Generating event lists
On the SEPEM server, an event is defined as a time period during
which a user selected parameter exceeds a user defined threshold. This
broad definition encompasses the usual definition of SEP events based on an
analysis of energetic proton flux time series, but also allows to
generate more specific lists based on
response functions.
The SEPEM reference event list has been
generated with the functionality provided on this page.
Data selection
The first step in the definition of an event list is to select a
time series. First, select between data tables or response functions
using the radio button. When no response
functions have been defined yet for your account, the response function
selection line will not be shown.
Next, select a data table or response function from the respective
selection lists. When a selection is made, the page reloads to display
additional selection menu's for data channels or radiation effects.
Event parameters
When a data channel or radiation effect has been selected, the page
reloads to display the event parameter menu. The value range at the top
is shown to guide the user with the selection of threshold parameters.
Six parameters are used to define events:
- start threshold: a trigger defining the start of an event (in the
units shown with the value range);
- end threshold: a trigger signalling the end of an event (in the
units shown with the value range);
- minimum peak value: setting this parameter to a value greater than
zero will reject all potential events during which the flux remains
very low. This can occur, for instance, when data gaps occur.
- minimum duration: if this parameter is set to a value larger than
zero (in hrs), all episodes between start and end thresholds with a
smaller duration will not be classified as an event. Using this parameter
allows to remove spurious threshold exceedance episodes.
- dwell time: this parameter is used to merge events that follow each
other very closely in time. If the value specified (in hrs) is greater
than zero, two consecutive events with a smaller time interval between the
end of the first event and the start of the second event will be considered
to be one compound event. This parameter allows to remove unwanted
effects whereby events can be split if the data series drops below the
end threshold for a short period of time.
- extension: the start time of the events selected by the above
criteria will be moved backward by the specified amount (in hrs). This
parameter can be used to make sure that, for instance, no rapid increases
in high energy channels are missed.
Finally, the time range of the dataset on which the event list
query will be run, can be restricted (the default is the full epoch
range).
The selection criteria are applied in the following order:
- find episodes between the start and end thresholds;
- reject the episodes shorter than the minimum duration;
- merge events separated by less than the dwell time;
- calculate the total fluence and peak value for each event;
- reject the events for which the peak value is below the minimum
value;
- subtract the extension from the start time of each event.
The event list search is started when the Run button is
pressed. The query can take several minutes, during which no navigation
on the server should be possible (please ensure that your
browser time-out value is set sufficiently
high, e.g. at least to ten minutes).
List name and description
The user should specify a list name (which will be used as a label to identify the model run, for instance on the
My SEPEM page) and a description for future reference.
The name and description need to be entered prior to pressing the Run button.
The model name cannot be left blank and should be unique.
Results
When the event list search is completed, the page will reload to
display the results. If no events were found, or too many, a message to
that effect will be displayed. In this case, please refine the query
parameters and try again.
If an acceptable number of events was found, the event list is stored
using the specified list name as identifier.
In addition, a entry will be
made in the user logbook for future reference.
At the bottom of the page, a table is displayed with the start and end
times of each event, and the peak and integrated values. In addition, a
plot icon is available which displays the data during the respective
events.
At the top of the table, links are available to:
- a text file containing the information displayed in the results
table;
- a plot icon for a time plot of the event peak values;
- a plot icon for a time plot of the event integrated values.
The event list can always be consulted on the
My SEPEM page.
Last modified on: 13 April 2017.