Homework # 5 Solutions

 

1. (Yes or No) Are isolines and isopleths the same thing?

 

            Yes.  Isopleth is just a fancy way to say isoline.

 

2. Does the following station plot give you the dewpoint or the dewpoint depression?

 

The temperature for this upper-level plot is – 46 degrees Celsius.  Where the dewpoint would normally be in a surface plot, there is a 12.  We know that the dewpoint temperature can never be greater than the actual temperature.  Therefore we know that this plot is showing us the dew point depression.

 

3. What is this station's dewpoint?

 

Now that we know we have the dewpoint depression, the dewpoint can be calculated as follows. 

 

Dewpoint = Temperature – Dewpoint Depression = - 46 – 12 = - 58 degrees Celsius.

 

4. If this station plot is taken from a 250 mb chart, what is the geopotential height at that level (in meters)?

 

If this were taken from a 250 mb chart, we would have to take the height given (069) and decode it by multiplying the value by ten and then adding 10,000.  This would give the geopotential height in meters.

 

Height (m) = 069 *10 = 690 + 10,000 = 10,690 m

 

Part 2--Use the 500mb map provided to answer the following:
Omaha, Nebraska (OAX)

 

 

Temperature:  

This is in the upper left part of the plot.  – 17 degrees Celsius

Dewpoint Depression: 

This is the lower left part of the plot and is 21.  (This is not the dewpoint!)

Dewpoint: 

This is calculated by subtracting the Dewpoint Depression from the Temperature

- 17 – 21 = - 38 degrees Celsius

Wind Speed:  

There is one triangle flag (50 knts), and 3 long flags (3*10 knts = 30 knts).  Therefore, the total wind speed is found by adding.

                        50knts + 3 * (10knts) = 80 knots

Wind Speed (in miles per hour): (Remember that 1.15 mph = 1 knt)

            80knts * 1.15 (mph/knt) = 92 miles per hour

Wind Direction in Degrees:

Apparently, I was in an evil mood the day I made this.  It is very difficult to judge degrees from a station plot.  As long as you said something close to 270 degrees, I gave you credit.

Wind Direction (Cardinal – N,S,E,W):

This is far simpler.  The wind is almost due West (W).  However, I did accept a little variability with this as well.

Geopotential Height:

This is given by the 563 in the upper right part of the plot.  This needs to be decoded though.  563 is not the correct answer.  The map I gave you was at 500mb.  Therefore, to decode the height, you must multiply what is given at the station by 10.  Therefore:

                        563 * 10 = 5630 m

Geopotential Height (in feet): (There are 3.28 feet in one meter)

            This is just a straightforward plug-and-chug conversion using the answer you found above.

                        (5630 m) * (3.28 ft/m) = 18,466 feet

Pressure:

This question takes a moment of thought.  You were told that you were given a map on a constant 500 millibar pressure surface.  Therefore, no matter where you go on the map, you will be at 500 millibars.  That is why the geopotential height is given.  It tells you how high the 500 millibar pressure surface is at any given station.  Therefore, the pressure at Omaha, Nebraska is 500 millibars.

 

Key West, Florida (EYW)

 

Temperature:

            This is given in the upper left part of the station plot and is – 7 degrees Celsius.

Dewpoint:

The value given in the lower left is not the dewpoint.  It is the dewpoint depression because it is warmer than the actual temperature.  Therefore, the dewpoint must be calculated.

-         7 – 2 = - 9 degrees Celsius

Geopotential Height:

            This is given by the value to the upper right and must be decoded at 500 mb. 

                        591 * 10 = 5910 meters

Geopotential Height (in kilometers): (1 km = 1000 m)

            The conversion is to just divide the value we found above by 1000.

                        (5910 m) * ( km / 1000 m) = 5.91 kilometers

 

5. If we accept that this is a typical 500mb map, what generally happens to temperatures as you move poleward at 500mb?

 

            Let’s look at a few temperatures starting in the south and going north.

 

DRT (Texas) =             - 7 degrees Celsius

AMA (Texas) =           - 10 degrees Celsius

DDC (Kansas) =          - 13 degrees Celsius

LBF (Nebraska) =       - 17 degrees Celsius

BIS (North Dakota) = - 31 degrees Celsius

 

This pattern shows that the temperature at 500 millibars decreases as you move north.

 

6. What happens to geopotential heights as you move poleward?

 

            I will do the same comparison.

 

            DRT =             5860 meters

            AMA =            5810 meters

            DDC =             5760 meters

            LBF =              5650 meters

            BIS =               5470 meters

 

            Again, this pattern shows that the geopotential heights at 500 millibars decrease as you move poleward.