6.20. `timesteps.nml`¶

This file sets the start and end time of the run. It can also be used to specify an optional spin-up procedure. It contains two namelists called JULES_TIME and JULES_SPINUP.

Warning

It is recommended that all times use not local time, but Coordinated Universal Time (UTC; known in some countries as Greenwich Mean Time GMT). The correct specification of the time is essential if the options causing the surface albedo to depend on the solar zenith angle are set. If the data are provided in local solar time, l_local_solar_time should be set to TRUE to assume local solar time throughout the model.

6.20.1. `JULES_TIME` namelist members¶

JULES_TIME::l_360¶

Type:: logical
Default:: F

Switch indicating use of 360 day years.

TRUE: Each year consists of 360 days. This is sometimes used for idealised experiments.
FALSE: Each year consists of 365 or 366 days.

JULES_TIME::l_leap¶

Type:: logical
Default:: T

Switch indicating whether the calendar has leap years. This flag is not used if l_360=T.

TRUE: Leap years are modelled i.e. each year consists of 365 or 366 days.
FALSE: Each year consists of 365 days.

JULES_TIME::l_local_solar_time¶

Type:: logical
Default:: F

Switch indicating whether the time-stamping of the driving data and throughout the run is to be interpreted as local solar time, not UTC.

TRUE: The driving data and all times within the model are interpreted as being in local solar time, irrespective of any data attributes.
FALSE: The time convention applying within the model and the driving data is assumed to be UTC.

JULES_TIME::timestep_len¶

Type:: integer
Permitted:: >= 1
Default:: None

Model timestep length in seconds (n.b. ‘special periods’ -1 (monthly) and -2 (annual) may not be used).

Typically, 30 or 60 minutes is chosen, depending on the driving data available.

Warning

If the timestep is too long, the model becomes numerically unstable.

JULES_TIME::main_run_start¶

JULES_TIME::main_run_end¶

Type:: character
Default:: None

The start and end times for the integration.

Each run of JULES consists of an optional spin-up period and the ‘main run’ that follows the spin-up. See below for more about the specification of the spin-up. These variables specify the start and end times for the ‘main run’.

The times must be given in the format:

"yyyy-mm-dd hh:mm:ss"

JULES_TIME::print_step¶

Type:: integer
Permitted:: >= 1
Default:: 1

Number of timesteps between printing timestep information to screen, i.e. if print_step = 48, then the timestep start time will only be printed every 48 timesteps.

6.20.2. `JULES_SPINUP` namelist members¶

JULES_SPINUP::max_spinup_cycles¶

Type:: integer
Permitted:: >= 0
Default:: 0

The maximum number of times the spin-up period is to be repeated:

0: No spin-up.
> 0: At least 1 and at most max_spinup_cycles repetitions of spin-up are used.

After each repetition, the model tests whether the selected variables have changed by more than a specified amount over the last repetition (see tolerance below).

If the change is less than this amount, the model is considered to have spun up and the model moves on to the main run.

JULES_SPINUP::spinup_start¶

JULES_SPINUP::spinup_end¶

Type:: character
Default:: None

Only used if max_spinup_cycles > 0.

The start and end times for each cycle of spin-up.

The times must be given in the format:

"yyyy-mm-dd hh:mm:ss"

JULES_SPINUP::terminate_on_spinup_fail¶

Type:: logical
Default:: F

Only used if max_spinup_cycles > 0.

Switch controlling behaviour if the model does not pass the spin-up test after max_spinup_cycles of spin-up.

TRUE: End the run if model has not spun up.
FALSE: Continue the run regardless.

Variables used to specify spin-up conditions

JULES_SPINUP::nvars¶

Type:: integer
Permitted:: >= 0
Default:: 0

Only used if max_spinup_cycles > 0.

The number of variables to use to assess if the model has spun up.

JULES_SPINUP::var¶

Type:: character(nvars)
Default:: None

Only used if nvars > 0.

List of variables to be used to determine if the model has spun up. Spin-up can be assessed in terms of soil temperature and soil moisture.

Possible values are:

c_soil: Soil carbon in each layer (summed over all pools) (kg m^-2).
c_veg: Vegetation carbon (summed over all vegetation types) (kg m^-2).
smcl: Moisture content of each soil layer (kg m^-2).
t_soil: Temperature of each soil layer (K).

JULES_SPINUP::use_percent¶

Type:: logical(nvars)
Default:: F

Only used if nvars > 0.

Indicates whether the tolerance for each variable is expressed as a percentage.

TRUE: Tolerance is a percentage.
FALSE: Tolerance is an absolute value.

JULES_SPINUP::tolerance¶

Type:: real(nvars)
Default:: None

Only used if nvars > 0.

Tolerance for spin-up test for each variable.

For each spin-up variable, this is the maximum allowed change over a spin-up cycle if the variable is to be considered as spun-up.

