Long-Term Oceanographic Observations in Massachusetts Bay, 1989-2006, Version 3, Principal Axes

U.S. Geological Survey Data Series 74, Version 3.0

Long-Term Oceanographic Observations in Massachusetts Bay, 1989-2006

Principal Axes

Principal axes for both the hour-averaged and low-pass-filtered currents were computed by year and month. Major and minor axes, orientation, and ellipticity were computed as

major axis = {[0.5 (UU + VV) + R] / n}^(1/2),
minor axis = {[0.5 (UU + VV) - R] / n}^(1/2)  ,
orientation = 90° - 0.5 tan^-1 [2 UV / (UU - VV)]  , and
ellipticity = 1 - (minor axis / major axis)  ,

where

UV = Sum(u*v) - n U V  ,
UU = Sum(u*u) - n U U  ,
VV= Sum(v*v) - n V V  ,
R = [ (0.5 (UU - VV) )² + (UV)² ]^(1/2) ,
U and V are the means of the east and north velocity components, respectively, and
and n is the number of points in the data series.

The orientation is measured clockwise from true north. 0 degress is true north, and 90 degrees is east.

Tables of ellipse parameters at LT-A and LT-B

Click on the links below for tables of ellipse parameters. Each pdf file has a page for each year of observation; use the arrow on the control panel to navigate through the pages. See the Mean Flow section for plots of the mean flow and ellipses. ~, about.

Thumbnail of table of ellipse parameters.

Thumbnail of table of principal axes.
Select from the tables below for full-size tables.

LT-A, Point Current Meter Observations


~5 m	Hour-averaged data	Low-pass-filtered data
~22 m	Hour-averaged data	Low-pass-filtered data
~31 m	Hour-averaged data	Low-pass-filtered data

LT-A, ADCP Observations


~5 m	Hour-averaged data	Low-pass-filtered data
~15 m	Hour-averaged data	Low-pass-filtered data
~22 m	Hour-averaged data	Low-pass-filtered data

LT-B, ADCP Observations


~5 m	Hour-averaged data	Low-pass-filtered data
~10 m	Hour-averaged data	Low-pass-filtered data
~17 m	Hour-averaged data	Low-pass filtered data

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