How common are bow wave cloud formations?

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Wave clouds over South Sandwich Islands January 27th 2004. (Image courtesy of Nasa)

20 years ago I saw the above fascinating photo by NASA. At first glance one might mistake them for ships sailing side by side. Instead, they are the South Sandwich Island peaks creating bow waves into clouds. Impressively, the cloud waves stretch nearly 300 km and the distance between the northernmost and southernmost islands is 400 km. If one of those mountains was in London, you would still see the ripples in Amsterdam.

How common are these formations? We’ll first describe how they form, then find our own example, and end with a surprise SAR finding.

1. How do they form?

At a precise level, this involves atmospheric stability and something called the Brunt–Väisälä frequency. But we don’t need equations to understand the macro picture.

After thinking about it and reflecting against ship-generated waves, we can conclude there are three basic formation requirements: 

• A stable air mass: The atmosphere must be layered and uniform at large scale. If conditions are chaotic, any wave pattern immediately dissolves.
  

• Strong wind flowing across an island: The island itself doesn’t move but the air does. When wind is strong enough, it is forced upward over the island.
  

• A tall, isolated mountain: The island must be high enough to force air upward and isolated enough that other terrain does not disrupt the pattern.

When these conditions align, the airflow doesn’t simply rise and settle but starts oscillating vertically like a ripple moving downstream. Where the air rises and cools, clouds form. Where it sinks and warms, they disappear.

The result is a stationary atmospheric wave stretching hundreds of kilometres over the open ocean. But that is enough theory, let’s go find some clouds. 

2. Finding a cloud over Tristan da Cunha

We could have just said “let’s just find places like in the NASA photo” without doing the formation thinking above, but a little extra understanding goes a long way. Either way, fitting locations that came to mind are:

• Tristan da Cunha

• Lesser Antilles

• Hawaii

• Aleutian islands

• Canary island (may be too clustered)

• Azores (Pico island only high enough)

• South Sandwich Islands (The NASA photo)

• Some Pacific islands but not sure if tall enough

Those are all volcanic islands as isolated oceanic islands tend to be. 

I first wanted to look at Tristan da Cunha in the middle of the South Atlantic. A British overseas territory and the remotest permanent human settlement on earth. To appreciate the remoteness, just take a look at the map below. I have considered visiting it but the lengthy trip on a supply ship from Cape Town a whopping 2800km away makes it quite time-consuming and expensive.

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Map showing Tristan da Cunha. Image courtesy of Google Earth.

But for finding wave clouds from an armchair, this solitary island standing 2000m above the Southern Atlantic offers excellent chances. The island sits at the northern edge of the Southern Westerly wind zone and the high elevation makes for a great obstacle for the prevailing winds.

I didn’t have to look far: On February 9th there was a clear wave cloud but I found a visually better candidate on 30th May 2025. The cloud stretches 200km east, is 50 kilometers at its widest with a wave length of 14.5km.

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Wave cloud over Tristan da Cunha May 30th 2025.

3. A bonus wave finding with SAR

My recent flood analysis experiments got me excited about SAR. I didn’t think it was helpful in this wave cloud analysis but then stumbled upon a 2021 example where ESA/NASA were tracking an iceberg near South Sandwich islands with SAR. They found the iceberg but also happened to see a strong wave cloud formation. 

I wanted to find a similar example with a true colour comparison, but there was no reliable SAR coverage over Tristan, and there were few passes where Sentinel 1 and 2 overlapped on days I wanted to see over South Sandwich island.

The clearest recent formation was April 7th 2023 in the image below. If you look carefully, you can even see a few dozen small white dots: Icebergs drawing their own lines across the ocean surface.

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Wave formation over South Sandwich Islands April 7th 2023

Why are these formations visible in SAR? My first thought was that perhaps the moisture differences or cloud ice crystals cause enough reflection differences to show up in SAR. A 2015 paper by A. Ivanov in the International Journal of Remote Sensing explains the associated wind of wave clouds affect the sea surface, causing alternating areas of smooth and rougher texture. That the effect is visible over hundreds of kilometres tells us two things: The atmospheric waves are powerful, and SAR is remarkably sensitive to subtle changes in surface roughness.

4. How common are these?

I thought these clouds needed optimal conditions because I have seen so few images. After thinking about the formation mechanics I realised the required conditions are not that rare after all.

This was confirmed simply by using Copernicus search both on SAR and True Colour. I continued focusing on the South Sandwich Islands before the ice season (Jan-May). I stopped counting as in SAR the formations appeared multiple times a month.

In True Colour, they were also common to see if not as common as in SAR. Perfect optical conditions, however, were rarer. This is where the condensation altitude of clouds and the overall cloud layer thickness plays a major role.

Conclusion

Wave clouds are impressive and the formation is easy to understand on macro level. They appear to be common though not always visually detectable. Even more surprising for me: SAR is able to detect them with ease.

See you,

Orbital Vantage