ON388 - TABLE 5

TIME RANGE INDICATOR
(PDS Octet 21)


Revised 04/08/2008
Red text depicts changes made since 06/16/2004


VALUE MEANING
0
 Forecast product valid for reference time + P1 (P1>0),
or
Uninitialized analysis product for reference time (P1=0).
or
Image product for reference time (P1=0)
1
 Initialized analysis product for reference time (P1=0).
2
 Product with a valid time ranging between reference time + P1 and reference time + P2
3
 Average
(reference time + P1 to reference time + P2)
4
 Accumulation
(reference time + P1 to reference time + P2) product considered valid at reference time + P2
5
 Difference
(reference time + P2 minus reference time + P1) product considered valid at reference time + P2
6
 Average
(reference time - P1 to reference time - P2)
7
 Average
(reference time - P1 to reference time + P2)
8-9
 reserved
10
 P1 occupies octets 19 and 20; product valid at reference time + P1
11-50
 reserved
51
 Climatological Mean Value: multiple year averages of quantities which are themselves means over some period of time (P2) less than a year. The reference time (R) indicates the date and time of the start of a period of time, given by R to R + P2, over which a mean is formed; N indicates the number of such period-means that are averaged together to form the climatological value, assuming that the N period-mean fields are separated by one year. The reference time indicates the start of the N-year climatology. N is given in octets 22-23 of the PDS.

If P1 = 0 then the data averaged in the basic interval P2 are assumed to be continuous, i.e., all available data are simply averaged together.

If P1 = 1 (the units of time - octet 18, code table 4 - are not relevant here) then the data averaged together in the basic interval P2 are valid only at the time (hour, minute) given in the reference time, for all the days included in the P2 period. The units of P2 are given by the contents of octet 18 and Table 4.
52-112
 reserved
113
 Average of N forecasts (or initialized analyses); each product has forecast period of P1 (P1=0 for initialized analyses); products have reference times at intervals of P2, beginning at the given reference time.
114
 Accumulation of N forecasts (or initialized analyses); each product has forecast period of P1 (P1=0 for initialized analyses); products have reference times at intervals of P2, beginning at the given reference time.
115
 Average of N forecasts, all with the same reference time; the first has a forecast period of P1, the remaining forecasts follow at intervals of P2.
116
 Accumulation of N forecasts, all with the same reference time; the first has a forecast period of P1, the remaining follow at intervals of P2.
117
 Average of N forecasts, the first has a period of P1, the subsequent ones have forecast periods reduced from the previous one by an interval of P2; the reference time for the first is given in octets 13-17, the subsequent ones have reference times increased from the previous one by an interval of P2. Thus all the forecasts have the same valid time, given by the initial reference time + P1.
118
 Temporal variance, or covariance, of N initialized analyses; each product has forecast period P1=0; products have reference times at intervals of P2, beginning at the given reference time.
119
 Standard deviation of N forecasts, all with the same reference time with respect to time average of forecasts; the first forecast has a forecast period of P1, the remaining forecasts follow at intervals of P2.
120 -122
 reserved
123
 Average of N uninitialized analyses, starting at the reference time, at intervals of P2.
124
 Accumulation of N uninitialized analyses, starting at the reference time, at intervals of P2.
125
 Standard deviation of N forecasts, all with the same reference time with respect to time average of the time tendency of forecasts; the first forecast has a forecast period of P1, the remaining forecasts follow at intervals of P2.
126-127
 reserved
128
 Average of forecast accumulations. P1 = start of accumulation period. P2 = end of accumulation period. Reference time is the start time of the first forecast, other forecasts at 24-hour intervals. Number in Ave = number of forecasts used.
129
 Average of successive forecast accumulations. P1 = start of accumulation period. P2 = end of accumulation period. Reference time is the start time of the first forecast, other forecasts at (P2 - P1) intervals. Number in Ave = number of forecasts used
130
 Average of forecast averages. P1 = start of averaging period. P2 = end of averaging period. Reference time is the start time of the first forecast, other forecasts at 24-hour intervals. Number in Ave = number of forecast used
131
 Average of successive forecast averages. P1 = start of averaging period. P2 = end of averaging period. Reference time is the start time of the first forecast, other forecasts at (P2 - P1) intervals. Number in Ave = number of forecasts used
132
 Climatological Average of N analyses, each a year apart, starting from initial time R and for the period from R+P1 to R+P2.
133
 Climatological Average of N forecasts, each a year apart, starting from initial time R and for the period from R+P1 to R+P2.
134
 Climatological Root Mean Square difference between N forecasts and their verifying analyses, each a year apart, starting with initial time R and for the period from R+P1 to R+P2.
135
 Climatological Standard Deviation of N forecasts from the mean of the same N forecasts, for forecasts one year apart. The first forecast starts wtih initial time R and is for the period from R+P1 to R+P2.
136
 Climatological Standard Deviation of N analyses from the mean of the same N analyses, for analyses one year apart. The first analyses is valid for  period R+P1 to R+P2.
137
 Average of forecast accumulations. P1 = start of accumulation period. P2 = end of accumulation period. Reference time is the start time of the first forecast, other forecasts at 6-hour intervals. Number in Ave = number of forecast used
138
 Average of forecast averages. P1 = start of averaging period. P2 = end of averaging period. Reference time is the start time of the first forecast, other forecasts at 6-hour intervals. Number in Ave = number of forecast used
139
 Average of forecast accumulations. P1 = start of accumulation period. P2 = end of accumulation period. Reference time is the start time of the first forecast, other forecasts at 12-hour intervals. Number in Ave = number of forecast used
140
 Average of forecast averages. P1 = start of averaging period. P2 = end of averaging period. Reference time is the start time of the first forecast, other forecasts at 12-hour intervals. Number in Ave = number of forecast used
141-254
 reserved


