Name_________________________
Spring 2015
SO441 Lab 4: Quasi-geostrophic analysis
Objectives:
- Analysis of the sign and location of regions of rising motion that come from “Term B” in
the Q-G omega equation: differential absolute vorticity advection between 1000 mb and
500 mb
- Analysis of the sign and location of regions of rising motion that come from “Term C” in
the Q-G omega equation: Laplacian of temperature advection at 850 mb
- Comparison of contributions to rising motion (omega) from Term B and Term C with
actual values of omega at 700 mb
General tasks / introduction.
In this Lab, you will be using supplied MATLAB variables (via .mat file) and script template
(via .m file) to create a global plot of 500 mb heights, differential absolute vorticity advection
with height, temperature advection at 850 mb, and the resulting omega values for the same dates
and times as the event that produced thunder snow in in New England on Saturday, 14 February
2015.
For this lab, you will use the generated charts (and you can also reference the Lab 3 slide deck)
to observe and describe the sign and location of term B and C with respect to the sign and
location of omega max and mins.
Note: in your plots of  from Terms B and C, the most important piece of information is the
sign of  (whether it is positive or negative). We have not exercised due-diligence and
calculated the scalar parameters in front of both terms. As such, the magnitude (how large/small)
each term is will not be reflected in your calculations and the figures you create.
Name_________________________
Spring 2015
Specific tasks.
** Throughout this lab you can reference the 14 February New England slide deck from lab 3 for
additional information.
1. Download the .mat and .m files from blackboard or the SO441 Website (Lab 4 zip folder). Then unzip
the folder contents to your working folder
2. Load the .mat file and open the .m files in your editor
3. Plot Global Omega at 700mb and observe the pattern of maxima and minima on the chart.
a. Type “run Omega_Lab4_Midn” in your Command Window
* This by itself will tell you where you have upward and downward vertical motion in the
atmosphere, but it will have more meaning when you have additional information to
compare it to.
b. Figures will be small, but click the maximize button in the upper right of the figure window
4. Add 500mb Height Contours to your plot of 700mb Omega
a. Go to the Omega_Lab4_Midn.m in your editor, then add the following lines to the bottom of
each figure (note that HH and MMDD must be the same as the rest of the data in the plot) :
hold on
contour(x,y,squeeze(hgt500_HHz_MMDD),4800:60:6000,'color','k','linewidth',2
b. Save each plot as a jpg file (make sure you are maximized first), and add them sequentially to
a power point file (which you will hand in electronically)
5. Plot Global Differential Absolute Vorticity Advection with Height (Term B in the Q-G Omega
Equation) between 1000mb and 500mb and observe the pattern of maxima and minima on the chart.
a. Type “run Omega_TermB_Lab4_Midn” in your Command Window
b. Figures will be small, but click the maximize button in the upper right of the figure window
i. You will notice that there are hot (positive) and cold (negative) spots throughout the
mid and high latitude regions of the globe.
ii. Note that this is differential vorticity advection, which is not the same as vorticity
advection or absolute vorticity at either level.
6. Add 500mb Height Contours to your plot of Global Differential Absolute Vorticity Advection with
Height (a portion of Term B in the Q-G Omega Equation) between 1000mb and 500mb
a. Go to the Omega_TermB_Lab4_Midn.m in your editor, then add the following lines to the
bottom of each figure (note that HH and MMDD must be the same as the rest of the data in the
plot) (also note that you could copy and paste from the lines of code you added to the omega
plots, but the dates and times must match!):
hold on
contour(x,y,squeeze(hgt500_HHz_MMDD),4800:60:6000,'color','k','linewidth',2
b. Save each plot as a jpg file (make sure you are maximized first), and add them sequentially to
a power point file (which you will hand in electronically)
Name_________________________
Spring 2015
7. Plot Global Temperature Advection at 850mb (a portion of Term C in the Q-G Omega Equation and
observe the pattern of maxima (WAA) and minima (CAA) on the chart.
a. Type “run Omega_TermC_Lab4_Midn” in your Command Window
b. Figures will be small, but click the maximize button in the upper right of the figure window
i. You will notice that there are hot (positive) and cold (negative) spots throughout the
mid and high latitude regions of the globe.
ii. Note that this can be directly compared with the Lab 3 850mb charts for the same
event.
6. Add 500mb Height Contours to your plot of Global Differential Absolute Vorticity Advection with
Height (a portion of Term B in the Q-G Omega Equation) between 1000mb and 500mb
a. Go to the Omega_TermC_Lab4_Midn.m in your editor, then add the following lines to the
bottom of each figure (note that HH and MMDD must be the same as the rest of the data in the
plot) (also note that you could copy and paste from the lines of code you added to the omega
plots, but the dates and times must match!):
hold on
contour(x,y,squeeze(hgt500_HHz_MMDD),4800:60:6000,'color','k','linewidth',2
b. Save each plot as a jpg file (make sure you are maximized first), and add them sequentially to a
power point file (which you will hand in electronically)
*** Now that you have all the plots we will move on to examining that Q-G Omega Equation and the
Plots.
Name_________________________
Spring 2015
The Q-G Omega Equation
 2 f02  2 
f 
R  2
 Vg  p  g  f  
 0
 p Vg  pT 
p 
2 




 p 
 p
p


A
B

C
Questions:
1. What effect does Term A have on the sign of ω (a sinusoidal variable) when compared to sign of Term
B and Term C (\each term individually not the combination)?
2. Term B
a. Identify Term B


b. Given that σ is positive. Explain why calculating and plotting Vg  p  g  f is a good
proxy for understanding the effects of term B on vertical motion (omega). Address the

