Pacific Glory

An optical phenomenon known as a “glory” is seen over a cloud-covered Pacific Ocean in this image from NASA’s Aqua satellite, acquired on June 20, 2012. Although the colors may make it look like a rainbow, the process behind its formation is somewhat different.

As vortices spiral off the leeward side of Guadalupe Island, off the western coast of Baja California, a shimmering spectrum of colors highlights a glory just west of the island. Glories are created when light from the Sun reflects back toward an observer off water droplets within clouds or fog. They are often seen from airplanes as a bright ring of light encircling a silhouetted shadow of the aircraft below, but are also visible from the ground and, sometimes, even from space.

From the NASA Earth Observatory website:

Although glories may look similar to rainbows, the way light is scattered to produce them is different. Rainbows are formed by refraction and reflection; glories are formed by backward diffraction. The most vivid glories form when an observer looks down on thin clouds with droplets that are between 10 and 30 microns in diameter. The brightest and most colorful glories also form when droplets are roughly the same size.

From the ground or an airplane, glories appear as circular rings of color. The space shuttle Columbia observed a circular glory from space in 2003. In the image above, however, the glory does not appear circular. That’s because MODIS scans the Earth’s surface in swaths perpendicular to the path followed by the satellite. And since the swaths show horizontal cross sections through the rings of the glory, the glory here appears as two elongated bands of color that run parallel to the path of the satellite, rather than a full circle.

Glories always appear around the spot directly opposite the Sun, from the perspective of the viewer. This spot is called the anti-solar point. To visualize this, imagine a line connecting the Sun, a viewer, and the spot where the glory appears. In this case, the anti-solar point falls about halfway between the two colored lines of the glory.

Click here to download the full-size image.

NASA image courtesy Jeff Schmaltz, LANCE MODIS Rapid Response. Read more here.

Blue Marble 2012: The Arctic Edition

This latest portrait of Earth from NASA’s Suomi NPP satellite puts the icy Arctic in the center, showing the ice and clouds that cover our planet’s northern pole. The image you see here was created from data acquired during fifteen orbits of Earth.

In January of this year Suomi NPP images of Earth were used to create an amazing “Blue Marble” image that spread like wildfire across the internet, becoming one of the latest “definitive” images of our planet. Subsequent images have been released by the team at Goddard Space Flight Center, each revealing a different perspective of Earth.

See a full-sized version of the image above here.

NASA launched the National Polar-orbiting Operational Environmental Satellite System Preparatory Project (or NPP) on October 28, 2011 from Vandenberg Air Force Base. On Jan. 24, NPP was renamed Suomi National Polar-orbiting Partnership, or Suomi NPP, in honor of the late Verner E. Suomi. It’s the first satellite designed to collect data to improve short-term weather forecasts and increase understanding of long-term climate change.

Suomi NPP orbits the Earth about 14 times each day and observes nearly the entire surface of the planet.

Image credit: NASA/GSFC/Suomi NPP

 

On the Edge of Titan

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Here’s a quick look at one of my favorite cosmic photo subjects – the varying layers of atmosphere that enshroud Saturn’s enormous moon Titan. The image above is a color-composite made from three raw images acquired by Cassini during its latest flyby.

On June 7 Cassini approached Titan within 596 miles (959 km) and imaged portions of the moon’s northwest quadrant with its radar instrument, as well as conducted further investigations of areas near the equator where surface changes were detected in 2010.

The image here was assembled from three raw images captured in red, green and blue visible light channels. It reveals some structure in the upper hydrocarbon haze layers that extend upwards above the moon’s opaque orange clouds — reaching 400-500 km in altitude, Titan’s atmosphere is ten times thicker than Earth’s!

The June 6 flyby was the second in a series of passes that will take Cassini into a more inclined orbit, where it will reside for the next three years as it investigates Saturn’s polar regions and obtains better views of its ring system.

Read more about the flyby here.

Image: NASA/JPL/Space Science Institute. Composite by J. Major.

Today’s Martian Weather: Partly Cloudy

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Changing seasons in Mars’ northern hemisphere brings a change in the weather, and the clouds have rolled in to cover part of the polar surface in this intriguing image from the Mars Odyssey spacecraft.

Mars Odyssey’s THEMIS visual imager (VIS) captured this image on Jan. 24, 2012, as it passed over the Red Planet’s northern pole during one of its 2-hour-long orbits.

