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We will simulate a volcano eruption by releasing some SO₂ from the Icelandic volcano Eyjafjallajökullperform a backward simulation to compute the residence time of the particles arriving to Inverness in Scotland.

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

The macro starts with defining the release like this:

rel_volcanoinv = flexpart_release(
    name            :   "VOLCANO", 
    starting_date   :   0,
    starting_time   :   15,
    ending_date     :   2,
    ending_time     :   12,
    area            :   [63.63,-19.6,63.63,-19.6],
    top_level       :   9000,
    bottom_level    :   1651,
    particle_count  :   10000,
    masses          :   1000000
    	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 45 24 h period between heights 1651 and 10000 m at the location of the volcano and we will release 1000 tons of material in totalin the lower 500 m layer at Inverness.

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#Run flexpart (asynchronous call!)
 
r = flexpart_run(
    	output_path     				:   	"result_fwd_concbwd",
    	input_path      				:   	"../data",
	simulation_direction	:	"backward",
    	starting_date   			:   	20120517,
    	starting_time   			:   	12,
    	ending_date     				:   	20120519,
    	ending_time     				:   	12,
    	output_field_type		:   	"concentrationrtime",
    output_flux     	:   "on",
    output_trajectory   :   "on",
    output_area     				:   	[40,-25,66,10],
    	output_grid     				:   	[0.25,0.25],
    	output_levels   			:   [500,1000,2000,3000,4000,5000,6000,7000,8000,9000,10000,11000,12000,13000,14000,15000],
    release_species 	:   8,
    releases        	:   rel_volcano
    	[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 gridded mass concentration and flux fields and plume trajectories residence time fields on output..

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_fw_concbwd'. 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 see two files thereone file here:

• conctime_s001.grib is a GRIB file containing the gridded concentration fields
• flux_s001.grib is a GRIB file containing the gridded flux fields
• residence time fieldstr_r1.csv is a CSV file containing the plume trajectories
  
  

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