Design Notes

Balloons and the Weather

As part of my "day job", I have actually spent some time studying trans-world balloon flights, including trying to run models to follow the balloons, and in one case aiding in trajectory calculations of a crossing last year. I had to do a little reading on the subject for this work.

Essentially balloons are passive in their horizontal transport. They move with the velocity of the wind. The only control they have is to go up or down. If they want to move in certain direction, they have to move their balloon to an altitude where the wind is blowing in that direction. Fairly limiting actually!

In fact this was the main reason we were never able to model the balloons accurately -- the particles we use to simulate stuff in the atmosphere were designed to advect and disperse, but not suddenly change vertical position.

For the one trajectory calculation we did in 1998 we released "particles" at different altitudes and used forecast winds to see were they ended up. This was based on the assumptions that we had the balloon at the right position in space at the start, and only allowed the balloon to go to one of the different altitudes and remain there.

All of these would be quite difficult and far too technical to simulate in an easy and quick game that is fun to play, but I did have some ideas for a game which preserves at least some of these ideas.

The map used to display the jet stream is the same projection as on atmospheric maps. This is convenient because it maximizes the play area in the region of interest -- the most likely locations of the jet streams.

Balloons move left to right as that is the direction of the prevailing "westerlies" in the northern hemisphere.

The game's Quadrant cards represent both the polar jet and the subtropical jet which is much higher, and extends well into the tropics. In addition to the prevailing weather conditions the balloons are competing in, the Local Wind cards introduce the variability of the balloons jockeying for the best altitude and latitude position.

The Quadrant cards marked with an asterisk (*) represent real occurrences where the jet stream undergoes a significant deviation. For weather aficianadoes, these are called "blocks", including "Trapped-low", "Rex"- and "Omega"-blocks. In game terms this means it can be hard to find lanes with westerly movement. The Friendly Weather rule was added because in real life, no balloonist on a long flight takes off in this kind of pattern.