Day of year of the first autumn frost (Tmin < 0 degrees C) in each
year. Hemisphere is selected by lat: in the Northern Hemisphere
(lat >= 0) the search starts at July 1 (DOY 183); in the Southern
Hemisphere it starts at March 1 (DOY 60), matching the autumn entry
for each.
Usage
ck_first_frost(tmin, dates, lat = 50)
Arguments
- tmin
Numeric vector of daily minimum temperatures (degrees C).
- dates
Date vector of the same length as tmin.
- lat
Numeric. Latitude in decimal degrees, used to select the
hemisphere convention. Default 50 (Northern Hemisphere).
Value
A data frame with columns period, value (day of year),
date (the frost date), index, and unit.
Examples
dates <- seq(as.Date("2024-07-01"), as.Date("2024-12-31"), by = "day")
set.seed(42)
tmin <- 15 - seq_along(dates) * 0.15 + rnorm(length(dates), sd = 3)
ck_first_frost(tmin, dates)
#> period value date index unit
#> 1 2024-01-01 241 2024-08-28 first_frost day of year