Tidal current sensitivity =========================================== * The Salish Sea MEOPAR model outputs daily averages and hourly averages of tracers and velocities at every grid point. It also outputs quarter-hourly results at the Ocean Networks Canada VENUS Central and East nodes. The image below indicates where the Central and East nodes are located. .. _VENUSlocation: .. figure:: nodeloc.png * We wonder if it is beneficial to compile the quarter-hourly data for the velocities and whether or not it would produce a more accurate tidal ellipse. * The quarter-hourly output has started on May 9th 2015, where as the hourly output has been produced with the current tidal configuration since November 26th 2014. * The separation of harmonic tidal constituents is important when we want to look at a single constituent's effect on the current. This is accomplished with a long time series. Therefore, we want to see the effects of the length of a time series on the tidal ellipses. * The figure below is a comparison of the depth profile of tidal ellipses for one month of quarter-hourly output, one month of hourly output and 6 months hourly output. .. _FrequencySensitivity-image: .. figure:: freqsens.png * The table below is populated with the values that were used to create the figure above. Table 1: Sensitivity to Frequency and Length Comparison ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +---------+------------+------------+---------------+------------+------------+---------------+------------+------------+---------------+ | Central | Quarter-Hourly | Hourly | Hourly (6months) | | | | | | +=========+============+============+===============+============+============+===============+============+============+===============+ | Depth | Major-Axis | Minor-Axis | Inclination | Major-Axis | Minor-Axis | Inclination | Major-Axis | Minor-Axis | Inclination | | (m) | (m/s) | (m/s) | (deg. ccw E) | (m/s) | (m/s) | (deg. ccw E) | (m/s) | (m/s) | (deg. ccw E) | +---------+------------+------------+---------------+------------+------------+---------------+------------+------------+---------------+ | 0.5 | 0.29 | -0.13 | 129 | 0.29 | -0.13 | 129 | 0.20 | -0.08 | 135 | +---------+------------+------------+---------------+------------+------------+---------------+------------+------------+---------------+ | 2.5 | 0.26 | -0.12 | 129 | 0.26 | -0.12 | 129 | 0.19 | -0.07 | 135 | +---------+------------+------------+---------------+------------+------------+---------------+------------+------------+---------------+ | 4.5 | 0.22 | -0.10 | 129 | 0.22 | -0.09 | 129 | 0.18 | -0.06 | 135 | +---------+------------+------------+---------------+------------+------------+---------------+------------+------------+---------------+ | 6.5 | 0.20 | -0.09 | 130 | 0.20 | -0.09 | 130 | 0.17 | -0.06 | 136 | +---------+------------+------------+---------------+------------+------------+---------------+------------+------------+---------------+ | 8.5 | 0.20 | -0.08 | 131 | 0.19 | -0.08 | 131 | 0.17 | -0.06 | 136 | +---------+------------+------------+---------------+------------+------------+---------------+------------+------------+---------------+ | 10.5 | 0.19 | -0.08 | 131 | 0.19 | -0.08 | 131 | 0.17 | -0.05 | 136 | +---------+------------+------------+---------------+------------+------------+---------------+------------+------------+---------------+ | 12.5 | 0.19 | -0.07 | 132 | 0.19 | -0.07 | 132 | 0.17 | -0.05 | 136 | +---------+------------+------------+---------------+------------+------------+---------------+------------+------------+---------------+ | 14.6 | 0.18 | -0.06 | 132 | 0.18 | -0.06 | 132 | 0.17 | -0.04 | 136 | +---------+------------+------------+---------------+------------+------------+---------------+------------+------------+---------------+ | 16.8 | 0.17 | -0.05 | 131 | 0.17 | -0.05 | 131 | 0.16 | -0.04 | 136 | +---------+------------+------------+---------------+------------+------------+---------------+------------+------------+---------------+ | 19.5 | 0.16 | -0.04 | 129 | 0.16 | -0.04 | 129 | 0.16 | -0.03 | 135 | +---------+------------+------------+---------------+------------+------------+---------------+------------+------------+---------------+ | 24.1 | 0.15 | -0.02 | 125 | 0.15 | -0.02 | 125 | 0.16 | -0.02 | 132 | +---------+------------+------------+---------------+------------+------------+---------------+------------+------------+---------------+ | 34.7 | 0.14 | -0.00 | 119 | 0.13 | -0.00 | 119 | 0.15 | -0.01 | 127 | +---------+------------+------------+---------------+------------+------------+---------------+------------+------------+---------------+ | 58.5 | 0.12 | 0.02 | 116 | 0.12 | 0.02 | 116 | 0.15 | -0.00 | 124 | +---------+------------+------------+---------------+------------+------------+---------------+------------+------------+---------------+ | 98.1 | 0.13 | 0.03 | 134 | 0.13 | 0.03 | 134 | 0.15 | 0.02 | 130 | +---------+------------+------------+---------------+------------+------------+---------------+------------+------------+---------------+ | 147.1 | 0.18 | 0.00 | 144 | 0.18 | 0.00 | 144 | 0.17 | 0.01 | 140 | +---------+------------+------------+---------------+------------+------------+---------------+------------+------------+---------------+ | 199.6 | 0.19 | 0.00 | 137 | 0.19 | 0.00 | 137 | 0.18 | 0.01 | 133 | +---------+------------+------------+---------------+------------+------------+---------------+------------+------------+---------------+ | 253.1 | 0.22 | -0.00 | 120 | 0.22 | -0.00 | 120 | 0.20 | 0.01 | 123 | +---------+------------+------------+---------------+------------+------------+---------------+------------+------------+---------------+ | 306.8 | 0.15 | 0.05 | 109 | 0.15 | 0.05 | 109 | 0.14 | 0.06 | 110 | +---------+------------+------------+---------------+------------+------------+---------------+------------+------------+---------------+ Frequency ~~~~~~~~~~ * One month of quarter-hourly values makes no significant difference on the tidal ellipse parameters at the ONC VENUS Central node. The changes are sparse and minimal. * We will need to wait until we have a longer quarter-hourly data set to see if it is beneficial for tidal ellipses, or try other more sensitive locations. Length ~~~~~~~~~ * The 6 months time series has two significant differences that lead us to believe that these ellipses are a better representation of the currents: * The smaller surface currents indicates that it averages out some of the surface currents that are due to winds or Fraser River outflow. * The smoother variations throughout the water column. It is not logical for the flow to fluctuate every couple of meters throughout the water column. * A longer time series enables us to separate and resolve the individual harmonic constituents so that we can be certain that we are only looking at the M2 tidal constituent. * We observe the benefits of a longer time series at the ONC VENUS East node as well. .. _FrequencySensitivityE: .. figure:: freqsenseast.png Seasons ~~~~~~~~~~~ Table 2: The effect of seasonality on tidal ellipse parameters ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +---------+------------+-----------+--------------+-------------+-----------+--------------+ | East | Winter (Nov 26, 2014 - Feb 26, 2015) | Spring (Feb 27, 2015 - May 27, 2015) | | | | | +=========+============+===========+==============+=============+===========+==============+ | Depth | Major-Axis | Minor-Axis| Inclination | Major-Axis | Minor-Axis| Inclination | | (m) | (m/s) | (m/s) | (deg. ccw E) | (m/s) | (m/s) | (deg. ccw E) | +---------+------------+-----------+--------------+-------------+-----------+--------------+ | 0.5 | 0.38 | -0.14 | 127 | 0.40 | -0.20 | 128 | +---------+------------+-----------+--------------+-------------+-----------+--------------+ | 2.5 | 0.33 | -0.11 | 127 | 0.35 | -0.16 | 128 | +---------+------------+-----------+--------------+-------------+-----------+--------------+ | 4.5 | 0.29 | -0.06 | 125 | 0.30 | -0.09 | 126 | +---------+------------+-----------+--------------+-------------+-----------+--------------+ | 6.5 | 0.27 | -0.04 | 122 | 0.26 | -0.04 | 124 | +---------+------------+-----------+--------------+-------------+-----------+--------------+ | 8.5 | 0.27 | -0.03 | 118 | 0.24 | -0.01 | 122 | +---------+------------+-----------+--------------+-------------+-----------+--------------+ | 10.5 | 0.27 | -0.03 | 115 | 0.24 | 0.01 | 119 | +---------+------------+-----------+--------------+-------------+-----------+--------------+ | 12.5 | 0.28 | -0.04 | 115 | 0.24 | 0.01 | 117 | +---------+------------+-----------+--------------+-------------+-----------+--------------+ | 14.6 | 0.29 | -0.04 | 116 | 0.25 | 0.00 | 116 | +---------+------------+-----------+--------------+-------------+-----------+--------------+ | 16.8 | 0.30 | -0.05 | 117 | 0.26 | -0.01 | 117 | +---------+------------+-----------+--------------+-------------+-----------+--------------+ | 19.5 | 0.31 | -0.05 | 119 | 0.27 | -0.02 | 119 | +---------+------------+-----------+--------------+-------------+-----------+--------------+ | 24.1 | 0.32 | -0.06 | 123 | 0.29 | -0.03 | 122 | +---------+------------+-----------+--------------+-------------+-----------+--------------+ | 34.7 | 0.31 | -0.05 | 127 | 0.29 | -0.03 | 127 | +---------+------------+-----------+--------------+-------------+-----------+--------------+ | 58.5 | 0.31 | -0.03 | 136 | 0.28 | -0.02 | 134 | +---------+------------+-----------+--------------+-------------+-----------+--------------+ | 98.1 | 0.35 | -0.05 | 143 | 0.36 | -0.07 | 142 | +---------+------------+-----------+--------------+-------------+-----------+--------------+ | 147.1 | 0.25 | 0.09 | 124 | 0.25 | 0.08 | 125 | +---------+------------+-----------+--------------+-------------+-----------+--------------+ * Larger, more circular currents at the surface in the spring * Narrower and smaller currents at mid-depths in the spring * The deep bottom currents are almost identical. .. _SeasonalityBoth: .. figure:: seasonal.png * The Central node has a similar but muted difference between the seasons. * The bottom ~150m are mostly the same throughout winter and spring. We expect this because there isn't much movement there. * The semi-major and semi-minor axis are larger throughout the upper part of the water column in the spring.