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This tutorial demonstrates how to run a backward simulation with FLEXPART and how to visualise the results in various ways.

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titleClick here to see the preparation instructions ...

Excerpt Include
Using FLEXPART with Metview
Using FLEXPART with Metview


Note

Please enter folder 'backward' to start working.


Info

In this exercise we will perform a backward simulation to compute the residence time of the particles arriving to Inverness in Scotland.

The simulation itself is defined by the 'bwd_time' FLEXPART Run icon and the 'rel_inv' FLEXPART Release icon, respectively. Both these are encompassed in a single macro called 'bwd_time.mv'. For simplicity will use this macro to examine the settings in detail. 

The macro starts with defining the release like this:

Code Block
languagepy
rel_inv = flexpart_release(
	name			:	"INVERNESS",
	starting_date	:	1,
	starting_time	:	12,
	ending_date		:	2,
	ending_time		:	12,
	area			:   57.44/-4.23/57.46/-4.21,
	top_level		:	500,
	bottom_level	:	0,
	particle_count	:	10000,
	masses			:	1
	)

This says that the backward release will happen over a 24 h period in the lower 500 m layer at Inverness.

Info

Please note that

  • for the masses we set 1 since any value given here will be normalised for the residence time computations
  • we used dates relative to the starting date of the simulation (see also in flexpart_run())

The actual simulation is carried out by calling flexpart_run():

Code Block
languagepy
#Run flexpart (asynchronous call!)

r= flexpart_run(
	output_path				:	"result_bwd",
	input_path				:	"../data",
	simulation_direction	:	"backward",
	starting_date			:	20120517,
	starting_time			:	12,
	ending_date				:	20120519,
	ending_time				:	12,
	output_field_type		:	"rtime",
	output_area				:	[40,-25,66,10],
	output_grid				:	[0.25,0.25],
	output_levels			:	[100,200,300,400,500,600,700,800,900,1000,1100,1200,1500,2000,3000,4000,5000],
	release_species			:	8,
	release_units			:	"mass",
	receptor_units			:	"mass",
	output_for_each_release	:	"on",
	releases				:	rel_inv
	)
 
print(r)

Here we defined both the input and output path and specified the simulation period, the output grid and levels as well. We also told FLEXPART to generate residence time fields on output..

Info

The actual species that will be released is defined as an integer number (for details about using the species see here). With the default species settings number 8 stands for SO2.

If we run this macro (or alternatively right-click execute the FLEXPART Run icon) the results (after a minute or so) will be available in folder 'result_bwd'. The computations were actually taken place in a temporary folder then metview copied the results to the output folder. If we open this older we will one file here:

  • time_s001.grib is a GRIB file containing the gridded residence time fields

Info

Please note that these are not the original outputs form FLEXTRA but were converted to formats more suitable for use in Metview. For details about the FLEXPART outputs please click here.