CHAPTER 19

WEATHER AND CLIMATE

WEATHER – describe the condition in the atmosphere at a particular time, on a particular day in a particular place.

• CLIMATE - describes the average of all weather conditions in a particular place over many many years, usually decades.

ELEMENTS OF WEATHER

• 1. TEMPERATURE – is the most important element of weather as it influences humidity, precipitation, air pressure, wind speed and direction,and cloud formation.

• 2.HUMIDITY – is the amount of water vapor present in the atmosphere.– RELATIVE HUMIDITY – refers to the ratio of

moisture actually present in the air compared to what the air can hold at a given temperature.

– HYGROMETER – used to measure humidity.3. ATMOSPHERIC PRESSURE - pressure exerted

by air.

HIGH PRESSURE AREAS – areas where the air is thicker. ( produces a good weather )LOW PRESSURE AREAS – areas where the air is not thick

( produces a bad weather )• 4. WIND AND AIR MASSES – WIND – moving air (continual rising and falling

of air) - it blows from an area of high pressure to an area of low pressure

2 GENERAL TYPES OF WINDA. LOCAL WINDS – flow from any direction and usually cover short distances.

B. GLOBAL WINDS - blow from a specific direction and almost always travel longer distances.

MINOR WINDS

• 1. SEA BREEZE - the wind that blows from the sea towards the land during daytime.

• 2. LAND BREEZE – the wind that blows from the land to the sea during the night.

AIR MASS - An air mass is a body of air that extends over a large area and has nearly uniform temperature and humidity in any horizontal direction. When air masses meet, there is a mixing of cold and warm air, this mixing will cause a disturbance in the atmosphere, and a thunderstorm may result.It may also result in FRONTS.

FRONT – 2 air masses that meet at a certain point.

TYPE OF FRONT ASSOCIATED WEATHER

1. COLD ( when a mass of cold air meets & replaces a mass of warm air)

Short precipitation occurs quickly but may be heavy, more violent storms, rapid movement, cooler temperature

2. WARM ( when a mass of warm air overtakes a cold air mass & moves over it)

Prolonged gentle precipitation, slow movement, warm temperature

3. OCCLUDED ( cold front overtakes a warm front & is rushed upward)

Complex weather, light rainshowers maybe followed by thunder storm, precipitation caused by rising warm air.

4. STATIONARY ( warm air mass meets a cold air mass & no movement occurs )

Long periods of the same weather, weather changes when front begins to move.

5. CLOUD FORMATION

• Water vapor and dust are involve in cloud formation.

• Clouds are formed as water condenses on particles called condensation nuclei in the atmosphere.

TYPES OF CLOUDS

• 1. CIRRUS - are thin and wispy. Formed at the highest altitudes usually

between 6000 – 10 000 m above the surface of the earth.

2. CUMULUS – are thick and puffy, with flat bottom. They look like cotton balls piled together. They are generally low clouds and known as “ fair weather” clouds.

STRATUS – are layered and sprea out over the whole sky like a blanket. Gentle rain may produced by stratus clouds.

NIMBUS – ( rain ) dark and heavy rain cloud that is going to bring rain.

6. PRECIPITATION – is the transfer of water from atmosphere back to the earth’s surface. ( rain, snow, hail, sleet )

FORMS OF PRECIPITATION DESCRIPTION

1. RAIN formed when snow melts as it falls

2. Snow Water vapor changes directly into solid crystals

3. SLEET Snow melts and falls through layers of cold air where it freezes

4. HAIL Sleet is pushed up and down in the atmosphere until it grows larger

snow

hail

WEATHER DISTURBANCES

• 1. THUNDERSTORM – is a small scale weather system with lightning and thunder, produced by cumulonimbus cloud that has a funnel shape, usually producing gusty winds, heavy rain and sometimes hail.

2. TROPICAL CYCLONE - is a low pressure system which generally forms over the tropics with wind and thunderstorm activity.It comes from Greek word KYKLOS w/c means “ cycling snake ”.

• They are huge, violent whirlwinds that happen in many parts of the earth.

• They are weather systems that rush in a spiral motion from different diections to a low pressure center called the “ eye of the storm ”.

1. TROPICAL DEPRESSION – tropical cyclones with maximum sustained surface winds of less than 62kph.

• 2. TROPICAL STORM – tropical cyclone that reaches wind of at least 62kph. ( name is given )

• 3. THYPOON – if winds reach 118kph• HURRICANE – in Atlantic

– PAGASA – Philippine Atmospheric, Geophysical, Astronomical Services Administration

SOUTHWEST MONSOON – ( HABAGAT ) comes from the word “ mausim” which means seasonal wind. It si generally warm and dry bur picks up moisture as it passes the warm waters Of Indonesian Sea and moves toward the equator with a low pressure.This brings rain to many parts of the Phil. From May to September.• Northeast monsoon – ( amihan ) comes in October to

February and brings rain mostly in Mindanao.

• INTERTROPICAL CONVERGENCE ZONE (ITCZ ) – is the meeting place of hot and cold tradewinds in the northern and southern hemispheres. It may result in rain showers to heavy rains in affected areas.

WEATHER INSTRUMENTS

• 1. BAROMETER – measures air pressure. It was built by an Italian named Evagelista Toricelli.

RAIN GUAGE – measures amount of precipitation

THERMOMETER – measures air temperature

LIGHTNING DETECTOR – it detects through radio frequency the activity of a storm. It indicates the distance of a lightning, and whether a storm is approaching or departing.

Psychrometer – measures relative humidity.

WIND VANE – measures wind speed

Weather balloon – it is sent into the atmosphere to note the weather conditions at very high altitudes

Weather satellite – it takes and sends photographs of air movements over large areas from the outer space.

CLIMATE CHANGE

• 1. EL NINO SOUTHERN OSCILLATION– The term El Niño—Spanish for "the Christ Child"—was

originally used by fishermen to refer to the Pacific Ocean warm currents near the coasts of Peru and Ecuador that appeared periodically around Christmas time and lasted for a few months. Due to those currents, fish were much less abundant than usual. At the present time we use the same name for the large-scale warming of surface waters of the Pacific Ocean every 3-6 years, which usually lasts for 9-12 months, but may continue for up to 18 months, and dramatically affects the weather worldwide. best-known for its association with floods, droughts and other weather disturbances in many regions of the world, which vary with each event

GREEN HOUSE EFFECT