Noctilucent clouds: The season starts now!
Noctilucent cloud season has begun! Normally, in late May or June, people at higher latitudes on the globe begin reporting these ethereal, electric-blue clouds after nightfall. The first batch of reports began this year on June 4, 2023. See the first night-shining clouds of the season below.
What are noctilucent clouds?
Noctilucent clouds, or night-shining clouds, are thin clouds high up in Earth’s atmosphere – the mesosphere – as much as 50 miles (80 km) above Earth’s surface. Scientists think they’re made of ice crystals that form on fine dust particles from meteors. They can only form when temperatures are incredibly low and when there’s water available to form ice crystals.
So, why do these clouds – which require such cold temperatures – form in the summer? It’s because of the dynamics of the atmosphere. In fact, you actually get the coldest temperatures of the year near the poles in summer at that height in the mesosphere.
Here’s how it works: during summer, air close to the ground heats up and rises. Since atmospheric pressure decreases with altitude, the rising air expands. But, when the air expands, it also cools down. This, along with other processes in the upper atmosphere, drives the air even higher causing it to cool even more. As a result, temperatures in the mesosphere can plunge to as low as -210 degrees Fahrenheit (-134 C).
In the Northern Hemisphere, the mesosphere reaches these temperatures by mid-May in most years.
We see noctilucent clouds when most of the sky has grown dark. But, the rays from the sun can still reach and reflect off these eerie, ethereal clouds. Indeed, they have an electric-blue appearance. When satellites or astronauts view them from space, they go by the name of polar mesospheric clouds. If you want to see them for yourself, now’s the time to look!
Where to watch for noctilucent clouds
As with the aurora, it helps to be closer to the poles to see this phenomenon. You can keep tabs on noctilucent clouds via SpaceWeather’s RealTime gallery, or on Facebook via the group Noctilucent Clouds Around the World.
It’s noctilucent cloud season
The season for noctilucent clouds at northerly latitudes is now. People at high latitudes report seeing noctilucent clouds. This happens every year, from about May through August in the Northern Hemisphere, and from November through February in the Southern Hemisphere.
In recent years, northern summertime noctilucent clouds have set records for low-latitude sightings. In 2019, for example, people observed them as far south as Las Vegas (+36N) and Los Angeles (+34N). Usually, though, they’re seen from higher latitudes.
How to see these night-shining clouds
To see noctilucent clouds, you’ll want to have certain conditions in your favor. One factor is when to look. Right about now – June to July – is typically when noctilucent clouds are most widespread.
You’ll also want to be positioned as far north as possible during the Northern Hemisphere’s peak season. Canada and the U.K. are two locations where you’ll have a better chance to spot night-shining clouds. (However, rocket launches can inject particles into the upper atmosphere and make noctilucent clouds visible to areas that aren’t so far north.)
Then, look west about 30 minutes after sunset. The farther north you are, the longer throughout the night you can see them. That’s because the sun doesn’t dip as far below your horizon.
Noctilucent clouds look like electric, luminous tendrils of blue-white light. They are the clouds that glow after other clouds have darkened.
What noctilucent clouds can teach us
Noctilucent clouds are sensitive to atmospheric temperatures. Therefore, they can act as a proxy for information about the wind circulation that causes these temperatures. First of all, they can tell scientists that the circulation exists. They can also tell us something about the strength of the circulation.
Scientists studying these clouds have gotten help from NASA’s Aeronomy of Ice in the Mesosphere (AIM) satellite. This satellite, launched in 2007, has observed noctilucent clouds using several onboard instruments to collect information such as temperature, atmospheric gases, ice crystal size and changes in the clouds. It even accounts for the amount of meteoric space dust that enters the atmosphere. You can find out what they are learning at NASA’s AIM page.
Studies have also shown that as the climate warms, noctilucent clouds become more visible.
Noctilucent clouds from 2023
Do you have images of the 2023 noctilucent clouds to share? We’d love to see them! Submit them to EarthSky Community Photos.
Noctilucent clouds from 2022
Bottom line: The first noctilucent clouds of the 2023 season are here! Learn more about how to see them and submit your photographs here.