# North Atlantic Ocean Basin Model

Parameter Values

## Description

The Ocean Basin Model encourages experiments with ocean surface circulation in a homogeneous, rectangular ocean basin, driven by surface winds, ocean bottom friction, horizontal pressure gradients and the Coriolis force. The rectangular image shown above represents the Atlantic Ocean above the equator.

The Ocean Basin Model is based on a model by Henry Stommel written about in "The Westward Intensification of Wind-Driven Ocean Currents from Transactions of the American Geophysical Union", Vol. 29, No. 2, 1948, pp 202-206. The model assumes a rectangular ocean basin.

The Stommel model is conceptually simple in comparison to present day models run on super computers. It is useful for the classroom as it allows users to investigate the processes that create strong ocean currents on the western boundary of ocean basins.

Investigations, located in the Teacher and Student Guides, will help students understand concepts of fluid dynamics and the behavior of fluids under varying conditions of:

• basin size (width and length)
• wind stress
• Earth shape and rotating state
• fluid friction

Students will learn about the behavior of streamline function, characteristics of vortices and laws determining fluid motion.

## Instructions

Use this model to study the effects on the ocean basin of various parameters.

### Controls

#### General

Ocean Size, Wind Stress, Basin Depth, Friction Force, Coriolis Force and Coriolis Force Variation with Latitude are all set to "Nominal" at start. Vary these above and below nominal to observe the effects of these parameters on the behavior of the model. The displayed image will update whenever adjustments are made to these settings.

#### Ocean Size

The ocean size parameter allows for experimentation with ocean size and understanding what effects this has in the context of the model.

#### Wind Stress

Wind stress is the frictional force exerted on the water surface by wind just above the surface. This force drives water around. The base value is 1 dyne/cm2.

#### Basin Depth

Basin depth represents the overall depth of the water in the model. Baseline depth is 200 meters.

#### Friction Force

The dissipative friction force is a viscous friction between the surface mixed layer and the deeper ocean layers or the shallow continental shelf. This is needed in the model to dampen the motion and to prevent the water from continuously accelerating.

#### Coriolis Force

Coriolis acceleration is felt by objects set in motion over the surface of a rotating sphere, like the earth. This is similar to walking from the center to the outer rim on a merry-go-round while it is in motion, you feel off-balance. On a rotating sphere, rotation speed at the equator is fastest and speed at the poles is slowest.

#### Coriolis Force Variation with Latitude

This variation in the Coriolis force as an object tries to move between pole and equator. At different latitudes it will experience a speed difference as it travels which will affect the path of travel.

#### Copy Image

This open a new window displaying the existing model image.

#### Parameter Values

These provide a readout of the current values for the different controlable parameters (to the right of the model display).

#### Image Style

The image style control allows one to select from a series of different model display types:

• Contour: this option will display a two dimensional image with color representing the different values for points along the length and width of the model. Warmer colors represent higher values and cooler colors represent lower values. Values for the contours are labeled along the boundaries between colors.
• Surface: a combination of the contuour and a three dimensional view of the data are displayed. In this case the height in the 3-D portion of the graph represents the values. Lower values correspond to the to lesser heights while higher values correspond to greater heights.
• E-W Plot: a 2-D display of 3 slices of data (for particular widths) with values running along the length of the basin.
• N-S Plot: similar display to the E-W Plot, except now the slices now run along the width of the basin from top to bottom (North - South)

#### Parameter

The parameter control allows one to change the type of data presented from a series of types:

• Streamlines: Streamlines of a fluid show the path that a small object with the same density as the fluid (water) would follow.
• Meridian Velocity (cm/s): This is the part (or component) of fluid velocity along the East-West direction. Flow with an eastward-moving component has a positive meridional velocity. Flow with a westward-moving component has a negative meridional velocity.
• Zonal Velocity (cm/s): Zonal Velocity (cm): This is the part (or component) of fluid velocity along the North-South direction. Flow with an northward-moving component has a positive zonal velocity. Flow with a southward-moving component has a negative zonal velocity.
• Water Level (cm): This represents the 'level' of water in the basin (equivalent to depth of the water that flows in the surface current). Like actual surface currents, the depth values used by the model are very shallow compared to the full depth of the ocean.
• Surface Current (cm/s): This is the speed of the surface current. Unlike velocity, it is independent of directions: East, West, North, South.