Noctilucent Clouds Spread and Mystify

Wired has a feature on noctilucent clouds, once seen only at high latitudes but increasingly visible now lower down the globe. The clouds result from ice crystals at altitudes of 50 miles, higher than five 9s of the atmosphere. What water ice is doing up there, in a region 100 million times drier than the Sahara desert, is only one of the mysteries associated with the clouds. They are a recent phenomenon: the first scientific description of noctilucent clouds was penned in 1885. For a time it was believed that the clouds were an effect resulting from the eruption of the Krakatoa volcano two years before. Since 2002, the clouds have been sighted — and photographed — as far south as Oregon, Colorado, and Utah. Some scientists believe that human-caused climate change is playing a role, but others doubt this. Two satellites are in orbit to study the clouds; NASA's AIM generated this day-by-day movie of clouds in the vicinity of the North Pole during 2008.

Comments

Why The Stripes

[AtomicSnarl]

The striped nature of the cloud features is probably because the data was gathered by the DMSP Weather Satellites using their low light detection sensors. These do not take a full-earth view of the world as the sun-synchronous GOES satellites do. DMSP vehicles operate in a lower orbit but a high angle and circular orbit. This brings them near the poles, and they cross the equator at roughly 9AM or 3PM locally to take advantage of the sun angle and shadows on clouds. They scan a wide path beneath them in visible and infrared channels, and have been used for years to do night light intensity mapping, such as for light pollution surveys.

The stripes are the paths from the several vehicles in orbit assembled over time when they passed near the poles.

Your tax dollars at work!

Re:Well there can be only one answer....

[drinkypoo]

If the hot water vapor left the planet, then the planet would be cooler and we'd have a water shortage to deal with. Otherwise, it's a closed system and there's no net change in temperature.

Water vapor sheds itself of heat through infrared radiation like everything else. It's radiated in all directions and the rays/photons/however you want to model them have a chance to strike something else and be absorbed on their way out of the atmosphere. Hot air rises and takes with it water vapor, which when it radiates its IR at high altitudes is less likely to heat other air.

Convection... it's not just for cooking on the cheap

Re:Just a wee bit sad.

[tsm_sf]

It's so much easier to beat up someone who's dying due to not having DDT, and there are a lot more of those around than that one fellow.

Not to sidetrack this topic, but let's just get this out of the way...

Rachel Carson never wanted to ban DDT. DDT has never been banned for use in fighting malaria.

From the wikipedia page on DDT:

In the 1970s and 1980s, agricultural use of DDT was banned in most developed countries. DDT was first banned in Hungary in 1968 then in Norway and Sweden in 1970 and the US in 1972, but was not banned in the United Kingdom until 1984. The use of DDT in vector control has not been banned, but it has been largely replaced by less persistent alternative insecticides.

The Stockholm Convention, which entered into force in 2004, outlawed several persistent organic pollutants, and restricted the use of DDT to vector control. The Convention has been ratified by more than 160 countries and is endorsed by most environmental groups. Recognizing that a total elimination of DDT use in many malaria-prone countries is currently unfeasible because there are few affordable or effective alternatives, the public health use of DDT was exempted from the ban until alternatives are developed. The Malaria Foundation International states that "The outcome of the treaty is arguably better than the status quo going into the negotiations...For the first time, there is now an insecticide which is restricted to vector control only, meaning that the selection of resistant mosquitoes will be slower than before."

Despite the worldwide ban on agricultural use of DDT, its use in this context continues in India, North Korea, and possibly elsewhere.

Today, about 4-5,000 tonnes of DDT are used each year for vector control. In this context, DDT is applied to the inside walls of homes to kill or repel mosquitos entering the home. This intervention, called indoor residual spraying (IRS), greatly reduces environmental damage compared to the earlier widespread use of DDT in agriculture. It also reduces the risk of resistance to DDT. This use only requires a small fraction of that previously used in agriculture; for example, the amount of DDT that might have been used on 40 hectares (100 acres) of cotton during a typical growing season in the U.S. is estimated to be enough to treat roughly 1,700 homes.