The figure below shows four profiles of the environmental lapse rate. Given that the dry adiabatic lapse rate is \( -10^\circ {C/km} \), the atmosphere is highly unstable for the profile:
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When analyzing lapse rates, remember that instability occurs when the environmental lapse rate is steeper (greater rate of temperature decrease) than the dry adiabatic lapse rate.
The environmental lapse rate (ELR) refers to the rate at which the temperature of the atmosphere decreases with altitude. The dry adiabatic lapse rate (DALR) is the rate at which the temperature of a rising parcel of dry air decreases with altitude. Step 1: Understanding the instability condition. The atmosphere is considered highly unstable when the environmental lapse rate is greater than the dry adiabatic lapse rate. This occurs when the temperature decreases rapidly with altitude, causing rising air to be warmer and less dense than the surrounding air, leading to further rising. Step 2: Analyzing the profiles. Profile \( OP \) shows a temperature decrease rate greater than the dry adiabatic lapse rate, making the atmosphere highly unstable for this profile. Other profiles, such as \( OQ \), \( OR \), and \( OS \), indicate more stable conditions (less steep temperature decrease with altitude). Conclusion: The atmosphere is highly unstable for the profile \( OP \), where the environmental lapse rate exceeds the dry adiabatic lapse rate.
