Frost Days FD0 Counter

Observed ETCCDIfrostdaysTN<0Cstrictendpoints/gapfreecompleteperiodexternallyverified,no missing-dayimputation. Actual independent units,calibration,measurement definitions/coverage and model applicability;not a climate forecast,causal determination,geodesy operation or safe travel/design approval.

Description

A frost day has a daily minimum temperature below freezing even if the day later warms above it.

A frost day has a daily minimum temperature below freezing even if the day later warms above it.^{[1, 2]}

This tool counts minima strictly below 0 °C over the complete period supplied by the caller.

When to use Frost Days FD0 Counter

Use this tool to apply the stated frost days fd0 counter operation with an explicit input and unit basis.

How to use Frost Days FD0 Counter and how it works

Establish the measurement basis and units described above.
Enter actualGapFreeDailyTemperaturesC and run the tool.
Read result.value using the output meanings below.
If input is rejected, correct the stated type, range, ordering or alignment issue and rerun; review successful results under the declared convention.

Input field	Meaning	Value type	Requirement
actualGapFreeDailyTemperaturesC	Complete daily minimum temperatures in °C for the chosen reporting period.	array of number	required; dense; align related rows as specified; further conditions in the algorithm

Require a nonempty finite daily-minimum series in Celsius. Count values less than zero and exclude exactly zero; no dates, annual completeness or actual ice formation are inferred.

FD = count(Tmin < 0 °C)

Apply the declared units, ordering and branch conditions.

Output field	Meaning	Value type
result	Object containing the declared output fields.	object
result.value	Count of qualifying daily records in the supplied period.	number

json

{
  "input": {
    "actualGapFreeDailyTemperaturesC": [
      0,
      -1,
      1
    ]
  },
  "output": {
    "result": {
      "value": 1
    }
  }
}

Limitations and assumptions

The output applies the declared operation to the values you supply. Establish the measurement basis, units, coefficients and any caller-selected rules before interpreting it. The tool does not independently collect or verify observations or decide whether a model or reference applies.

Supply explicit required fields with the documented types and dense aligned arrays. Unknown fields, wrong types and nonfinite numbers are rejected. Branch-specific constraints are explained above. A returned boolean, signed difference or tied result follows the stated convention; an input error instead means the required input contract was not satisfied. Very large inputs or outputs may be rejected by shared resource limits.

Climdex distinguishes the daily maximum and minimum series and strict temperature comparisons for these indices. This tool counts the supplied records; it cannot establish completeness of an annual or monthly period.

Alternative or Complementary methods

For a related operation, use Tropical Nights TR20 Counter. Tropical-night counts summarize how often overnight temperatures remain above a defined threshold.

For a related operation, use Summer Days SU25 Counter. Summer-day counts summarize daily heat under a fixed threshold definition.

References

Frost Days FD0 Counter — tool.io
Climdex temperature indices — Climdex

Similar or alternative tools

Tropical Nights TR20 Counter
Tropical-night counts summarize how often overnight temperatures remain above a defined threshold.
Summer Days SU25 Counter
Summer-day counts summarize daily heat under a fixed threshold definition.