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With these settings we specified the trajectory type to be three-dimensional (see below for the list of IDs for trajectory types) and set the starting point to volcano Katla (on Iceland) with the height of 1512m.

Remarks
Tip
titleFormatting time

The format of parameters holding dates is yyyymmdd. Any dates having less than 8 digits are interpreted as relative dates. E.g, -1 = yesterday, 0 = today, 1 = tomorrow etc.

The format of parameters holdings times is hh:mm:ss with the following rules:

  • If mm:ss is omitted it defaults to hh (without the colon!). E,g. 12 = 12 h
  • The leading zero is not mandatory for hh. E.g.: 2 = 2 h
  • If ss is omitted it defaults to hh:mm. E.g. 12:30 = 12 h 30 m

Parameters Flextra Trajectory Length, Flextra Starting Time Interval and Flextra Output Interval Value have the format of hhh:mm:ss. The following rules apply:

  • If ss is omitted it defaults to hhh:mm. E.g. "120:30" = 120 h 30 m 0 s
  • If mm:ss is omitted it defaults to hhh. E.g. 120 = 120 h
  • The leading zero is not mandatory for hhh. E.g.: 12 = 12 h
Info

We set the trajectory type by its ID. The possible values are as follows:

  1. Three-dimensional
  2. Model layer
  3. Mixing layer
  4. Isobaric
  5. Isentropic

The level units were also given by an ID. The possible values are as follows:

  1. Metres above sea level
  2. Metres above ground leve
  3. Hectopascals

 

Parameter Flextra Output Interval Mode controls how the trajectory points are written out into the output file. It can have three values:

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We only specified one starting point but in Part 11 in  the chapter on multiple_outputs we will see how to work with multiple starting points for a NORMAL run.

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Key

Description

Return value

date

Date.

list of dates

eta

Model level.

vector

lat

Latitude.

vector

lon

Longitude.

vector

pres

Pressure.

vector

pv

Potential vorticity.

vector

startDate

Date of starting point.

string

startEta

Model level of starting point.

string

startLat

Latitude of starting point.

string

startLon

Longitude of starting point.

string

startPres

Pressure of starting point.

string

startPv

Potential vorticity of starting point.

string

startTheta

Potential temperature of starting point.

string

startTime

Time of starting point.

string

startZ

Height (above sea) of starting point

string

startZAboveGround

Height (above ground) of starting point

string

stopIndex

Stop index of computations.

string

theta

Potential temperature.

vector

z

Height above sea level.

vector

zAboveGroundLevel

Height above ground level.

vector

Anchor
multiple_output
multiple_output
Multiple Outputs

In this exercise we will see how to deal with multiple output files generated in a single FLEXTRA run. Please open folder 'multi' in folder 'flextra_tutorial' to start the work.

...

With these settings we specified the trajectory type to be three-dimensional (see below for the list of IDs for trajectory types) and set the starting point to volcano Katla (on Iceland) with the height of 1512m.

Remarks

The format of parameters holding dates is yyyymmdd. Any dates having less than 8 digits are interpreted as relative dates. E.g, -1 = yesterday, 0 = today, 1 = tomorrow etc.

...

Key

Description

Return value

date

Date.

list of dates

eta

Model level.

vector

lat

Latitude.

vector

lon

Longitude.

vector

pres

Pressure.

vector

pv

Potential vorticity.

vector

startDate

Date of starting point.

string

startEta

Model level of starting point.

string

startLat

Latitude of starting point.

string

startLon

Longitude of starting point.

string

startPres

Pressure of starting point.

string

startPv

Potential vorticity of starting point.

string

startTheta

Potential temperature of starting point.

string

startTime

Time of starting point.

string

startZ

Height (above sea) of starting point

string

startZAboveGround

Height (above ground) of starting point

string

stopIndex

Stop index of computations.

string

theta

Potential temperature.

vector

z

Height above sea level.

vector

zAboveGroundLevel

Height above ground level.

vector

Multiple Outputs

In this exercise we will see how to deal with multiple output files generated in a single FLEXTRA run. Please open folder 'multi' in folder 'flextra_tutorial' to start the work.

...

Code Block
#Metview Macro 

flx=read("res_multi.txt")

Now variable flx holds all the data in our FLEXTRA output containing two groups of trajectories. We can use the [] operator to access a particular group in it. Keeping this in mind we will create two visualiser objects: one for the first group and another one for the second group.

...

We simply pass these objects to the plot() command:

Code Block
plot(plot_Katla, plot_Stromboli)

...

Tip

When we worked with the FLEXTRA Visualiser icon we specified the index of the trajectory group to be visualised. This approach is working in macro as well. E.g. in our macro we could have written the code for volcano Stromboli as:

Code Block
plot_Srtromboli=flextra_visualiser(
 	flextra_data: flx,
 	flextra_group_index: 2
 )

Data Access in Macro

In this example we will see how to access metadata and data from a FLEXTRA output file containing multiple trajectory groups.

...

Code Block
#Metview Macro 

flx=read("res_multi.txt")

Now variable flx holds all the data in our FLEXTRA output. First, we will find out the number of trajectory groups we have by using the count() function.

Code Block
num=count(flx)

Now we will create a for loop to go though all the trajectory groups and extract and print some data out of them:

...

Here we used the flextra_group_get() function to read the value for a list of metadata keys from the i-th trajectory group. Please note that just as in the previous step we specified the trajectory group by the [] operator.

In the next step we will read some data from the first trajectory of the second trajectory group (volcano Stromboli). It goes like this:

...

All the required fields, with one exception, can be retrieved from ECMWF's MARS archive. The only exception is the vertical velocity because FLEXTRA needs the following field for its computations:

 

Mathinline
\dot \eta \frac{\partial \eta}{\partial p}
 

The problem with this product is that only is archived in MARS and the full product needs to be computed during the data preparation process.

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