Air Masses, Fronts & Pressure — Drills · Grade 9 Science

Chapter: Atmosphere & Weather

What these drills covers

By the end of Air Masses, Fronts & Pressure you should be able to:

8 questions, multiple choice, numeric and written answer, each with a worked explanation.

Vocabulary used: air mass, front, air pressure, barometer.

Problem 1

A cold front occurs where
  1. cold air advances and undercuts warmer air
  2. warm air advances over cold air
  3. two air masses stop moving
  4. pressure is highest
Answer and explanation

cold air advances and undercuts warmer air

Dense cold air pushes under the warm air, forcing it up steeply.

Problem 2

Air flows from
  1. low pressure to high pressure
  2. high pressure to low pressure
  3. hot to cold only
  4. north to south always
Answer and explanation

high pressure to low pressure

Pressure differences drive wind from high toward low.

Problem 3

A low-pressure system is usually associated with
  1. clear settled weather
  2. rising air, cloud and precipitation
  3. no wind
  4. falling temperatures only
Answer and explanation

rising air, cloud and precipitation

Rising air cools and its vapour condenses, forming cloud and rain.

Problem 4

An air mass forming over a warm ocean is likely to be
  1. cold and dry
  2. warm and moist
  3. cold and moist
  4. warm and dry
Answer and explanation

warm and moist

An air mass takes on the temperature and humidity of the surface it forms over.

Problem 5

Pressure falls from 1,012 hPa to 996 hPa in six hours. What is the fall in hectopascals?
Answer and explanation

16 hPa

1,012 − 996 = 16 hPa, a rapid fall that often signals an approaching storm.

Problem 6

Closely spaced isobars on a weather map indicate
  1. light winds
  2. strong winds
  3. no wind
  4. high temperature
Answer and explanation

strong winds

A steep pressure gradient over a short distance drives faster wind.

Problem 7

Explain why a cold front usually brings a short, intense burst of rain and a warm front a longer, gentler spell.
Answer and explanation

A cold front forces warm air upward steeply along a narrow boundary, so condensation is rapid and concentrated, producing tall clouds and brief heavy rain. A warm front has warm air riding gently up over cold air along a shallow slope, so cloud forms over a wide area and precipitation is lighter but lasts far longer. The slope of the boundary accounts for the difference.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

Problem 8

Explain how an air mass acquires its characteristics and why that matters for forecasting.
Answer and explanation

An air mass takes on the temperature and moisture of the surface it sits over for long enough — cold and dry over polar land, warm and moist over tropical ocean. Knowing where an approaching air mass formed therefore predicts what weather it brings, and knowing what it crosses on the way predicts how it will be modified, which is the basis of a forecast built from pressure maps.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

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