CHIMP tutorial outline
This is a short list of demos of phenomena that can be demonstrated with the CHIMP
prototype. These demos could be used to develop a classroom module at the high-school
or undergraduate level. There are notes to CHIMP developers interspersed. The settings
listed are not comprehensive; settings that aren’t listed tend to not be too important to the
demo in question. I have included some notes for non-oceanographers. For most purposes
it is best to have the update rate set as fast as possible.
Jay Austin
10/2005
Estuarine Salinity Structure
Settings:
 Susquehanna: high flow
 wind: off
This demonstrates the canonical state of estuarine circulation, with a strong source of
fresh water at the head of the estuary. The plan view shows low salinity at the head of the
estuary and high salinity at the mouth, where oceanic water is being pulled into the
estuary. The cross-section shows saltier water at the bottom, and fresher water at the
surface, due to the difference in density due to salt content. Water at the bottom of the
estuary tends to be flowing upstream (easier to see in the 24h update mode). The further
up the estuary the salty water flows the more surface fresh water is mixes with. Could we
get some arrows put on the cross-section?
Dry Season
Settings:
 Susquehanna: off
 Wind: off
This demonstrates the up-estuary propagation of salt during the dry season. Typical
annual cycles of freshwater are such that the spring has the highest levels of runoff (from
snow melt) and fall is the lowest. It would be nice to include some climatological data in
the module.
Tides
Settings:
 Wind: off
 Update rate: 1-2h
Tides are due to the gravitational influence of the moon and sun. There are roughly two
“high tides” per day (actual period for M2 is 12.42h). These give rise to currents which
flood into the bay before high tide and ebb out of the estuary after high tide. Tides are
easily observable with the drifters, but also by looking carefully at the salinity field, or by
using the velocity arrows (this is still a bit messy). With the velocity arrows, you can
actually see the propagation of the tide up the estuary. The surface height display also
shows the propagation of the tides, as does the cross-section. It would be nice to be able
to generate and display a time series of a property from a location in the bay. Tidal
currents at the mouth of the bay are on the order of 1m/s (2mph). Tides are important for
determining the level of mixing in an estuary.
Influence of winds: currents
Settings:
 Wind: off; direction: N
 Update rate: 1-2h
Turn the display to the drifters, which are wiggling back and forth with the tides. Turn the
wind speed up (high) such that the wind is blowing strongly to the north. The drifters are
all displaced to the south, but eventually reach an equilibrium location around which they
wiggle with the tides. Note on the cross-section that the surface height is depressed when
the wind blows out of the N. Likewise, if the wind blows from the S, the drifters are
displaced to the N and the Bay fills with water. This is what causes flooding during a
storm.
Influence of winds: mixing
Settings:
 Wind: off
 Susquehanna: high
With the wind off, significant stratification (layering) builds up throughout most of the
bay, best seen in the cross-section. When the wind is turned up (high, direction is largely
unimportant) we see that the layers are washed away, and at any location the whole water
column takes on a salinity between the original surface and bottom salinities. The
stronger the wind, the quicker this mixing takes place. During the summer, we have very
few strong wind events, and the stratification in the central bay becomes quite strong.
This isolates the bottom layer away from the surface, so that it is not in contact with the
atmosphere. Combine this with bacterial decomposition of detritus, and the oxygen can
be depleted in the lower layer of water. This is known as hypoxia (low oxygen) or anoxia
(no oxygen) depending on how severe it is, and makes the bay uninhabitable for fish and
other animals. A severe storm can mix the water column and provide oxygen to the whole
bay.
Plume structure
Settings:
 Wind: off
 Susquehanna: high
When fresh water leaves the estuary, it tends to turn to the right and move along the coast
as a plume. Water off of Virginia Beach tends to be water that has recently left the Bay.
This phenomenon can also be demonstrated by turning off the Susquehanna for a while,
let the bay get salty, and then turn on the Potomac. The freshwater plume from the
Potomac also tends to turn south inside the bay. This is due to the rotation of the earth.
This also accounts for the fact that water on the east side of the bay tends to be somewhat
saltier than the west side.
Upwelling and downwelling
Settings:
 Wind: off
 Potomac plume developed
Once the Potomac plume is somewhat developed, blow the wind gently from the north.
The plume should tighten up against the shore to the S of the mouth of the Potomac. This
is due to Ekman transport in the surface layer, where surface waters tend to want to travel
to the right of the direction of the wind. In this case, surface waters in the central bay
move west, squishing the plume against the shore. If you blow the wind gently from the
S, the plume gets spread out into the bay as the surface waters move east.