 Vg  p  g  f   , and Term B in whole.
sign of Vg  p  g  f  ,

p 
Name_________________________
Spring 2015
c. Examine the 1200z 14 FEB 15 Differential Absolute Vorticity Advection from 1000mb
to 500mb plot and think about the physical meaning of the min and max values found on
the chart.
1) Do positive values mean that only positive vorticity advection is present at 1000mb
and 500mb, and negative values mean that only negative vorticity advection is
present at 1000mb and 500mb? Explain.
2) Closely examine the trough over NE Canada and the great lakes. Where is Maximum
positive value of differential absolute vorticity advection from 1000mb and 500mb in
this trough? At the base of the trough, or ahead of the trough?
i. What type of vertical motion would you expect at this location given the large
positive value of differential absolute vorticity advection?
ii. What will be the sign of ω in this case? (use the Q-G ω equation).
iii. Based on what you have learned thus far, is this where you would expect the
maximum positive value to be located in a trough?
3)
Now look at the ridge over the Hudson Bay. Where is the Maximum negative value
of differential absolute vorticity advection from 1000mb and 500mb in this ridge?
Behind the ridge, at the apex of the ridge, or ahead of the ridge?
i. What type of vertical motion would you expect at this location given the large
negative value of differential absolute vorticity advection?
Name_________________________
Spring 2015
ii. What will be the sign of ω in this case? (use the Q-G ω equation).
iii. Based on what you have learned thus far, is this where you would expect the
negative value to be located in a ridge?
d. Now look at the remaining differential vorticity advection charts in the sequence and reference
the same trough as in “c.2)”
1) As time progresses, where do we start to see large positive values of differential vorticity
advection between 1000mb and 500mb with respect to the trough?
2. Term C
a. Identify Term C:
b. Given that R, p, and σ are positive. Explain why calculating and plotting Vg  pT is a good
proxy for understanding the effects of term C on vertical motion (omega). Address the
sign of 2p Vg  pT , 2p Vg  pT , 2p Vg  pT , and Term C in whole.






Name_________________________
Spring 2015
c. Examine the 1200z 14 FEB 15 Temperature Advection at 850mb plot and think about the
physical meaning of the min and max values found on the chart.
1) What do large positive and negative values indicate?
2) Now look at the trough that you previously referenced in the Term B section. Where
is the maximum positive value with respect to the trough? at the base of the trough,
or ahead of the trough?
i. What type of vertical motion would you expect at this location given a positive
value of temperature advection at 850mb?
ii. What will be the sign of ω in this case? (use the Q-G ω equation).
iii. Based on what you have learned thus far, is this generally where you would
expect the maximum positive value to be located in a trough?
3) Look at the trough again. Where is the max negative value of temperature advection
with respect to the trough? at the base of the trough, or ahead of the trough?
i. What type of vertical motion would you expect at this location given a negative
value of temperature advection at 850mb?
ii. What will be the sign of ω in this case? (use the Q-G ω equation)
iii. Based on what you have learned thus far, is this generally where you would
expect the maximum negative value to be located in a trough?
Name_________________________
Spring 2015
d. Now look at the remaining temperature advection at 850mb charts in the sequence.
1) What happens to the magnitude of the positive values ahead of the trough with time?
i. What does this mean with respect to the impact of temperature advection on
vertical motion with time?
3. Omega (Putting it all together)
a. What to large positive and negative values indicate respectively on this plot?
b. Examine the 1200z 14 FEB 15 global omega plot and locate the same trough that you
used in previous sections, and have your differential vorticity advection and temperature
advection plots handy for the same time period.
1) What type of vertical motion (from the omega plot) is present where you found strong
positive value of differential absolute vorticity advection from 1000mb and 500mb?
2) What type of vertical motion is present (from the omega plot) where you found strong
negative values of temperature advection?
3) If the motion in 1) and 2) are not what you expected, why would that be?
4) With respect to the trough, where DO you see upward and downward motion respectively on
the omega plot at this time? Is this where you would expect it to be?
Name_________________________
Spring 2015
c. Now look at the remaining omega plots in the sequence
1) As time progresses what happens to the negative values ahead of the trough?
i. How do the negative values ahead of the trough correlate with the large positive values
of differential vorticity advection you discussed in 1.d.1)?
ii. How do the negative values ahead of the trough correlate with the positive values of
temperature advection you discussed in 2.d.1)?