HORIZONTAL AIR MOTIONS

HOW WIND ARISES AT THE LAND AND OCEAN SURFACE

DEFINITION:

PRESSURE GRADIENT = DIFFERENCE IN PRESSURE FROM ONE POINT TO ANOTHER

VERTICALLY, PRESSURE DECREASES EXPONENTIALLY, BUT

HORIZONTALLY PRESSURE VARIES BY SMALL AMOUNTS,

TYPICALLY 1 MILLIBAR PER 100 KM.

P/ X = P

VERTICAL ATMOSPHERIC PRESSURE PROFILE

P

Z

Pressure Records around the Earth

Note, Hurricane Wilma, Oct. 2005 set new Atlantic record at 882 mb.

Newton’s 1 stLaw is appliedhere!

Method of pressuremeasurement

NON-ROTATING EARTH MERIDINAL CIRCULATION

TYPICAL WIND DIRECTIONS AND VELOCITIES

UPPER LEVEL (TROPOPAUSE) ZONAL WINDS---

WEST TO EAST (WITH NORTH-SOUTH UNDULATIONS)AT VELOCITIES OF 20-30 METERS/SEC...

SURFACE WINDS ...

WESTERLIES [WEST TO EAST AT MID-LATITUDES]...

TRADE WINDS [EAST TO WEST AT TROPICALLATITUDES]...

BOTH WESTERLIES AND TRADES HAVE 5-20METERS/SEC VELOCITIES

MERIDIONAL WINDS:

NORTH TO SOUTH WINDS AT VELOCITIES OFABOUT 2 METERS/SEC...

VERTICAL WINDS [RETURN IN CIRCULATION CELLS] VELOCITY OF ABOUT 0.2 METERS/SEC...

Remove the Earth and the spacecraft travels tangentially away from the Earth at > 7 km/sec.

MORE EXAMPLES OF ORBITS

DEFINITION:

VORTICITY IS DEFINED AS THE TOTAL AMOUNT OF ROTATION ASSOCIATEDWITH AN AIR PARCEL.

FOR THE ROTATING EARTH:

VORTICITY = ROTATION

LOW VORTICITY NEAR EQUATOR:

TROPICAL WEATHER PATTERNS

HIGH VORTICITY AT TEMPERATURELATITUDES:

MID-LATITUDE WEATHER PATTERNS

AMONG EFFECTS OF VORTICITY:

PRODUCTION OF MID-LATITUDE CYCLONES

TORNADOES

HURRICANES

The Earth rotates once each day, that is Ώ x number of seconds per day!

A CONSEQUENCE OF THE ROTATING EARTH:

WIND ON A ROTATING PLANET (EARTH) AND NEWTON’S FIRST LAW

EFFECT OF FRICTION ON DIRECTION OF WIND

DEFLECTION OF WIND DUE TO THE CORIOLISFORCE IS LATITUDE DEPENDENT BECAUSE THEFORCE ITSELF DEPENDS ON LATITUDE.

WINDS ALOFT ARE DUE TO PRESSURE GRADIENT AND CORIOLIOS FORCE ACTING TOGETHER!

JET STREAM IS GEOSTROPHIC WIND PLUS THERMAL WIND

THERE ARE TWO COMPONENTS TO WINDS ALOFT.

WE KNOW THAT TEMPERATURE DIFFERENCES INDUCE PRESSURE CHANGES WITH HEIGHT.

JET STREAM OR ZONAL WINDS ARE SYNOPTIC AND UNDULATE

ACTUAL GLOBAL CIRCULATION DEPENDS UPON ROTATION OF EARTH

GRADIENT WINDS AROUND CURVED ISOBARS

HIGH PRESSURE (CW ROTATION) ---> vG > vg;

TYPICALLY REACHING ~ 12 METERS/SECOND

LOW PRESSURE (CCW ROTATION) ---> vG < vg;

TYPICALLY REACHING ~ 9 METERS/SECOND

SUMMARIZING ORIGINS OF WINDS

1. PRESSURE GRADIENT FORCE.

2. CORIOLIS FORCE CURVING MOTION AND CAUSING ROTATION.

3. EXCHANGE OF EARTH AND ATMOSPHERE ROTATION DUE TO CONSERVATION OF ANGULAR MOMENTUM = VORTICITY.

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: SIM 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: SIM 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.