[′tem·prə·chər i′fish·ən·sē ‚rā·shō] (ecology) For a given location and month, a measure of thermal efficiency; it is equal to the departure, in degrees Fahrenheit, of the normal monthly temperature above 32°F (0°C) divided by 4: (T- 32)/4. Abbreviated T-E ratio. Also known as thermal-efficiency ratio.