ATM OCN (Meteorology) 100

Answers for Homework 3

Summer 1998

Date Due: Tuesday, 22 July 1998

The total maximum points were  100.  Point distribution for each question is noted below. 

PART 1. ATMOSPHERIC OPTICS

a. For the following atmospheric optical phenomena, identify:

1. Mirage (Superior or inferior):

 

PHYSICAL CAUSE(S): Refraction of light by density differences in the atmosphere  THE AGENT(S): Lower atmosphere with a strong vertical temperature -- and ultimately vertical density gradient.  WHERE (WHEN) FOUND: Large vertical temperature and density gradients, such as the hot pavement and cool air immediately above, or the cold lake and warm overlying air mass.

 

2. Halo (22°):

3. Corona:

4. Rainbow (Primary):

 

PHYSICAL CAUSE(S): Refraction and dispersion of light entering the raindrop, the internal reflection of this light from the back surface of the drop and the refraction of the reflected light.  THE AGENT(S): Falling liquid raindrops.  WHERE (WHEN) FOUND: Look away from the low sun (due to geometry considerations, the sun should be no higher than 42 above the horizon) and toward a rain shaft of falling raindrops.

 

 

Rayleigh scatter occurs when the incoming radiation (typically polychromatic sunlight) is scattered by gas molecules or other particles in the atmosphere that have a diameter typically less than one tenth the size of the wavelength of the incident radiation - or on the order of 0.05 micrometers. This type of scattering is wavelength dependent, with the short or blue and violet wavelengths preferentially scattered more than the longer wavelength red light.  Mie scatter occurs when the incoming radiation is scattered by large aerosols or cloud droplets that have wavelengths at least as large as the wavelength of the incoming radiation. This type of radiation is independent of wavelength, meaning that the polychromatic white light is scattered and still appears as a milky white light.

 

Cite an example of each of these two scattering processes.

 

Blue skies - an example of Rayleigh scatter  White clouds (at least when viewed from the side or above) - an example of Mie scatter.  Note that red sunsets in relatively clean air would represent Rayleigh scatter, but if sufficient aerosol loading of the atmosphere were present, vivid red sunsets would indicate additional Mie scatter.

 

PART 2. ATMOSPHERIC MOTIONS

[30 pts at 2 pts each]

A. VERTICAL PRESSURE GRADIENT FORCE

 

DIRECTION:  Vertical and upward (from high pressure near the surface toward low pressure aloft, or opposite of down).  MAGNITUDE depends upon:  The preferable answer is that magnitude of vertical pressure gradient force depends upon the vertical spacing of the pressure surfaces, which depend upon the density or average temperature of the layer (see discussion below for #3).  Altitude is acceptable.

 

B. HORIZONTAL PRESSURE GRADIENT FORCE

 

DIRECTION:  Horizontal and upward pointed from high pressure toward low pressure (as seen on a weather chart).  MAGNITUDE depends upon:  Packing of the isobars on a horizontal, constant altitude weather chart (which describe horizontal pressure gradient or difference in pressure over a given horizontal distance).

 

C. GRAVITATIONAL FORCE or "GRAVITY"

 

DIRECTION:  Vertical and downward (toward the center of the earth).  MAGNITUDE depends upon:  The masses of the earth and the object and upon the separation between their centers (according to I. Newton)  or equivalently, upon the altitude above the earth's surface.

 

D. CORIOLIS EFFECT or "FORCE" (Horizontal Component)

 

DIRECTION:  To the right of the direction of the intended motion in the Northern Hemisphere and to the left in the Southern Hemisphere.  MAGNITUDE depends upon:  a.  Speed of the object  b.  Latitude  [Two (2) separate variables]  NOTE: The Coriolis effect also depends upon the rotation rate of the earth (an alternate answer).

 

E. FRICTIONAL FORCE (Horizontal Component)

 

DIRECTION:  To opposite of the motion.  MAGNITUDE depends upon:  a.  Wind speed  b.  Type of surface (surface roughness) [Two (2) separate variables]  NOTE: Other acceptable answers include:              altitude above the surface or              turbulence due to heating.

 

F. CENTRIPETAL FORCE

 

DIRECTION:  Inward toward the center of rotation.  MAGNITUDE depends upon  a.  Speed of object  b. Radius of curvature  [Two (2) separate variables]

 

2. What is the primary physical significance of the hydrostatic balance relationship?

[4 pts]
 

3. From this hydrostatic balance relationship, how does the magnitude of the vertical pressure gradient in a warm air column compare with the vertical pressure gradient in a column of cold air?

[4 pts]
 

4. a) What forces are balanced in the geostrophic wind model?

[2 pts.]
 

[6 pts or 2 pts. each]
 

5. On the horizontal surface pressure map in the Northern Hemisphere (within the friction layer), locate the regions of high and low pressure, placing a large block H and L, respectively. Make a force diagram by neatly drawing thin arrows to signify the direction and relative magnitudes of the horizontal pressure gradient force (FHPG), the Coriolis force (FCOR), the friction force (FFRC). Label each of these forces. Neatly draw a thick, double bladed arrow to represent the resultant wind (VRES); label this wind vector:

[12 pts]

URL Address: aos100/homework/98hmk03a.htm