Exercise and Data
A.7. Data Analysis: Tides and Winds
The data files below contain hourly data (sf_23m_hr_hw.dat) and low-pass filtered data (tides removed: sf_23m_hw.dat). The current meter data are for the period 1998–1999 at the Georges Bank “Southern Flank” location on map A.1. Wind stress (txhw, tyhw) is from the same location and is in dyne/cm2. Sea level (zhw) is from Boston and is in cm. (Boston is just off the map to the west.) Currents (uhw, vhw, uuhw, vvhw) are in cm/s. All the vectors are in (east, north) coordinates. Time (thr, thw) is in 1995 days.
- Make a sensible coordinate rotation for the vector time series. Explain your choice, preferably in terms of the statistics of the flow field.
- Using least-squares fits, find the amplitudes of the M2 and K1 tides for both u and v.
- Using correlations (or some other statistical tool) and the low-pass-filtered data, explore the relations between currents, winds, and sea level. Explain what you find in physical terms.
The data necessary for this exercise are available in the zip files to be downloaded here. Each zip file includes an ascii flat file as follows:
Hourly data file: sf_23m_hr_hw.dat
| Column | Variable | Units | Description |
|---|---|---|---|
| 1 | thr | 1995 days | Time (hourly) |
| 2 | uhr | cm/s | Eastward current |
| 3 | vhr | cm/s | Northward current |
Smoothed data file: sf_23m_hw.dat
(tides and other higher frequency motions removed)
| Column | Variable | Units | Description |
|---|---|---|---|
| 1 | thw | 1995 days | time (4 times per day) |
| 2 | txhw | dyne/cm2 | Eastward wind stress |
| 3 | tyhw | dyne/cm2 | Northward wind stress |
| 4 | uhw | cm/s | Eastward current |
| 5 | vhw | cm/s | Northward current |
| 6 | zhw | cm | Barometrically adjusted Boston sea level |