Chesapeake Bay Virtual Environment
The Chesapeake (means Great Shellfish Bay from the Algonquin Indians) Bay is the largest estuary in the United States and serves as nursery grounds or spawning areas for many commercially important species [LIKE: Blue crab and oysters]. It is one of the most productive and commercially important but a threatened ecosystem. There is an abundant growth of pelagic [definition?], benthic [definition?] and vegetative communities, all of which are affected by seasonal and annual variations in the circulation, environmental forcing and inputs of nutrients from the local watershed. Also, the urbanisation of the surrounding watershed is harmfully affecting the Chesapeake Bay ecosystem.
The Chesapeake Bay Vitual Environment is the solution for a need for an application which could simulate such governing factors and their effects on the ecosystems, and provide the users to examine the output in a clear and concise manner [this sentence does not make sense]. The Chesapeake Bay data set is generated using the Princeton Ocean Model, a three dimensional hydrodynamic circulation model. The model solves the time-dependent, nonlinear equations of motion in a free surface formulation as well as the governing equations for temperature and salinity. The data is a fifteen day simulation of the effects of winds, tides and river runoff on the general circulation features of the Chesapeake Bay and on the transport of passive larval fish in to the Bay from the adjacent continental shelf. The data describes the temporarily varying 3D fields such as salinity, temperature, density, velocity etc. from the circulation model. This data set, which consists of these numerically generated outputs, and other observations is then loaded up in the CAVE6D application which provides a multiuser, collaborative, interactive 3D visualization environment for the Chesapeake Bay.
1. Click on the left wand button to bring up the menu. Then click on the 'Graphical Objects' Panel, to bring up the graphical objects panel.
2. There would be lots of
different parameters in the graphical objects panel. Click on the
'topography', the ''contour salinity', 'surface_Horz_Vec'
and 'tracers_iso' buttons. [Did we ever clarify
what these parameters mean?]
Topography - The terrain of the data.
- is the water tide velocity at the surface of the water.
On making this movable it can be moved up/down in the depths
of water. The more the plane of this parameter is closer to the
surface, the more predorminant are the effects of the wind blowing
on the surface. This parameter is shown by black coloured vectors.
- it is the water tide at the bottom of the water body, in
and the channels of the water. These are light blue in color.
- This defines the contours of the salinity levels
at various points of the
surface. They have numbers written on them, and thus one counter
( all the points on the surface of water connected by this line ) will
have the same salinity level. These are red in color.
- These show the
salinity levels based on color. Red is the upper level of salinity,
and blue the lower. As Larry mentioned, though this provides a good visual cue
to the variations in the salinity levels over time in the simulation, it sometimes
exaggerates the differences. There is a very slight difference in the salinity
levels between red and blue, but looking at the color it really looks to be a lot.
- Pink in color, these give an additional cue to the velocities
of the tides. This is a plane
in the North-South axis and the depth, and it can be moved in an east-west direction.
Vert_East_west - Red in color, they also provide another plane to visualize the velocities of the tide.
This plane is defined in the east-west axis and depth, and can be moved in the
3. Click on the global/local buttons corresponding to the 'topography', 'surface_horz_Vec', and 'tracers_Iso' buttons, which makes them seen globally. Close the panel, and start the simulation (time) by clicking on the '' button.
4. Now whenever the other particapants join you, their initial set up is the same as yours, so they need not be told about the options they need to select. They can see 'atleast' the parameters you have opened and made global. and can add their view by putting on other parameters. Each one of them would also be synchronised together with time.
5. Now press the middle button and turn around the world to about 180 degrees, so that now you are looking at the Bay from the other side, facing south. This position lets you face the other collaborators when they join in the session.
6. Now move closer to the mouth of the bay, and ask the others to come closer to it too, and face you, so they while you are standing north of the bay facing south and they are standing south of the mouth facing the north.
7. As certain objects are global, you can show them the circulation at the mouth. The flow pattern there consists of buoyant water outflowing along the southern reaches of the Bay entrance and over the shoals, whereas inflow of dense, saline shelf water is generally restricted to the bathymetric depresssions [what is this?] or channels, in the opposite direction. It is shown by the difference of directions of vectors with the depth. This can be shown at an instance in the simulation by stopping the time [Can you really show me this?]
8. Pointing at the salinity blob at the entrance of the bay, tell the users that - The salinity field ( more red - more saline, more bluish lesser saline ) is controlled primarily by fresh water runoff, changes in rainfall or drainage, evaporation, and wind direction and velocities. [So is there a way to observe these factors in relation to the blob of salinity?]
9. Wait till the simulation plays for 1/3 of the whole cycle. SInce the whole simulation is for 15 days, this would mean data for 5 days. At this point stop the time. Till this period in the simulation, environmental forcing was limited to river discharge and the resultant circulation and salinity fields are consistent to this outflow which is more than the inflow from the sea. Thus uptill now the bay water was quite saline ( red ).
10. The low salinity water discharged from the river sources has moved down the western side of the Bay and out of the Bay mouth to form a buoyant plume. The plume rotated anticyclonically (clockwise) as it exited the estuary due to the effect of the earths rotation. [Can we observe this rotation?] A coherent downcoast-flowing coastal current was visible south of the Bay mouth. Outflowing buoyant water was seen to be confined to the south side of the Bay mouth and a weak return subsurface flow of saline shelf water was evident on the northern side. [Have to look at the simulation and read this at the same time]
11. Start the time again, and stop it this time, when it has reached half of its cycle. At this time, approx 8 days of simulation strong seaward flow is evident, at maximum ebb stage.
[At this point it's quite clear that we/I need to look at the simulation closely and correlate it with this text below]
12. Saline shelf water enters the bay stilll in the nothern side of the bay mouth at max. flood stage, yet the outflow plume is still present south of the bay mouth. Flow strength decreased with depth due to bottom friction and lateral gradients were high in the areas between the channels and the shoals. Mixing effects are clearly seen by the temporarily varying color gradations in the salinity field.
13. At this stage turn the isosurfaces also to global, and start the time again. A region containing concentrations of fish larvae was established just offshore of the Bay mouth, represented by the isosurfaces. Wind from the southwest resulted in the advection of larval fish away from the Bay mouth to the north and east. At day 12 (3/4 of the simulation cycle), when the winds were reversed and blowing from the northeast (downwelling favorable), saline shelf water was advected into the Bay on the northern side of the Bay mouth. The distribution of simulated larval fish was then advected shoreward and larvae entered the Bay on the flood tide.
14. Towards the last 1/4
th of the cycle, winds have reversed to be blowing from the north, in the
process moving the larval fish
distribution into the tidally influenced region near the Bay mouth.
Note the strengthening coastal
current south of the Bay mouth, the resurgence of the outflow
plume and the variability in circulation
throughout the domain.
15.Once in the Bay proper, individual larvae may decrease their depth through self guided motion during slack water, sink to depths where tidal velocities are small to avoid flushing on the ebb tide, then rise again and subsequently move to more favorable nursery grounds farther north up the Bay on the subsequent flood phase.