## Aug 20, 2010

### Visualize weather pattern with random walk

When talking about the “good” weather, the daily temperature change is important, slow steady change from day to day is much better than sudden temperature increase or drop.

Here is the daily mean temperature for Bloomington, Indiana.

We define a piecewise function to classify the day to day temperature change. x is (T – Tprevious day), y is the threshold to define the weather change: 1 ~ no change, 2 ~ cold move, 3 ~ mild cold, 4 ~ mild hot, 5 ~ hot move.

Then we can apply the same random walk trick used in the post Visualize irrational number as random walk. The classification results are mapped into the moves: 1 ~ no move {0, 0}, 2 ~ move south {0, –1}, 2 ~ move west {-1, 0}, 3 ~ move east {1, 0}, 4 ~ move north {0, 1}. Then we can get a random walk image (the green dot is starting point {0, 0}, the red one is the end).

This is probably nothing interesting. However, we can use it to compare the patterns among different cities. Here is the results from Washington, Columbus, Indianapolis, Kansas City, Denver. The threshold is 3.5 degree. This shows the certain pattern among cities from ocean to inland.

When we compare the cities across the ocean, a different pattern is shown.

Down the weatherwalk.nb for the detail.