I asked the source of the graph, and he said it was so long because it doesn’t rain in the troposphere. This seems a believable explanation. (though also, why doesn’t it rain?)
Not sure if there’s some other reason, but in the stratosphere you don’t afaik* get big convective updrafts like there are in the troposphere, which I presume is due to the rate at which temperature declines with altitude getting smaller than the rate at which a rising air body will cool due to expansion.
*Actually I think that this property is basically what defines the stratosphere vs the troposphere?
Yeah, thanks for highlighting this. I started writing about it but realised I was out of my depth (even further out of my depth than for the rest of the post!) so I scrapped it.
Thanks for clarifying with Robert Rohde!
I reached roughly the conclusion you did. When water vapour is injected into the troposphere (the lowest level of the atmosphere) it is quickly rained out, as you point out. However, the power of the Hunga-Tonga explosion meant that the water vapour was injected much higher, into the stratosphere (what the diagram calls the ‘upper atmosphere’). For some reason, water vapour in the stratosphere doesn’t move back down and get rained out as easily so it sits there. Which is why ‘upper atmosphere’ water vapour levels are still elevated almost two years after the explosion.
I asked the source of the graph, and he said it was so long because it doesn’t rain in the troposphere. This seems a believable explanation. (though also, why doesn’t it rain?)
Not sure if there’s some other reason, but in the stratosphere you don’t afaik* get big convective updrafts like there are in the troposphere, which I presume is due to the rate at which temperature declines with altitude getting smaller than the rate at which a rising air body will cool due to expansion.
*Actually I think that this property is basically what defines the stratosphere vs the troposphere?
Yeah, thanks for highlighting this. I started writing about it but realised I was out of my depth (even further out of my depth than for the rest of the post!) so I scrapped it.
Thanks for clarifying with Robert Rohde!
I reached roughly the conclusion you did. When water vapour is injected into the troposphere (the lowest level of the atmosphere) it is quickly rained out, as you point out. However, the power of the Hunga-Tonga explosion meant that the water vapour was injected much higher, into the stratosphere (what the diagram calls the ‘upper atmosphere’). For some reason, water vapour in the stratosphere doesn’t move back down and get rained out as easily so it sits there. Which is why ‘upper atmosphere’ water vapour levels are still elevated almost two years after the explosion.