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1 \section{The calendar package \texttt{cal}
2 \label{sectioncal}}
3 \begin{rawhtml}
4 <!-- CMIREDIR:sectioncal: -->
5 \end{rawhtml}
6
7 \textit{Christian Eckert, MIT/EAPS, May-2000}
8
9 This calendar tool was originally intended to enable the use of
10 absolute dates (Gregorian Calendar dates) in the ocean general
11 circulation model MITgcmuv. There is, however, a fair amount of
12 routines that can be used independently of the MITgcmuv. After
13 some minor modifications the whole package can be used either
14 as a stand-alone calendar or in connection with any dynamical
15 model that needs calendar dates. Some straightforward extensions
16 are still pending e.g. the availability of the Julian Calendar,
17 to be able to resolve fractions of a second, and to have a time-
18 step that is longer than one day.
19
20 \subsection{Basic assumptions for the calendar tool}
21
22 It is assumed that the SMALLEST TIME INTERVAL to be resolved is
23 ONE SECOND.
24
25 Further assumptions are that there is an INTEGER NUMBER OF
26 MODEL STEPS EACH DAY, and that AT LEAST ONE STEP EACH DAY is
27 made.
28
29 Not each individual routine depends on these assumptions; there
30 are only a few places where they enter.
31
32 \subsection{Format of calendar dates}
33
34 In this calendar tool a complete date specification is defined
35 as the following integer array:
36
37 \begin{verbatim}
38 c integer date(4)
39 c
40 c ( yyyymmdd, hhmmss, leap_year, dayofweek )
41 c
42 c date(1) = yyyymmdd <-- Year-Month-Day
43 c date(2) = hhmmss <-- Hours-Minutes-Seconds
44 c date(3) = leap_year <-- Leap Year/No Leap Year
45 c date(4) = dayofweek <-- Day of the Week
46 c
47 c leap_year is either equal to 1 (normal year)
48 c or equal to 2 (leap year)
49 c
50 c dayofweek has a range of 1 to 7.
51 \end{verbatim}
52
53 In case the Gregorian Calendar is used, the first
54 day of the week is Friday, since day of the Gregorian
55 Calendar was Friday, 15 Oct. 1582. As a date array
56 this date would be specified as
57
58 \begin{verbatim}
59 c refdate(1) = 15821015
60 c refdate(2) = 0
61 c refdate(3) = 1
62 c refdate(4) = 1
63 \end{verbatim}
64
65 \subsection{Calendar dates and time intervals}
66
67 Subtracting calendar dates yields time intervals.
68 Time intervals have the following format:
69
70 \begin{verbatim}
71 c integer datediff(4)
72 c
73 c datediff(1) = # Days
74 c datediff(2) = hhmmss
75 c datediff(3) = 0
76 c datediff(4) = -1
77 \end{verbatim}
78
79 Such time intervals can be added to or can be subtracted from
80 calendar dates. Time intervals can be added to and be
81 subtracted from each other.
82
83 \subsection{Using the calendar together with MITgcm}
84
85 Each routine has as an argument the thread number that it is
86 belonging to, even if this number is not used in the routine
87 itself.
88
89 In order to include the calendar tool into the MITgcm
90 setup the MITgcm subroutine "initialise.F" or the routine
91 "initilise\_fixed.F", depending on the MITgcm release, has
92 to be modified in the following way:
93
94 {\footnotesize
95 \begin{verbatim}
96 c #ifdef ALLOW_CALENDAR
97 c C-- Initialise the calendar package.
98 c #ifdef USE_CAL_NENDITER
99 c CALL cal_Init(
100 c I startTime,
101 c I endTime,
102 c I deltaTclock,
103 c I nIter0,
104 c I nEndIter,
105 c I nTimeSteps,
106 c I myThid
107 c & )
108 c #else
109 c CALL cal_Init(
110 c I startTime,
111 c I endTime,
112 c I deltaTclock,
113 c I nIter0,
114 c I nTimeSteps,
115 c I myThid
116 c & )
117 c #endif
118 c _BARRIER
119 c #endif
120 \end{verbatim}
121 }
122
123 It is useful to have the CPP flag ALLOW\_CALENDAR in
124 order to switch from the usual MITgcm setup to the
125 one that includes the calendar tool. The CPP flag
126 USE\_CAL\_NENDITER has been introduced in order to enable
127 the use of the calendar for MITgcm releases earlier
128 than checkpoint 25 which do not have the global variable
129 *nEndIter*.
