocean floor, it creates waves in the lower, denser layer of water,” Earth Observatory explains.
“These waves, internal waves, can be tens of kilometers long and can last several hours.”
The steady crash of waves pounding the shore draws vacationers to beaches across the world when temperatures climb.
Driven by the wind and tides, these familiar waves ride across the top of the ocean.
But deeper waves also move through ocean waters, visible only from their influence on ocean currents.
These waves are internal waves, and they run through lowest layers of ocean water, never swelling the surface.
This image shows both internal waves and surface waves on the Indian Ocean near the Andaman Islands.
The active Barren Island Volcano, part of the Andaman Islands, is shown emitting puffs of steam on the left side of the image.
The Advanced Land Imager (ALI) on the Earth Observing 1 satellite acquired the image on March 6, 2007.
Sunlight reflecting off the water’s surface gives it a pale, silvery blue color.
The tiny wrinkles running roughly horizontally across the ocean are surface waves.
Internal waves paint long diagonal lines across the ocean on the right side of the image.
Internal waves happen because the ocean is layered.
Deep water is cold, dense, and salty, while shallower water is warmer, lighter, and fresher.
The differences in density and salinity cause the various layers of the ocean to behave like different fluids.
When tides drag the ocean over a shallow barrier such as a ridge on the ocean floor, it creates waves in the lower, denser layer of water.
These waves, internal waves, can be tens of kilometers long and can last several hours.
As internal waves move through the lower layer of the ocean, the lighter water above flows down the crests and sinks into the troughs.
This motion bunches surface water over the troughs and stretches it over the crests, creating alternating lines of calm water at the crests and rough water at the troughs.
It is the pattern of calm and rough water that makes the internal wave visible in satellite images.
Calm, smooth waters reflect more light directly back to the satellite, resulting in a bright, pale stripe along the length of the internal wave.
The rough waters in the trough scatter light in all directions, forming a dark line.
Links :
- NASA : internal waves, Sulu Sea
- NASA : internal waves in the Tsushima Strait
- NASA : internal waves in San Francisco bay
- NASA : internal waves, Strait of Gilbraltar (other)
From Michael Reilly (DiscoveryNews)
Stiv Wilson of the ocean conservation group 5 Gyres has made a first attempt to tally how much plastic is in the global ocean.
We've all heard about the Texas-sized "garbage patch" swirling in the North Pacific, and recently we've been warned that the Atlantic's got a plastic problem, too. Rather than distinct patches, the planet's interconnected watery parts are effectively a thin soup of plastic refuse, with perhaps larger concentrations of rubbish in five large rotating gyres of water like the Pacific's.
The more people look, the more grim the situation looks. But how can we get our heads around how big the problem really is? How much plastic is really in the ocean, and can we clean it up?
In a new post on 5gyres.org, Wilson takes what appears to be the first-ever stab at trying to figure it out.
The number he comes up with is staggering: he conservatively estimates there are 315 billion pounds of plastic in the oceans right now.
Now, Wilson will be the first to admit a lot of assumptions were made in order to arrive at that number, but most of them err on the side of caution. It's worth going through his thought process and calculations here.
To help visualize that massive heap of trash, Wilson divides by a "supertanker" -- that is, a giant ship that could theoretically sail through the seas, skimming out the plastic junk as it goes (much of which hovers down to 90 feet below the surface).
No such ship has been outfitted to skim plastic. But let's say it did, and it could hold 500 million pounds of plastic. You'd need 630 of them to do the job (143 billion kilograms), or about 17 percent of the planet's current fleet of oil tankers.
To make it a little more personal, every American produces about 600 pounds of garbage each year. The proportion of plastic varies from household to household, but overall about half of all waste is synthetic. Some of that probably ends up in landfill, or recycled (Wilson says only about 3 percent of virgin plastic gets recycled).
Either way, the pile of plastic you inadvertently dump into the ocean each year is probably more than you can lift.
The point of the calculations is this: cleaning up the plastics in the ocean ain't gonna happen. Well-intentioned programs designed to take the fight to the high seas, like Project Kaisei and the Environmental Cleanup Coalition, for example, are exercises in futility.
"I'm not trying to call them out," Wilson told Discovery News. "What I really fear is a barge full of plastic coming in under the Golden Gate bridge, the media taking pictures and people thinking 'oh good, we've solved that problem.'"
A real cleanup would be astronomically expensive, both in terms of dollars and equipment.
But hope is not lost. Wilson added that if we can ratchet down the amount of plastic we throw away, the gyres will naturally spin out much of the junk floating in them. Eventually it will wash ashore, where it can easily be removed.
