Clear Sky Transmissivity Estimate

Estimate observed clear-sky bulk transmissivity from paired integrated surface/extraterrestrial energies; observations must be independently identified clear-sky, not assumed clear from station elevation.

Description

Bulk clear-sky transmissivity compares surface solar energy with the corresponding top-of-atmosphere energy.

Bulk clear-sky transmissivity compares surface solar energy with the corresponding top-of-atmosphere energy. Energy weighting gives larger-radiation periods greater influence on an aggregate ratio.^[1]

When to use Clear Sky Transmissivity Estimate

Use this tool to estimate observed clear-sky bulk transmissivity from paired integrated surface/extraterrestrial energies; observations must be independently identified clear-sky, not assumed clear from station elevation.

Prepare the climate observations and independently chosen model parameters. Confirm units, daily coverage, chronological order and the intended seasonal window.

How to use Clear Sky Transmissivity Estimate and understand its results

Prepare the climate observations and independently chosen model parameters. Confirm units, daily coverage, chronological order and the intended seasonal window.
Enter measuredClearSkyRadiationMjPerM2, correspondingExtraterrestrialRadiationMjPerM2 using the field table and calculation rules, then run the tool.
Read observedClearSkyTransmissivities, energyWeightedClearSkyTransmissivity. The explanation below defines the units, signs, ordering and any flags or placeholder values.
If the tool reports an input issue, correct the values and run it again. Apply the stated assumptions when interpreting a successfully returned result.

Input field	Meaning	Value type; see rules below	Requirement
measuredClearSkyRadiationMjPerM2	Measured clear sky radiation mj per m2	list of number	Required
correspondingExtraterrestrialRadiationMjPerM2	Corresponding extraterrestrial radiation mj per m2	list of number	Required

Pair nonnegative measured clear-sky energies with positive corresponding extraterrestrial energies in MJ/m². Each ratio must lie from zero to one. The tool returns those individual ratios and the ratio of total energies, rather than an unweighted mean of ratios.

Paired lists must be nonempty and have equal lengths.

transmissivity_i = surfaceEnergy_i/extraterrestrialEnergy_i; aggregate = Σ surfaceEnergy/Σ extraterrestrialEnergy

Units, indexing, boundary conditions and exceptional cases are defined in the calculation rules above.

Output field	Meaning	Value type
observedClearSkyTransmissivities	Observed clear sky transmissivities	list of number
energyWeightedClearSkyTransmissivity	Energy weighted clear sky transmissivity	number

json

{
  "input": {
    "measuredClearSkyRadiationMjPerM2": [
      10,
      20
    ],
    "correspondingExtraterrestrialRadiationMjPerM2": [
      20,
      40
    ]
  },
  "output": {
    "observedClearSkyTransmissivities": [
      0.5,
      0.5
    ],
    "energyWeightedClearSkyTransmissivity": 0.5
  }
}

Limitations and assumptions

Clear-sky identification and matched observation periods must be established independently. This tool does not estimate transmissivity from elevation, remove cloud effects or diagnose why an observed ratio is implausible.

Numeric inputs must be finite. Follow the calculation-specific rules for overflow, underflow and exceptional cases. Numeric lists are limited to 100,000 entries; the rules above may require smaller limits. Missing required fields, extra fields, wrong value types and violations of the calculation rules are input errors.

Alternative or Complementary methods

Use Extraterrestrial Radiation Daily: Integrate geometric daily extraterrestrial solar radiation from independently supplied declination/distance correction, handling polar day/night without apparent sunrise/refraction or cloud attenuation. For a complementary task, use Angstrom-Prescott A-B Coefficient Solver: Fit measured Angstrom–Prescott sunshine/solar fraction coefficients and predict supplied sunshine fraction, exposing calibration-range extrapolation; no universal local coefficients or sunshine forecast.

References

Clear Sky Transmissivity Estimate — tool.io

Similar or alternative tools

Extraterrestrial Radiation Daily
Integrate geometric daily extraterrestrial solar radiation from independently supplied declination/distance correction, handling polar day/night without apparent sunrise/refraction or cloud attenuation.
Angstrom-Prescott A-B Coefficient Solver
Fit measured Angstrom–Prescott sunshine/solar fraction coefficients and predict supplied sunshine fraction, exposing calibration-range extrapolation; no universal local coefficients or sunshine forecast.