L4 Humidity and Stability

Flashcards based on Meteorology Lesson 4: Humidity and Stability.

Absolute Humidity

The amount of water vapor in the atmosphere.

Water Vapor

Invisible gas present in all places in the atmosphere.

Temperature and Water Vapor

Air's ability to hold more water vapor increases with temperature.

Saturation

When air holds the maximum water vapor possible without condensation.

Dew Point

The temperature at which air becomes saturated.

Wide Temperature/Dew Point Spread

Indicates a high cloud base or no cloud at all.

Narrow Temperature/Dew Point Spread

Indicates the possibility of low cloud or fog.

Relative Humidity

Percentage of water vapor a parcel of air is holding compared to the amount it could hold before saturation.

Saturation

Value at 100% RH.

Humidity Mixing Ratio

The ratio in grams of water vapor to kilograms of dry air.

Saturation Mixing Ratio

The value of Humidity Mixing Ratio that corresponds to saturation.

Absolute Humidity

Measure of mass of water vapor per unit volume of air.

Specific Humidity

Measure of mass of water vapor per unit mass of air.

Moist Air

Less dense than dry air.

States of Water

Solid, Liquid, Gas.

Change of State Energy

Water changing from solid to liquid to gas absorbs energy; water changing from gas to liquid to solid releases energy.

Latent Heat

Energy gained or released during a change of state.

Sublimation

Change of state from solid to gas.

Deposition (UK usage)

Change of state from gas to solid.

Temperature Lapse Rate

The rate at which temperature changes with a change in height.

Environmental Lapse Rate (ELR)

Actual rate of temperature change with height.

Dry Adiabatic Lapse Rate (DALR)

Lapse rate of dry air rising at 3°C per 1000 ft.

Saturated Adiabatic Lapse Rate (SALR)

Lapse rate of saturated air rising at approximately 1.8°C per 1000 ft.

Adiabatic

No energy is gained or lost from the rising parcel of air.

Absolutely Stable Atmosphere

ELR is less than the SALR (<1.8°C)

Absolutely Unstable Atmosphere

ELR is greater than the DALR (>3.0°C)

Conditionally Unstable Atmosphere

ELR is between the SALR and DALR (>1.8°C, <3.0°C)

Atmospheric Stability

Tendency of air to resist vertical motion.

Stable Atmosphere

Air returns to its original level when displaced vertically.

Unstable Atmosphere

Air may continue to move vertically when displaced.

Stable Atmosphere

Like a calm sea, resists vertical motion.

Unstable Atmosphere

Like a rough sea, promotes vertical motion.

ELR Greater than DALR and SALR

Rising air is always warmer than the environment, so continues to rise.

ELR Lower than SALR

Rising air is colder than the environment and sinks back down.

Conditionally Unstable

Stable if unsaturated, unstable if saturated.

Neutral Stability

Air will neither rise nor sink; very unlikely in real world conditions.

Atmosphere Unstable

Heating from below tends to make this.

Unstable Atmosphere

Characterized by choppy flying conditions and convective clouds, but good visibility outside showers.

Atmosphere Stable

Cooling from below tends to make this.

Stable Atmosphere

Smooth flying conditions and flat, layered cloud formations often characterize it.

Standard Temperature Profile

Atmosphere is cooler at altitude.

Temperature Inversion

When temperature increases with increasing height.

Formation of Inversions

From surface cooling during cold nights in winter.

Formation of Inversions

At weather fronts when warm air settles over cold air.

Formation of Inversions

Above 'temperature inversion turbulence', due to mixing.

Formation of Inversions

From subsidence in stable air masses.

Invisible

Water vapour is an gas.

Expands

A parcel of air rises, it and cools.

Decreases

As air is cooled, the amount of water content it can hold as a gas .

Saturation

If there is a small gap between temperature and dew point, the air is close to .

Low, Fog

A narrow temperature/dew point spread implies the possibility of cloud or even _.

Dry

A wide temperature/dew-point spread implies relatively air, and high cloud (if any).

