Just saw a picture of clouds forming in a triangle shape over the land area only of a triangular shaped atoll island. Looks interesting for a pilot flying by. Any idea what causes this effect? I think the central part is filled with shallow water. Its called Aldabra.http://www.snf.org/uploads/photos/zoom/1728_1.jpgAl

My guess is that the lagoon is warmer than the surrounding ocean so when the air above is heating and rises it interacts with the cooler seabreeze causing condensation and clouds. It's an educated guess though--I can't be entirely sure.

My guess is that the lagoon is warmer than the surrounding ocean so when the air above is heating and rises it interacts with the cooler seabreeze causing condensation and clouds. It's an educated guess though--I can't be entirely sure.

No it's a flying saucer contrail!!!!! :(

Those clouds are your standard fair weather cumulus caused by surface heating. The clouds take the shape of the ground and not the water if you look closely, also they are offset a little rather than being directly above the ground, this is obviously caused by the wind.The air rises, quite rightly stated above because of radiation heating of the ground (this is how we all feel warm air), it's the ground that heats up the air in contact with it causing it to rise up, the reason the moisture is present in the form of cloud is simply down to the fact that the "parcel" of air has risen high enough to reach it's dewpoint (or saturation point) and can no longer support the amount of moisture in the air thus turning it into visible moisture.

As some of the above explanations have pointed out, it's a perfectly normal bank of cumulus clouds. They are formed by the sun heating the ground, the heat then radiates out of the ground, which causes air to expand and rise up (aka a thermal) It will continue to rise until it cools again when matched by the temperature of the air higher up, whereupon moisture in the air condenses to form a cloud. The clouds themselves will drift downwind away from where the thermal originally 'popped'. We are more used to seeing these over large land masses, so the shape is unusual in reflecting how it formed from rising air off the land, but the phenomenon itself is perfectly normal.The reason cumulus clouds are fluffy like that by the way, is that as they cool and condense, the action of doing so generates heat, which causes another 'mini thermal' within the cloud and that makes the air rise again a little bit more, so you get bits of the cloud going slightly higher on that heated air. This is also why there is usually turbulence in cumulus clouds.Eventually, there can be a long line of them downwind from where they are popping. A line of such clouds that have drifted downwind is known as a 'cloud street', although the average lifetime of a cumulus cloud is only about ten minutes, so how long the cloud street will be (if there is one) is dependent on the strength of the wind. In the picture, you can see the clouds in the foreground are decaying too fast to form a cloud street, which is an indication that the wind is not very strong. Observing that is a useful trick to determine the wind speed when planning a landing in an unfamiliar place that has cumulus clouds above it.You can actually use such clouds to navigate when sailing in or flying too, since the clouds will be visible in the distance long before the land is. And for fact fans, the average combined weight of all the water droplets in a typical cumulus cloud, is a surprising 200,000 kilogrammes, which is roughly the same weight as a heavy jet airliner.Al

Alan,I often learn more from your posts, than from reading books. Thanks for your continued insight!Cheers!

You can see similar formations of clouds near mountains. The air is deflected upwards by the wind and as it cools, forms the clouds.

Yup, those are called 'orographic clouds' because they are formed by winds traversing features of the landscape itself rather than rising thermal currents. The most common type of these clouds is called a lenticular cloud, because it is shaped like a lens, due to the curving rise and fall of the wave airflow over the terrain below. These are the clouds which are occasionally mistaken for UFOS, since they very often do look like a flying saucer.Technically, they are a type of altostratus cloud, although unlike normal altostratus clouds, orographic clouds do not move across the landscape with the wind, since they form as the wind rises up the side of a hill and decay as the wind goes back down the other side, which keeps the cloud itself in one place. They behave in the same way that you sometimes see a standing wave in a shallow river when water is passing over some rocks; the water is moving, but the wave itself stays in the same place.Because such orographic clouds are formed by a standing wave of lift, glider pilots will flock to them like moths around a flame, since if you get into the upgoing part of the airstream at the front of one and turn your aircraft into the wind, you will go up like a rocket even though your aircraft is descending through the air. If flying slowly enough, you will either remain stationary over the land in the lift, or on occasion even traverse backwards across the landscape as you go up, and it is fun to watch the shadow of your aircraft going across the ground backwards. Conversely, if you get into the downgoing airflow on the back side of a mountain wave, it can be extremely dangerous, since the air mass often descends much faster than your aircraft's maximum rate of climb, in which case you will be forced down into the terrain.This is handy to know if you are ever in a situation where your engine cuts over mountainous terrain, since even a very heavy aircraft can maintain height or increase its altitude if the air mass is going up faster than the aircraft is descending. You can actually try this in FSX by the way. If you load up the glider tutorial mission number 7 and tick the 'allow changes' option, then swap the glider for the Piper Cub for example, you will find that it is possible to switch off the engine of the Cub and still have it climb well above its normal service ceiling whilst in a descent through the air, purely because the lift wave lift over Minden is outpacing your aircraft's rate of descent.Al

Thanks Alan and everyone for your interesting posts. Really enjoyed reading all that. I think I read somewhere that pilots and/or sailors in the South Pacific used to navigate with just clouds and no instruments. Not sure if that's entirely true or not but if so it would be pretty brave. Al