THE ATMOSPHERE.
· THE AIR EXTENDS 200KM ABOVE THE SURFACE.
· THE VARIOUS LAYERS ARE:
· INOSPHERE 80-200KM
· MEROSPHERE 50 –80 KM.
· STRATOSPHERE 8/16 -S/L.
· ALL WEATHER CHANGES OCCUR IN THE TROPOSPHERE.ALSO ALL THE WATER VAPOUR TOO.
· IN THE STRATOSPHERE THE AIR TEMPERATURE REMAINS FAIRLY CONSTANT,UPTO 56.5 DEGREE K.
ADIABATIC CHANGE.
IT IS THE CHANGE IN THE TEMPERATURE DUE TO INCREASE OR DECREASE IN ITS VOLUME.WITHOUT ANY EXCHANGE OF HEAT FROM THE SURROUNDINGS
D A L R
DRY ADIABATIC LAPSE RATE:THE TEMPERATURE OF A DRY PARCEL OF AIR WHICH IS MADE TO RISE , FALLS AT A STEADY RATE OF 10 DEGREES C.
FOR EVERY KILOMETRE OF ASCENT.
S A L R.
SATURATED ADIABATIC LAPSE RATE.: THE TEMPERATURE FALLS BY AN AVERAGE OF FIVE DEGREES C,PER K.M. OF ASCENT.
WHY S A L R LESS THAN D A L R.
AS THE SATURATED AIR IS COOLED ITS CAPACITY TO HOLD WATER DECREASES AND THE EXCESS MOISTURE CONDENSES TO FORM WATER DROPLETS. THIS CONDENSATION GIVES A LATENT HEAT WHICH WARMS THE AIR UP.
DIURNAL VARIATION IN TEMPERATURE.
MAXIMUM AT 1400 HRS(LT)
MINIMUM AT HALF AN HOUR AFTER SUNRISE.
# DIURNAL OVER LAND CAN BE 20 DEGREES WHILE OVER SEA CAN BE AS LOW AS 1 DEGREE.
REASON: LAND BEING SOLID HAS A LOW VALUE OF SPECIFIC HEAT SO HEATS UP OR COOLS EASILY.
· HEAT RECEIVED BY THE SUN IS RETAINED BY THE TOP LAYER OF LAND (FEW CMS. )
· NEGLIGIBLE EVAPORATION OCCURS OVERLAND.
SEMI-DIURNAL VARIATION IN ATMOSPHERIC PRESSURE.
# MAX AT 1000 AND 2200 HRS
# MIN AT 0400 AND 1600 HRS
THE AVERAGE LAPSE RATE BEING 115 MB. PER KILOMETRE OF ASCENT.
BAROMETRIC TENDENCY: THE DIFFERENCE BETWEEN ATMOSPHERIC PRESSURE AT THE TIME OF OBSERCATION AND THREE HOURS EARLIER AT THE PLACE.
FOHN WIND EFFECT:
# STARTING OUT WE HAVE DEW PT 15 DEG. C AND THE TEMPERATURE 25 DEG C
# D A L R APPLIES AS AIR RISES.
# TEMPERATURE DROPS TO 15 DEG C. FOR THE FIRST K.M. OF ASCENT.
# AIR IS THUS SATURATED, HENCE SALR. APPLIES (5 DEG. C) AND THE MOISTURE IS GIVEN OFF AS AN OROGRAPHIC CLOUD.
D E F I N I T I O N S.
1) DEW: WHEN WATER VAPOUR CONDENSES INTO DROPLETS OF WATER AND GETS DEPOSITED ON EXPOSED SURFACES ON OR NEAR THE GROUND IT IS CALLED DEW.
2) HOAR FROST: IT IS THE NAME GIVEN TO ICE CRYSTALS DEPOSITED ON EXPOSED SURFACES ON OR NEAR THE GROUND. WHEN THE GROUND TEMPERATURE IS MUCH LOWER THAN FREEZING POINT IN THIS CASE WATER VAPOUR DIRECTLY TURNS INTO ICE WITHOUT BECOMING WATER
3) GLASED FROST: IT IS A TRANSPARENT SMOOTH LAYER OF ICE FORMED WHEN RAIN OR DRIZZLE FALLS ON A SURFACE WHOSE TEMPERATURE IS BELOW FREEZING. IN U.K. IT IS ALSO CALLED “BLACK ICE”
4) RIME: IF THE TEMPERATURE OF WATER PARTICLES IN A FOG IS BELOW 0 DEG,C. THEY ARE SAID TO BE SUPERCOOLED DROPLETS OF WATER. WHEN THEY COME IN CONTACT WITH VERY COLD SOLID OBJECTS SUCH AS SHIPS SUPERSTRUCTURE THEY FREEZE IMMEDIATELY.
5) DRIZZLE: FINE DROPLETS OF WATER WHOSE DIAMETRE IS LESS THAN 0.5 MM.
6) RAIN: DROPLETS LARGER THAN 0.5 MM. IN DIAMETER
7) FREEZING RAIN: DROPS FREEZE ON IMPACT WITH COLD GROUND.
8) SNOW FLAKES: LOOSE CLUSTER OF ICE CRYSTALS HAVING BRANCHES.
9) ICE PELLETS: PELLETS OF ICE LESS THAN 0.5 MM.
