Weather module 1 Flashcards
Describe the extent, circulation and characteristics of a low
Can vary greatly in size, and associated with cloudy weather. circulation is counter-clockwise
Pressure tendency is
The change with time of the pressure reported by a station.
What is radiation cooling?
At night, when radiation from the sun stops, the earth will continue to radiate its heat and become cooler. The air near the surface of the earth will give up its heat to the colder earth through conduction.
Define subsidence
The downward motion of air
What are the 2 adiabatic lapse rates?
Dry = 3 degrees/1000ft Saturated = 1.5 degrees/1000ft
Define lapse rate
The rate of temperature change with height
If air is forced to ascend it? (2)
expands and cools
List the 3 causes of pressure variation over time
- Movement of pressure systems
- Variation in intensity of systems
- Diurnal variations in pressure
If the atmospheric lapse rate is greater than the adiabatic lapse rate of a parcel of air the air is considered:
Unstable
What is the internation standard lapse rate?
1.98 degrees /1000ft
isobars on surface weather maps form:
pressure patterns
When air expands we say that ____ or _____ has occured
Expansion or Adiabatic cooling
What are the typical atmospheric conditions for stable air?
- Stratiform clouds
- Continuous or intermittent precip
- Fog
- reduced visibility
- Drifting snow
- Little turbulence
What happens to latent heat during the evaporation and condensation process.
The heat energy needed during evaporation is stored in the water molecule as “latent heat”.because there is a loss of energy there will be a cooling of the air. If air is cooled to the saturation point, the vapor will change state to a liquid and the latent heat will be transferred to the ambient air as sensible heat.
If there is no variation in temperature with altitude it is referred to as
Isothermal
give the 3 units of pressure measurement and state the standard pressure for each
1 Hectopascals 1013
- Kilopascals 101.3
- Inches of mercury 29.92
When air near the surface accumulates in a region, the excess air is forced to rise. what is this called?
Convergence
Describe the conditions under which to provide PBS
- Request from customer
- Specific request
- unsolicited information
- Foreign request
- AWWS assistance
Define Dew point
The temperature to which air would have to be cooled to achieve saturation.
Define Radiation
The process of heat energy transfer in the form of electromagnetic waves
List the 4 terms used when the central pressure is changing with low and high pressure systems
LOW 1.Deepening
2. Filling
High 1. Building
2. Weakening
List the 2 processes by which the atmosphere is cooled
- Radiation cooling
2. Advection cooling
What is the relationship between station pressure and elevation
The higher the station elevation, the lower the station pressure.
Define pressure gradient
The rate of change of pressure with horizontal distance
What is the basic principle of heat transfer.
In a system of 2 bodies, the one with the higher temperature transfers its heat to the cooler body.
Solid particles in the atmosphere are important for 2 reasons.
Enable condensation and freezing and can reduce visibility.
Define relative humidity
The ratio of the amount of water vapor actually in the air compared to the maximum amount of water vapor that the air can hold at that particular temperature.
What causes diurnal variation in pressure
Daytime heating and night time cooling
What are the 5 lifting processes
1. Convection 2 Mechanical Turbulence 3. Orographic lift 4. Frontal Lift 5. Convergence
What are the 2 types of inversions that occur at lower levels
- Nocturnal Inversions
2. Frontal inversions
What is the isobaric interval on surface maps?
intervals of 4 hpa above or below 1000 hpa
Define absolute instability:
As long as the lapse rate in the atmosphere is greater than the dry adiabatic lapse rate vertical movement will be prolonged.
Define latent heat
The quantity of energy needed to change a substance from one state to another
50% of the atmosphere’s weight is below
18000 ft
Daytime heating is..?
Short wave radiation is absorbed and re-emitted by the earth as long wave radiation that heats the atmosphere
What is the general circulation of weather systems over Canada
West to East
Define Positive lapse rate
A decrease of temperature with height
Define Heat
Heat is energy in the process of being transferred from one object to another because of the temperature difference between them
What is stability?
The atmospheric resistance to vertical motion
What are the 3 properties of the atmosphere
- Mobility
- The ability to be compressed
- the ability to be expanded
List the 4 processes by which the atmosphere is heated
- Radiation
- Conduction
- Convection
- Advection
What are the 3 requirements for condensation
- Condensation Nuclei
- Cooling of the air
- Saturated Air.