Clouds on Mars have been seen before, both from orbit and from the surface. They are made up of fine water ice particles and are usually at altitudes of 10 to 15 km high. Read more about Martian weather here.

The full THEMIS scan of the area is below.

Martian polar clouds as seen by THEMIS

The area imaged is about 21 km wide by 73 km high  (13 x 45 miles).

Image credit: NASA / JPL / Arizona State University. Hat-tip to Mr. Bill Dunford at Riding With Robots (@ridingrobots). 

The Sky Is Falling, Scientists Report

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Ok, maybe not the sky itself… but the clouds. According to recent research by climate scientists in New Zealand, global cloud heights have dropped.

Researchers at The University of Auckland have reported a decreasing trend in average global cloud heights from 2000 to 2010, based on data gathered by the Multi-angle Imaging SpectroRadiometer (MISR) on NASA’s Terra satellite. The change over the ten-year span was 30 to 40 meters (about 100 to 130 feet), and was mostly due to fewer clouds at higher altitudes.

It’s suspected that this may be indicative of some sort of atmospheric cooling mechanism in play that could help counteract global warming.

“This is the first time we have been able to accurately measure changes in global cloud height and, while the record is too short to be definitive, it provides just a hint that something quite important might be going on,” said lead researcher Professor Roger Davies.

A steady reduction in cloud heights could help the planet radiate heat into space, thus serving as a negative feedback in the global warming process. The exact cause of the drop in cloud altitude is not yet known, but it could reasonably be resulting from a change in circulation patterns that otherwise form high-altitude clouds.

Rendering of the Terra spacecraft. (NASA)

Cloud heights are just one of the many factors that affect climate, and until now have not been able to be measured globally over a long span of  time.

“Clouds are one of the biggest uncertainties in our ability to predict future climate,” said Davies. “Cloud height is extremely difficult to model and therefore hasn’t been considered in models of future climate. For the first time we have been able to accurately measure the height of clouds on a global basis, and the challenge now will be to incorporate that information into climate models. It will provide a check on how well the models are doing, and may ultimately lead to better ones.”

While Terra data showed yearly variations in global cloud heights, the most extreme caused by El Niño and La Niña events in the Pacific, the overall trend for the years measured was a decrease.

Continuing research will be needed to determine future trends and how they may impact warming.

“If cloud heights come back up in the next ten years we would conclude that they are not slowing climate change,” Davies said. “But if they keep coming down it will be very significant.”

The team’s study was recently published in the journal Geophysical Research Letters.

Terra is a multi-national, multi-disciplinary mission involving partnerships with the aerospace agencies of Canada and Japan. An important part of NASA’s Science Mission, Terra is helping scientists around the world better understand and protect our home planet.

Read more on the NASA/JPL news release here.

Satellite Captures Unusual “Cloud Streets”

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I love looking at unusual cloud formations, and these have to be some of the most intriguing. These long, horizontal rolls of clouds are called “cloud streets” and NASA’s Terra satellite had a “drive by” of these clouds, observing them over Hudson Bay, Canada on November 20, 2011 at 12:25 p.m. EST (17:25 UTC). These rows of clouds stretch from northwest to southeast over the Hudson Bay.

Cloud streets are long lines or bands of cumulus clouds that usually form within the lower one to three kilometers of the atmosphere, and come from eddies in the atmosphere.

According to NASA’s Earth Observatory and the Goddard Space Flight Center Flickr page, cloud streets form when cold air blows over warmer waters, while a warmer air layer—or temperature inversion—rests over top of both. The comparatively warm water of Hudson Bay gives up heat and moisture to the cold air mass above, and columns of heated air—thermals—naturally rise through the atmosphere. As they hit the temperature inversion like a lid, the air rolls over like the circulation in a pot of boiling water. The water in the warm air cools and condenses into flat-bottomed, fluffy-topped cumulus clouds that line up parallel to the wind.

Hudson Bay is a large body of saltwater located in northeastern Canada. Also in the image, are several snow-covered islands in Hudson Bay. The larger island to the north is South Hampton Island, and the smaller island east is Coats Island, and further east is Mansel Island.

