CLIMATE AND WEATHER IN THIS POST I WILL BE COVERING :
MID-LATITUDE CYCLONES
MID-LATITUDE CYCLONES MID-LATITUDE CYCLONES ORIGINATE WHEN THE WARM TROPICAL WESTERLY WINDS (30 DEGREES N/S) MEET THE COLD POLAR EASTERLY WINDS (90 DEGREES N/S) AT THE POLAR FRONTS.
THE POLAR FRONTS OCCURS AT THE 60 DEGREES N/S LATITUDE
ALERNATE NAMES FOR MID-LATITUDE CYCLONES ARE:
TEMPERATE CYCLONES,FRONTAL DEPRESSIONS,WAVE DEPRESSION AND EXTRA-TROPICAL CYCLONES
GENERAL CHARACTERISTICS ARE:
>THEY OCCUR BETWEEN THE 30 TO 60 DEGREES N/S LATITUDES
>MOVE FROM WEST TO EAST OR EASTWARDS
>STEERED BY THE WESTERLIES IN THE WESTERLY WIND BELT
>TEMPERATE CYCLONES CONSIST OF FRONTS-(WARM AND COLD FRONTS)
>SIZE:THEY ARE VERY LARGE CYCLONES -WITH A DIAMETER OF ABOUT 1000KM
>OCCUR THROUGHOUT THE YEAR BUT AFFECTS SOUTH AFRICA MAINLY IN WINTER
>IT LAST BETWEEN 4 TO 14 DAYS.
CONDITIONS NECESSARY FOR FORMATION
>WARM SUB-TROPICAL AIR MEETS WITH THE COLD POLAR AIR AT THE POLAR FRONT
>BOTH AIR MASSES MOVE PARALLEL TO EACH OTHER IN OPPOSITE DIRECTIONS
>FRICTIONAL DRAG BETWEEN THE AIR MASSES CAUSE THEM TO INTERACT WITH EACH OTHER.THIS FRICTIONAL DRAG OCCURS AS A RESULT OF:
>DIFFERENCES IN THE SPEED AT WHICH BOTH AIR MASSES MOVE
>AN UNEVEN SURFACE OVER WHICH THEY MOVE
>TEMPERATURE DIFFERENCES BETWEEN LAND AND SEA SURFACE
STAGES IN FORMATION OF A MID-LATITUDE CYCLONE:
>THE INITIAL STAGE
-WARM TROPICAL AIR FROM 30 DEGREES SOUTH AND COLD POLAR AIR FROM 90 DEGREES SOUTH CONVERGE AT POLAR FRONT (60 DEGREES SOUTH)
-CORIOLIS FORCE DEFLECTS BOTH AIR MASSES IN THE SOUTHERN HEMISPHERE TOWARDS THE LEFT CAUSING THEM TO MOVE PARALLEL TO EACH OTHER IN OPPOSITE DIRECTIONS
>WAVE FORMATION
-THE WAVE STAGE OCCURS WHEN FRICTIONAL DRAG TAKES PLACE BETWWEN THE TWO AIR MASSES
-A WEDGE OF WARM AIR BEGINS TO BE UPLIFTED BY THE COLD AIR
-FRONTS BEGIN TO FORM AS AIR CONVERGES IN A CLOCKWISE DIRECTION IN THE SOUTHERN HEMISPHERE TOWARDS THE LOW PRESSURE CENTRE
-WHAT IS A COLD FRONT? IT IS THE LEADING EDGE OF A MOVING BODY OF COLD AIR
-WHAT IS A WARM FRONT?IT IS THE LEADING EDGE OF A MASS OF MOVING WARM AIR
>MATURE STAGE
-THE WAVE DEEPENS OR INTENSIFIES AND ISOBARS AT THE FRONTS KINK AND POINT AWAY FROM THE LOW PRESSURE
-THE COLD AND WARM FRONTS AND SECTORS ARE FULLY DEVELOPED IN A WELL FORMED V SHAPE
-COOLING,CONDENSATION,CLOUD FORMATION AND RAIN ARE ASSOCIATED WITH THE RISING AIR
-THE COLD FRONT IS ASSOCIATED WITH TOWERING CUMULONIMBUS CLOUDS AND THE WARM FRONT WITH A BROAD BAND OF STRATUS CLOUDS
>OCCLUSION STAGE
