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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.

  1. Make a sensible coordinate rotation for the vector time series. Explain your choice, preferably in terms of the statistics of the flow field.
  2. Using least-squares fits, find the amplitudes of the M2 and K1 tides for both u and v.
  3. 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

1thr1995 daysTime (hourly)
2uhrcm/sEastward current
3vhrcm/sNorthward current

Smoothed data file: sf_23m_hw.dat

(tides and other higher frequency motions removed)

1thw1995 daystime (4 times per day)
2txhwdyne/cm2Eastward wind stress
3tyhwdyne/cm2Northward wind stress
4uhwcm/sEastward current
5vhwcm/sNorthward current
6zhwcmBarometrically adjusted Boston sea level