130
131 \subsection{The individual calendars}
132
133 \subsubsection{Simple model calendar}
134
135 This calendar can be used by defining
136
137 \begin{verbatim}
138 c TheCalendar='model'
139 \end{verbatim}
140
141 in the calendar's data file "data.cal".
142
143 In this case a year is assumed to have 360 days. The
144 model year is divided into 12 months with 30 days each.
145
146 \subsubsection{Gregorian Calendar}
147
148 This calendar can be used by defining
149
150 \begin{verbatim}
151 c TheCalendar='gregorian'
152 \end{verbatim}
153
154 in the calendar's data file "data.cal".
155
156 \subsection{Short routine description}
157
158 {\footnotesize
159 \begin{verbatim}
160 c o cal_Init - Initialise the calendar. This is the interface
161 c to the MITgcm.
162 c
163 c o cal_Set - Sets the calendar according to the user
164 c specifications.
165 c
166 c o cal_GetDate - Given the model's current timestep or the
167 c model's current time return the corresponding
168 c calendar date.
169 c
170 c o cal_FullDate - Complete a date specification (leap year and
171 c day of the week).
172 c
173 c o cal_IsLeap - Determine whether a given year is a leap year.
174 c
175 c o cal_TimePassed - Determine the time passed between two dates.
176 c
177 c o cal_AddTime - Add a time interval either to a time interval
178 c or to a date.
179 c
180 c o cal_TimeInterval - Given a time interval return the corresponding
181 c date array.
182 c
183 c o cal_SubDates - Determine the time interval between two dates
184 c or between two time intervals.
185 c
186 c o cal_ConvDate - Decompose a date array or a time interval
187 c array into its components.
188 c
189 c o cal_CopyDate - Copy a date array or a time interval array to
190 c another array.
191 c
192 c o cal_CompDates - Compare two calendar dates or time intervals.
193 c
194 c o cal_ToSeconds - Given a time interval array return the number
195 c of seconds.
196 c
197 c o cal_WeekDay - Return the weekday as a string given the
198 c calendar date.
199 c
200 c o cal_NumInts - Return the number of time intervals between two
201 c given dates.
202 c
203 c o cal_StepsPerDay - Given an iteration number or the current
204 c integration time return the number of time
205 c steps to integrate in the current calendar day.
206 c
207 c o cal_DaysPerMonth - Given an iteration number or the current
208 c integration time return the number of days
209 c to integrate in this calendar month.
210 c
211 c o cal_MonthsPerYear - Given an iteration number or the current
212 c integration time return the number of months
213 c to integrate in the current calendar year.
214 c
215 c o cal_StepsForDay - Given the integration day return the number
216 c of steps to be integrated, the first step,
217 c and the last step in the day specified. The
218 c first and the last step refer to the total
219 c number of steps (1, ... , cal_IntSteps).
220 c
221 c o cal_DaysForMonth - Given the integration month return the number
222 c of days to be integrated, the first day,
223 c and the last day in the month specified. The
224 c first and the last day refer to the total
225 c number of steps (1, ... , cal_IntDays).
226 c
227 c o cal_MonthsForYear - Given the integration year return the number
228 c of months to be integrated, the first month,
229 c and the last month in the year specified. The
230 c first and the last step refer to the total
231 c number of steps (1, ... , cal_IntMonths).
232 c
233 c o cal_Intsteps - Return the number of calendar years that are
234 c affected by the current integration.
235 c
236 c o cal_IntDays - Return the number of calendar days that are
237 c affected by the current integration.
238 c
239 c o cal_IntMonths - Return the number of calendar months that are
240 c affected by the current integration.
241 c
242 c o cal_IntYears - Return the number of calendar years that are
243 c affected by the current integration.
244 c
245 c o cal_nStepDay - Return the number of time steps that can be
246 c performed during one calendar day.
247 c
248 c o cal_CheckDate - Do some simple checks on a date array or on a
249 c time interval array.
250 c
251 c o cal_PrintError - Print error messages according to the flags
252 c raised by the calendar routines.
253 c
254 c o cal_PrintDate - Print a date array in some format suitable for
255 c the MITgcmuv's protocol output.
256 c
257 c o cal_TimeStamp - Given the time and the iteration number return
258 c the date and print all the above numbers.
259 c
260 c o cal_Summary - List all the setttings of the calendar tool.
261 \end{verbatim}
262 }
263

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