Dear Robb
Thanks for your posting about this and sorry for the delay in response. I
presume it's the quantities in your long names that you would like standard
names for. Your list raises a number of questions (below).
I'm glad you're working on this; it would be good to define equivalences
between CF and standards such as METAR. When we have settled such questions as
below, we should probably set up a table describing the mapping as we have for
GRIB and AMIP (they're linked from the standard name table HTML document).
Thanks for your help. Best wishes
Jonathan
observation time: Can we use just "time" for this? We use the standard name of
time for forecast validity/analysis time, so that would be consistent. Since
some of the quantities in the report apply to an interval of time, such as peak
wind speed and accumulated precipitation, the time coordinate variable should
have boundary coordinates to record the start and end times of the interval.
time nominal: What is this used for? Do METARs record two different times?
Peak wind speed: The peak wind speed within a time interval does not need a
special standard name, as it can be given a standard name of wind_speed, with a
cell_methods attribute of the variable indicating that it is a maximum in time.
Wind gust: What is the difference between this and the peak wind speed?
Peak wind direction: I presume this is the direction of the wind which has the
maximum speed within the time interval. Is that right? If so, that is a new
kind of idea for CF, because it defines a quantity in terms of the within-cell
variation of another quantity. I am not sure whether we should simply define a
standard name for this, or whether there's something more general we should
introduce.
Peak wind time: This is a related question. Whatever its standard name, I
suggest this should be encoded in the same way as other times i.e. time-units
since reference-time, not as a character string.
Wind from direction minimum/maximum: I am not sure what these directions mean.
Visibility in air direction: I presume this is the direction in which the
horizontal visibility was measured. Is that right? If so, we probably don't
need a specific standard name for it. We could introduce a standard name of
plain "direction", which will be a coordinate for the variable of visibility,
like this:
dimensions:
visibility_direction=1;
variables:
float visibility_direction(visibility_direction);
visibility_direction:standard_name="direction";
float visibility(visibility_direction);
visibility:standard_name="visibility_in_air";
It could alternatively be put in a scalar coordinate variable, to avoid
defining a dimension of size one.
variables:
float visibility_direction;
visibility_direction:standard_name="direction";
float visibility;
visibility:standard_name="visibility_in_air";
visibility:coordinates="visibility_direction";
Why would you use a character string for the direction, rather than a floating-
point number?
Visibility in air: I agree we need vertical_visibility_in_air, so probably we
should introduce a new standard name of horizontal_visibility_in_air and make
the existing standard name of visibility_in_air an alias for it. But I note
that for horizontal visibility you introduce "surface". Is visibility sometimes
measured or reported at levels above the surface? If so we ought to put
"surface" in both horizontal and vertical standard names.
low/medium/high cloud: Are these three defined in terms of cloud type or
altitude range, or are they simply a set of (up to) three layers that can be
reported, regardless of their height? In the former case, we need definitions
for low/medium/high. In the latter case, the definition is the cloud base
altitude which you are also supplying. In that case I don't think we need new
standard names, because the information can be structured like this:
dimensions:
cloud_altitude=3;
variables:
cloud_altitude(cloud_altitude); // coordinate variable
cloud_altitude:standard_name="cloud_base_altitude";
fraction(cloud_altitude); // data variable
fraction:standard_name="cloud_area_fraction";
weather: If we define a standard_name of weather_phenomenon, we should define
also the values it can have, by either pointing to or copying the table. Do you
have a URL for "WMO #306, code table 4658"? I guess it is similar to the
abbreviations in
http://www.asy.faa.gov/safety_products/metar-taf99.html.
amounts of precipitation: New standard names aren't needed for these, as you
can use precipitation_amount and snowfall_amount. The default interpretation
for these quantities is an accumulation within the time interval, because they
are extensive in time (the values depend on the length of the time interval).
The time interval is recorded in the boundary variable of the time coordinate
variable. If the quantities are in units of distance, such as inches, the
standard_names should be lwe_thickness_of_precipitation_amount and
lwe_thickness_of_snowfall_amount (lwe=liquid water equivalent). For some reason
the former isn't already in the table and obviously should be added.
Received on Sun Mar 07 2004 - 08:31:11 GMT
