Current cyclones and Watching

Sand mist and cyclones

Le 27 juin 2020 à 18:00

By Olivier Tisserant
4.87/5 (220)

We have been experiencing an episode of particularly intense and dense sand mist for a week. The effects are important on our physiology and for some it turns into real hell. I will sell in a future article on the reasons for the haze of sand and the journey through the ocean.

But for now the question is: what about the effects of this haze on cyclones, their development and their intensity?

Sand mist in the Atlantic

The indirect effects of the sand mist

Indirect effects are those which affect the environment and make it more or less favorable to the genesis of cyclones. The sand mist generates several indirect effects on this environment, the most important of which is the temperature of the water.

The temperature of the water at the surface is linked to several parameters: surface currents, swell, convection, sunshine, etc. The part related to sunshine is not in itself decisive in normal periods, but it can increase in importance in exceptional situations.

In the case of fog episodes, the denser it is, the more it blocks solar radiation, which can no longer heat the ocean surface during the day. And the longer the episode, the stronger the effect.

1 week Atlantic water temperature anomaliesFor this exceptional period, we have a particularly dense mist which has been present for more than a week (and which should continue a little longer) and the result is obvious when we look at the map of water temperature anomalies (SST) over the tropical Atlantic over the last 7 days. A large part of the area covered by the mist has been in a negative anomaly for a week, while for the past month we have been in positive anomalies almost permanently.

This effect is of course temporary and will slowly fade as it becomes less and less dense, but it is possible that this will ultimately make us gain a few small tenths of a degree over the season, which is always good to take! There is also a precedent with the 2006 season which was planned to be rather active (after the memorable 2005 season) and which found itself particularly light with 10 named cyclones and 2 Cat hurricanes. 3 for the most intense. There is an article on the subject, published by scientists at NASA which you can find here:

The direct effects of the sand mist

Direct effects are those that directly affect a cyclone or disturbance. The effects on disturbances (low pressure waves or troughs) must be separated from the effects on already active and cyclonic systems.

For the former, the sand mist will significantly limit the risk of reinforcement. The dry air that envelops the mist will dry out the immediate environment and limit convection, which is the engine behind the development of cyclones.

For the latter, the principle is the same, namely dry air which thwarts convection, but the result is often the endangering of the organization of the system. On entering the external circulation, the dry air will infiltrate all the internal circulation and dry out the convection. This will have the effect of blocking the reinforcement but also of thwarting the vertical circulation of the wind inside the system which will most often weaken it enormously.

The mist of sand, one of the nightmares of cyclones!

We can see it clearly, the haze of sand is a sworn enemy of the cyclonic genesis. In the past, there are many cases of systems that were weakened or could not be strengthened before the West Indies. In 2019 for example, Hurricane Dorian, which terribly impacted the northern Bahamas, was only able to strengthen once it got out of this haze which perfectly contained it before passing north of the Virgin Islands.

This mist is therefore a major ally of circumstance for us concerning the cyclonic risk. Just like the shear which is probably even more important and that the water temperatures at a little lower level.

We are suffering a lot right now from this haze ... but in the end, it's bad for good 😉

Image credit: Tropical tidbits et UW-CIMSS

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