Hydrostatic Equilibrium Questions and Answers

Q: Which lapse rate does saturated ascent follow?

Latent heat release offsets some of the adiabatic cooling, so the saturated rate is less than 9.8 and varies from about 4 kelvin per kilometre in warm moist air to nearly the dry value in very cold air. It increases with height as the moisture is depleted, which makes the last option partly right, but the essential point is that it is smaller than the dry rate and not constant. Naming the cost of a choice alongside its benefit is what turns a fact into a design decision.

Q: Which temperature range gives the smallest saturated lapse rate?

The saturated rate depends on how much water is available to condense, and by Clausius-Clapeyron that is greatest at high temperature, so warm tropical air gives rates near 4 kelvin per kilometre. In very cold air there is almost no water and the rate approaches the dry value. This is why tropical soundings lie so much closer to the moist adiabat than polar ones. The shared properties explain why these belong to one family, and the differences explain why more than one exists.

Q: Which quantity does precipitable water measure?

Precipitable water is the vertically integrated water vapour expressed as an equivalent depth of liquid, typically 10 to 25 millimetres in mid-latitudes and up to 60 in the deep tropics. It is an upper bound on what could fall from a column but a poor predictor of actual rainfall, since convergence continually resupplies moisture into a precipitating system. Values well above the seasonal normal are one of the standard indicators used when assessing the potential for extreme rainfall.

Q: Which relationship holds between precipitable water and observed rainfall totals?

Low level convergence continually feeds new moisture into a storm, so a system can produce several times the precipitable water of the column it occupies. Moisture flux convergence rather than the standing moisture content is what determines the total. This is why the quantity is used as an environmental indicator rather than as a quantitative forecast of accumulation.

Q: Which instrument measures precipitable water continuously?

The wet delay in navigation satellite signals passing through the atmosphere is proportional to the integrated water vapour, so a network of geodetic receivers doubles as a humidity observing system. It provides continuous measurement at a few minute intervals, unlike a radiosonde which gives two profiles a day. The technique was a by-product of geodesy and is now assimilated operationally.

Q: Which principle does Archimedes' result express for a parcel of air?

The net upward force on a parcel is the weight of the air it displaces, so a parcel less dense than its surroundings rises and one denser than its surroundings sinks. Buoyancy is exactly the residual left when hydrostatic balance is subtracted from the vertical momentum equation, which is why the two ideas are inseparable. Expressing the result per unit mass gives an acceleration proportional to the fractional density difference, which for the atmosphere is more conveniently written in terms of virtual temperature.

Q: Which quantity should be used when comparing parcel and environment for buoyancy?

Buoyancy depends on density, and moist air is lighter than dry air at the same temperature, so the comparison must be made using virtual temperature. In the tropics the correction is comparable with the temperature excess of a convective plume, so neglecting it can change the sign of the buoyancy. Potential temperature is the right variable for comparing parcels at different levels but not for evaluating buoyancy at one level.

Q: Which acceleration does a parcel one kelvin warmer than its surroundings experience?

The buoyant acceleration is gravity times the fractional temperature excess, so one kelvin in 300 gives about 0.033 metres per second squared. Sustained over a few kilometres that is enough to produce updraughts of several metres per second, which is why quite small temperature excesses drive vigorous convection. Working the estimate once makes the magnitude of convective forces intuitive.

Q: Which speed would that acceleration produce over a five kilometre ascent?

Taking the acceleration as constant and using the kinematic result gives a speed of about 18 metres per second after 5 kilometres, which is the parcel theory estimate. Observed updraughts are usually weaker because entrainment of drier environmental air and the weight of condensed water both reduce the buoyancy. The parcel theory value is therefore an upper bound rather than a prediction.

Q: Which processes make observed updraughts weaker than parcel theory predicts?

