Weather cells & weather systems

Jet Streams & History In the upper troposphere “rivers” of rapidly moving air circle

around the Earth.

First discovered in the 1920s by Wasaburo Ooishi.

In 1934, Wiley Postan American pilot.

1939 by a German meteorologist named H. Seilkopf when he used

it in a research paper

Knowledge of the jet stream increased during World War II while

flying between Europe and North America.

Types of jet streams Polar jet streams

Sub tropical jet streams

150 – 500 km wide

0.9-2.2 km thick

Speeds may exceed 300 km/h

Tropopauseheight

18 000 m

12 000 m

6 000 m

Discontinuity or step in tropopause height

“Rivers” of strong wind where cold and warm meet

Jet Stream Cross Section

See: www.avsim.com/avwx/avsim_wxus_jetstream.html

Weather features associated

Jet streaks cause air to rise, lowering the air pressure at the

Earth's surface.

When surface pressures are low, the rising air can form clouds,

precipitation and storms.

Jet streams & Indian monsoon

Sub tropical jet during Summer seasons

1. Air Masses

2. Frontal Systems

3. Mid-latitude Cyclones

4. Thunderstorms

5. Tornadoes

6. Hurricanes

Weather systems

Air mass

Air mass an extremely large body of air (thousands of square

kilometers) whose properties of temperature and moisture are fairly

similar in any horizontal direction at any given altitude.

AIR MASS CLASSIFICATION SOURCE REGIONS

Maritime (m) – originates over oceans or large bodies of water

Continental (c) – originates over land

THERMAL TYPES

Tropical (T) – from low latitudes

Polar (P) – from mid-high latitudes

Arctic (A) – from high latitudes (> 65°N)

Classification of air masses

Fronts

Front:

Front is the transition zone between air masses with distinctly different properties.

Frontogenesis:

A formation, strengthening or generation of a front. This is due to increased contrast of temperature conditions between two air masses.

Frontolysis:

The weakening or dissipation of a front this is due to decreased in temperature contrast between two air masses.

How to identify a front on a surface weather map

Sharp temperature changes over a relatively short distance

Change in moisture content

Rapid shifts in wind direction

Pressure changes

Clouds and precipitation patterns

Types of fronts

WARM FRONT COLD FRONT

STATIONARY FRONT OCCLUDED FRONT

Cold fronts

Cold front symbol

Heavy precipitation

Clouds associated with a cold frontCloud types occur ahead of a cold front.

Cirrus

CumulonimbusAltocumulus

Stratocumulus

ParametersParameters BeforeBefore DuringDuring After After

TemperatureTemperature WarmWarm Sharp fallSharp fall Slight fallSlight fall

Dew PointDew Point HighHigh Sharp fallSharp fall Slight fallSlight fall

WindsWinds SSWSSW ShiftShift W to NW to N

PressurePressure FallFall LowestLowest RiseRise

Identifying a cold front’s passage

Precipitation generally falls in the vicinity of the cold front.

Warm fronts Warm front symbol

Clouds associated with a warm front

Cirrus Nimbostratus

Altostratus

Cirrostratus

STATIONARY FRONT

EXTRA TROPICAL/ MID-LATITUDE CYCLONES

Synoptic scale low pressure weather systems that occur

in the middle latitudes, connected with fronts and

horizontal gradients in temperature and dew point

along anticyclones.

Capable of producing CloudinessMild showersheavy galesThunderstorms.

Life cycle of a mid-latitude cyclone

Cyclogenesis

Open stage

Occluded stage

Dissolving stage

Cyclogenesis

Open stage

Occluded stage

Dissolving stage

THUNDERSTORMS

It is a type of storm characterized by the presence of lightening and

its acoustic effect on the earths atmosphere known as thunder.

Congenial conditions to form:

Moisture

Unstable Air

Upward drift

THUNDER STORMS

Stages of development

Weather phenomena associated

Down burst of winds

Lightening & Acoustic sounds

Hail storms

Heavy precipitation & flash floods

TORNADOES

Tornadoes are narrow, funnel-shaped spiraling wind that rotate at

speeds of up to 500 km/hr because of extreme pressure gradients.

Tornadoes are ranked from F0 (weakest) to F5 (strongest) using

the Fujita Intensity scale.

Most tornadoes move to the east or northeast at an average speed

of approximately 50 km/hr.

Tornadoes are associated with thunderstorms and develop in

association with mesocyclones within the thunderstorm cell.

Tornado formation:• Early stage:

Contrasting vertical wind speeds generate local winds that rotate

about a horizontal axis.

• Updraft stage:

Mesocyclones may be up to 10 km in diameter.

•Tornado stage:

More intense spiraling winds within a tornado that extend

downward from a cloud base toward the ground surface .

Tornado

Management of tornado

Warning in advance

Precautions to protect the agricultural produce

Quick removal of debris

Water sprouts

HURRICANES / TROPICAL CYCLONES

It is a rapidly rotating storm system characterized by a low

pressure center, strong winds, and a spiral arrangement of

thunder storm that produce heavy rain.

Chief characteristics:

High winds (more than 119 km/hr)

Heavy rainfall (10-25 cm)

Storm surges (sudden rise in sea level) along coastlines.

HURRICANES/ TYPHOONS/CYCLONES/WILLY WILLY:

Anatomy of hurricane

Factors favor to form:

Water temperature of at least 26.5 °C to a depth of at least 50 m

Heat of condensation energy

pre-existing system of disturbed weather

High humidity in lower-to-mid troposphere

Low amounts of wind shear

Saffir-Simpson hurricane intensity scale