Dear all
Heinke Hoeck, Alison Pamment and I have had a long debate on the email list,
and more recently in trac ticket 33
http://cf-pcmdi.llnl.gov/trac/ticket/33,
about the metadata needed to describe quantities which relate to the number of
occurrences and the spell-length of extreme events. Heinke and I have developed
a proposal which involves using cell_methods and is illustrated by an example
to be added to the conventions. The main part of the proposal is for some new
kinds of standard name, as follows:
A variable whose standard name has the form
number_of_days_with_X_below|above_threshold must have a coordinate variable or
scalar coordinate variable with the a standard name of X to supply the
threshold(s). It must have a climatological time variable, and a cell_methods
entry for "within days" which describes the processing of quantity X before the
threshold is applied. A number_of_days is an extensive quantity in time, and
the cell_methods entry for over days should be "sum".
A variable whose standard name has the form
spell_length_of_days_with_X_below|above_threshold must have a coordinate
variable or scalar coordinate variable with the a standard name of X to supply
the threshold(s). It must have a climatological time variable, and a
cell_method entry for "within days" which describes the processing of quantity X
before the threshold is applied. A spell_length_of_days is an intensive
quantity in time, and the cell_methods entry for over days can be any of the
methods listed in Appendix E appropriate for intensive quantities
e.g. "maximum", "minimum" or "mean".
Both kinds of quantity are dimensionless (they are counts). We propose to
add these definitions to the standard_name guidelines. They would fit in the
"Transformations" section.
The following new standard names are proposed now, following these patterns:
number_of_days_with_air_temperature_below_threshold
number_of_days_with_air_temperature_above_threshold
number_of_days_with_lwe_thickness_of_precipitation_amount_above_threshold
number_of_days_with_wind_speed_above_threshold
spell_length_of_days_with_air_temperature_below_threshold
spell_length_of_days_with_air_temperature_above_threshold
spell_length_of_days_with_lwe_thickness_of_precipitation_amount_above_threshold
spell_length_of_days_with_lwe_thickness_of_precipitation_amount_below_threshold
This proposal has received some support in trac. As I said, it is the outcome
of a long discussion, which can be found in the email list archives.
Cheers
Jonathan
Received on Thu Oct 30 2008 - 03:20:06 GMT
