Homework #9 – Spring 2011 - Solutions 8.8b: Tropical thunderstorms exhibit higher cloud tops than mid-latitude thunderstorms primarily due to the amount of energy they obtain from the conversion of water vapor to liquid water. This latent heat release warms the parcel providing additional buoyancy. You should also be able to identify this feature on a skew-T diagram. Since there is generally more moisture (higher precipitable water) in the tropics, more energy can be obtained through this mechanism. Damaging winds are rarely observed for a similar reason. Damaging downdrafts typically require the presence of dry environmental air at some level. In the Midwest, we discuss the need for dry mid-levels for the generation of downbursts. These dry mid-levels rarely exist in the tropics and, therefore, cannot contribute to the strengthening of the existing downdrafts. 8.8c: The bump above the updraft on a cumulonimbus cloud is called the overshooting top. This occurs when an exceptionally strong updraft has acquired a great deal of velocity by the time it reaches the equilibrium layer. The updraft doesn’t immediately stop at this layer, but continues past it, decelerating until its velocity reaches zero. However, the parcel continues to cool at the moist adiabatic lapse rate as it passes the equilibrium layer. This additional cooling causes additional condensation allowing it to remain visible. The strength of the updraft determines how far about the equilibrium layer a parcel will travel. 8.8d: Severe thunderstorms breakout out over the central US more in the spring because the essential ingredients needed are present more often than any other season. These conditions are listed in section 8.3.1c on page 348 in your text. 8.8e: Ordinary thunderstorms exhibit relatively short lifetimes primarily due to the lack of horizontal shear in the environment. This lack of shear causes an overlap between the updraft and the downdraft. The downdraft eventually takes over the whole cloud destroying the updraft completely which leads to the dissipation of the thunderstorm. .