使用非格列高利历法转换时代

Question

我正在与一堆气候模型输出（CMIP5 models，特别是）。这些是时间戳温度，风等的netcdfs。

它们都使用UTC中的days since YYYY-mm-dd 00:00:00约定。我已经转化为更容易日期（不日期时间）对象使用lubridate：

library(tidyverse) 
input$date.utc = 
    ymd_hms('0001-01-01 00:00:00', tz = 'UTC') + 
    days(floor(input$time)) 

我已经打了两个问题。一个是每个模型都有不同的时代。这很容易解决。另一个更棘手的问题是，并非所有的模型都使用公历。有些人使用365天的变化，那里没有闰年。

我没有看到任何方法在lubridate函数中指定非格里历日历。这可能吗？

Answer 1

我无法找到lubridate此功能，所以我写了一个函数来至少计算日期的向量的每个元素和给定时期之间的飞跃天数：

# count_leap_days: returns an integer for the number of leap days between a 
# supplied vector of dates and a fixed epoch 
count_leap_days <- function(dates, epoch = ymd('1850-01-01'), proleptic = FALSE) 
{ 
    require(lubridate) 

    # check input 
    if (!is(epoch, 'Date') | !is(dates, 'Date')) 
    { 
    stop('count_leap_days: both arguments must be Date objects.') 
    } 
    if (any(dates <= epoch)) 
    { 
    stop('count_leap_days: dates should all be later than epoch.') 
    } 
    if (proleptic = FALSE & epoch < ymd('1582-10-15')) 
    { 
    message('count_leap_days: ', 
     'no leap days before 1582-10-15 unless proleptic = TRUE.') 
    epoch = ymd('1582-10-15') 
    } 

    # get the year range 
    # exclude start (end) years if they begin after (start before) feb 29 
    y.epoch = year(epoch) + 
    ifelse(epoch >= ymd(paste0(year(epoch), '-03-01')), 1, 0) 
    y.dates = year(dates) - 
    ifelse(dates <= ymd(paste0(year(dates), '-02-28')), 1, 0) 
    span = y.dates - y.epoch + 1 

    # a year is a leap year if it's: 
    # - divisble by 4. but 
    # - NOT if it's also divisible by 100, unless 
    # - it's also divisible by 400. 
    # all years div. by 4 are also div. by 100, and 
    # all years div. by 100 are also div. by 400. 
    # hence, total days = (div. by 4) - (div. by 100) + (div. by 400) 
    div4 = span %/% 4 + 
    ifelse(
     (y.epoch %% 4) %in% c(0, (4 - (span %% 4) - 1):(4 - 1)) & 
     (y.dates %% 4) %in% 0:(span %% 4 - 1), 
    1, 0) 
    div100 = span %/% 100 + 
    ifelse(
     (y.epoch %% 100) %in% c(0, (100 - (span %% 100) - 1):(100 - 1)) & 
     (y.dates %% 100) %in% 0:(span %% 100 - 1), 
    1, 0) 
    div400 = span %/% 400 + 
    ifelse(
     (y.epoch %% 400) %in% c(0, (400 - (span %% 400) - 1):(400 - 1)) & 
     (y.dates %% 400) %in% 0:(span %% 400 - 1), 
    1, 0) 
    return(div4 - div100 + div400) 
} 

有了这个，我可以从365天的日历转换为格里高利只需添加缺少跳跃天数：

input$date.utc = input$date.utc + 
    count_leap_days(input$date.utc, epoch = epoch)