Metr2413 Lab 10
Assigned: March 26, 2004
Due: April 2, 2004

Balance of Forces

Calculate each of the forces acting on a parcel of air at Norman, OK. The center of the low-pressure system is 60 miles north of Amarillo, TX. Amarillo is 260 miles west of Norman. Pressure below is in millibars. Assume all calculations are for the horizontal plane only. All equations and answers are per unit mass. Be sure and use MKS unit notation. Make sure your answers are all in scientific notation (2 decimal places). Wind shown at Norman is in knots.

Constants:

1.22kg/m^3 Density of dry air
35 N Latitude of Norman and Amarillo (approximately)
7.29 X 10^-5 s^-1 Coriolis Paramater (Omega)
9.8 m/s^-2 Gravitational constant
1000m Boundary layer thickness
2.2x10^-3 Drag coefficient for grassland prairies

Pressure Gradient Force

Gravitational Force

Coriolis Force

Centrifugal Force

Where R is the radius of curvature

Values for s:

Northern Hemisphere: flow around low (1), flow around high (-1)
Southern Hemisphere: flow around low (-1), flow around high (1)

Frictional Force

Where C is the drag coefficient and M is the magnitude of the wind speed, and z is the boundary layer thickness

Summary

Make sure your answers are all in scientific notation (2 decimal places)

Force (per unit mass)	X-Direction	Y-Direction
Pressure Gradient
Gravitational
Coriolis
Centrifugal
Frictional
Net

Questions:

1) Draw the balance of forces as they apply to this synoptic setup for Norman, OK. Include all applicable forces and the resulting wind vector. Draw the force vectors to scale using the power of the answer you calculated above.

2) Which forces (if any) are dominant in the horizontal field at the surface? Why or why not?

3) Which forces (if any) are small enough that they can usually be ignored at the surface? Why or why not?