In my workplace, we have a bit of an in-joke that goes like this:
[someone else] : It’s lunchtime
[one of us] : It’s always lunchtime somewhere in the world
(Except that’s not funny, so we tend to try to use it inappropriately on purpose, for example, ‘It’s always Friday somewhere in the world’, or ‘it’s always Christmas somewhere in the world’.)
Anyway, today it was a fairly mundane one: ‘it’s always raining somewhere in the world’ - which sparked the conversation over whether that’s absolutely true.
So the question is this: Must it always be raining somewhere in the world?
I’m **not **asking whether, statistically, it’s highly probable that it will be raining in one or many places at any one time.
I’m asking: Is it possible for there to be a moment* at which it’s not raining** anywhere?
Can our planet do that? (no matter how improbable)
Or is it the case that a certain general amount of rain has to be falling at any one time, because of the energy input from the sun, the changing conditions at the daylight terminators, etc.
let’s say ten seconds
**we’ll define ‘raining’ as the point where rain actually strikes the surface of the earth, the sea, or an object at local ground level
It is possible for all the oxygen particles in a room to collect in a far corner for long enough to suffocate a human being. But that doesn’t mean it’s ever happened, because the probability is so incalculably low as to be incomprehensible in practice. The best we can say is that this event is “not impossible.”
Similarly, of course it is possible for it to never be raining anywhere in the world. It doesn’t happen, but it’s not impossible. The whole of the earth is not enveloped in cloud cover 100% of the time.
This is just a WAG, but I’d think it must be orders of magnitude more likely for it not to be raining anywhere on the world than it is for all the oxygen molecules in a normal sized room to collect in one corner.
In fact, if we go back far enough in prehistory, the former may well have happened. I’m thinking of an ice-ball earth scenario,
While it is not absolutely required by the laws of physics, it is essentially always raining somewhere in the Intertropical Convergence Zone. I would say that this area is so large that the chances that it is not raining somewhere in it are so small as to effectively be zero. Beyond this there are mountainous areas in the tropics where it rains pretty much every day.
Thanks - this was the sort of thing I was looking for.
(Not that the dicussion about particle-level probability phenomena isn’t interesting, and entirely valid - but the question here chiefly relates to meteorological systems and phenomena that can be understood entirely at their own macroscopic level)
Similarly, there’s always at least one pair of points on exactly opposite sides of the Earth where it’s exactly the same temperature and barometric pressure.
But on to the OP’s question. We can get a back-of-the-envelope estimate of how likely it is to not be raining somewhere. It looks like the ITCZ is somewhere in the vicinity of 1000 km wide, and 40000 km long. A typical storm might be around 400 square kilometers in area, or about 1/100000 the area of the ITCZ. And let’s say that at any given moment, at any given point in the ITCZ, there’s about a 50% chance that it’s raining (I don’t know how good that last figure is; that’s just a guess on my part). That would mean that, at any given moment, there’s about 1 chance in 2[sup]100000[/sup] that there’s no point in the ITCZ where it’s raining (assuming that the weather is uncorrelated over scales larger than a single storm). I could go on to consider the odds for the rest of the world in a similar way, and then multiply the figures together, but frankly, 2[sup]100000[/sup] is damn big enough already. You’ll have a lot better luck finding a time when the ITCZ didn’t exist, like maybe a time when the whole planet’s frozen, or when it was molten.
Actually, in the ICTZ what you generally get are convective thunderstorms, which are a much smaller scale. (There’s one going on outside my window as I type). They are maybe a few kilometers across. However, going by conditions in Panama during the rainy season (when the ICTZ is over us) at any particular point there is a high probability that it will rain for at least one hour a day. (It doesn’t rain every day; but on the other hand, sometimes it rains all day long).
OK, then, let’s say instead that the ICTZ is 10 million times the area of a single storm, and that the probability of rain at any given moment and location is 10% (assuming that your “at least one hour a day” means “usually about 2 or 3 hours a day”). The lower probability of local rain drives down the odds by about 6 orders of magnitude, but the smaller storms drives them up by about 30 orders of magnitude. In other words, the odds are still combinatorically huge (that’s much larger than astronomically) against, and in fact worse than what I said before.
Statistically, it’s possible for someone, sitting and minding their own business, having all of the water of their body come to a boil.
It’s never happened.
THAT said, the surface area of the Earth is about 1015 × 0.510 m^2. That’s A LOT of area to get NO rain.
And it’s less probable to get ANY area of that not getting rain than it is to get someone not griping about politics in the US for that long…
Oops, one highly, ULTRA low probability vs 1:1…
Forget that reference.
