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DID YOU KNOW? PART 17

Welcome to Did You Know'. A daily OCC segment where we tackle some of the easy and not so easy questions we come across on our social networks. Tonight's question is about the sea-breeze and how it creates thunderstorms.




Did You Know:

"How do sea breezes start storms?"


ANSWER

The leading edge of the sea breeze creates a boundary line between cooler dense air coming from the water, and warmer less dense air located over land. That collision of air-masses results in strong lift of the warmer air over the cooler air and if other conditions are met, a storm can form.

Want to know more? well read on

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Make sure you check out the last 'Did You Know' about what a seabreeze is, how it forms and the properties of the sea breeze air. I am going to assume you know all that for this segment.


So it is often thought that in the tropics we hardly ever see a 'cold front' an area where cold dense air meets warm less dense air. In fact, during Spring and Summer we see shallow cold fronts on an almost daily basis across Northern Australia. That's what a sea breeze is, it's a cool airmass that forces itself inland and at its leading edge it creates a collision zone forcing the warmer air to rise as it pushes itself further inland. Check out this Wikipedia image below. Notice that at the leading edge, the cool dense sea-breeze forces that warm landmass air to rise?




Now if the air is too dry or too stable over the inland area, it is unlikely that the seabreeze can do much more than create a few fluffy fair weather cumulus clouds because remember the sea breeze circulation only extends to around 1-2kms up in the atmosphere (see our last 'Did You Know' if you forgot this). That's far too shallow to form a thunderstorm. If the pre existing land mass air is too dry, the moisture the sea breeze brings with it will be lifted to create some shallow clouds and then as that cloud development process gives off latent heat and the air lifts further, the cloud tops will evaporate. If the air is too stable the lift will also create some shallow cloud before it hits a cap because the sea breeze is strongest within a few hundred metres of the surface and weakens quickly above that point. Therefore the greatest amount of forcing the sea breeze produces occurs very close to the land's surface. So the sea breeze will not be able to counteract a deeply stable environment and nor will it be able to work its magic in a dry environment.


However, if we can combine a deep level of moisture with a 'potentially' unstable air-mass, the sea breeze front can be the vital trigger for the lift of the air above the warm landmass and can help to push that air through a pre-existing limiter like a weak temperature inversion (it isn't strong enough to make a stable atmosphere unstable, but it can be strong enough to help rising air burst through a small stable layer near the surface that might have been keeping a lid on any cloud development).


In a 2019 study it was the potential instability and the strength (lack of) of the temperature inversion that were the key dictating factors in the development of sea-breeze thunderstorms in the tropics (in the simulation study it was assumed that there was enough moisture in the atmosphere - a big assumption in the Australian Tropics). There was very little relationship between how strong the sea-breeze was and whether it was able to create storms. This was slightly surprising to me because I have always assumed a stronger sea breeze creates a stronger sea breeze boundary which has the potential to create a stronger lift. This was not necessarily found to be the case in this simulated study. https://ams.confex.com/ams/18MESO/meetingapp.cgi/Paper/361331


Sea breezes can start thunderstorms but they can also kill them and kill them quickly. Find out why tomorrow. Also sea breezes can collide with each other, creating an even stronger source of lift and if we have time before the weather gets too hectic we can have a chat about that in the next few weeks.



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