GeographyISC Class 11 · Atmospheric Temperature

Temperature Distribution, Inversion, Isotherms and Practical Work (ISC Class 11 Geography)

Updated 17 October 2026 · Fact-checked

Temperature depends on latitude, altitude, distance from the sea, ocean currents, relief and surface. Anomaly is the difference from the latitude mean; inversion is a rise of temperature with height near the ground. Isotherms join equal temperatures; daily mean = (max + min)/2 and annual range = warmest minus coldest month mean.

Frost-covered shore of a Scottish loch at dawn, with mist lying low over the water and hills behind, in cold, still air. — On calm, clear nights cold air sinks into the valley, so frost and mist form low down while the air above is warmer. This is a temperature inversion.
Picture: John Allan · CC BY-SA 2.0 · Wikimedia Commons

Normally air cools as you go up; in an inversion on a clear night, a warm layer sits over cold ground and traps fog and smog.

Illustration drawn for QuestionBuddy.

Understand Temperature Distribution, Inversion, Isotherms and Practical Work

Factors. Latitude (insolation falls poleward); altitude (6.5 degrees C per km fall); distance from the sea (continentality gives large ranges, as at Delhi, maritime places small ranges, as at Mumbai); ocean currents and air masses (North Atlantic Drift warm, Labrador and Peru cold); relief and aspect (the Himalayas shield India from Central Asian cold air; sunny slopes warmer); cloud, vegetation and surface (snow reflects, dark soil absorbs).

Anomaly. Mean temperature of a place minus the mean of its latitude; positive over warm oceans in high northern latitudes in winter and continents in summer, negative over continents in winter (Siberia).

Inversion. Normally temperature falls with height; in an inversion it rises with height in a layer near the ground. Conditions: long winter nights, clear skies, calm dry air. Valleys become frost pockets as cold air drains down at night; inversions cause fog and trap smog over cities such as Delhi in winter.

Isotherms. Lines joining equal temperature, reduced to sea level. They run roughly east-west, bend at land-sea boundaries (towards the equator over cold continents in January, towards the poles over warm oceans), are regular in the southern and irregular in the northern hemisphere, and closeness shows a steep gradient. The thermal equator lies north of the geographical equator for most of the year.

Practical. Maximum thermometer (mercury, constriction), minimum thermometer (alcohol, index), Six's thermometer combines both; kept in a Stevenson screen about 1.2 m above ground. Daily mean = (max + min)/2; daily range = max - min; monthly mean = average of daily means; annual range = warmest month mean - coldest month mean. A line graph of monthly means shows seasonal variation.

Temperature Distribution, Inversion, Isotherms and Practical Work: key facts

Daily mean and range: $M e an = (ma x + min) /2∣ R an g e = ma x - min$
Annual range: Warmest month mean - coldest month mean | Large inland, small on coasts
Anomaly: $A n o ma l y = m e an o f pl a ce - m e an o f i t s l a t i t u d e ∣ P os i t i v eor n e g a t i v e$
Inversion conditions: Long nights
Clear sky
Calm dry air

How to answer Temperature Distribution, Inversion, Isotherms and Practical Work questions

Questions blend explanation (4 marks) with data handling (4 marks).

1For factors, give a place example for each.
2For inversion, list conditions then effects.
3For data, compute daily means, ranges and annual figures with working.
4Comment on continentality or altitude from the graph.

Temperature Distribution, Inversion, Isotherms and Practical Work in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Daily record

Suppose a station records (maximum, minimum) of (34, 21), (37, 23) and (35, 22) degrees C on three days.

Find each daily mean and the average mean.

Try it first, then show the solutionSolution

Means: (34+21)/2 = 27.5; (37+23)/2 = 30.0; (35+22)/2 = 28.5.
Average = (27.5 + 30.0 + 28.5)/3 = 86/3 = 28.67, about 28.7 degrees C.

Answer: 27.5, 30.0 and 28.5; average about 28.7 degrees C.

Memory hook: Add max and min, halve.

Frost pocket

Suppose an orchard planted on the floor of a narrow valley loses blossom to frost while orchards on the slope escape.

Explain why.

Try it first, then show the solutionSolution

At night cold dense air drains downslope.
It pools on the valley floor, so the valley is coldest: an inversion.

Answer: Cold air drains into the valley, causing frost there.

Memory hook: Cold air flows downhill.

Tricks to remember Temperature Distribution, Inversion, Isotherms and Practical Work

Short memory aids. Say each one aloud once, then use it on a question the same day.

Coast cool, inland swing
Maritime places have small ranges; continental ones have large ranges.
Use it when: Distance from the sea.
Inversion needs calm clear night
Long, clear, calm, dry.
Use it when: Conditions.

Temperature Distribution, Inversion, Isotherms and Practical Work: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Instrument · 1 mark · MCQBoard level

The thermometer that records the lowest temperature of the day is the:
(a) maximum thermometer
(b) minimum thermometer
(c) barometer
(d) hygrometer

Try it first, then show the solutionSolution

Alcohol with index.

Answer: (b) Minimum thermometer.

