Jumat, 26 Juni 2015

Article#433 - Overcast


This is map of cloudy Earth speaking. And this map will give you an information, on how cloudy (white) or clear (dark blue) the sky of a particular point on Earth's surface in average, between July 2002 and April 2015, as observed by MODIS Aqua satellite.

With that being said, it's evident that the map will not take differences of seasons into account, since some weather patterns persist only during some particular time of the year.
The Sahel semi-arid region, within the light blue tint on African landmass near the middle of the map, proves to be a great portrayal of this averaging effect – while it does experience a short rainy season, it is renowned for its abundant sunlight.

The first notable features to be recognized, however, will probably be that dark blue patches starting just north of Sahel. There, the world-renowned Sahara boasts their scorching, barren landscapes. Just on the other side of Red Sea, Arabian Desert steals the spotlight, with the dark blue tint comparable to that of Sahara's – if not darker.

Taking a path through the historic Silk Road will bring you away from Thar of South Asia, but will introduce the likes of Kyzyl Kum, Taklamakan and Gobi. Stretching from the land of Kazakhs in the west to the land of Han people to the east, these desert areas offer the images of cold, freezing winters—in contrast to the stereotypical image of a scorchingly hot desert, as depicted by the likes of Dasht-e-Kavir and Dasht-e-Lut in Iran—where sand grains may be heated up to 70°C.
Well, they are obviously dry; that's why we call them "deserts" in the first place. But when it is said that they are cold in winters, scientists really mean it – it's not uncommon for temperatures to dip as low as -30°C in this part of the world within winter months.

There's a completely legit reason of mentioning cold and dry deserts. Because, when we talk about the true biggest desert in the world, the answer might not be what you intuitively expect. No, not that famous Sahara; even though it is arguably one of the biggest.
See that vast dark blue area, down to the south side of the map? There is Antarctica, a continent mostly known for its frigid climate and icy nature. It may sound mind-boggling, that this land of ice is where the precipitation falls for the slightest, even in some marks beating the Atacama of South America, where extreme aridity has attracted astronomers to build telescopes all over the mountains.

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Hey hey, wait right there.
The image is depicting the cloudiness of Earth, so how come we have been conversing about deserts all over..?!

It's time to put our sights away from the stark blue patches, and look at the mire commonly scattered white patches. (Sorry Mojave-Sonora of North America, Namib-Kalahari of southern Africa, or Great Victoria-Gibson of Australia—this really is not the time for you guys to shine.)
And there's this white bang stretching over the equator; an area known as Inter-Tropical Convergence Zone (ICTZ). This zone contributes to the abundant cloud within the tropics, tapering the heat while drenching the lands with rain at the same time.
A look further north or south may reveal other belts of white clouds within the high-latitude areas. And a bluer area in between is what called the "desert belt" – a collection of area with less clouds, thus less precipitation, and in turn more prevalence of deserts.

This alternating "belts" of cloudy skies and clear skies may be somewhat reminiscent to the bands observed on the likes of Jupiter, where its gaseous nature and abundant moons, among others, make for a pronounced dark and bright bands of ammonia clouds.
But, in contrast to Jovian bands, these Earthly cloud belts are more closely related to the result of convection process occuring within the atmosphere. ICTZ and the so-called "desert belt" are connected with a circulation cell called Hadley cell, whereas the high-latitude belts are associated with the so-called Ferrel cell and polar cell.

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At the end of the post, let's take look at the more subtle feature. Let's take a look at how apparent the geographical features are in the image. You can easily distinguish the coastal lines, islands, mountain ranges, lakes, or even rivers. All of the details, on a map solely depicting the overall cloudiness of the whole Earth.

Does that tell you something?

More reading:
http://earthobservatory.nasa.gov/IOTD/view.php?id=85843
http://www.nasa.gov/image-feature/cloudy-earth
http://www.slate.com/blogs/bad_astronomy/2015/05/09/cloudy_earth_map_of_cloud_coverage.html

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