Weather

Revise Weather for Geography 0460 (O Level) — revision notes and instant AI marking.

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Cambridge IGCSE Geography

Weather — The Complete Revision Guide

The Big Idea: Weather stations use a set of standardised instruments, placed in exact positions for exact reasons, to collect daily data on temperature, rainfall, wind, pressure, humidity and sunshine — and geographers then plot, calculate and interpret that data to describe, compare and explain what's happening in the atmosphere.

Summary — What This Chapter Covers

Collecting Weather Data: the Stevenson screen and every individual instrument inside/outside it — why each one is built and placed the way it is.
Weather Data: how to actually calculate rainfall totals, temperature ranges, mean values, wind descriptions, pressure systems and relative humidity — with the exact formulas.
Weather Data Interpretation: how to read and describe climate graphs, dispersion graphs, wind roses, wind barbs, isoline/choropleth maps and synoptic charts.
Clouds & tropical storms as a special weather topic — cloud types, how they form, and how tropical storms develop and are categorised.

1. Collecting Weather Data

The Stevenson Screen

Think of the Stevenson screen as a "fair test box" for measuring air temperature and humidity. If you just left a thermometer sitting on the ground in direct sun, you wouldn't be measuring air temperature at all — you'd be measuring how hot that one patch of ground got, plus the effect of direct sunlight cooking the thermometer itself. The Stevenson screen exists to strip all of that away so every weather station on Earth is measuring the same thing, the same way.

Every design feature solves one specific measurement problem:

Feature	Why it's built that way
Painted white	Reflects the sun's rays instead of absorbing heat, so the box itself doesn't warm up and skew the reading
Made of wood	Wood is a poor conductor of heat, so heat from outside doesn't transfer into the box
Slatted (louvred) sides	Lets air move freely through the box, so the thermometers are reading the surrounding air, not trapped stagnant air
Double-layered roof with airspace	Extra insulation against heat from above
Stands on legs at 121 cm	Keeps the thermometer bulbs at the standard height of 125 cm, well clear of heat radiating up off the ground
Placed on grass, not concrete	Grass reflects and radiates far less heat than a hard surface like concrete or tarmac
Readings taken at the same time daily	Keeps data comparable day to day — a fair test over time

ROOF (double-layered, airspace) ← insulation ___________ | slats | ← air can move freely | (white) | 125 cm → | [therm.] | ← standard thermometer height |___________| || 121 cm → legs || ~~~~~~~ grass surface ~~~~~~~ ← reflects less heat than concrete

Instruments found where Inside the screen: maximum-minimum (Six's) thermometer, wet & dry bulb hygrometer
Outside the screen: rain gauge, wind vane, anemometer

Exam Tip — Weather vs Climate Weather is day-to-day (rain, sun, snow today) — measured over days. Climate is what you expect over the long run (warm summers, cold winters) — measured over a minimum of 30 years. Examiners specifically check students can tell these apart.

Practice Question

Wind Direction & Wind Speed

where is the wind coming from?

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Also in the full note

2. Working With Weather Data — Calculations
3. Interpreting Weather & Climate Data
What to Memorise
Concepts Checklist
Exam Tips — Common Mistakes & Examiner Traps
Rain Gauge (Precipitation)
Temperature — Six's Thermometer & Thermograph
Humidity — The Hygrometer

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