% Generated by roxygen2: do not edit by hand
% Please edit documentation in R/heatwave.R
\name{ck_cwn}
\alias{ck_cwn}
\title{Cold-Wave Number (CWN)}
\usage{
ck_cwn(tmin, dates, ref_start = 1961L, ref_end = 1990L, min_spell = 3L)
}
\arguments{
\item{tmin}{Numeric vector of daily minimum temperatures (degrees C).}

\item{dates}{Date vector of the same length as \code{tmax}. Must contain
data covering the reference period.}

\item{ref_start, ref_end}{Integer. Reference period boundary years
(inclusive). Defaults to 1961 and 1990.}

\item{min_spell}{Integer. Minimum spell length in days (default 3,
the ET-SCI standard).}
}
\value{
A data frame with columns \code{period}, \code{value}, \code{index}, and \code{unit}.
}
\description{
ET-SCI cold-wave family index. Annual count of distinct cold-wave
events, where a cold wave is a span of at least three consecutive
days with daily Tmin below the 10th percentile of the calendar-day
distribution from a reference period (default 1961 to 1990).
}
\examples{
set.seed(1)
dates <- seq(as.Date("1961-01-01"), as.Date("1991-12-31"), by = "day")
tmin <- 5 + 8 * sin(2 * pi * as.integer(format(dates, "\%j")) / 365) +
        rnorm(length(dates))
tail(ck_cwn(tmin, dates))
}