Relative Humidity

The weather information given to pilots does not include the , but it is of great interest

Saturation

The higher the relative humidity (RH) of a parcel of air, the closer it is to .

Saturation

At 100% RH ‘ of air by water vapour' occurs and cloud, mist or fog may form.

Mixing Ratio

As the air gets warmer or colder, the remains constant but the relative humidity and the Saturation Mixing Ratio will change.

Content of water vapour in the air

Humidity Mixing ratio describes?

Solid, Liquid, Gas

Water exists in the atmosphere in three states, which are , and .

Absorbs

Whenever water changes state from solid to liquid to gas it energy from the surrounding air

Releases

Whenever water changes state from gas to liquid to solid it energy to the surrounding air.

No energy is gained by or lost from the rising parcel of air itself

The word adiabatic means what?

Neutrally stable

If the ELR happens to be the same as the SALR in cloud (i.e saturated) or the same as the DALR in clear air (i.e. unsaturated), the air will be .

tendancy

Stability describes the of the air to resist vertical motion.

Heating, Cooling

Stability is generally affected by or of the atmosphere by the surface.

Choppy flying conditions, and convective clouds.

Give an example of what an unstable atmosphere is characterised by?

Smooth flying conditions

Give an example of what a stable atmosphere usually means.

Inverted

The Environmental Lapse Rate is during temperature inversions.

Up to 4 g of water vapour

1 kg of air can hold at 0°C how much water vapour?

Up to 10 g of water vapour

1 kg of air can hold at 15°C how much water vapour?

Up to 27 g of water vapour

1 kg of air can hold at 30°C how much water vapour?

2°C per 1000 ft

What is the average figure when discussing temperature lapse rate?

3°C per 1000 ft

When dry air rises, what is its lapse rate?

approximately 1.8°C per 1000 ft

When saturated air rises, what is its lapse rate?

Various items of information, including temperature

What does a radiosonde balloons transmit?

London Gatwick

EGKK METAR reports refer to which airport?

Manchester

EGCC METAR reports refer to which airport?

The amount of water vapour in the atmosphere

What is the definition of humidity?

Pressure, temperature and humidity

What are the 3 most important atmospheric measurements that uses forecasting weather in computer models?

Deposition

Water changing from gas to solid

Sublimation

In the USA water changing from gas to solid and solid to gas is called?

Radiosonde balloons

Instrument used to collect information, including temperature, as they climb through the atmosphere.

heat energy is released as water vapour condenses into liquid droplets condensation

Why is SALR less than DALR?

Choppy

An unstable atmosphere is characterised by what flying conditions?

Smooth

A stable atmosphere is characterised by what flying conditions?

A humid atmosphere with the possibility of low cloud and fog

What could a narrow temperature/dew point spread imply?

Relatively dry air, and high cloud (if any)

What could a wide temperature/dew point spread imply?

Moist air (high humidity) is less dense than dry air (low humidity).

What is the effect of water vapour on air density?

In meteorological observations and reported in actual weather reports

How is dew point measured?

Atmosphere where temperature increases with altitude

Define a temperature inversion.

Heaped clouds with vertical development

What type of clouds can you expect in an unstable atmosphere?

Layered clouds

What type of clouds can you expect in a stable atmosphere?

Temperate

In what type of climate is the SALR value of 1.8°C typical?

Radiosonde balloons

What tool do weather forecasters use to collect real-time atmospheric information?

Ground cools quickly, chilling the air directly above it

How surface cooling during cold nights in winter, lead to temperature inversion?

AVGAS fuel

Give one example of a volatile liquid

That a wide Temperature/Dew Point Spread is present

What does a high cloud base or no cloud at all mean?

Narrow temperature/dew-point spread

What type of air implies moist air, and low cloud or fog?

The ratio in grams of water vapour to kilograms of dry air

What is the full definition of Mixing Ratio?

The percentage of water vapour a parcel of air is holding, compared to the amount it could hold before becoming saturated

What is the full definition of Relative Humidity?

The rate at which temperature changes with a change in height

What is the full definition of Temperature Lapse Rates?