Example 2: Anomaly · 2 marks · Short answerBoard level

A place has a mean annual temperature of 24 degrees C while the mean for its latitude is 18 degrees C. Find the anomaly and its sign.

Try it first, then show the solutionSolution

Anomaly = 24 - 18 = 6 degrees C.
It is positive.

Answer: +6 degrees C.

Example 3: Annual data · 4 marks · Long answerHarder board level

Monthly means (degrees C) are Jan 9, Feb 11, Mar 16, Apr 22, May 27, Jun 30, Jul 29, Aug 28, Sep 25, Oct 19, Nov 13, Dec 10. Find the annual mean and the annual range, and say whether the station is continental or maritime.

Try it first, then show the solutionSolution

Sum = 239; annual mean = 239/12 = 19.9 degrees C.
Warmest month June 30; coldest January 9.
Annual range = 30 - 9 = 21 degrees C.
A large range indicates a continental location.

Answer: Annual mean about 19.9 degrees C; range 21 degrees C; continental.

Example 4: Isotherm bends · 4 marks · Long answerHarder board level

Describe how land and sea affect the shape of January isotherms in the northern hemisphere and say what happens to the pattern in July.

Try it first, then show the solutionSolution

In January land cools faster than water.
Continents are colder than the ocean at the same latitude, so isotherms bend equatorward over land.
Oceans stay warmer, so isotherms bend poleward over them.
In July the pattern reverses.

Answer: Land cools more than ocean in winter, so isotherms bend equatorward over land and poleward over oceans.

Example 5: Inversion case · 5 marks · Case-basedHOTS / competency

Case: A valley town has a still, clear winter night, dense fog in the morning and polluted air that does not clear. (a) Name the condition. (b) List three conditions that cause it. (c) Explain why smog is trapped.

Try it first, then show the solutionSolution

(a) Temperature inversion.
(b) Long night, clear sky, calm dry air.
(c) Cold air near the ground is under warmer air above, so it does not rise and pollutants stay trapped.

Answer: (a) Inversion (b) long night, clear sky, calm air (c) cold air cannot rise.

Where students lose marks in Temperature Distribution, Inversion, Isotherms and Practical Work

The slips examiners see most often, and what to write instead.

Mistake: Dividing by the wrong number in a mean
Mean taken as (max - min)/2.
Wrong working
(36 - 24)/2 = 6
Right working
(36 + 24)/2 = 30
Do this: Mean = (max + min)/2.
Usually costs: 1 mark.
Mistake: Calling anomaly the range
Terms confused.
Do this: Anomaly is place mean minus latitude mean; range is warmest minus coldest.
Usually costs: 1 mark.
Mistake: No reduction to sea level for isotherms
Altitude effect ignored.
Do this: Mention reduction to sea level.
Usually costs: 1 mark.

Exam tips

Show the formula for mean and range.
Give a place example for each factor.
List inversion conditions in three words.
Mention Stevenson screen height 1.2 m.

Practice questions on Temperature Distribution, Inversion, Isotherms and Practical Work

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
Isotherms are lines joining places with equal:
(a) pressure
(b) rainfall
(c) temperature
(d) height
Hint
Thermo.
Answer
(c) Temperature.
Q2 · 4 marks · Long answerHarder board level
A Six's thermometer gives (36, 24), (38, 26) and (35, 23) for three days (maximum, minimum). Find each daily range and the mean of the three daily means.
Hint
Max minus min; mean average.
Answer
Ranges: 12, 12, 12. Daily means: 30, 32, 29; average = 91/3 = 30.33, about 30.3 degrees C.
Q3 · 4 marks · Long answerHarder board level
Compare the annual ranges of a coastal and an inland station at the same latitude and give reasons.
Hint
Water versus land.
Answer
Inland stations have a larger annual range because land heats and cools quickly; coastal stations have a smaller range because water heats slowly and moderates temperature.
Q4 · 3 marks · Short answerHarder board level
A station is at 2,000 m and its sea-level equivalent is 28 degrees C. Estimate the station temperature and explain isotherms use sea-level values.
Hint
6.5 per km.
Answer
Fall = 6.5 x 2 = 13 degrees C; station = 28 - 13 = 15 degrees C. Isotherms are reduced to sea level to remove the effect of altitude.
Q5 · 4 marks · Case-basedHOTS / competency
Case: A farmer grows fruit on a hill slope rather than the valley floor. (a) Name the hazard. (b) Explain why the slope is better. (c) Name the opposing normal temperature trend.
Hint
Frost pocket.
Answer
(a) Frost from inversion. (b) Cold air drains off slopes into the valley. (c) Normally temperature falls with height.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Daily mean formula?Show answer
(max + min)/2.
2.Alcohol thermometer?Show answer
Minimum.
3.Cold air pools in valleys?Show answer
Inversion or frost pocket.
4.Isotherms near land-sea?Show answer
They bend.
5.Thermal equator position?Show answer
North of the geographical equator.

Temperature Distribution, Inversion, Isotherms and Practical Work: frequently asked questions

Why reduce temperature to sea level?

To remove the effect of altitude.

Are isotherms regular in the south?

Yes, the southern hemisphere is mostly ocean.

Is Delhi continental?

Yes, it has a large annual range.