This supermoon has a twist – floods are expected, but the lunar cycle masks the effects of rising sea levels.

Brian McNordi,<クラス="ライセンス" href =""> CC BY-ND “width =” 754 “height =” 425″/>

This simplified graph shows how the lunar node cycle suppresses and enhances the effects of rising sea levels in Miami. The base model assumes a constant linear increase in sea level and therefore does not capture the expected acceleration of sea level rise. credit: Brian McNordi, CC BY-ND

The “super full moon” is coming on April 27, 2021. Coastal cities like Miami know that it means one thing. It increases the risk of tide floods.

Very high tides are common when the moon is closest to Earth (called Perigee) and when the tide is high or high. If it is informally known as the full moon, it is a full moon and is at stake.

But something else is happening in the way the moon orbits the earth, which people should know. It is called the lunar node cycle and hides the looming risk that is currently not negligible.

We are currently in the stage of a 18.6 year lunar cycle to mitigate the lunar’s impact on the ocean. As a result, the risk of coastal floods can appear to be flat, which can make sea level rise less noticeable.

But the community should not be complacent. With global warming, the world’s sea level is still rising, and its 18.6 year cycle will soon be against us.

I am an atmospheric scientist at the Rosenstiel Department of Atmospheric Sciences at the University of Miami, watching over Miami’s rising sea levels. Here’s what you need to know:

That the moon is associated with coastal floods

The lunar attraction is the main reason we have tides on Earth. More specifically, the Earth rotates once a day under the Moon, and the Moon orbits the Earth once a month, which is a major reason why the ocean is constantly sloshing.

This supermoon has a twist – floods are expected, but the lunar cycle masks the effects of rising sea levels.

The lunar node is the point where the lunar path intersects the ecliptic and is the plane of the Earth’s orbit, shown as a view of the Sun from the Earth over a span of one year.Credit: Wikimedia

Simply put, the lunar attraction creates a bulge in the seawater closest to the moon. Due to the inertia of the water, there is a similar bulge on the other side of the planet. As the Earth spins through these bulges, high tides appear in each coastal area every 12 hours and 25 minutes. Depending on the geography, some tides are higher than others.

The sun also plays a role. The rotation of the earth and the elliptical orbit around the sun produce tides that change throughout the day and year. However, the impact is less than half of what the moon contributes.

This gravity tug of war was discovered nearly 450 years ago, but has been around for nearly 4 billion years. In short, the Moon has a very strong control over how we experience the surface of the sea. It does not affect sea level rise, but it can be hidden or exaggerated.

So what is the lunar section cycle?

First, we need to think about the orbit.

The Earth orbits the Sun in a particular plane — it is called the ecliptic plane. For simplicity, imagine that the plane is horizontal. Next, imagine the moon orbiting the earth. Its orbit is also on a plane, but it is slightly tilted about 5 degrees with respect to the ecliptic plane.

This means that the orbital plane of the moon intersects the orbital plane of the earth at two points called nodes.

This supermoon has a twist – floods are expected, but the lunar cycle masks the effects of rising sea levels.

The ecliptic and equatorial planes of the earth. Credit: NASA

The lunar orbital plane precesses or wobbles up to +/- 5 degrees, up to a maximum and a minimum of +/- 5 degrees, in about 18.6 years. The natural cycle of this orbit is called the lunar node cycle. The tides of the Earth are exaggerated when the lunar surface is more closely aligned with the equatorial plane of the Earth. Conversely, if the lunar surface tilts further away from the equatorial plane, the tides of the earth will be relatively weakened.

The lunar section cycle was first formally documented in 1728, but has been known to be enthusiastic about astronomical observers for thousands of years.

How does it affect sea level?

The effect of the nodal cycle is gradual. Nothing is noticed by people unless they pay tremendous attention to the precise movements and tides of the moon for decades.

However, dozens of astronomical factors, including the lunar node cycle, are taken into account when predicting tides.

It is also worth recognizing this impact and taking advantage of it. As it is today, the most rapid descending phase of the lunar node cycle moderates the observed sea level rise a bit, but all other conditions are the same.

These are the years for implementing infrastructure plans to protect coastal areas from rising sea levels.

Reaching the bottom of the cycle around 2025 and starting the upward phase, the lunar node cycle begins to contribute more and more to the perceived rate of sea level rise. During those years, sea level rise has virtually doubled in places like Miami. The impact will vary from location to location, as the details of sea level rise and the contribution of the lunar node cycle are different.

Another “super full moon” will appear on May 26th, so it’s a Perigian full moon, like April. Cities like Miami need to anticipate coastal floods, even if there is a lunar node cycle at this stage.

The climax of 18.6 years set this week in the UK

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This supermoon has a twist – floods are expected, but the lunar cycle masks the effects of rising sea levels.

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