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MODULE 4 STABILITY, CLOUD & PRECIPITATION questions well answered
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MODULE 4 STABILITY, CLOUD & PRECIPITATION questions well answered
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MODULE 4 STABILITY, CLOUD &PRECIPITATION
Must be able to Define (a) Adiabatic process (b) ELR (c) DALR (d) SALR (e) super adiabatic lapse rate. -
correct answer ✔✔(a) Adiabatic process is when the volume of air changes temperature but not its state
within a closed relationship. The most common Adiabatic process is the vertical displacement of the
volume of air due to changes in temperature produced by conductive and convective forces or
mechanical uplift.
(B) ELR is the environmental lapse rate, and it is the actual change in temperature with altitude in the
atmosphere at a given point in time. (2°C/1000ft)
(C) DALR is the dry adiabatic lapse rate, and it is the rate at which a dry parcel of air changes
temperature with altitude. (3°C/1000ft - constant value)
(D) SALR is the saturated adiabatic lapse rate, and it is the rate at which a saturated parcel of air changes
temperature with altitude. (1.5°C/1000ft - constant value)
(E) Super adiabatic lapse rate is any ELR that is greater than 3°C/1000ft as this will create extreme
instability in the atmosphere.
Should be able to Explain (a) Why the SALR & DALR differ (b) How the ELR is calculated and (C) Why the
SALR is not constant with altitude. - correct answer ✔✔(a) Why does the SALR & DALR differ?
SALR (1.5°C/1000ft) is lower than DALR (3°C/1000ft) because the water vapour inside the saturated
parcel of air undergoes condensation. Condensation is a diabatic process of exothermic which is the act
in which energy is released into its environment therefore, it take longer to cool the parcel of air and that
is why the SALR is different to DALR.
(b) How is the ELR calculated?
ELR is calculated by measuring the actual change in temperature with altitude using appropriate
meteorological instrumentation and readings from aircraft and satellites.
, (c) Why is SALR not constant with altitude?
SALR is not constant with altitude because, with the increase in altitude, the atmosphere progressively
dries out meaning that the moisture content in a volume of air would have already condensed and
precipitated out. But it approaches and eventually matches the DALR.
Ideally will be able to Differentiate between (a) adiabatic & (b) diabatic processes. - correct answer
✔✔(a) Adiabatic process - Adiabatic processes are when the volume of air changes temperature but not
its state in a closed relationship which means that it does not interact with the surrounding
environment.
(b) Diabatic process - Diabatic processes are when the volume of air changes state but not its
temperature in an open relationship which means that it does interact with the surrounding
environment.
Must be able to Define the following stability conditions (a) absolute stability (b) absolute instability (c)
conditional stability (d) convective stability & instability (e) diurnal stability & instability. - correct answer
✔✔(a) Absolute stability - Absolute stability is when ELR is greater than SALR. This means that dry &
saturated air cools faster than the surrounding environment and becomes stable.
(b) Absolute instability - Absolute instability is when ELR is less than SALR. This means that dry &
saturated air cools slower than the surrounding environment and becomes unstable.
(c) Conditional stability - Conditional stability is when DALR>ELR>SALR. This means that dry air is stable
and saturated air is unstable.
(d) Convective stability & instability - It is when volumes have dry and wet layers.
Unstable - lower layer wet, upper layer dry
Stable - lower layer dry, upper layer wet
(e) Diurnal stability & instability - It is the short-term variations in stability within the friction layer due to
warming & cooling of the atmosphere near the surface.
Should be able to use appropriate meteorological information to identify & calculate absolutely stable,
absolutely unstable & conditionally stable conditions. - correct answer ✔✔To calculate stability
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