NOTES:
1) For analysis products, or the first of a series of analysis products, the reference time (octets 13 to 17) indicates the valid time.
2) For forecast products, or the first of a series of forecast products, the reference time indicates the valid time of the analysis upon which the (first) forecast is based.
3) Initialized analysis products are allocated numbers distinct from those allocated to uninitialized analysis products.
4) A value of 10 allows the period of a forecast to be extended over two octets; this accommodates extended range forecasts.
5) Where products or a series of products are averaged or accumulated, the number involved is to be represented in octets 22-23 of Section 1, while any number missing is to be represented in octet 24.
6) Forecasts of the accumulation or difference of some quantity (e.g. quantitative precipitation forecasts), indicated by values of 4 or 5 in octet 21, have a product valid time given by the reference time + P2; the period of accumulation, or difference, can be calculated as P2 - P1.


A few examples may help to clarify the use of Table 5:

For analysis products P1 is zero and the time range indicator is also zero; for initialized products (sometimes called "zero hour forecasts") P1 is zero, but octet 21 is set to 1.

For forecasts, typically, P1 contains the number of hours of the forecast (the unit indicator given in octet 18 would be 1) and octet 21 contains a zero.

Value 51 allows for the identification of the most common climatological entities. With P1=0, it could represent (or identify) the multiple year climatology of anything from daily means (or less) to semi-annual means (or more, up to a full year). The assumption is that all the available values within the basic period P2 are averaged together. (An "annual mean climatology" would just be an average over the total climatological period - Table 5, entry 3.) P1=1 allows for a diurnal sub-stratification of the data within the P2 period, such as 30-year climatology of February mean 00Z temperature starting at a date certain, or all the 12Z surface radiation fluxes averaged for all the days in a season, or whatever. If other sub-stratifications are appropriate they could be identified by different values of P1. Value 115 would be used, typically, for multiple day mean forecasts, all derived from the same initial conditions.

Value 117 would be used, typically, for Monte Carlo type calculations: many forecasts valid at the same time from different initial (reference) times.

Averages, accumulations, and differences get a somewhat specialized treatment. If octet 21 (Table 5) has a value between 2 and 5 (inclusive) then the reference time + P1 is the initial date/time and the reference time + P2 is the final date/time of the period over which averaging or accumulation takes place. If, however, octet 21 has a value of 113, 114, 115, 116, 117, 118, 123, or 124 then P2 specifies the time interval between each of the fields (or the forecast initial times) that have been averaged or accumulated. These latter values of octet 21 require the quantities averaged to be equally separated in time; the former values, 3 and 4 in particular, allow for irregular or unspecified intervals of time between the fields that are averaged or accumulated.


Office Note 388 - GRIB