Cloud Parcel Modelling - Part 0: Required Inputs

🌩️ Inputs Required for a Cloud Parcel Model Simulation

To simulate the evolution of supersaturation and cloud droplet growth in a cloud parcel model, you need several categories of input data. These include thermodynamic conditions, aerosol properties, updraft velocity, and microphysical constants.

🧾 Minimal vs Advanced Input Set

Category Minimal Input Set Advanced Input Set
Thermodynamics T₀, p₀, RH₀ T₀, p₀, RH₀, qv₀, moist air constants
Updraft Forcing Constant w Time-varying w(t), or diagnosed from environment
Aerosol Properties Single Dp, Na, κ Size-resolved Dp distribution, κ(D), chemical composition, mixing state
Microphysics Basic diffusivity and thermal conductivity Temperature-dependent Dv, Ka, accommodation coefficients
Numerics Δt, total time Adaptive time-stepping, bin/moment resolution
Additional Physics None BC heating, radiative feedbacks, turbulence, entrainment

🌡️ 1. Thermodynamic Initial Conditions

ParameterDescription
T₀Initial temperature of the air parcel (K)
p₀Initial pressure (Pa or hPa)
RH₀Initial relative humidity (%)
qv₀Initial water vapor mixing ratio (kg/kg)
Lv, cp, RdThermodynamic constants

💨 2. Dynamical Forcing

ParameterDescription
wUpdraft velocity (m/s) — can be constant or time-varying
dT/dtHeating rate (can be derived from w)
parcel_typeReversible, pseudo-adiabatic, or diabatic parcel assumption

☁️ 3. Aerosol Properties

ParameterDescription
NaTotal aerosol number concentration (#/cm³)
DpDry diameter(s) — single value or distribution
κHygroscopicity parameter (from κ-Köhler theory)
σsSurface tension of the solution (N/m)
ρsSolute density (kg/m³)
msaltDry solute mass per particle (if using mass-based approach)
compositionChemical type: e.g., ammonium sulfate, NaCl, organics, BC

💧 4. Microphysical Constants

ParameterDescription
DvDiffusivity of water vapor in air
KaThermal conductivity of air
ρwDensity of liquid water
LvLatent heat of vaporization
σwSurface tension of pure water
MWwMolecular weight of water

🧮 5. Numerical Parameters

ParameterDescription
ΔtTime step for simulation (s)
simulation_timeTotal simulation duration (s)
grid_pointsNumber of bins or resolution elements

🧪 6. Optional Physical Features

ParameterDescription
Activation criterionCritical supersaturation Sc for each particle
Gas uptakeAccommodation coefficient, gas-phase limitations
Radiative heatingFrom absorbing aerosols like black carbon
TurbulenceEntrainment or stochastic updraft variation

📌 This breakdown helps researchers or students decide how simple or complex their parcel model should be, depending on the purpose: educational, mechanistic understanding, or process-level validation for climate models.

🧾 Minimal vs Advanced Input Set with Value Ranges

Category Parameter Minimal Input Advanced Input Typical Range / Units
Thermodynamics T₀ Yes Yes 250–310 K
p₀ Yes Yes 600–1013 hPa
RH₀ Yes Yes 60–100%
qv₀ No Optional 0–30 g/kg
Updraft Forcing w Yes (constant) Yes (variable) 0.01–5 m/s
w(t) No Optional Function of height/time
Aerosol Properties Na Yes Yes 10–10,000 cm⁻³
Dp Yes (mono) Yes (multi-bin) 0.01–1 µm
κ Yes Yes 0–1.3 (unitless)
Composition No Yes NaCl, sulfate, organics, BC
Microphysical Constants Dv Default Temperature dependent ~2.5 × 10⁻⁵ m²/s
Ka Default Temperature dependent ~0.025 W/m·K
ρw Yes Yes 1000 kg/m³
σw Yes Optional by solute 0.072 N/m
Numerics Δt Yes Adaptive optional 0.01–1 s
Total Time Yes Yes 100–1000 s
Grid/Bins No Yes 10–200 bins
Extra Physics BC Heating No Optional ~0–1 K/min warming
Radiative Cooling No Optional e.g., –1–0 K/min
Turbulence No Optional Stochastic or entraining w(t)

🧪 This table serves as a practical reference for building a cloud parcel model, helping you decide which inputs are essential for your study level (educational, process-level, or research-grade).

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