Mixing with cooler drier environmental air dilutes the buoyancy, and the weight of suspended condensate acts as an additional load, so real updraughts fall well short of the undiluted parcel value. Both effects are represented in convective parameterisation schemes through entrainment rates and condensate loading terms. Radiation and Coriolis effects are negligible on convective timescales.

91.

Which lapse rate does saturated ascent follow?

A.A constant rate of 6.5 kelvin per kilometre
B.A rate that increases with height as the amount of water vapour available for condensation becomes smaller
C.A rate smaller than the dry adiabatic and varying with temperature
D.A rate of 9.8 kelvin per kilometre, which is the same value that applies to unsaturated adiabatic ascent

Answer: C

Latent heat release offsets some of the adiabatic cooling, so the saturated rate is less than 9.8 and varies from about 4 kelvin per kilometre in warm moist air to nearly the dry value in very cold air. It increases with height as the moisture is depleted, which makes the last option partly right, but the essential point is that it is smaller than the dry rate and not constant. Naming the cost of a choice alongside its benefit is what turns a fact into a design decision.

Discuss in Forum

92.

Which temperature range gives the smallest saturated lapse rate?

A.Very cold polar temperatures near 230 kelvin, where the air is close to saturation with respect to ice
B.Temperatures near freezing
C.Temperatures just below freezing, where the difference between the ice and water saturation values is largest
D.Warm tropical temperatures near 300 kelvin

Answer: D

The saturated rate depends on how much water is available to condense, and by Clausius-Clapeyron that is greatest at high temperature, so warm tropical air gives rates near 4 kelvin per kilometre. In very cold air there is almost no water and the rate approaches the dry value. This is why tropical soundings lie so much closer to the moist adiabat than polar ones. The shared properties explain why these belong to one family, and the differences explain why more than one exists.

Discuss in Forum

93.

Which quantity does precipitable water measure?

A.The depth of liquid if all vapour in a column condensed
B.The amount of rainfall that will actually reach the ground from the cloud currently present above the site
C.The relative humidity
D.The mass of water vapour contained within a single cubic metre of air at the level being considered here

Answer: A

Precipitable water is the vertically integrated water vapour expressed as an equivalent depth of liquid, typically 10 to 25 millimetres in mid-latitudes and up to 60 in the deep tropics. It is an upper bound on what could fall from a column but a poor predictor of actual rainfall, since convergence continually resupplies moisture into a precipitating system. Values well above the seasonal normal are one of the standard indicators used when assessing the potential for extreme rainfall.

Discuss in Forum

94.

Which relationship holds between precipitable water and observed rainfall totals?

A.Rainfall equals the precipitable water multiplied by the efficiency of the precipitation process in the cloud
B.Rainfall can greatly exceed the precipitable water present
C.Rainfall can never exceed the precipitable water, since that is all the moisture the column actually contains
D.The two are equal

Answer: B

Low level convergence continually feeds new moisture into a storm, so a system can produce several times the precipitable water of the column it occupies. Moisture flux convergence rather than the standing moisture content is what determines the total. This is why the quantity is used as an environmental indicator rather than as a quantitative forecast of accumulation.

Discuss in Forum

95.

Which instrument measures precipitable water continuously?

A.A radiosonde
B.A ceilometer, which determines the height of the cloud base from the time taken for a light pulse to return
C.A ground based GPS receiver
D.A rain gauge, which collects the precipitation reaching the ground and therefore measures the same quantity

Answer: C

The wet delay in navigation satellite signals passing through the atmosphere is proportional to the integrated water vapour, so a network of geodetic receivers doubles as a humidity observing system. It provides continuous measurement at a few minute intervals, unlike a radiosonde which gives two profiles a day. The technique was a by-product of geodesy and is now assimilated operationally.

Discuss in Forum

96.

Which principle does Archimedes' result express for a parcel of air?

