The desert dips below freezing on winter nights but if you want ice in the summer, how do you get it? This is a story of human innovation using natural processes.
In the 17th century BCE the Persians (Iranians) figured out how to make ice in the desert and store it through long hot summers. They used this method for 3,600+ years until electric refrigeration replaced it in the 20th century.
Though water is scarce in Iran, the method works well because the air is so dry. The process requires many steps: deliver water, make ice, store ice and keep it cool.
Deliver water to the ice-making location: The Persians built underground water channels called qanats to deliver water from uphill wells to the downhill population. Water in the qanat does not evaporate in the sun and stays cooler because it’s underground.
Make ice: To make ice the Persians built plaza-like ponds, shaded by a high wall, where the shallow water froze on winter nights. Collecting the ice before sunrise, they stored it in the ice house (dome in the background). Here are two photos of the same ice plaza no longer in use. People give it a sense of scale.
Store the ice: The ice house, called a yakhchal, stored ice underground, where conditions are naturally cooler, and protected it with an insulated dome. The hole at the top of the dome allowed hot air to escape.
Keep the ice cool: The ice was kept cool using natural ventilation to draw in cold air and remove hot air. Windcatcher towers in some towns were quite ornate.
Here’s a video that puts it all together.
(photos from Wikimedia Commons; click on the captions to see the originals)
Today is one of two days per year when the sun stands still.
By the time you read this article the December solstice has already happened. The sun paused over the Tropic of Capricorn at 10:02 UTC, the same moment everywhere on Earth. In Pittsburgh it occurred at 5:02am local time, more than two and a half hours before sunrise.
If you wanted to experience sunrise and the December solstice simultaneously the best place would have been Georgetown, Guyana where the sun rose at 5:59am and the solstice occurred 3 minutes later at 6:02am local time (GYT). It’s too late to do that this year but 2021 is a possibility. By then we hope to travel safely thanks to the COVID-19 vaccine.
The good news for now is that the days are already getting longer in Pittsburgh. Tomorrow will be 3 seconds longer than today.
It began snowing here in Pittsburgh on Wednesday morning, 16 December 2020, and didn’t stop for 17.5 hours. By 7:30 the next morning there were 9.25 inches of snow in Oakland. City lights glowed against the snow and clouds.
Yesterday I took a long walk to Pitt’s campus, Carnegie Library and Schenley Park to appreciate the beauty. Here are a few of the scenes I encountered.
On my way home I found one of Santa’s elves near the Library!
Though the snow didn’t melt it did compress in 24 hours. Here are two snapshots of the Pitt peregrine nestbox at 7:30am on Thurs 17 Dec and Fri 18 Dec. Though there is still a lot of snow it is not as daunting, even if it hasn’t been shoveled.
No peregrines visited the nest yesterday but I know they are present. I saw Morela perched on a gargoyle.
UPDATE 18 Dec 2020, 4:08pm: Morela examines the snow.
(photos by Kate St. John; statues photo by Richard St. John)
An event of astronomical proportions will happen on Monday 21 December 2020 when two bright planets — Jupiter and Saturn — converge in the night sky, visible just after sunset.
A “conjunction” occurs when two astronomical bodies appear close to each other as seen from Earth. This one is called “Great” because it involves the two largest planets, Jupiter and Saturn.
A Great Conjunction happens every 20 years but this one is rare, as NASA explains:
It’s been nearly 400 years since the planets passed this close to each other in the sky, and nearly 800 years since the alignment of Saturn and Jupiter occurred at night, as it will for 2020, allowing nearly everyone around the world to witness this “great conjunction.”
When Steve Gosser took the photo above on Friday 11 December the two planets had not yet converged but you can see Saturn’s rings at top left and Jupiter with four moons at bottom right (the fourth moon is faint in the bottom right corner).
If you follow me on Facebook or Twitter you’ve seen my best photo of the week, perhaps for the whole year, with only a brief description: Merlin eating a junco at sunset, Schenley Park golf course, 7 December 2020. Here’s the back story.
This week Pittsburgh suffered through six days in a row of unrelenting overcast “Pittsburgh Gray” skies. During that period there was only one moment when the sun made an appearance and I was determined to be outdoors with a big view of the sky when it happened: The Gleam At Sunset on Monday December 7.
During winter Pittsburgh often has overcast skies all day and clear skies at night. When the transition happens at sunset you can see clear sky approaching from Ohio but it will arrive too late to enjoy the sun. We have 10 minutes of happy sunshine and then it’s dark. The Gleam At Sunset.
A gleam was predicted for Monday so I walked to Schenley Park golf course to reach high open ground. The sky started to clear. The sunset was going to be beautiful.
Passing through Fezziwig Grove, I began to think about the merlin(s) that visit the golf course in winter. As I scanned the dead snags a merlin flew in with prey, a dark-eyed junco. My cellphone is not a robust camera so I positioned myself for the merlin silhouette.
I was lucky to photograph both: a merlin and The Gleam at Sunset.
Every November air pollution spikes in India as farmers in the Punjab burn their fields in preparation for the next crop. Because the practice causes terrible air pollution it was outlawed in 2015, but small farmers cannot afford to buy the machines needed to clear the fields so the practice continues year after year.
When the stubble burns Delhi is smothered in dangerous air pollution. The smoke from thousands of fires swirls high in the atmosphere and can be seen from satellites.
Meanwhile glaciers in the Himalayas have been retreating for the past decade. Scientists wondered if atmospheric carbon air pollution, landing on the white ice, was a factor in their warming. A team led by Yuan Q placed air pollution monitors in remote locations on the northern side of the Himalayas. Their report, published by the American Chemical Society on 4 November 2020, found an amazing thing:
Using electron microscopy, the researchers unexpectedly found that about 28% of the thousands of particles in the air samples from the Himalayan research station were tarballs, and the percentage increased on days with elevated levels of pollution.
Microscopic tarballs form from brown carbon in the smoke of organic fires — in this case, stubble burning. They are so lightweight that they travel far, rising over the Himalayas to deposit on the other side. Their dark color absorbs sunlight and causes the glaciers to melt faster.
Stubble burning is a persistent annual problem in India as shown in the 2018 video from France 24 below.
Dec 2018: Crop burning crisis: India chokes as farmers set fields on fire, France 24 News
As India’s government provides community-shared machines for clearing stubble, the burning will come to an end. Will it be soon enough for the glaciers? Probably not.
(photos from Wikimedia Commons, chart embedded from acs.org; click on the captions to see the originals)
The study is here: Yuan Q et al. Evidence for Large Amounts of Brown Carbonaceous Tarballs in the Himalayan Atmosphere. Environmental Science & Technology Letters. Published 4 November 2020. https://doi.org/10.1021/acs.estlett.0c00735
Clouds are not holding in heat. They are emitting it!
Clouds absorb heat during the day just as the earth does. When the temperature falls clouds emit heat in all directions including downward to us below. Their warmth can be just enough to keep us above freezing.
On a clear night there is nothing to warm us so we have frost in the morning.
Did you know you can avoid frost on your windshield if you park beneath a tree on clear, near-freezing nights? The tree is emitting heat, too. No frost in the morning.
Either it is very cold in this picture or the car was not parked under a tree.