Noctilucent clouds: The season starts now!

Noctilucent clouds: Foreground of car with headlight shining, background of thin, wispy light-blue clouds in darkening sky. — View at EarthSky Community Photos. | Villiam Hansen in Bornholm, Denmark, captured this image of noctilucent clouds on June 4, 2023. Villiam wrote: “Noctilucent clouds started last night while watching the moonrise in the other direction. I noticed a small dust on the lens and tried to blow it away with my mouth. That gave the fog effect on the lights, and I kind of like it. Over the car we see clouds that light up in the darkness.” Thank you, Villiam!

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.

First noctilucent clouds of the season in Estonia. Photo from Simuna. pic.twitter.com/jxQgh53a2e

— Kairo Kiitsak ?? (@kairokiitsak) June 4, 2023

Best I could manage of the faint and small noctilucent clouds in Dublin this morning. Take it for the first of the season. pic.twitter.com/AFIqlzS3fg

— Sryan (@SnowbieWx) June 5, 2023

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. You actually get the coldest temperatures of the year near the poles in summer at that height in the mesosphere.

Rising air

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. 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. 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!

Black space, shining ripply layer of clouds, dark orange narrow stripe above black silhouette of Earth. — Astronauts in the International Space Station (ISS) took this photo on January 5, 2013, when the ISS was over the Pacific Ocean, south of French Polynesia. Below the brightly lit noctilucent clouds, across the center of the image, the pale orange band is the stratosphere. Image via NASA.

Where to watch for noctilucent clouds

Like 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.

The year 2021 was excellent for noctilucent clouds, with many sightings over the U.K. and comparable latitudes. Spaceweather.com said that the frequent sightings in 2021 were probably due to extra water in the mesosphere.

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 UK 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.

Chart showing location of sun below Earth from observer's point of view and clouds high above in light. — Noctilucent clouds (NCLs) are night-shining clouds because they are so high up that after the other clouds are dark the sun can still reach NCLs. These polar mesospheric clouds appear as eerily blue in a mostly darkened sky. Chart via John Jardine Goss/ EarthSky.

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.