Meteorology

Chapter 12

The Causes of Weather

• Meteorology- The study of atmospheric phenomena and weather

• Weather- current state of the atmosphere

• Climate- long term variation in earth’s weather.– Usually an average over 30 years or more

The Causes of Weather• Different parts of the world receive

differing amounts of energy form the sun

• The constant movement of air and water currents distributes this energy around the globe

The Causes of Weather

• Air Masses- a large body of air that takes on the characteristics of the area over which it forms.– Continental tropical (cT)- warm and dry– Maritime tropical (mT)- warm and wet– Continental polar (cP)- cold and dry– Maritime polar (mP)- cold and wet

The Causes of Weather

• Air Masses:

The Causes of Weather

The Causes of Weather

• Air mass modification occurs when air masses move from one area to another and start to take on the characteristics of the new area.

Weather Systems

• Coriolis Effect- moving particles, such as air, are moved to the right in the northern hemisphere and the left in the southern hemisphere because of the rotation of the earth.

Weather Systems

• Wind systems- three basic zones in the northern and southern hemisphere– Trade winds- 0o and 30o (Hadley’s cell)

• Horse latitudes- very little air movement at 30o

• Intertropical convergence zone (ITCZ)- also known as the doldrums at equator

– Prevailing Westerlies- 30o and 60o

– Polar Easterlies- 60o and 90o

Weather Systems

Weather Systems

• Jet Stream- Narrow bands of fast, high-altitude, westerly winds

Weather Systems

• Fronts- a narrow region separating two air masses.– Can bring dramatic changes in local weather

Weather Systems

• Cold Front- cold, dense air displaces warmer air and forces it up along a steep front.– Can cause the most sever weather

Weather Systems

• Warm Front- warm air displaces cooler air.– Typical cloudiness and precipitation

Weather Systems• Stationary Front- two air masses meet but

neither moves into the other’s territory.– Occur because the air masses have been

modified to an extent that they are not very different from each other

– Usually will not have extensive cloudiness or precipitation.

Weather Systems

• Occluded front- sometimes a cold air mass will move rapidly enough to over take a warm air mass moving the same direction.

Weather Systems

• Pressure systems- – Rising air = low pressure

• Rainy weather

– Falling sir = high pressure• Clear weather

Gathering Weather Data

• Surface Data-– Thermometer- temperature– Barometer- air pressure– Anemometer- wind speed– Hygrometer- humidity– Ceilometer- cloud height

Gathering Weather Data

• Upper level data-– Radiosonde- carried by weather balloon

• Wind speed and direction

• Temperature and humidity

Gathering Weather Data

• Weather Radar-– Doppler Radar- plots the direction that rain

drops move toward or away from the radar.

Gathering Weather Data

• Weather Satellites- – Gathers data on cloud type and precipitation– Infrared imagery- detect differences in thermal

energy

Weather Analysis

• Station model- a record of weather data at a particular site at a particular time.

Weather Analysis

• Isopleths- lines that connect points of equal or constant values– Isobars- connect points of equal pressure.

Isobars close together indicate strong winds. Widely spaced isobars indicate weaker winds

Weather Analysis

• Digital forecast- use of computer models to process data for forecasting

• Analog forecast- involves comparing current weather patterns with patterns that took place in the past.