Met 421 Exam 2 Flashcards
Isentropes
-Line of constant potential temperature which is a line of constant entropy.
Advantages of Isentropic Analysis
- Provides clear visual depiction of air parcel motion
- Provides explicit representation of vertical motion on horizontal maps.
- Adiabatic assumption is quite good
How does error introduced by diabatic processes effect omega?
- Error introduced by diabatic processes does not change sign of omega; stronger but of same sign.
Isentropic analysis with cross-isobar wind
- Wind blowing from high to low pressure: Rising motion (ascent)
- From low to high pressure: Sinking motion (subsidence)
Isentropic Vertical Motion Equation Terms
- Term A: Local Pressure tendency
- Term B: Pressure advection.
- Term C: Diabatic heating/cooling.
Frozen Wave Approximation
-Following the motion of the weather system, the value of S is constant.
Classifying cyclones based on Potential Vorticity: Extratropical Low Pressure System
- Main cyclonic PV feature is of stratospheric origin, with some contribution from diabatic processes.
- Fig 4.6 A
Classifying cyclones based on Potential Vorticity: Tropical Low Pressure System
- Main PV feature is of diabatic origin.
- Has a warm core structure
- Absence of stratospheric influences
- Fig 4.6 B
Classifying cyclones based on Potential Vorticity: Subtropical Low Pressure System
- PV feature originates from both stratospheric and diabatic processes.
- Fig 4.6 C
How is PV similar to potential temperature?
-PV represents the vorticity the air would have if it were adiabatically adjusted to a reference latitude.
What role do cyclones play in Earth’s system?
- Precipitation
- Drive downward Hadley branch
- Equator to pole energy transport.
- Latent heat transport
Cyclone formation: Upper waves
-Upper waves create patterns of divergence aloft.
Frontal zone and vorticity
- Vorticity spins up twice as fast in tht frontal zone relative to locations outside of the zone.
- Cyclones prefer to spin up in areas of large pre-existing vorticity such as fronts and inverted troughs.
What happens to the strength of the upper wave as trough deepens?
-Upper wave strengthens as trough deepens, ridge builds to the east.
WAA/CAA and heights aloft
- Warm air advection -> Thickness increases -> Heights rise aloft
- Cold air advection -> Thickness decreases -> Heights falls aloft
Sutcliffe-Petterssen Self Development
- Upper wave pattern amplified due to thermal advection.
- Shorter wavelength
- Larger amplitude
- Strong differential vorticity advection
- Lower surface pressure
- Strong winds
Miller Type A vs Type B cyclogenesis
- Type A: Low pressure center moves continuously NE along coast, NO REDEVELOPMENT.
- Type B: Low pressure center REDEVELOPS along coast, primary dies inland/
Cyclone classifications
- Petterssen type A
- Petterssen type B
- Petterssen type C
- Miller type A
- Miller type B
What method is the frozen wave approximation?
-LaGrangian method
What is a front?
-There isnt much consensus as to what the exact definition is, but Fronts can be thought of as air mass boundaries. Or as hyoergradients of temperature.
Across-front length scale
-100km
Along-front length scale
-1000km
Why do we expect fronts to often be accompanied by clouds and precipitation?
- Areas of strong temp. gradient are often associated with disruption of thermal wind balance.
- QG forcing
9 Frontal Characteristics
- Large horizontal contrast in temp. or moisture
- Minimum in pressure and maximum in cyclonic vorticity
- Strong wind shear (wind shift)
- Large static stability
- Ascending air which leads to clouds and precip
- May trigger sever weather
- Dictates precipitation type
- Not always obvious from isotherm field
- Usually most intense at surface and diminishes aloft
Why do fronts matter?
- Initiation of sever weather
- Cloud and precipitation forecasts
- Wind speed and direction
- Temperature and humidity forecast
- Precipitation types forecast
How does shearing affect cold/warm fronts?
- Shearing STRENGTHENS COLD front
- Shearing WEAKENS WARM front.
Frontogenesis vs Frontlysis
- Frontogenesis: warm air gets warmer and cold air gets colder.
- Frontolysis: Opposite of frontogenesis.
Deformation pattern and the axis of dilatation. FG or FL?
- Axis of dilatation ORTHOGONAL to isotherms = FRONTOLYSIS.
- Axis of dilatation PARALLEL to isoherms = FRONTOGENESIS
Axis of dilatation parallel to isotherms
FRONTOGENESIS
Axis of dilatation orthogonal to isotherms
FRONTOLYSIS
How does SHEARING change frontal intensity?
-Through differential temperature advection by FRONT PARALLEL component of flow
How does CONFLUENCE change frontal intensity?
-Through differential temperature advection by FRONT NORMAL component of flow
How does TILTING change frontal intensity?
-Through differential vertical motion.
What processes does Differential Diabatic Heating include?
- Radiation
- Latent heat release/absorption
- Surface fluxes
Anafronts vs Katafronts location of precipitation
- Katafront: Precipitation at or ahead of surface cold front.
- Anafront: Precipitation at or behind surface front.
Strong vs Moderate temperature gradients
- Strong: 8 Degrees C/ 110 km
- Moderate: 8 Degrees C/ 220 km
Definition of Frontogenesis
-Using potential temperature as our scalar field, the frontogenesis function is defined as the time rate of change of the horizontal potential temp gradient.
4 Terms of the Frontogenesis Equation
- Shearing
- Confluence
- Tilting
- Diabatic
How does vertical potential temp gradient relate to PV?
-Increase in vertical theta gradient = increase in PV.
