Why does RH increase even before the cloud?

The parcel keeps the same vapor pressure e while temperature drops; saturation pressure e_s(T) falls with T, so RH = e/e_s(T) climbs until it reaches 100% at the dew point.

Is Γ_m = 6.5 K km⁻¹ exact?

No. Real moist-adiabatic lapse rates depend on pressure, temperature, and latent heating; they are curved on a thermodynamic diagram. The constant Γ_m here is a simple continuation for visualization.

Does the cloud draw water conservation?

The cartoon cloud marks where the model switches to a moist lapse. It does not track condensed water, precipitation, or entrainment of dry air.

Adiabatic Cloud Parcel

Lift moist air: dry Γ, LCL, toy moist lapse; RH and cartoon cloud vs height.

About this model

A toy lifted parcel keeps its water-vapor pressure e fixed (no entrainment/detrainment). Saturation vapor pressure e_s(T) follows a Magnus-type formula. Dew point T_d solves e_s(T_d) = e. While rising, the parcel cools at a constant dry adiabatic lapse Γ_d ≈ 9.8 K km⁻¹ until T = T_d; that height is the lifting condensation level (LCL), sketched as cloud base. Above the LCL a constant moist lapse Γ_m ≈ 6.5 K km⁻¹ stands in for a pseudoadiabat — adequate for qualitative meteorology, not for skew-T analysis or precipitation forecasting.

Who it's for: High-school or intro atmospheric-science students linking humidity, lapse rates, and cloud base; pairs with climate toy models.

Key terms

lifting condensation level
dew point
dry adiabatic lapse rate
moist adiabatic
relative humidity
parcel model

How it works

Moist air lifted adiabatically cools at roughly the dry lapse rate until it becomes saturated at the lifting condensation level (LCL) — then condensation is drawn as cloud. The profile above LCL uses a simplified moist lapse for illustration.

Frequently asked questions

Why does RH increase even before the cloud?: The parcel keeps the same vapor pressure e while temperature drops; saturation pressure e_s(T) falls with T, so RH = e/e_s(T) climbs until it reaches 100% at the dew point.
Is Γ_m = 6.5 K km⁻¹ exact?: No. Real moist-adiabatic lapse rates depend on pressure, temperature, and latent heating; they are curved on a thermodynamic diagram. The constant Γ_m here is a simple continuation for visualization.
Does the cloud draw water conservation?: The cartoon cloud marks where the model switches to a moist lapse. It does not track condensed water, precipitation, or entrainment of dry air.

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Adiabatic Cloud Parcel

About this model

How it works

Frequently asked questions

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Frequently asked questions