A.The upward force equals the weight of the parcel itself, so that every parcel is always exactly in balance
B.The parcel always sinks
C.The upward force depends on the surface area of the parcel rather than upon the volume that it occupies
D.The upward force equals the weight of the displaced air

Answer: D

The net upward force on a parcel is the weight of the air it displaces, so a parcel less dense than its surroundings rises and one denser than its surroundings sinks. Buoyancy is exactly the residual left when hydrostatic balance is subtracted from the vertical momentum equation, which is why the two ideas are inseparable. Expressing the result per unit mass gives an acceleration proportional to the fractional density difference, which for the atmosphere is more conveniently written in terms of virtual temperature.

Discuss in Forum

97.

Which quantity should be used when comparing parcel and environment for buoyancy?

A.Virtual temperature
B.Actual temperature, since it is what a thermometer measures and therefore what the observations provide
C.Potential temperature
D.Dew point temperature, which indicates how much water vapour the parcel is carrying with it as it rises

Answer: A

Buoyancy depends on density, and moist air is lighter than dry air at the same temperature, so the comparison must be made using virtual temperature. In the tropics the correction is comparable with the temperature excess of a convective plume, so neglecting it can change the sign of the buoyancy. Potential temperature is the right variable for comparing parcels at different levels but not for evaluating buoyancy at one level.

Discuss in Forum

98.

Which acceleration does a parcel one kelvin warmer than its surroundings experience?

A.About 3 metres per second squared, which would carry the parcel to the tropopause within a few minutes
B.About 0.03 metres per second squared
C.About 9.8 metres per second squared, which is the full acceleration due to gravity acting on the parcel
D.About 0.3 metres per second squared

Answer: B

The buoyant acceleration is gravity times the fractional temperature excess, so one kelvin in 300 gives about 0.033 metres per second squared. Sustained over a few kilometres that is enough to produce updraughts of several metres per second, which is why quite small temperature excesses drive vigorous convection. Working the estimate once makes the magnitude of convective forces intuitive.

Discuss in Forum

99.

Which speed would that acceleration produce over a five kilometre ascent?

A.About 100 metres per second
B.About 50 metres per second, which is the speed reached within the strongest supercell updraughts observed
C.About 18 metres per second
D.About 2 metres per second, which is comparable with the updraught within an ordinary fair weather cumulus

Answer: C

Taking the acceleration as constant and using the kinematic result gives a speed of about 18 metres per second after 5 kilometres, which is the parcel theory estimate. Observed updraughts are usually weaker because entrainment of drier environmental air and the weight of condensed water both reduce the buoyancy. The parcel theory value is therefore an upper bound rather than a prediction.

Discuss in Forum

100.

Which processes make observed updraughts weaker than parcel theory predicts?

A.Radiative cooling of the ascending parcel, which removes the buoyancy before it can reach the cloud top
B.The Coriolis force
C.Friction against the surrounding air, which acts in the same way as viscous drag upon a falling raindrop
D.Entrainment of environmental air and water loading

Answer: D

Mixing with cooler drier environmental air dilutes the buoyancy, and the weight of suspended condensate acts as an additional load, so real updraughts fall well short of the undiluted parcel value. Both effects are represented in convective parameterisation schemes through entrainment rates and condensate loading terms. Radiation and Coriolis effects are negligible on convective timescales.

Discuss in Forum

Loading…

Topics

Other Subjects

Tags: Hydrostatic Equilibrium Questions and Answers || Hydrostatic Equilibrium MCQ Questions and Answers || Hydrostatic Equilibrium GK Questions and Answers || Hydrostatic Equilibrium GK MCQ Questions || Hydrostatic Equilibrium Multiple Choice Questions and Answers || Hydrostatic Equilibrium GK || GK on Hydrostatic Equilibrium || Atmospheric Thermodynamics Questions and Answers || Atmospheric Thermodynamics MCQ Questions and Answers || Atmospheric Thermodynamics GK Questions and Answers || GK on Atmospheric Thermodynamics

Hydrostatic Equilibrium Questions and Answers

Topics

Other Subjects

About Us

Stay informed about all important Dates & Notifications