chapter 17 air masses & tamp; fronts

“Physical & General Geography (Paper I) for CSS & PMS” By Imran Bashir

In the Name of

Allah,

the Boundlessly Merciful, the InfinitelyCompassionate. Praise be to Allah, the Lord of theworlds; and peace and blessings of Allah be uponHis Prophet

Muhammed

Chapter 21: AIR MASSES, FRONTS AND ATMOSPHERIC

DISTURBANCES

“Geography for CSS / PMS ………. Author: Imran Bashir”

AIR MASS..... INTRODUCTION

An air mass is a large mass of air havingsimilar temperature and moisturecharacteristics over its horizontal extent.An air mass occupies thousands of squaremiles of the Earth's surface.

Source region

• The part of earth where air masses acquire theirdistinguish qualities are called source regions.

The abbreviations used to classify air masses

Word Meansc

Continental Dry

Maritime Moist

Tropical warm

Polar Cold

Arctic Very cold

warm and moist cold and dry

• Air masses are classified according :• 1. Latitudinal position• 2. Underlying surface

AIR MASS CLASSIFICATION

• With respect to “Latitudinal Positions”, five types of air masses are as follows:

Air Mass Symbol Source Regions

Arctic A Arctic Ocean and fringing (bordering) landsAntarctic AA Antarctica

Polar P Continents and oceans (50° – 60° North and South)

Tropical T Continents and oceans (20° – 35° North and South)

Equatorial E Oceans close to equator

• With respect to “Underlying Surface”, two further sub-divisions are imposed on the preceding type as follows:

Air Mass Symbol Source Regions

Maritime M Oceans

Continental C Continents

• By combining types based on “Latitudinal Positions” with those based on “Underlying Surface”, a list of six important air masses results as under:

Air Mass Symbol Properties

Continental Arctic cA Cold, dry

Continental Antarctic cAA Very cold, very dry (winter)

Continental Polar cP Cold, dry (winter)

Maritime Polar mP Cold, moist (winter)

Continental Tropical cT Warm, dry

Maritime Tropical mT Warm, moist

Maritime Equatorial mE Warm, very moist

• Source Areas• Typical Characteristics

1. CONTINENTAL ARCTICAND ANTARCTIC (CA&CAA)

2.CONTINENTAL POLAR(CP)

• Source Areas • Typical Characteristics

3.MARITIME POLAR (MP)

4.CONTINENTAL TROPICAL(CT)

5.MARITIME TROPICAL (MT)

• The name maritime equatorial is sometimes applied to very moist and warm air masses, originating within a few degrees of equator. These are a pronounced form of maritime tropical air masses. This air mass holds about 200 times as much water vapour as the extremely cold Arctic and Antarctic air mass

6.MARITIME EQUATORIAL (ME)

Global distribution of air masses

AIR MASSES OF NORTH AMERICA

Five main air masses affect EuropeAIR MASS OF EUROPE

WHAT IS A FRONT?• Simply, we can say that the line of

contact along the separation plane between air masses and the surface is termed as a Front.

1. Cold FrontA frontal contact zone in which cold air is invading warm air zone is termed as a “cold front”.

Weather associated with cold front

2.Warm FrontA warm front is that in which warm air is moving into a region of colder air.

Weather associated with warm front

3. Occluded frontsCold fronts normally move along the ground at afaster rate than warm fronts. Hence, when bothtypes are in the neighbourhood, as they are in thecyclonic storms, the cold front may overtake thewarm front. An “occluded front” then results. Thecolder air of the fast-moving cold front remainsnext to the ground, forcing both the warm air andthe less cold air to rise over it. The warm air massis lifted completely free of the ground.

SEVERE WEATHER

TornadoesA tornado is an intense system of low pressure

with violent updrafts and converging winds.Tornadoes have been documented in almost allthe regions of the Earth, though they are mostprevalent in the United States.Tornadoes are spawned from severethunderstorms.

“Physical & General Geography (Paper I) for CSS & PMS” By Imran Bashir“Geography for CSS / PMS ………. Author: Imran Bashir”

5. HURRICANES

A hurricane (or typhoon) is a large rotatingcyclonic system born in the tropics.They are the largest and most destructivestorms on Earth.

How Hurricanes Form?

“Physical & General Geography (Paper I) for CSS & PMS” By Imran Bashir“Geography for CSS / PMS ………. Author: Imran Bashir”

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