BharatNotes Isotherm
nounUsage in a UPSC answer
In mapping the country's deepening climate stress, planners increasingly rely on shifting isotherms, whose poleward and altitudinal migration signals the encroachment of heat-stressed zones onto once-temperate agricultural belts.
Synonyms
Word Family
isothermal (adj), isothermally (adv), isothermics (n)
Root
Greek isos = equal; thermē = warmth, heat; coined by Humboldt, 1817 via French isotherme
Etymology
From French isotherme, coined by Alexander von Humboldt in 1817, combining Greek isos ("equal") and thermē ("warmth, heat").
Memory Hook
ISO = "equal" + THERM = "heat" (as in thermometer/thermal): an isotherm joins places of equal heat, i.e. the same temperature.
How This Word Works in UPSC Writing
A line joining places of equal temperature. Reading isotherm maps is a skill the exam tests indirectly, and two Indian patterns recur. In January the isotherms run broadly east to west, roughly parallel to the latitudes, because the sun is over the southern hemisphere and the Himalayas shut out cold air from the north. In July they bend sharply and the highest temperatures occur not at the lowest latitude but over north-west India, because continentality, meaning distance from the moderating influence of the sea, outweighs latitude in summer. Isotherms also bend where they cross a coastline for the same reason. The general rule is that closely spaced isotherms indicate a steep temperature gradient, which is the same reading convention used for contours and isobars.
Don’t Confuse It With
An isotherm joins points of equal temperature, an isobar of equal pressure, an isohyet of equal rainfall and a contour of equal elevation, all being kinds of isoline. The temperature gradient is what the spacing reveals, close spacing meaning rapid change over a short distance. Note the separate physical sense in which an isothermal process is one conducted at constant temperature, which is a condition of a process rather than a line on a map.
Hindi Meaning
समताप रेखा (samatāp rekhā); समदाब रेखा for isobar and समवर्षा रेखा for isohyet.
Common Questions
- What is an isotherm?
- A line on a map joining places that have the same temperature at a given time or the same average temperature over a period.
- Why are India's July isotherms not parallel to the latitudes?
- Because in summer continentality dominates, so the interior of north-west India heats far more than coastal areas at the same latitude, bending the isotherms away from an east-west alignment.
Tip: press Alt+S to hear pronunciation