Coming Soon – Night Shining Noctilucent Clouds

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Soon you may see an eerie spectacle on clear summer nights if you are located at latitudes between 50° and 70° north and south of the equator: Noctilucent Clouds.

These ghostly apparitions are a delight to see and are quite rare. It is incredibly difficult to predict exactly when they will appear, but we do know they should begin to appear soon.

The season for Noctilucent Clouds (Noctilucent = Latin for “Night Shining”) starts early June and continues into late July. They are seen just after dusk, or before dawn and an apparition can last around an hour.

These mysterious clouds, with their bizarre tenuous wispy shapes reminiscent of ripples in sand or the changing surface of a pool of water, spread like a glowing web across the northern sky. Colours can range from brilliant whites, with tinges of blue, pink and orange.

Formed by tiny ice crystals, they are the highest clouds in the Earth’s atmosphere, located in the mesosphere at altitudes of around 76 to 85 kilometers (47 to 53 miles) almost at the edge of space.

They are normally too faint to be seen, and are visible only when illuminated by sunlight from below the horizon, while the lower layers of the atmosphere are in the Earth’s shadow. Noctilucent clouds are not fully understood and are a recently discovered meteorological phenomenon, only being recorded for about 120 years.

Noctilucent clouds can only form under very restrictive conditions, and their occurrence can be used as a guide to changes in the upper atmosphere. Since their relatively recent classification, the occurrence of noctilucent clouds appears to be increasing in frequency, brightness and extent.

There is evidence that the relatively recent appearance of noctilucent clouds and their gradual increase, may be linked to climate change. Another recent theory is that some of these bright displays come from particulates and water vapour in the atmosphere left over from Space Shuttle launches.

How can you see them? Over the next couple of months look north during dusk and dawn and try and spot this mysterious and elusive phenomenon. They are best seen when the sun is between 6 and 16 degrees below the horizon, and seem to occur more frequently in the Northern hemisphere than the Southern.

Good luck!

Noctilucent clouds over Blair, Nebraska, USA. Credit: Mike Hollingshead

What Are Clouds Made Of?

Clouds

When we think of clouds we think of those white cotton ball masses in the air. What we don’t really think about is what are clouds made of. We all know about the water cycle in some form. We know that clouds are created from the water that evaporates from various lakes, rivers, and oceans. We also know that at some time this evaporated water becomes rain and starts the cycle all over again.

However there are important questions about clouds we overlook. First, how are clouds visible if water vapor is normally supposed to be invisible like air or at least dissipate quickly after the first gush of steam? Second, why do clouds last so long in their different forms? Finally, what gives clouds their white or grey colors? As you can see there is a lot we take for granted in our understanding of clouds and how they are formed.

We know that clouds are made of water vapor, what we don’t know or at least forget is the important role that condensation plays in making clouds visible. For the most part water vapor is invisible. This is proven by the fact that the air we breathe regularly has some water vapor as part of its composition. However we don’t see it since its apart of the air. Condensation is what makes water vapor visible.

Basically high temperatures excite water molecules until they change from a liquid state to a gaseous one. However lower temperatures can cause enough water vapor to condense back into liquid form. This small amount stays as very small droplets that can stay suspended in the air mostly thanks to small dust particles that they attach themselves to.

It is pretty much the same way you see small bits of glitter suspended in clear glue. The drops are small enough to stay trapped in the air until condensation reaches a point of no return making rain. One result of this is that light becomes reflected and refracted. This is what makes clouds visible.

Now if you think about it we also just answered the second question about why clouds last so long. You may understand the first explanation because you can see your breath on a cold day. However after a while depending on the weather you notice that later in the day you can no longer see your breath. Clouds are visible because of colder temperatures in the upper atmosphere.

You have to remember that in the upper reaches of the atmosphere that the temperatures are much colder. This means that water vapor once condensed can no longer return fully to its gas state. Since temperatures don’t change in this region clouds are able to keep shape longer.

Finally, clouds have color. Some are white, some are grey, and in special circumstances such as major storms can have weird colors like green or red. This goes back to refraction. Most color that we can see is visible because are eyes perceive how objects absorb or reflect certain wavelengths of light. The white colors of clouds come from the condensed water vapor having a high reflective quality.

