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15 Cards in this Set
- Front
- Back
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State whether the following conditions are stable or unstable:
a) ELR 5c/km RH 30% b) ELR 0.8c/100m RH 100% c) ELR 1.2c/100m RH 20% |
a) stable
b) Unstable (conditionally) c) Unstable |
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Define stability in the context of air movement
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The environment is considered stable when the upward displacement of a parcel of air results in it returning to it's original level when the displacing force is removed.
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Define instability in the context of air movement
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The environment is considered unstable when a parcel of air continues to rise once the lifting force has been removed.
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Explain why the slope of the SALR when plotted on a temp/pressure diagram becomes steeper with increased altitude.
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At higher altitudes the air holds less mositure as it is colder. Therefore there is less water to condense and release latent heat so the SALR gets closer to the DALR
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Give the main reason why the SALR is different from the DALR
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Air which is saturated holds mositure which condenses as it rises. Condensation release latent heat which offsets some of the adiabatic cooling.
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State the average value of the SALR attributed to the lower levels of the troposhere.
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0.6c/100m 1.8c/1000ft
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State the value of the DALR
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1c/100m 3c/1000ft
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Describe, qualitatively the adiabatic changes in air temperature that can take place.
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As pressure decreases temperature decreases. As pressure increases temperature increases
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State the meaning of an adiabatic change
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Adiabatic change is the change in temperature due to pressure
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What determines the height of the top of the cloud formed because of instability.
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Assuming the air doesn't run out of moisture, the cloud top will be determined where the ELR meets the SALR. The air then ceases to rise.
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What type of cloud can form in an unstable environment?
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Convective, Cumulus & Cumulonimbus
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What information is obtained using Normand's Theorem?
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The theoretical condensation level
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Given that the surface temp is +12c and the temp at 3000ft is +1.5c, what is the ELR and how would the atmosphere be described?
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3.5c/1000ft
Absolutley unstable as the ELR is greater than both the DALR and SALR |
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Explain the meaning of the term 'conditionally unstable'.
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The atmosphere is stable only whilst it remains dry.
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In the formation of convective cloud, is the zero degree isotherm higher or lower in cloud than in the surrounding clear air?
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Higher
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