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On the tephigram, the green line represents the Dry Adiabatic Lapse Rate because:
  • A
    The DALR is a linear decrease in air temperature with altitude at a constant rate.
  • B
    The dry adiabatic lapse rate is not constant, its approximate lapse rate is 3°C/1000 ft, but it can vary.
  • C
    The DALR is not linear as latent heat is released, and this is represented accordingly on the tephigram.
  • D
    The dry adiabatic cooling is not represented by the green line.
TEPHIGRAM. “T – phi – gram”, where “T” stands for temperature and “phi” for entropy. These describe the axes of the diagram. The x-axis represents lines of constant temperature and the y axis represents isobars.
  • Red lines – Saturated adiabatic lapse rate;
  • Green lines – Dry adiabatic lapse rate (cooling of unsaturated parcel of air, 3ºC/1 000 ft);
  • Brown dashed lines – Constant Saturation Mixing Ratio (Dew point lines)
The Saturated Adiabatic lapse rate lines are the most visibly curved lines on the diagram, being almost vertical at high pressures (near the surface, or bottom of the diagram) and approaching the dry adiabatic with decreasing temperature. Saturated air cools at a lesser rate than dry air due to the release of latent heat as water condenses out; and the rate varies due to the non-linear variation of saturation vapour pressure with temperature. SALR are curved lines representing a slower decrease in temperature with altitude. Whereas DALR lines are straight representing the linear decrease of temperature with altitude.

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