The Tricellular Circulation is highly dynamic, varying with the seasons and bringing thePolar front back and forth across the USA.

RANGE OF THEPOLAR FRONT

THE POLAR FRONT IS THE REGION OF FORMATION OF ANTICYCLONES ANDCYCLONES IN THE MID-LATITUDES. The anticyclone and cyclone are CLOSEDCirculation wind patterns.

The anticyclone pressure gradient forces wind OUTWARD across isobars, and CoriolisForce forces the wind to turn rightward, while friction causes wind to move from HI to LOWpressure, resulting in a clockwise rotation and DIVERGENCE.

The cyclonic flow is INWARD in response to the pressure gradient, Coriolis, and frictional forces,And turns counterclockwise (CCW). Low pressure centers, hurricanes, and tornados are cyclonic.

W IND TYPES A ND ORIGINS

1. PRESSURE G RADIENT W IND

O RIGIN: PRESSURE D IFFERENCESD IRECTION: ACROSS ISOBARSVELOCITY: TYPICALLY 10-20 M PH (5-10 M PS)

2 . G EOSTROPH IC W IND

ORIGIN: PRESSURE GRADIENT AND CORIOLIS FORC ED IRECTION: PARALLEL TO ISOBARSVELOCITY: S IM ILAR TO PRESSURE GRADIENT W IND

3. G RADIENT W IND

O RIGIN: PRESSURE GRADIENT AND CORIOLISFOR CE,

BU T W ITH A IR M OVING A ROUND CLOSEDISOBARS

D IRECTION: AROUND CLOSED ISOBARSVELOCITY: S IM ILAR TO G EOSTROPH IC W IND, B UT

HIGHER AROUND H IGH PRESSURE CENTERTHAN AR OUND LOW PRESSURE C ENTER(EXCEPT FOR EFFECTS O F GREATER PRESSUREGRADIENTS IN THE CASE OF A TORNADO ORHURRICANE.

Typical pattern of a mature mid-latitude Northern hemisphere cyclone, showing isobars, and wind velocities. The pressure gradient shown here is very high, resulting in hurricane force wind.

DEFINITION:

BAROTROPIC REGION:

A REGION OF CONSTANT PRESSURE, DENSITY, ANDTEMPERATURE... I.E. WHERE LITTLE IS HAPPENING

DEFINITION:

BAROCLINIC REGION:

A REGION OF VARYING DENSITY, CONSTANTPRESSURE, BUT CHANGING TEMPERATURE.

BAROCLINIC REGIONS POSSESS POTENTIAL ENERGYTHAT, WHEN RELEASED, CAN DRIVE THE FORMATIONOF MID-LATITUDE CYCLONES.

DEFINITION: FRONT

THE BOUNDARY BETWEEN AIR MASSES OF DIFFERINGBAROCLINICITY

I.E. (D IFFERING TEMPERATURE AND DENSITY)

BJERKNES' POLAR FRONT THEORY

IN THE 1920'S, DEVELOPED THE THEORY OFCYCLONE FORMATION, DEVELOPMENT ANDDISSIPATION.

DEFINITION: CYCLOGENESIS

THE DEVELOPMENT AND STRENGTHENING OF A MID-LATITUDE CYCLONE

Relative advection brings air of different temperatures atop one another and results in a changeIn the environmental lapse rate, as shown the advection STEEPENS the lapse rate.

The frontal zone tilts TOWARD the cold front as the denser cold air under runs the lighter warm air.

When air velocity differs between regions (V1 and V2), convergence or divergence can occur.Convergence, as shown here, typically increases lapse rates, making air tend toward instability.

In addition to divergence and convergence, winds can be compressional (katabatic).

Cyclones and Anticyclones work together to create CIRCULATION CELLS in theAtmosphere. Both are an expression of VORTICITY in the atmosphere, and the resulting turbulence in the mid-latitudes.

VERTICALLY AS WELL AS HORIZONTALLY, MID-LATITUDE CYCLONESAND ANTICYCLONES OPERATE LIKE AN ATMOSPHERIC HEAT ENGINE !

CYCLOGENESIS.

As shown here, arotation has developedabout a low pressurecenter as relative advection occurs, alongwith the effects ofvorticity, producing aWave Cyclone.

The Wave Cycloneseen horizontally alongthe black line revealsThe three dimensionalnature of the process.

Specific Clouds areAssociated withDevelopment of aCyclone and its Passage.

Cloud types observed in association with polar front weather.

Approach of a warm front

Approach of a Cold Front

Cyclogenesis, Development to Dissipation

Types of Occluded Fronts

The progression of wave cyclones through maturation and dissipation produces specific cloud types, wind directions, and precipitation that can aid in the prediction of weather.