A rain shadow forms on the leeward side of a mountain range because
Answer: B
Much of the moisture is lost as precipitation on the windward ascent, and the descending air then warms adiabatically. It arrives on the far side both drier in absolute terms and further from saturation than before it began.
Please log in or register to report this question.
Consider the following statements about orographic lifting.
1. Precipitation tends to fall on the windward slope.
2. Descending air on the lee side warms and dries.
3. The air returns to its original temperature after descending.
Answer: C
Correct answer: 1 and 2 only
Statements 1 and 2 are correct: the air is cooled as it rises and precipitates on the windward slope, and it warms and dries as it descends the lee. Statement 3 is wrong and is the whole point of the foehn effect - the air ascended partly at the saturated rate but descends entirely at the dry rate, so it arrives at the original level warmer and much drier than it began. That asymmetry is what produces a rain shadow.
Please log in or register to report this question.
Assertion (A): Air descending the lee slope of a range is warmer than the air that started up the windward side.
Reason (R): Latent heat released during condensation stays with the parcel while the condensed water falls out.
Answer: D
Both are true and the reason gives the asymmetry, and this is the physics of the foehn or chinook wind. The parcel ascends at the saturated rate but descends at the larger dry rate. The difference between the two rates is the whole of the warming observed.
Please log in or register to report this question.
State whether the following is true or false.
An atmosphere in which the environmental lapse rate exceeds the dry adiabatic rate is absolutely unstable.
Answer: A
Correct answer: True
If the environment cools with height faster than a rising dry parcel does, then any parcel displaced upward finds itself warmer than its surroundings and keeps rising, whether it is saturated or not. That is absolute instability, and it is why such lapse rates are found only in shallow layers near a strongly heated surface - convection removes them as fast as they form.
Please log in or register to report this question.
Match each stability condition with its criterion.
List I
A. Absolutely stable
B. Conditionally unstable
C. Absolutely unstable
D. Neutral
List II
1. environmental rate above the dry rate
2. environmental rate below the saturated rate
3. environmental rate equal to the dry rate
4. environmental rate between the two rates
Answer: B
The word conditional means the instability appears only once the parcel is saturated. Most atmospheres capable of producing deep convection are conditionally unstable rather than absolutely so. The distinction turns entirely on whether the parcel has reached saturation.
Please log in or register to report this question.
Conditional instability means the atmosphere is unstable
Answer: C
An unsaturated parcel cools at the dry rate and is stable, but once it reaches its condensation level it cools more slowly and may become buoyant. The lifting needed to reach that level is what makes such a situation depend on a trigger.
Please log in or register to report this question.
Assertion (A): A conditionally unstable atmosphere may produce no convection at all on a given day.
Reason (R): The parcel must first be lifted to its level of free convection by some external mechanism.
Answer: D
Both are true and the reason gives what is missing, and the energy needed to reach that level is the convective inhibition. A capping inversion strong enough to prevent it can hold back a very unstable profile all afternoon.
Please log in or register to report this question.
Three of the following favour deep convective cloud. Which is the odd one out?
Answer: A
An inversion caps the ascent and prevents parcels from reaching their level of free convection. The other three are the classic ingredients meteorologists look for when deep convection is expected. Any one of them missing is usually enough to keep the day quiet.
Please log in or register to report this question.
Entrainment of environmental air into a growing cumulus tends to
Answer: B
Drier and cooler surroundings mixed in evaporate some of the droplets, which cools the parcel further and reduces its buoyancy. It is the main reason observed updraught temperatures fall short of the undiluted adiabatic value.
Please log in or register to report this question.
Assertion (A): Observed cumulus updraughts are cooler than an undiluted parcel calculation predicts.
Reason (R): Environmental air entrained through the cloud edges evaporates droplets and cools the parcel.
Answer: C
Correct answer: Both A and R are true, and R is the correct explanation of A
Both are true and the reason gives the mechanism. A real updraught is not sealed: turbulence mixes drier environmental air in through its edges, and evaporating cloud droplets to saturate that air takes latent heat out of the parcel. The result is an updraught cooler and less buoyant than the undiluted parcel calculation predicts, which is why simple parcel theory overestimates cloud tops.
Please log in or register to report this question.
