# Determine the number of days with North-East wind direction from the number of days with North and East wind direction? [closed]

I have some data like:

Wind flow from north direction = “X” Numbers of days.

Wind flow from east direction = “Y” Numbers of days.

Then is there any formula to know numbers of days wind flows from North-East direction?

## closed as unclear what you're asking by Brandon Enright, Kyle Kanos, Colin McFaul, Kyle Oman, alemiJul 16 '14 at 23:57

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• What do you call wind from North-East direction? Is it simply the days in which the wind comes both from the north and the west? Normally, wind-speed is a vector, meaning it has a magnitude, and a direction. As such, do you define the wind coming from the north, as having a direction of 180 $\deg$? This means that if the wind is coming from the north, it is coming from the north only, and thus, no east-west component is present, making north-east wind impossible. I suggest you post a sample of your data, as well as tell us something more about your method (e.g. programming or something else) – ROIMaison Jul 16 '14 at 7:07
• Is the average of the two way off? – BMS Jul 16 '14 at 15:32
• What is the actual problem you are trying to solve? Are you sure that the dataset is as you describe, or is it a set of wind components in the U (E-W) and V (N-s) direction, which is standard for weather data? – EnergyNumbers Jul 17 '14 at 10:55

## 1 Answer

Generally speaking there will be some correlation between wind directions. For example if on some specific day the wind blows from the North or East it is quite likely there was a North-East wind in the week or so around that day. By contrast if the wind is from the South-West on a particular day it is less likely there was a North-East wind in the week or so around that day.

However these are statistical correlations. If you measure wind directions over many days and analyse your data you'll find this type of correlation. The degree of correlation will vary with location and season, and possibly other variables I haven't thought of. So there is no answer to your question unless you make it more precise.

• Well, there is the "pigeon-hole" theorem, ie if $X + Y$ exceeds the number of days in the observation set, you can place a lower bound on the number of North-East days. :-) – Carl Witthoft Jul 16 '14 at 11:46
• @CarlWitthoft: damn, I didn't think of that. I'll update my answer immediately :-) – John Rennie Jul 16 '14 at 14:36