Data from CTD+F casts have now been processed. Casts were made from a small boat on dye release days. The CTD+F setup included a Seabird CTD and WET Labs single-channel fluorometer. Casts were generally made from near the surface to the bed.
Below is an example of mean dye and temperature profiles from 6 May, 2012.
Data are now available via the ftp site in a directory called CTD. See previous posts on how to access the ftp site. Data from each day of casts are in .mat files with filenames data_nr12_CTD_mmdd.mat, where mmdd represents the two digit month and two digit day. Each data file contains the following variables:
>> load data_nr12_CTD_0512.mat
Name Size Bytes Class Attributes
Dgrid 101×50 40400 double
Sgrid 101×50 40400 double
Tgrid 101×50 40400 double
date 1×8 16 char
tcast 50×1 400 double
xcast 50×1 400 double
ycast 50×1 400 double
zgrid 101×1 808 double
“Dgrid”, “Tgrid”, and “Sgrid” are the dye (ppb), temperature (deg C), and salinity (psu) vertical profiles for each day of casts, where each column is an individual cast. Data are interpolated onto “zgrid”, which spans the water column from the surface (z = 0 m) to the depth of the deepest cast with 0.1 m vertical resolution. Data below the deepest point of a given cast are filled with NaNs. For the example variables above, if
>> [m,n] = size(Dgrid)
then m = 101 is the number of vertical grid points (z = 0 to -10 m), and n = 50 is the number of casts.
The variables “tcast”, “xcast”, and “ycast” give the times and locations of each cast, where, e.g., tcast(k) corresponds to Dgrid(:,k). Time units for “tcast” are in seconds (EDT) of the given day (which is saved in each .mat file as the variable “date”). The variables “xcast” and “ycast” are the familiar RIVET coordinates x and y, respectively, both in meters.
All the Wirewalker data has now been processed. Below are plots for WW1 deployment 2 and WW2 deployments 1 & 2. Note in the plots below that the dark cross-hatched areas are times when the WW data is bad. See the previous post for the map of the WW locations.
We now have our first look at the wirewalker (WW) mooring observations. The wirewalkers use the up and down motion of the sea-surface to move a CTD+fluorometer profiling package up and down the water column. As such, good vertical and tempral resolution of the watercolumn can be acheived with a single sensor. During RIVET-I, we deployed 2 WW in appoximately 8 m depth. WW1 was deployed just offshore of the “new” channel at approximate locations (x,y) = (1000,0) m. See the legend of the figure below summarizing instrument locations.
Each WW as deployed twice for ~11 days. Below is the results of the 1st deployment of WW1. A semi-diurnal temperature signal is evident over the 11 days as inlet water comes out the New River Inlet on ebb tide. Typically a salinity signal is associated as well.
Dye was released on May 6, 7, 8th (note this is equivalent to time 5, 6, 7) on the plot above as the xaxis is days from 0000 1 May. Note also data collection had begun on Apr 30th (day = -1). For each of the dye releases there is a clear dye signal at WW!. For the 1st two releases, the dye passes the WW relatively quickly and appears to be well mixed consistent with the temperature and salinity. However, on the 3rd release, the resulting dye signal is more complex. The dye first passes at t=7.7, and superficially does not appear to be well mixed. However, approximately 12 hours later, dye is again present at WW1. This indicates that dye had been recirculated back into the inlet on the flood tide and ejected again on the subsequent ebb. There is another weaker dye signal on the next semi-diurnal cycle as well.
Animation of “dye” concentration from New River Inlet on May 11th 2012. Dye concentration is derived by differencing measured light at two wavelengths and is indicated by the black color. Dye is released in a single bomb up the inlet ~500 m from the junction with the inter-coastal waterwaterway (ICW). It propagates downstreamon the ebb tide. Unlike previous releases, the dye spreads across the entire channel and exits both the old and new channels. However, the tide switches to flood and sucks back the dye that was leaving the old channel.
For other information on this dye relase day go here and here.
The .mov file (which is much more crisp than the youtube video) can be downloaded here.
We’ve also gotten the May 8th dye movie put together. Check out the youtube video or the link to the .mov file below.
The dye qualitatively behaves similar to on May 7th (see previous post). However, the dye does not get advected as far downcoast. However, there are a number of coherent structures clearly visible in the dye field. The most dramatic are perhaps the eddies spinning off of the jet escaping out the small channel to the SW of the inlet. See frame at time 1711 at x=250m and y=-800m (approx).
REMUS operations starting ~1.5 hours before max ebb were conducted during the 5/19 and 5/20 dye releases. Conditions were rough during the 5/19 mission outside of the inlet and no dye was visible during REMUS ops. However comparison plots of river Colored Dissolved Organic Matter (CDOM) versus Rhodamine concentrations show that the dye was present, just at low concentrations (~0.5 ppb). The mission was designed to track the advecting river plume from the inlet mouth to the river plume extent observed from earlier missions (~ 1.2 km offshore). Mission time was ~3.5 hrs.
The same mission was performed during the dye release on 5/20/2012. Significantly higher concentrations of dye (6 – 10 ppb) were advected outside of the inlet and were observed in the evolving river plume.
