To understand how humidity can impact something like the stock market, it pays to know a little about the mechanics of markets, and how stocks and other financial instruments are traded in the real world of the 21st century. [...] Where stocks were once held for weeks or month, or perhaps even years for certain companies, increasingly sophisticated technologies have driven the hold time down to days, hours, and even seconds. The idea with these trades is still the same — buy low, sell high — but the amount the stock appreciates over short time periods is minimal, often amounting to fractions of a penny. But when it’s a fraction of a penny profit on each of a million shares, and thousands of transactions can be executed every second, the profits can really pile up. [...]
As you can imagine, the technology needed to accomplish this is highly specialized, with custom algorithms running on server farms to gather the information needed and execute the trades. [...] The problem is that the systems traders use need to be connected to each other, and like any other network always have to contend with latency. To minimize latency, high-frequency traders tend to locate as close of physically possible to the exchanges, as less distance to cover means less time to send and receive messages that have a speed limit determined by the laws of physics. [...]
But what in the world does the weather have to do with all this? How can a hot, humid day possibly negatively impact the world of high-frequency trading? As it turns out, those microwave connections are the weak link in the system. During the early July [2018] heatwave, the links were experiencing slight delays in transmission times over that 16-mile path and throwing off the timing of the trading algorithms. The delay was minuscule — on the order of 10 microseconds — but in a business where millions are made and lost in seconds, that’s substantial.
The physics underlying this uniquely first-world problem are well known. We tend to think that radio waves travel at the speed of light, and while that’s true in a vacuum, propagation speed varies slightly in different media. Air makes microwaves slower; increased humidity makes them slower still. In addition, microwaves are absorbed and therefore attenuated by water vapor in the atmosphere.
So humidity deals a double whammy to the high-frequency traders’ links, both delaying the microwave signals and reducing their signal strength. [...]
https://hackaday.com/2018/08/06/feeling-the-heat-of-high-frequency-trading/
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