Section 6A: Isobaric Patterns, Air Masses and Fronts

Question 1

With the aid of a sketch, briefly explain each one of the seven basic isobaric patterns. State the weather conditions that may be associated with each one.

Answer 1

1. Low Pressure System (Depression): A set of closed, concentric isobars with lower pressure values towards the center. This represents a low pressure area or depression. The winds blow counterclockwise around the center in the Southern Hemisphere. Associated with cloudy, rainy, and stormy weather conditions.
2. High Pressure System (Anticyclone): A set of far apart, concentric isobars with higher pressure values towards the center. This represents a high pressure area or anticyclone. The winds blow clockwise around the center in the Southern Hemisphere. Associated with fair, dry, and stable weather conditions.
3. Trough: A elongated area of low pressure represented by a dashed line on the weather map. The winds converge towards the trough line. Associated with increased cloudiness, precipitation, and potential for thunderstorm development.
4. Ridge: An elongated area of high pressure represented by a curved line on the weather map. The winds diverge away from the ridge line. Associated with fair and dry weather conditions.
5. Warm Front: Represented by a red line with semi-circles. It marks the boundary where warm air is replacing cooler air. Associated with gradual temperature rise, steady precipitation, and low cloud cover.
6. Cold Front: Represented by a blue line with triangles. It marks the boundary where cooler air is replacing warmer air. Associated with a sudden temperature drop, gusty winds, and potential for thunderstorms and heavy precipitation.
7. Occluded Front: Represented by a purple line with alternating triangles and semi-circles. It forms when a cold front overtakes a warm front. Associated with a mixture of weather conditions from both fronts. Thunderstorms.

Question 2

What are air masses? Classify them according to their principal source regions as well as temperature.

Question 3

List and briefly explain the factors affecting the properties of an air mass.

Question 4

What is a front? Define: a.) Warm front, b.) Cold front.

State the weather associated with each.

Question 5

What is a frontal depression? Using sketches, briefly outline the formation of a frontal depression.

Question 6

Outline the possible weather sequence experienced by a stationary observer situated on the passage of a frontal depression.

Question 7

What is an occluded front? How does it occur?

Question 8

Draw the symbols of warm, cold, occluded and stationary fronts. Indicate for each the side on which the warmer and colder air is located.