6.20.3. Note on time conventions¶

When specifying start times (e.g. main_run_start, spinup_start), the time is taken to be the start of the first timestep. When specifying end times (e.g. main_run_end, spinup_end), the time is taken to be the end of the last timestep. Also, the time “00:00:00” always refers to midnight at the start of the day concerned. Take the following setup:

&JULES_TIME
  timestep_len   = 3600,
  main_run_start = "1997-01-01 00:00:00",
  main_run_end   = "1998-01-01 00:00:00",

  # ...
/

With this setup, exactly one whole year of timesteps will be run. The first model timestep begins at 1997-01-01 00:00:00, the second at 1997-01-01 01:00:00 etc. The final model timestep begins at 1997-12-31 23:00:00 and ends at 1998-01-01 00:00:00. Note that even though only 1997 is simulated, JULES may nevertheless need to access data file(s) for subsequent timesteps (January 1998 in this example), depending on the interpolation flag settings in Temporal interpolation.

For example, if your driving data set extends to the end of 1997 only, then you may need to either stop the simulation 1-2 data timesteps before the end of 1997 (by modifying main_run_end and spinup_end; n.b. if these data timesteps are at the end of the year/month then an annual/monthly average will not be calculated) or generate dummy driving data for the start of 1998 (which must be realistic because they will be used for interpolation during the last few model timesteps).

The maximum extent of your driving data should be specified by data_start and data_end. The periods of the main run (main_run_start to main_run_end) and spin-up (spinup_start to spinup_end) must be contained within data_start to data_end.

Note that all times are recommended to be in Coordinated Universal Time (UTC), not local time (see Warning at top of this page). Note also the limitations on timestep mentioned in Temporal interpolation and on run length mentioned in Known limitations of the code.

6.20.4. Note on solar zenith angle¶

When the characteristics of the surface relevant to solar radiation are represented in a simple manner, the cosine of the solar zenith angle itself is not required and all that is needed is the downward shortwave flux provided by the forcing data. In such cases it is sufficient to set l_cosz = FALSE, which will set the cosine of the solar zenith angle to a default value of 1.0.

However, more elaborate treatments of the surface albedo and of solar radiative transfer in plant canopies do depend on the actual value of the cosine of the solar zenith angle, as well as the downward flux, so it is more realistic to set l_cosz = TRUE, and, indeed, the results obtained with l_cosz = FALSE may be significantly in error. To calculate the cosine of the zenith angle, the times of the forcing data must be specified accurately. The consistent use of UTC is strongly recommended. Nevertheless, certain forcing data, widely used within the land-surface community, are specified in local solar time, even though the metadata in the file may refer to UTC. In such cases l_local_solar_time should be set to TRUE when l_cosz = TRUE.

6.20.5. Examples¶

6.20.5.1. A run without spin-up¶

&JULES_TIME
  timestep_len   = 3600,
  main_run_start = "1997-01-01 00:00:00",
  main_run_end   = "1999-01-01 01:00:00"
/

&JULES_SPINUP
  max_spinup_cycles = 0
/

This specifies a run with a timestep length of one hour. The run will begin at midnight on 1st January 1997 and end at 01:00 UTC on 1st January 1999. max_spinup_cycles = 0 means there is no spin-up.

6.20.5.2. A run with spin-up over a period that immediately precedes the main run¶

&JULES_TIME
  timestep_len   = 3600,
  main_run_start = "1997-01-01 00:00:00",
  main_run_end   = "1999-01-01 01:00:00"
/

&JULES_SPINUP
  max_spinup_cycles = 5,
  spinup_start      = "1996-01-01 00:00:00",
  spinup_end        = "1997-01-01 00:00:00"

  # <spinup variable specification>
/

This specifies a spin-up period from midnight on 1st January 1996 to midnight on 1st January 1997. This spin-up will be repeated up to 5 times, before the main run from midnight on 1st January 1997 until 01:00 UTC on 1st January 1999.

6.20.5.3. A run with spin-up over a period that overlaps the main run¶

&JULES_TIME
  timestep_len   = 3600,
  main_run_start = "1997-01-01 00:00:00",
  main_run_end   = "1999-01-01 01:00:00"
/

&JULES_SPINUP
  max_spinup_cycles = 5,
  spinup_start      = "1997-01-01 00:00:00",
  spinup_end        = "1998-01-01 00:00:00"

  # <spinup variable specification>
/

This specifies a spin-up period from midnight on 1st January 1997 to midnight on 1st January 1998. This spin-up will be repeated up to 5 times, before the main run from midnight on 1st January 1997 until 01:00 UTC on 1st January 1999.

6.20.5.4. Example of specifying requirements for spin-up¶

&JULES_SPINUP
  # <spinup time specification>

  terminate_on_spinup_fail = T,

  nvars = 2,
  var         = "smcl"  "t_soil",
  use_percent =     F         T ,
  tolerance   =   1.0       0.1
/

With this setup, terminate_on_spinup_fail = TRUE means that if the spin-up has not ‘converged’ after max_spinup_cycles cycles, the run will end. Convergence is measured using the moisture content and temperature of each soil layer. At every point and in every layer, soil moisture must change by less than 1 kg m^-2, while soil temperature must change by less than 0.1%.