Define Moisture content
Water vapour content in the air expressed as absolute humidity, relative humidity or as a dew point temperature.
the rate of temperature change with height inside a parcel of air due to expansion or compression is called?
Adiabatic lapse rate
Define Negative lapse rate
An increase of temperature with height
Frontal lift occurs :
- With a cold front, when advancing cold air undermines warmer air ahead forcing it upward.
- With a warm front, when less dense warm air rises above retreating cold air.
In all cases it is the warm air that is lifted.
What are bulges in the sides of high and low pressure areas called, respectively
- Ridges
2. Troughs
What are the typical atmospheric conditions for unstable air?
- Cumuliform clouds
- Showery Precip
- Good visibilty (except in showers)
- Blowing snow
- Turbulence
- thunderstorms
If the atmospheric lapse rate is lower than the adiabatic lapse rate of a parcel of air the air is considered:
Stable
Describe the extent, circulation and characteristics of a high
Always hundreds of KM in diameter and associated with clear weather. The flow around them is clockwise.
Define Temperature
The condition which determines the ability of a body to transfer heat to other bodies
Why is the lapse rate in rising saturated air less than rising dry air?
Latent heat is released during condensation
Define Mean sea level pressure
The atmospheric pressure reduced to sea level
what is orographic lift?
The horizontal movement of air being forced up sloping terain
What does MSL represent on surface weather maps?
Station pressures reduced to a common level by adding an imaginary column of air that extends from the station down to MSL.
What are the 2 causes of convection
- Radiation Heating
2 Cold air advection
Define atmospheric pressure
The force per unit area exerted by the weight of the air at a specific level.
define conditionally unstable
When the atmospheric lapse rate is between the dry and saturated lapse rate.
State Functional goal number 1
- Uniform application of approved standards and procedures
- Professional Communications;and
- Full time attentive flight monitoring and flight information service. All other assignments are secondary. full and active individual support is essental.
Define absolute humidity
The amount of water vapor contained in a unit of air
What is a frontal inversion caused by?
Warm air advection over a cooler air
Define Conduction
The process of heat transfer by contact of 2 bodies at different temperatures
Define station pressure
The actual atmospheric pressure at the elevation of the observing station.
what is sublimation?
Change of state between the solid state and the gaseous state (or vice versa)
Define Isobar
Lines of equal MSL pressure on a surface weather map
What are shallow and steep lapse rates?
- a shallow lapse rate is a small decrease in temperature with height
2 a steep lapse rate is a large decrease in temperature with height.
Define Isothermal layer
No change of temperature with height
What is a nocturnal inversion caused by?
Radiation cooling
Describe the significance of temperature in determining relative humidity
The higher the temperature the greater the capacity the air has for holding water vapor.
When air compresses we say that ____ has occured
Adiabatic heating
If there is an increase in temperature with height it is called an
inversion
How effective is conduction as a heat transfer process in the atmosphere.
The air is a poor conductor of heat, only the bottom meter of the atmosphere is heated by conduction. it becomes more effective when it is combined with a mixing or an eddying motion of the air.
If air is forced to descend it? (2)
compresses and heats
Define Advection
The process of transporting warm or cold air horizontally by the wind. If it heats the air it is called advection heating, if it cools the air it is called advection cooling.
Night-time cooling is?
No incoming radiation but outgoing radiation continues. Less heat is radiated and and the temperature will start to cool.
What is the assumption made in an adiabatic process
that No heat is transferred between between the parcel of air and the ambient air surrounding the parcel.
over a 24 hour period when are pressure minimums and maximums occuring
4am and 4 pm for minimum
10 am and 10pm for maximum
Define Convection
The process of heat energy transfer by vertical motion
Define Saturation
The condition in which the amount of water vapor is the maximum possible at the existing temperature.
What is the most important gas in the atmosphere and why?
Water Vapor, because it can change state under normal atmospheric temperature and pressure.
Station pressures are reduced to MSL for which 2 reasons?
- For representing the pressure distribution on surface weather maps
- For setting aircraft altimeters.
What are the 3 factors that influence the intensity of mechanical turbulence and to what height does it influence
- Uneveness of the ground
- Speed of the wind
- stability of the air (greater instability = greater mech)
- up to 3000ft
