Confusion with results produced when changing sampling time interval and type
Posted: June 28th, 2021, 1:40 pm
I have been using HYSPLIT (the desktop client, to be specific) to retrieve a vertical profile of concentration of Sulphur Mustard gas for use in a radiative transfer model, the objective being to assess the capability of detecting this gas with a specific instrument.
To collect test results I had initially modelled a 100kg release over a 36 second time period and sampled within a 1x1 km grid, with vertical levels every meter up to around 300 m. The sampling interval was every 15 minutes within a 3 hour period, which produced one set of viable results (at the first 15 minute mark after the release was completed, with all subsequent results showing zero concentration). This, once processed and used with the radiative transfer model, led to the sort of result I was expecting/aiming for, but my next task was to establish how the concentration (and therefore the detectability) of the gas varied over time. Since the gas was gone from the sampling area by the 30-minute mark, I thought it logical to switch to a 30 minute sampling duration and to sample every minute, collecting 30 sets of data to then produce a graph of concentration over time from. However, I found that in the results of this new data set, there was only a non-zero value for the concentration at the 1-minute mark, with the value changing to zero from minute two onwards! This was unexpected and confusing, and led to me realising that I had overlooked the sampling type setting in the sampling grid set up.
However, I was more confused when I tested to see what results looked like with both the snapshot and time-averaged sampling types for both the 1-minute and the 15-minute sampling intervals, and found that my original configuration (time-averaged sampling type, 15-minute interval) was the only configuration that produced a concentration at any point beyond 1 minute. While it makes sense that there would be a value for the concentration at 15 minutes in a time-averaged configuration since the average would include the reading from minute 1 alongside all of the readings of zero for subsequent minutes, what's strange is that the values obtained in my original dataset at the 15-minute point, despite being time averaged over the fifteen minute period which presumably includes several readings of zero concentration, are of the same order as the concentrations recorded in the data sets with a one-minute sampling interval.
My questions are these:
- Why would these values be of the same order if the time periods over which they are averaged are drastically different?
- Why does changing one or both of the sampling time and sampling type have an unexpectedly drastic impact on the results? I understand from the user manual what each setting does in theory, but parts of the results (such as the similarity in order from results with drastically different inputs) have me confused.
- What configuration should I be using to try and collect the data that I need?
I'm sure I'm just missing something simple but I'm still not super experienced with the model, so if anyone could enlighten or guide me with this I'd be greatly appreciative. I'm happy to provide screenshots of my settings if necessary, along with whatever extra information I can give.
To collect test results I had initially modelled a 100kg release over a 36 second time period and sampled within a 1x1 km grid, with vertical levels every meter up to around 300 m. The sampling interval was every 15 minutes within a 3 hour period, which produced one set of viable results (at the first 15 minute mark after the release was completed, with all subsequent results showing zero concentration). This, once processed and used with the radiative transfer model, led to the sort of result I was expecting/aiming for, but my next task was to establish how the concentration (and therefore the detectability) of the gas varied over time. Since the gas was gone from the sampling area by the 30-minute mark, I thought it logical to switch to a 30 minute sampling duration and to sample every minute, collecting 30 sets of data to then produce a graph of concentration over time from. However, I found that in the results of this new data set, there was only a non-zero value for the concentration at the 1-minute mark, with the value changing to zero from minute two onwards! This was unexpected and confusing, and led to me realising that I had overlooked the sampling type setting in the sampling grid set up.
However, I was more confused when I tested to see what results looked like with both the snapshot and time-averaged sampling types for both the 1-minute and the 15-minute sampling intervals, and found that my original configuration (time-averaged sampling type, 15-minute interval) was the only configuration that produced a concentration at any point beyond 1 minute. While it makes sense that there would be a value for the concentration at 15 minutes in a time-averaged configuration since the average would include the reading from minute 1 alongside all of the readings of zero for subsequent minutes, what's strange is that the values obtained in my original dataset at the 15-minute point, despite being time averaged over the fifteen minute period which presumably includes several readings of zero concentration, are of the same order as the concentrations recorded in the data sets with a one-minute sampling interval.
My questions are these:
- Why would these values be of the same order if the time periods over which they are averaged are drastically different?
- Why does changing one or both of the sampling time and sampling type have an unexpectedly drastic impact on the results? I understand from the user manual what each setting does in theory, but parts of the results (such as the similarity in order from results with drastically different inputs) have me confused.
- What configuration should I be using to try and collect the data that I need?
I'm sure I'm just missing something simple but I'm still not super experienced with the model, so if anyone could enlighten or guide me with this I'd be greatly appreciative. I'm happy to provide screenshots of my settings if necessary, along with whatever extra information I can give.