Geology

Posted: August 25th, 2021

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Geology

1a. Based on the data, which one of the following options prevented thunderstorms from occurring at all: stability at 500 mb, a capping inversion, or low wind shear?

For a storm to form, there must be unstable air with a significant LIFT (lifted) index. Stability of  500mb is sufficient to prevent any updraft, and thus, no storm is formed. Notably, the larger the negative index, the stronger the storm which is formed.  

1b. What is the average lifted index, considering only the thunderstorm cases (Case 1-6, & 8)? This will be the average you will use for comparisons in 1c and 1d below.

The average index is the sum of the seven indices divided by the seven cases.  -1(6.4+3.1+4.3+4.1+7.5+3.5+7.5) = – 36.4

36.4/7= -5.2

1c. What do the three air mass storm cases all have in common: above average (less negative) lifted indices, lack of a capping inversion, or relatively low wind shear? Choose 1 option.

The three have relatively low wind shear. In particular, their wind shears in knots are 20, 5, and 5 respectively. This is unlike other cases in the table where wind shear exceeds 49. 

1d. What do the four supercell storm cases all have in common: below average (more negative) lifted indices, capping inversions, or relatively high wind shear? Choose 2 options.

For the four cases, the highest numbers of wind shear in knots are observed. In particular, the fur supercell cases have 52, 74, 53, and 61 knots respectively. These are relatively high compared to other cases. Meanwhile, three of the four supercell cases have capping inversions.    

1e. Based on your data, which storm input has a larger effect in determining the storm’s severity after a thunderstorm has already formed: lifted index or wind shear?

Although larger negative lifted index explains the formation of a severe thunderstorm, most of these thunderstorms are a result of unstable air which results in wind shear. A drastic change in wind direction with height allows both downdraft and updraft. This is what allows thunderstorms to form, persist, and become stronger. Rotational wind shear leads to supercells which are the severest thunderstorms.      

2a.  Which one of the five cases would not produce a thunderstorm at all? This should be your rank 5.

Case number 5 should produce no thunderstorm. Apparently, it has a very high positive lifted index, and for a thunderstorm to form, there must be a negative lifted index. 

2b. Of the remaining four cases, which two would likely be weaker thunderstorms? Label these as air mass storms in your table, and make sure to indicate which is rank 3 and which is rank 4 based on what you learned in Exercise 1.

Cases 2 and 3 would have the weakest thunderstorms. To start with, they have a relatively low lifted index. Besides, their CAPE is relatively low as well. 

2c. Thus, which two of the five cases favor the formation of stronger storms? Label these as supercell storms in your table, and make to indicate which is rank 2 and which is rank 1 based on what you learned in Exercise 1.     

Cases 1 and 4 have the highest lifted index and their CAPE is as well extremely high. With regard to ranking, they cause the most severe thunderstorms. 

2d. Directional wind shear (which you can specifically look at by comparing Columns D & F) is very important for tornadoes since it provides a twist to the air columns. Given this, which one of your supercell cases is most likely to produce a tornado? This should be your rank 1.

Case 8 is ranked number 1 with regard to directional wind shear in both columns D and F. In both columns, the surface wind direction (deg) has the lowest values, 150 and 200 respectively. This is relative to other supercell cases. This case 8 has the highest probability of producing tornadoes.

3a. How well do your rankings scale with your CAPE*SHEAR values? In other words, when the CAPE*SHEAR values are higher, are the storms generally more severe?

Apparently, there seems to be an ambiguous correlation between CAPE*SHEAR and severity of storms. The most severe storm has the highest CAPE*SHEAR value. Surprisingly, the second most severe storm has the lowest CAPE*SHEAR value. This means that the two variables do not have a positive or negative correlation. Thus, when the CAPE*SHEAR values are higher, the storms are not generally more severe. 

3b. Do you agree with this statement: “You can have all the shear in the world, but without instability, there is no storm in the first place.”?

Yes. To start with, there must be instability for a storm to form. Thus, with shear and zero instability, there is no likelihood of a storm developing. 

3c. If a surrounding has a positive value of CAPE that was calculated from 300mb to 700mb, would the LIFT index be positive or negative?

This asks us to determine the type of correlation between CAPE and lifted index. Notably, a higher negative lifted index is associated with a higher value of CAPE. As the CAPE decreases, the lifted index approaches zero. Thus, low CAPE values are likely to lead to positive lifted index.      

4a. Would you expect this type of ‘night-time’ inversion to be strongest at dusk, midnight, or just prior to sunrise given calm winds?

Given calm winds, the night-time inversion would be extreme just prior to sunrise. Notably, a capping inversion is where environmental temperatures increase with height. The sun heats the upper atmosphere, and this means the lower layers of the atmosphere are cooler. The trapped energy is what is later released violently forming storms.  

4b. Based on seasonal day lengths, would you expect this type of ‘night-time’ inversion to be strongest during the spring or during the summer given calm winds?

Assuming there are calm winds, the night-time inversion would be strongest during summers as opposed to the spring seasons. This is because, in summer, heat from the sun warms the air drastically and based on atmospheric height.  

4c. If a stronger night-time inversion occurs, would you expect thunderstorms to occur earlier or later in the day assuming that the inversion is eventually broken by surface heating?

They would occur later in the day. Notably, surface heating intensifies as the daytime progresses. The trapped heat during a stronger night-time inversion would be released only after extreme heat in the atmosphere is experienced, and this can only occur later during the day.    

4d. The graph below shows the distribution of severe (white columns) and tornadic (black columns) storms over the year for the Great Plains.

Stronger storms are shown to develop more frequently in the spring and early summer rather than in the middle of summer. Do you think that night-time inversion strength may influence this distribution? Why?

Night-time inversions are notoriously known for trapping heated air just above the round. When trapped in an extreme amount, a release of this heated air can cause severe storms. The strength of night-time inversion depends on seasons, and it influences the distribution of storms.