The dye release on Sat 19 May was interesting. 30 gallons of dye were released for 5 hours starting at 0430 (AM!) in approximately 10 m water depth a few meters (3-4 m) above the bed between buoy #6 and #8 in the channel Dye went up the inlet towards the ICW on the flood. Dye that had reached the surface could also be observed to enter the marsh at the start of the S-turn. By the start of the ebb, the marsh was really pink with Rhodamine concentrations of approximately 10 ppb. As sampling occured on the ebb tide, concentrations of the order of 1-2 ppb were observed coming out of the inlet. This had lead some specularion that the marsh stored a signficant fraction of the dye. But that is not the case.
First the dye was released in the lower water column in 10 m depth. Only the top 0.5 m at most fo the water column could make it into the marsh. Most of the dye had to make it’s way up the inlet. Second, dye was input at 5 mL/sec at a concentration of 2e+8 ppb. 1 mL = 1 cm^3 = 1e-6 m^3. So the pumped flux of dye into the inlet is about Q=1000 ppb m^3/s.
To balance this coming out of the inlet, one needs a water velocity V, a depth h, and channel width L, and a concentration D – Assuming a rectangular channel and a uniform velocity and dye concentration. Then the flux is Q = L*h*V*D.
Taking representative values for V=1 m/s, h= 5 m, L=200 m this implies that to balance the input flux one needs….. drum roll…… D = 1 ppb. Which is the order of magnitude that we were measuring coming down the inlet during the duration of the flood.
It will be interesting to see what a more detailed dye mass/volume balance will show.
Here is another aerial image to complement those posted earlier by Falk. This photograph shows some very cool eddies, and it is also a great illustration of how thin the surface layer of dye was to the SW of inlet. The dye-free streak on the right side of the photograph was left in the path of our dye sampling WaveRunner.
Today (Sunday May 13th) is instrument turnaround day and general catching up. We also have a report on the dye-bomb release we did on May 11th. In short, it was an amazing dye of observing the ocean. The RIVET community had many assets in the water measuring dye, currents, temperature, and salinity. Here we’ll focus on a few observations to give a quick overview of what happenned during the day.
In contrast to the previous releases where we continuously pumped dye for 1.5-2.5 hours, this time we poured 20 gallons of Rhodamine WT at ~0800 into the inlet 300 m down from the junction with the Inter-coastal waterway. Below you can see the dye getting poured in.
As the tide was ebbing rapidly the dye gets stretched and stirred rapidly. It is quickly well mixed (confirmed with CTD+F) casts and makes its way down the inlet. As it approaches the inlet mouth, the dye has spread all the way across the inlet and (in contrast to the point releases) the dye moves out both “old” and “new” channels.
The conditions on May 11 were very benign. Very small waves and extremely light winds during the entire release. The dye then gets rapidly ejected offshore out of the two channels and the SW near-beach channel.
By shortly after 0900 dye is clear of most of the inlet. CTD+F casts offshore of the main or “new” channel reveal a surface concentrated (< 2 m) dye field of about 20 ppb with no dye at all below. This is associated with a strong halocline. This is in part due to the weak mixing that is induced due to the light winds and lack of waves and whitecapping. See the figure below.
The fresher water of the inlet simply slides on top of the saltier (and slighly colder) oceanic water. Thus forming a “lens” within which the dye is contained. The weak winds likely contribute to the maintenance of this strong water-mass gradient. These type of vertical structure conditions will be a very significant challenge for models to reproduce as a) they may not have enough vertical coverage and more importantly b) the model-induced mixing is often far too strong to maintain such a gradient.
The tide then starts to flood at ~1000, and begins to pull water back from “old channel”
Notice the wispy dye to the SW of the inlet. This is all very much surface concentrated. Often boats and jetskis driving in it left a trail of dye-free water behind. This was confirmed by the CTD casts, which show an even thinner surface layer of dye with lower max dye. Dye stratification is again is influenced largely by a strong halocine, but here there is also a stronger thermocline than in the previous set of casts
As the tide started to seriously flood, the dye patch was broken into two parts. 1) an offshore component that spread itself out from the main channel entrance to the SW and 2) a patch that got sucked back up the inlet. This mostly occured from dye in the “old” channel. As the dye approached the “S”-turn of the inlet, it converged strongly on the ever-present scum line, just as the drifters had (see previous post). See the photo below.
This sort of “front” will also be a challenge for models to reproduce as the lateral (horizontal) eddy viscosities that they have may preclude the formation of such convergence zones in these rapidly changing regions.
The dye release yesterday (May 8th) was very interesting. The dye release was initiated shortly after slack tide as the water started ebbing. 30 gallons of Rhodamine WT were released in 2:24 min. As usual the mounted instruments, the jetskis, NPS/RSMAS crew, REMUS, towed ET array, and the Partenavia were all measuring the dye plume. At first, as the tide was still not very low, the dye poured down the main channel and then oozed out over the southern shoal. See the aerial hyperspectral image below (taken at 1339 local time, from Luc Lenain and Nick Statom). Up the inlet near where the dye was released, the surface dye is very patchy because the dye is released about 3 m above the bed in ~9 m water depth. At times it seems like the surface dye patch has a periodic signature. The dye moves offshore of the south-western shoal in jets and squirts.
The nice thing about this image below is that it can be used to quantify Rhodamine dye concentration. As light is measured across a spectrum of wavelengths, information at absorption and emmision wavelengths of dye will be used to calibrate dye concentration against in situ sensors.
Below are some SLR camera images of the plume at similar stages. These are useful for providing context but are nowhere near as quantitative.