Exercises: Energy Transfer and Extreme Weather

Name the three ways thermal energy is transferred. Give one example of each in the atmosphere or at Earth's surface (for example, from a hot parking lot, from the Sun, or in a rising warm air parcel).

Water vapor releases energy when it condenses into liquid droplets. Name this energy, and explain why it is important for the strength of hurricanes, which need warm ocean water of at least about $26.5\,^\circ\text{C}$.

The central United States is often called Tornado Alley. Name the two types of air masses that commonly meet there in spring and explain in one or two sentences why their meeting leads to severe thunderstorms.

Condensation of water vapor releases about $2.26 \times 10^{6}\ \text{J}$ of energy per kilogram. A large thunderstorm condenses about $5.0 \times 10^{8}\ \text{kg}$ of water (illustrative value).

1. Calculate the total energy released.

2. One kiloton of TNT is $4.184 \times 10^{12}\ \text{J}$. Express your result in kilotons of TNT.

3. Explain where this energy originally came from, tracing it through the hydrosphere and atmosphere.

A watershed of $2.0\ \text{km}^2$ receives $50\ \text{mm}$ of rain in one storm. The runoff coefficient (fraction of rain that becomes surface runoff) is 0.10 for forest and 0.90 for pavement.

1. Calculate the total volume of rain that falls (in m$^3$).

2. Calculate the runoff volume if the watershed is forest and if it is entirely paved.

3. Explain how urbanization changes the risk of flash floods in a city such as Houston.

The sea-surface temperature in part of the Gulf of Mexico rises from $27\,^\circ\text{C}$ to $30\,^\circ\text{C}$ over the summer.

1. Explain how warmer water increases the energy available to a hurricane.

2. Explain how rising sea level can make storm surge more destructive even if wind speeds do not change.

3. Distinguish between a change in the frequency and a change in the intensity of hurricanes, and give an example of each.

On a spring afternoon near Dallas, Texas, the surface temperature is $27\,^\circ\text{C}$ and the dew point is $21\,^\circ\text{C}$, with a southeast wind of $5\ \text{m/s}$. At about 5 km altitude, winds blow from the west at $30\ \text{m/s}$. A dry, warm layer sits above the moist surface air, and a cold front is approaching from the northwest.

1. Identify the ingredients for severe thunderstorms and tornadoes that are present in this scenario (moisture, instability, lift, and wind shear), and justify each.

2. Explain how the Gulf of Mexico, the land surface, and the atmosphere exchange thermal energy to produce these conditions.

3. Predict the most likely type of severe weather and explain one human action that reduces risk.

Two coastal counties on the Gulf Coast each face a hurricane with a $3.0\ \text{m}$ storm surge. County A has intact marshes and mangroves and low-density housing. County B has filled in most wetlands, has dense housing on land only $1.5\ \text{m}$ above current sea level, and has had $0.3\ \text{m}$ of sea-level rise in recent decades.

1. Calculate how deep the floodwater would be over the lowest land in County B (ignoring waves), and compare it with the situation if sea level had not risen.

2. Analyze natural and human factors that affect the severity of damage in each county.

3. Write a CER argument stating which human decisions could most reduce the damage from future hurricanes, and which factors people cannot control.