The daily mean wind speed was recorded from the 1st December 1981 to 28th February 2000
at two cities, Nantes and Rennes, in France. This analysis compares the frequency
distributions of wind speeds at the two cities and investigates the relationship between
wind speeds during summer and winter months in each country, as well as the relationship
between the wind speeds on the same day in the same cities.
Histograms of the summer and winter wind speeds in Nantes are shown in figure 1. The
summer wind speeds have mean 3.5ms-1, standard deviation 1.2ms-1 and a slight positive
moment skewness of 0.39. The winter wind speeds were slightly higher, with a mean
4.3ms1, standard deviation 2.0 ms-1 and also a positive moment skewness of 0.50. The
quantile-quantile plot in figure 2a confirms these differences between the two distributions.
The points fall approximately on a straight line through the origin, indicating that the shapes
of the distributions are similar and that the differences between the distributions can be
explained by a change in scale. The summary statistics in table 1 confirm this, the ratios
between the statistics in summer and in winter are all about 1.4, suggesting that the totals
in winter are approximately 40% higher than the totals in summer.
Summer
Winter
Ratio
Mean
3.5
4.3
1.2
Q1
2.5
2.9
1.2
Q2
3.3
4.0
1.2
Q3
4.1
5.5
1.3
IQR
1.6
2.6
1.6
SD
1.2
2.0
1.6
Table 1: summary statistics for daily wind speeds (ms-1) between summer and winter in Nantes. The
ratio between the summary statistics is also shown. Q1, Q2 and Q3 are the first, second and third
quartiles; IQR is the interquartile range; SD is the standard deviation.
Histograms of the summer and winter speeds in Rennes are shown in figure 1. The summer
wind speeds have mean 3.4ms-1, standard deviation 1.2ms-1 and a slight positive moment
skewness of 0.17. The winter speeds again were slightly higher, with a mean wind speed
4.0ms1, standard deviation 2.0ms-1 and also a positive moment skewness of 0.34. By looking
at the quantile-quantile plot in figure 2b we can see that the points fall approximately on a
straight line through the origin, indicating that the shapes of the distributions are similar
and that the differences between the distributions can be explained by a change in scale.
The summary statistics in table 2 confirm this, the ratios between the statistics in summer
and in winter are all approximately 1.3, suggesting that the totals in winter are
approximately 30% higher than the totals in summer.
Summer
Winter
Ratio
Mean
3.4
4.0
1.2
Q1
2.5
2.5
1.0
Q2
3.3
3.8
1.2
Q3
4.1
5.1
1.2
IQR
1.6
2.6
1.6
SD
1.2
2.0
1.6
Table 2: summary statistics for daily wind speeds (ms-1) between summer and winter in Rennes. The
ratio between the summary statistics is also shown. Q1, Q2 and Q3 are the first, second and third
quartiles; IQR is the interquartile range; SD is the standard deviation.
We can compare the winter wind speeds in Rennes and Nantes. As we can see from our
summary statistics in table 3, the two distributions are very similar, all with ratios of
approximately 1.1. This is most likely because Rennes and Nantes are both cities in France
and only approximately 70 miles apart.
Rennes
Nantes
Ratio
Mean
4.0
4.3
1.1
Q1
2.5
2.9
1.2
Q2
3.8
4.0
1.1
Q3
5.1
5.5
1.1
IQR
2.6
2.6
1.0
SD
2.0
2.0
1.0
Table 3: summary statistics for daily winter wind speeds between Rennes and Nantes. The ratio
between the summary statistics is also shown. Q1, Q2 and Q3 are the first, second and third
quartiles; IQR is the interquartile range; SD is the standard deviation.
We can compare the summer wind speeds in Rennes and Nantes. Again, as we can see from
our summary statistics in table 4, the two distributions are very similar, all with ratios of
approximately 1.0. This is most likely because Rennes and Nantes are both cities in France
and only approximately 70 miles apart.
Rennes
Nantes
Ratio
Mean
3.4
3.5
1.0
Q1
2.5
2.5
1.0
Q2
3.3
3.3
1.0
Q3
4.1
4.1
1.0
IQR
1.6
1.6
1.0
SD
1.2
1.2
1.0
Table 4: summary statistics for daily summer wind speeds between Rennes and Nantes. The ratio
between the summary statistics is also shown. Q1, Q2 and Q3 are the first, second and third
quartiles; IQR is the interquartile range; SD is the standard deviation.