wind Archives - Universe Today

October 30, 2013December 23, 2015

New Space Station Instrument Raises Windy Science From The Dead

Here’s a cool example of a satellite recycling project. NASA used to have a probe called QuikSCAT that took a look at ocean wind speeds — including hurricanes, storms and typhoons. After 10 years of loyal service, the satellite failed in 2009 and a full replacement looked expensive. Now, however, spare parts for QuikSCAT are going to be used on the International Space Station for a low-budget fix (which the agency says will work just fine).

The parts are old — they are from the 1990s — but incredibly, they are functional. NASA also added some newer, commercially available hardware to make ISS-RapidScat fit in the space station as well as the SpaceX Dragon spacecraft that will bring it to orbit in early 2014.

Because this is very much a low-cost project, certain design compromises were made — like not using radiation-hardened computer chips, which is normal in scatterometers of this sort. (This type of device harmlessly sends low-energy microwaves off the Earth’s service to get the information it needs.)

Artist's conception of how ISS-RadScat will work. Credit: NASA/JPL-Caltech/Johnson Space Center — Artist’s conception of how ISS-RadScat will work. Credit: NASA/JPL-Caltech/Johnson Space Center

“If there’s an error or something because of radiation, all we have to do is reset the computer. It’s what we call a managed risk,” stated Howard Eisen, the ISS-RapidScat project manager at NASA’s Jet Propulsion Laboratory.

There’s another big difference with this scatterometer mission: it’s flying in a different orbit that most. A typical mission will do a sun-synchronous orbit, making it cross the Earth’s equator at the same local time every time it orbits the planet (say, 12 p.m. local.) The ISS, however, passes over different parts of Earth at different times.

“This means the instrument will see different parts of the planet at different times of day, making measurements in the same spot within less than an hour before or after another instrument makes its own observations,” NASA stated.

A view of Hurricane Irene taken by the GOES satellite at 2:55 p.m. Eastern Daylight Time on August 24, 2011. Credit: NASA

“These all-hour measurements will allow ISS-RapidScat to pick up the effects of the sun on ocean winds as the day progresses. In addition, the space station’s coverage over the tropics means that ISS-RapidScat will offer extra tracking of storms that may develop into hurricanes or other tropical cyclones.”

NASA plans to share information with the European MetOp ASCAT scatterometer. Between the two missions, NASA expects that about 90% of Earth’s surface will be examined at least once a day,with some parts visible several times a day.

All in all, NASA is presenting the recycling project as a boon at a time when the agency is grappling with its 2014 budget request. Instead of an estimated cost of $400 million to launch a replacement QuikSCAT, the cost of ISS-Rapidscat is expected to reach $26 million.

Source: NASA

November 17, 2011December 24, 2015

MRO Spots Martian Dunes in Motion

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The benefit of long-term observations from orbit became evident today with the release of images from NASA’s Mars Reconnaissance Orbiter showing the subtly shifting motion of large sand dunes on the red planet, proving that the surface of Mars is much more dynamic than previously believed!

The atmosphere of Mars is extremely thin – only 1% as dense as Earth’s. This means that Martian winds would seem barely perceptible to a human, and has to blow at high speeds to move even the smallest particles on its surface.

Although scientists have known that Mars contains many dunes and vast expanses of sandy regions it has been assumed that these features must move very slowly – if at all – due to the thin air.

“We used to think of the sand on Mars as relatively immobile, so these new observations are changing our whole perspective.”

– Nathan Bridges, lead author

604863main_pia14878-946 — A rippled dune near Herschel crater undulates in the thin Martian wind. (Click to play.)

Now, images taken at different intervals by the MRO’s HiRISE camera have been seen to clearly show the shifting motion of several large sand dune features (called bedforms) in various locations on Mars.

“Mars either has more gusts of wind than we knew about before, or the winds are capable of transporting more sand,” said Nathan Bridges, planetary scientist at the Johns Hopkins University’s Applied Physics Laboratory and lead author of a paper published online in the journal Geology. “We used to think of the sand on Mars as relatively immobile, so these new observations are changing our whole perspective.”

Sandy particles on Earth that could be moved by a 10 mph breeze would require an 80 mph gust of Martian wind. Weather data and climate models have shown that such winds should be rare on Mars; these recent findings by MRO indicate that either high-speed winds are more common than once thought or else they are more capable of moving sand around… or a combination of both!

Not all of Mars’ dunes are so restless, though. The study showed that there are regions that show no movement.

“The sand dunes where we didn’t see movement today could have larger grains, or perhaps their surface layers are cemented together,” Bridges said. “These studies show the benefit of long-term monitoring at high resolution.”

Ten years ago the belief was that dunes on Mars are either static or move too slowly to detect. Thanks to MRO and the HiRISE team – and the authors of this new paper – we now know that idea is all just dust in the wind.

What Causes Wind?

It was not until recent memory that what causes wind was understood. Wind is caused by air flowing from high pressure to low pressure. The Earth’s rotation prevents that flow from being direct, but deflects it side to side(right in the Northern Hemisphere and left in the Southern), so wind flows around the high and low pressure areas. This movement around is important for very large and long-lived pressure systems. For small, short-lived systems (outflow of a thunderstorm) the wind will flow directly from high pressure to low pressure.

The closer the high and low pressure areas are together, the stronger the pressure gradient, so the winds are stronger. On weather maps, lines of constant pressure are drawn(isobars). These isobars are usually labeled with their pressure value in millibars (mb). The closer these lines are together, the stronger the wind. The curvature of the isobars is also important to the wind speed. Given the same pressure gradient (isobar spacing), if the isobars are curved anticyclonically (around the high pressure ) the wind will be stronger. If the isobars are curved cyclonically (around the low pressure) the wind will be weaker.

Friction from the ground slows the wind down. During the day convective mixing minimizes this effect, but at night(when convective mixing has stopped) the surface wind can slow considerably, or even stop altogether.

Wind is one way that the atmosphere moves excess heat around. Directly and indirectly, wind forms for the primary purpose of helping to transport excess heat in one of two ways: away from the surface of the Earth or from warm regions(tropics) to cooler regions. This is done by extratropical cyclones, monsoons, trade winds, and hurricanes. Now, you have the answer to what causes wind and its primary function on our planet.

We have written many articles about the wind for Universe Today. Here’s an article about wind energy, and here’s an article about how wind power works.

If you’d like more info on wind, check out Visible Earth Homepage. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.