When all wavelengths of light are reflected back you see white. The grey color comes from seeing clouds from beneath. White clouds are white if you notice, on sunny days. This is because you can see the sunlight directly hitting them and see that light almost completely reflected back. On cloudy days most sunlight is blocked by the translucent and refractive quality of cloud cover. This makes clouds appear darker in color as part of the light has been uniformly absorbed.

We have written many articles about clouds for Universe Today. Here’s an article about the types of clouds, and here’s an article about cirrocumulus clouds.

If you’d like more info on clouds, check out an article aboutClouds. And here’s a link to NASA Spaceplace Page about Clouds.

We’ve also recorded an episode of Astronomy Cast all about the Atmosphere. Listen here, Episode 151: Atmospheres.

Cloud Pictures

Mammatus Clouds

Here are some cool cloud pictures.

Here’s a photo of mammatus clouds, taken by NASA. These are a type of cloud associated with thunderstorms and bad weather.

Lenticular Clouds

Here’s a picture of lenticular clouds. This kind of cloud looks lens shaped, and sometimes even like a flying saucer. They form when moist air flows over top of a mountain, creating a series of standing waves in the atmosphere. If the temperature drops below the dew point, lenticular clouds may form.

These are Morning Glory clouds, a very rare type of cloud formation seen in Australia. They look like long lines of rolling clouds moving across the landscape. They can be more than 1,000 km long and 1-2 km high. They move 60 km/h across the landscape. Scientists aren’t really certain how they form.

Cumulus Clouds

Here’s a classic example of a cumulus clouds. These are the common fluffy white clouds we see when warm air rises and the moisture in the air condenses.

Orographic Clouds

This is an image of orographic clouds. These are formed when air masses are forced from low elevation to go over higher terrain like a mountain. As the air gains altitude, expands and cools forming clouds.

We’ve written many articles about clouds for Universe Today. Here’s an article about how clouds are formed, and here’s an article about different types of clouds.

If you’d like more information on clouds, check out NASA’s cloud gallery. And here’s a link to more information on clouds.

We’ve also recorded an episode of Astronomy Cast about atmospheres. Listen here, Episode 151: Atmospheres.

How are Clouds Formed?

Atmospheric Pollution

[/caption]I bet some of you are fascinated with certain cloud formations. My eldest son once pointed to the sky, excited upon seeing a bunch of clouds taking shape of a menacing dragon. He was however disappointed after a few minutes when the dragon cloud slowly began to deform and fuse with the rest. So how are clouds formed?

First, water evaporates, rises, and fills up the atmosphere. The evaporated water, a.k.a. water vapor then clings to other numerous particles or dust found in the atmosphere. This dust comes from automobiles, fires, volcanoes, bacteria, and sea spray.

As water vapor rises, it cools. Now, the lower the temperature of air, its capacity to hold water vapor (also known as the saturation point of air) also drops.

Eventually, the rising water vapor condenses and forms the structure of the cloud. You can’t however see this structure unless it has its own color. Well, we know that clouds are either white or dark, and that’s why we’re able to see them.

Most clouds are white. That’s because water and ice particles that make up a cloud have just the right amount and sizes to scatter light in all possible wavelengths. When light of practically all wavelengths combine, the result is white light.

However, when too many water and ice particles build up, just like in a storm cloud, much of the scattered light is simply re-scattered into the cloud. In other words, too much particles prevent some of the light from escaping. Hence is the reason why storm clouds are dark.

Try slowly adding milk in water and notice how its color slowly shifts from white to dark as more milk is added.

I’m sure you’ve noticed that clouds easily form on mountains. How are clouds formed on mountains? When a wall of air and water vapor encounters a mountain side, it has nowhere else to go but up the slopes. Well, if you recall, rising water vapor cools and eventually condenses to form clouds.

Thus, mountains don’t have special particles that enhance cloud formation. Rather, it is the barriers that they so form that forces the water vapor to rise and hence develop into cloud structures. A cloud formed due to topographical features is called an orographic cloud.

We’ve got lots of articles about clouds here in Universe Today. For starters, here are two:
Cloud Types
Cirrus Clouds

Here are the links of two more articles from National Oceanic and Atmospheric Administration (NOAA):
Cloud Classifications and Characteristics
Western Region Technical Attachment
Here are two episodes at Astronomy Cast that you might want to check out as well:
Orbit of the Planets, Green Stars, and Oort Cloud Contamination
Sky Surveys