10) HAIL: BALLS OF HARD ICE OF 0.5 TO 50 MM. IN DIA.
11) SEA (WAVES) : CAUSED AS A RESULT OF WIND FORCE AS PER THE BEAUFORT SCALE. THE HEIGHT IS DIRECTLY PROPORTIONAL TO THE STRENGTH OF WIND.
12) SWELL: WAVES ON THE SEA SURFACE FORMED BY WIND WHICH HAS STOPPED BLOWING AT SOME OTHER PLACE FAR AWAY.
13) GUST: SUDDERN INCREASE IN WIND SPEED FOR A VERY SHORT PERIOD OF TIME CAUSED BY TERRISTIAL OBSTRUCTIONS.
14) SQUALL: IT IS A SUDDERN INCREASE IN WIND FORCE BY 3 STAGES OF BEAUFORT SCALE.
#REACHING ATLEAST UPTO FORCE 6 AND LASTING ATLEAST FOR ONE MINUTE.
F O G
TYPES OF FOG:
1) RADIATION FOG: ALSO CALLED LAND FOG BECAUSE IT FORMS ONLY OVER LAND.
THE CONDITIONS FAVOURABLE FOR THIS TYPE ARE:
· LARGE MOISTURE CONTENT IN THE LOWER LAYERS OF THE ATMOSPHERE.
· LITTLE OR NO CLOUD COVER AT NIGHT.
· LIGHT BREEZE AT THE SURFACE.
· COLD WET SURFACE OF LAND.
2) ADVECTION FOG: ALSO CALLED SEA FOG BECAUSE IT IS MOSTLY FOUND OVER SEA
IT IS FORMED WHEN A MOIST WIND BLOWS OVER A COLD WET SURFACE.
ADVECTION FOG CAN BE PREDICTED BY TAKING HOURLY READINGS OF THE SEA WATER TEMPERATURE AND CALCULATING DEW POINT OF THE ATMOSPHERE. THE VERTICAL AXIS HAS THE SCALE FOR TEMPERATURE AND THE HORIZONTAL AXIS HAS THE LMT SCALE. HOURLY READINGS OF THE DEW POINT TEMPERATURE AND SEA WATER TEMPERATURE ARE OBTAINED AS CURVES THE POINT WHERE THE TWO CURVES ARE PREDICTED TO INTERSECT IS THE TIME FOG MAY BE ANTICIPATED AND DUE PRECAUTIONS TAKEN.
3) SMOG: RADIATION FOG MIXED WITH INDUSTRIAL SMOKE.
4) ARCTIC SEA SMOKE: WHEN COLD DRY AIR PASSES OVER A RELATIVELY COLD SURFACE THE WATER VAPOUR EVAPORATING FROM THE SEA SURFACE CONDENSES INTO WATER VAPOUR VISIBLE AS VERTICAL STEAMING STREAMERS.
4) HILL OR OROGRAPHIC FOG: WHEN WIND COMES AGAINST A MOUNTAIN RANGE AND BEGINS TO CLIMB OVER IT, IT COOLS ADIABATICALLY. EHEN ITS DEW POINT IS REACHED FURTHER COOLING RESULTS IN ITS MOISTURE CONTENT TO CONDENSE.
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TYPES OF CLOUDS:
# CLOUDS GROUPED ACCORDING TO THEIR HEIGHT ABOVE SEA LEVEL:
1) LOW CLOUDS HAVE THEIR BASES BETWEEN SEA LEVEL AND 2 KM. COMPRISING MAINLY OF WATER VAPOUR.
2) MEDIUM CLOUDS CALLED “ALTO” HAVE THEIR BASES 2 TO 6 KMS. ABOVE SEA LEVEL COMPRISING MAINLY OF WATER VAPOUR AND ICE PARTICLES.
3) HIGH CLOUDS HAVE THE PREFIX “CIRRO” MADE UP ENTIRELY OF ICE PARTICLES.
# CLOUDS GROUPED ACCORDING TO THEIR APPEARANCE:
1) “CIRRUS”: A SILVERY CLOUD IN THE FORM OF FEATHERS OR FIBRES SEEN HIGH UP.
2) “CUMULUS”: A WHITE CLOUD SHAPED LIKE A CAULIFLOWER WITH GREAT VERTICAL EXTENT.
3) “STRATUS”: AN EVEN LAYER OF GREY CLOUD NON RAIN BEARING.
4) “NIMBOSTRATUS”: AN EVEN LAYER OF CLOUD RAIN BEARING.
BUYS BALLOTS LAW:
FACE THE TRUE WIND AND THE LOW PRESSURE REGION WILL BE TOWARDS THE RIGHT HAND SIDE IN THE NORTHERN HEMISPHERE.
# IT SHOULD NOT BE APPLIED IN THE VICINITY OF LAND AS THE WIND EXPERIENCED IS NOT FREE AND UNOBSTRUCTED AND IT MAY BE DEFLECTED BY LAND.
# IT SHOULD NOT BE APPLIED WITHIN A FEW DEGREES OF THE EQUATOR AS THE CORIOLIS FORCE IS NEGLIGIBLE THERE AND THE WIND DIRECTLY BLOWS OVER FROM THE HIGH-PRESSURE REGION TO THE LOW-PRESSURE REGION.
