CSIR NET June 2016 Q45: Meteorology
Isotherms trace lines of equal temperature; their latitude can be strongly displaced by elevation, since temperature drops with altitude (environmental lapse rate) independent of latitude. High-elevation plateaus can therefore have winter isotherms reaching much lower latitudes than would be expected from latitude alone.
The Tibetan Plateau sits at an average elevation of over 4,000-5,000 m, making it exceptionally cold in winter despite its relatively low latitude (roughly 30°N). This high-altitude cooling pushes the -16°C isotherm to a lower latitude over Tibet than over other northern-hemisphere winter locations such as northern Siberia (which, despite its extreme cold, sits at a higher latitude) or lower-elevation regions like Canada.
Option 1 (Canada) and option 2 (Northern Siberia) are cold in winter but at higher latitudes, so the -16°C isotherm over them does not reach as low a latitude as over Tibet.
Option 3 (Tibet) is correct because its extreme elevation drives severe winter cooling at a comparatively low latitude.
Option 4 (Sri Lanka) is a warm, low-latitude tropical location, nowhere near cold enough for a -16°C isotherm.
Option 3 (Tibet) is correct because its extreme elevation drives severe winter cooling at a comparatively low latitude.
Option 4 (Sri Lanka) is a warm, low-latitude tropical location, nowhere near cold enough for a -16°C isotherm.