6.20.6. Notes on spin-up¶

Spin-up is assessed using the difference between instantaneous values at the end of consecutive cycles of spin-up. For example, if the spin-up period is from 2005-01-01 00:00:00 to 2006-01-01 00:00:00 then every time the model gets to the end of 2005 the spin-up variables are compared with their value at the end of the previous cycle. The model is considered spun-up when all the spin-up variables are spun-up at all points. A spin-up variable is considered spun-up if, at each point, the absolute value of the change (percentage change if use_percent = TRUE) over the spin-up cycle is less than or equal to the given tolerance.

At present the analysis of whether the model has spun up or not is limited to aspects of the ‘physical’ state of the system, and does not explicitly consider carbon stores, making it less useful for runs with interactive vegetation (the equilibrium mode of TRIFFID is designed to spin-up TRIFFID) or prognostic soil carbon.

During the spin-up phase of a run, JULES provides the correct driving data (for example, meteorological data) as the model time ‘cycles’ round over the spin-up period. Consider the case of a spin-up from 2005-01-01 00:00:00 to 2006-01-01 00:00:00. At or near the end of 31st December 2005 during the spin-up, the driving data will start to adjust to the values for 1st January 2005. The calculated driving data may vary slightly between the start or end of the first cycle and similar times in later cycles, because of the need to match the data at the end of each cycle to that at the start of the next cycle. When the main run begins after a period of spin-up, the driving data is reset to the start of the main run - no effort is made to adjust the data for a smooth transition. Generally this does not cause a problem.

Depending upon the details of the input data and any temporal interpolation, the driving data may vary rapidly at the end of a cycle of spin-up, causing an extreme response from the model. In most cases the model will adjust, possibly with large heat fluxes over a few hours, but the user should be aware that unusual behaviour near the end/start of a spin-up cycle may be the result of this adjustment. Consider the case of a spin-up from 2005-01-01 00:00:00 to 2006-01-01 00:00:00. At or near the end of 31st December 2005 during the spin-up, the driving data will start to adjust to the values for 1st January 2005, which could be very different from conditions on 31st December 2005. The length of time over which the driving data adjust depends on the frequency of the data, and the choice of temporal interpolation. For example, with 3-hourly data that is interpolated onto a one hour timestep, the adjustment will take place over 3 hours. However, hourly data and an hourly timestep will force an instantaneous adjustment at the start of 1st January 2005.

Although max_spinup_cycles specifies the maximum number of spin-up cycles, some of which might not be used if the model is considered to have spun up earlier, it is possible to specify the exact number of cycles that will be performed. This can be done by demanding an impossible level of convergence by setting tolerance < 0 (remember that tolerance is compared with the absolute change over a cycle) and setting terminate_on_spinup_fail = FALSE so that the integration continues when spin-up is judged to have failed after max_spinup_cycles cycles.

Although it is expected that a spin-up phase will be followed by the main run in the same integration, it is possible to do the spin-up and main run in separate integrations. This can be done by demanding an impossible level of convergence by setting tolerance < 0 and setting terminate_on_spinup_fail = TRUE so that the integration stops when spin-up is judged to have failed. The final state of the model, after max_spinup_cycles cycles of spin-up, will be written to the final dump, and a subsequent simulation can be started from this dump.

A limitation of the current code is that it cannot cope with a spin-up cycle that is short in comparison to the period of any input data. For example, a spin-up cycle of 1 day cannot use 10-day vegetation data. The code will likely run but the evolution of the vegetation data will probably not be what the user intended! However, it is unlikely that a user would want to try such a run.

Occasionally, the model fails to diagnose a spun up state when in fact the integration has reached a quasi-steady state that is not detected by the procedure of assessing spin-up through comparison of instantaneous values at the end of consecutive cycles of spin-up. An example of this is ‘period-2’ behaviour, where the model state repeats itself over a period of 2 cycles. Such behaviour should be apparent in the model output during spin-up, and the user can opt to repeat the integration over a given number of spin-up cycles, and not to wait for a spun-up state to be diagnosed.

6.20. `timesteps.nml`¶

6.20.1. `JULES_TIME` namelist members¶

6.20.2. `JULES_SPINUP` namelist members¶

6.20.3. Note on time conventions¶

6.20.4. Note on solar zenith angle¶

6.20.5. Examples¶

6.20.5.1. A run without spin-up¶

6.20.5.2. A run with spin-up over a period that immediately precedes the main run¶

6.20.5.3. A run with spin-up over a period that overlaps the main run¶

6.20.5.4. Example of specifying requirements for spin-up¶

6.20.6. Notes on spin-up¶

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6.20. timesteps.nml¶

6.20.1. JULES_TIME namelist members¶

6.20.2. JULES_SPINUP namelist members¶

6.20.3. Note on time conventions¶

6.20.4. Note on solar zenith angle¶

6.20.5. Examples¶

6.20.5.1. A run without spin-up¶

6.20.5.2. A run with spin-up over a period that immediately precedes the main run¶

6.20.5.3. A run with spin-up over a period that overlaps the main run¶

6.20.5.4. Example of specifying requirements for spin-up¶

6.20.6. Notes on spin-up¶

6.20. `timesteps.nml`¶

6.20.1. `JULES_TIME` namelist members¶

6.20.2. `JULES_SPINUP` namelist members¶