"I really want to see people's efforts focused on beach cleanups," he said. "They're free, can be organized in a grassroots way, and they can make a massive difference. A hundred people on a beach picking up plastic for a weekend can clean up as much as a barge can hold."
Links :
From University of Hawaiʻi at Mānoa
The possible spread of the oil spill from the Deepwater Horizon rig over the course of one year was studied in a series of computer simulations by a team of researchers from the School of Ocean and Earth Science and Technology (SOEST) at the University of Hawaiʻi at Mānoa.
Eight million buoyant particles were released continuously from April 20 to September 17, 2010, at the location of the Deepwater Horizon oil rig.
The release occurred in ocean flow data from simulations conducted with the high-resolution Ocean General Circulation Model for the Earth Simulator (OFES).
“The paths of the particles were calculated in 8 typical OFES years over 360 days from the beginning of the spill,” says Fabian Schloesser, a PhD student from the Department of Oceanography in SOEST, who worked on these simulations with Axel Timmermann and Oliver Elison Timm from the International Pacific Research Center, also in SOEST.
“From these 8 typical years, 5 were selected to create an animation for which the calculated extent of the spill best matches current observational estimates.”
The dispersal of the particles does not capture such effects as oil coagulation, formation of tar balls, chemical and microbial degradation.
Computed surface concentrations relative to the actual spill may therefore be overestimated.
The animation, thus, is not a detailed, specific prediction, but rather a scenario that could help guide research and mitigation efforts.
The animation shows the calculated surface particle concentrations for grid boxes about 10-km-by-10-km in size into April 2011.
For an estimated flow of oil from the Deepwater Horizon of 50,000 barrels per day over a 150 day period, a concentration of e.g. 10 particles per grid box in the animation corresponds roughly to an oil volume of 2 cubic meters per 100 square kilometer.
The oil spreads initially in the Gulf of Mexico, then enters the Loop Current and the narrow Florida Current, and finally the Gulf Stream.
“After one year, about 20% of the particles initially released at the Deepwater Horizon location have been transported through the Straits of Florida and into the open Atlantic,” explains Timmermann.
This animation suggests that the coastlines near the Carolinas, Georgia, and Northern Florida could see the effects of the oil spill as early as October 2010.
The main branch of the subtropical gyre is likely to transport the oil film towards Europe, although strongly diluted.
The animation also shows that as the northeasterly winds intensify near Florida around October and November, the oil in the Atlantic moves closer to the eastern shores of the US, whereas it retreats from the western shores of Florida.
The narrow, deep Straits of Florida force the Florida Current into a narrow channel, creating a tight bottleneck for the spreading of oil into the Atlantic.
As the animation suggests, a filtering system in the narrowest spot of the Florida Current could mitigate the spreading of the oil film into the North Atlantic.
This research was supported by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), NASA and NOAA through their sponsorship of the International Pacific Research Center in the School of Ocean and Earth Science and Technology at the University of Hawaiʻi at Mānoa.
Links :
- SOEST
- NASA image of the oil slick in the Gulf of Mexico (acquired July 4)
49ers are without doubt the fastest and probably the most temperamental Olympic class sailboat, particularly now that the Tornado catamarans have been shut out of the 2012 London games.
These planing dinghies carry a lot of canvas, and their crews are engaged in a constant, high-speed balancing act as the tippy craft rocket around at speeds many power boats can't match.
From BBC News
A vessel in distress on the Ireland waterways between Kesh and Enniskillen owes its happy ending to an iPhone application.
Motor cruiser, the Wee Rascal, called 999 in the early hours of Sunday morning asking for assistance as the weather worsened.
However, an extensive search of the area around its reported position by Enniskillen RNLI and the Erne Coastguard Rescue team was fruitless.
With no flares, flash lights or VHF radio onboard, the Wee Rascal was unable to signal its position to rescuers.
It was then that the Belfast Coastguard resorted to mobile phone technology a locator iPhone app was able to give rescuers the vital latitude and longitude they needed.
The Maritime and Coastguard Agency said the cruiser was finally located 25 miles away from its reported position, dangerously amongst the rocky shoreline off Eagle Point ("Gubnagole Point").
It was brought away from the rocks by Enniskillen and taken to the safety of Belleek marina.
Coastguard Watch Manager Steven Carson said it was a "combination of luck and technology" that saved those onboard.
"They had charts on board but obviously no real idea of how to get to their destination or how to report their position in an emergency," he continued.
"Vital hours were wasted eliminating one possible location after another, time that we wouldn't have had if the vessel had struck the rocks and sunk."
"I hope that this experience will help the crew to realize why navigation training is essential for all mariners, whether you're on a lough or the open sea."
Links :
An image showing internal and surface waves on the Indian Ocean near the Andaman islands has been published by NASA’s Earth Observatory website.
