Clairemorris, Ireland Wind Speed data (1970.7 - 1973.7)
As part of the Future Learn Environmental Modeling class we are given some data from Clairemorris Ireland. Clairemorris is located in the west of Ireland about 30 miles north of Galway. The wind speed data (Figure 1) reveals some long period (roughly annual) oscillations in speed along with seasonal changes in the wind speed variation.
Figure 1: Wind speed measurements from 1970.7 to 1973.7. Speed is in knots.
The amplitude spectrum of wind speed is characterized by a general decay of amplitudes with frequency(Figure 2). Low frequency (long period) amplitudes are greater than the higher frequency (short period) variations.
Figure 2: Amplitude spectrum of wind speed observations at Clairemorris.
A frequency of 0.1 corresponds to a period of 10 days and 0.5 to 2 days.
A closeup view of the spectrum from 0 to 0.1 cycles/day (Figure 3) reveals that the highest amplitude components of the wind speed variation occur with annual and semiannual period. There are some additional relatively high amplitude peaks in the data around 26 and 14 day periods. A low pass filter is designed to extract the annual, semi annual variations and longer period variations in the data. A cutoff frequency of 0.01 cycles/day (100 day periods) is used.
Figure 3: Closeup view of wind speed spectrum out to 0.1cycles/day.
The low pass filtered output provides a more seasonal view of the average fluctuations through the period of observation. The scatter in observations about the long period response highlights changes in the standard deviation through time. The plot reveals peak winds in the fall-early winter of 1970 and 1973. There is also a period of high winds mid year 1972. The period of observations is not long enough to reveal consistent annual wind patterns.
Figure 4: The low pass filtered output (red) shows the longer period oscillations
extracted by low pass filtering.
The
Figure 5: Change points identified in the wind speed differences (bottom) are
projected onto the input data (top)
Figure 6: The derivative or difference is easily calculate in the frequency domain
through multiplication of the spectrum by i x angular frequency.
Figure 7: Wind speed standard deviations.
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