-THIS STAGE IS REACHED WHEN THE COLD FRONT CATCHES UP WITH THE WARM FRONT
-OCCLUSION STARTS AT THE APEX BECAUSE IT IS THE SHORTEST DISTANCE BETWEEN THE TWOFRONTS.AN OCCLUSION CAN EITHER BE A WA RM OR A COLD FRONT OCCLUSION
-A COLD FRONT OCCLUSION TAKES PLACE WHEN THE COLDEST AIR IS FOUND BEHIND THE COLD FRONT,AND THIS CAUSES THE WARM AIR TO BE UPLIFTED ALONG THE COLD FRONT>THE COLD FRONT UNDERCUTS THE WARM FRONT
-A WARM FRONT OCCLUSION TAKES PLACE WHEN THE COLDEST AIR IS FOUND AHEAD OF THE WARM FRONT AND THIS CAUSES THE COLD AIR TO BE UPLIFTED ALONG THE WARM FRONT
-WHEN ALL THE WARM AIR HAS BEEN UPLIFTED THE CYCLONE IS IN THE DISSIPATING OR DEGENERATING STAGE
WEATHER ASSOCIATED WITH THE PASSAGE OF A MID-LATITUDE CYCLONE
AS EACH SECTOR OF THE MID-LATITUDE CYCLONE MOVES OVER AN AREA,THERE IS A CHANGE IN WEATHER
IN WINTER THE MID-LATITUDE CYCLONE MIGRATES NORTHWARDS THUS HAVING A GREATER IMPACT OVER THE LAND.IN SUMMER HOW EVER THEY MIGRATE SOUTHWARDS AND HAVE VERY LITTLE OR NO IMPACT ON THE WEATHER OVER THE LAND
CYCLONE FAMILIES
MID-LATITUDE CYCLONES DO NOT OCCUR IN ISOLATION.THEY FORM IN GROUPS IN THE WEST WIND BELT AND MOVE EASTWARDS.SOMETIMES AS MANY AS FOUR OR FIVE PASS THROUGH A CERTAIN AREA IN QUICK SUCCESSION AND ARE VISIBLE ON A SYNOPTIC WEATER MAP. THEASE ARE CALLED "CYCLONE FAMILIES"
PRECAUTIONARY AND MANAGEMENT STRATEGIES:
>CONSTRUCTION OF HOUSES AND INFRA-STRUCTURE SHOULD BE AVOIDED IN LOW-LYING AREAS TO PREVENT THE THREAT OF FLOODING.
>AN EFFICIENT DRAINAGE SYSTEM IN URBAN AREAS WILL REDUCE FLOODING RISKS
>LIVESTOCK, EG. SHEEP, SHOULD BE PLACED IN A KRAAL, SHED OR ANY OTHER ENCLOSED AREA TO PREVENT LOSSES DURING SEVERE SNOWFALL
>FARMERS SHOULD HAVE SUFFICIENT GRAIN AND FODDER TO MINIMISE/PREVENT LIVESTOCK LOSS
>IT IS IMPORTANT TO KEEP UPDATED ON WEATHER CONDITIONS IN WINTER BEFORE PLANNING HIKES AND OUTDOOR ACTIVITIES
>DO NOT VENTURE OUT INTO THE OPEN SEA DURING FRONTAL WEATHER. SECURE FRISHING VESSELS TO THE HARBOURS AND KEEP TRACK OF THE WEATHER VIA TV OR RADIO BEFORE ATTEMPTING TO GO OUT
>AS VISIBILITY IS VERY POOR, MINIMISE DRIVING AND REMAIN INDOORS UNTIL WEATHER CLEARS
>DANGER FROM ROCK FALLS IS ALSO INCREASED AT THIS TIME RESULTING IN LOSS OF LIFE, INJURY AND DAMAGE TO PROPERTY.
>STOCK UP TIMEOUSLY ON ESSENTIALS AS ELECTRICITY BLACKOUTS,LOSS OF COMMUNICATION CHANNELS AND SHORTER TRADING HOURS IS COMMON DURING THIS TIME.
THE END
IN MY NEXT POST I WILL BE COVERING TROPICAL CYCLONES
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