Dear all,
additional information/comments:
I agree with John that rainfall includes drizzle (in my mind, in all
models and observations I know of.
I have learned that at least one CLOUDSAT data product is called
"snowfall" and it doesn't distinguish between different forms of frozen
precipitation (see email from Norm Wood below). Also, for global
climate models, at least, snowfall seems to represent all forms of
frozen precipitation.
I propose that the definition of "snow" in the CF standard be clarified
along the lines:
"snow is usually meant to include all forms of frozen precipitation"
So I retract by earlier suggestion that we might want to define
"solid_phase_precipitation_flux" in favor of just clarifying what is
meant by "snow".
Best regards,
Karl
email from Norm Wood, lead developer for the 2C-SNOW-PROFILE product
(see
http://www.cloudsat.cira.colostate.edu/dataSpecs.php?prodid=95 )
You'd asked if the snow profiles include all forms of frozen
precipitation. The answer is yes, but there are some caveats that would
affect the interpretation of the product.
First, the retrieval algorithm doesn't distinguish between snow,
graupel, or hail. It uses simple thresholds on radar reflectivity and
temperature to decide if frozen precipitation is present in the radar
profile. If the thresholds and some other conditions are met, a
retrieval is performed, using microphysical assumptions appropriate for
snow. So even though what is actually seen by the radar might be hail
or graupel, the algorithm treats it as snow.
One of the conditions is that the profile must appear to contain precip
reaching the surface as snow, rather than rain or mixed phase. So in
the cases of virga or of snow transitioning to rain through a melting
layer, we don't currently do a retrieval even though there is snow
aloft.
The second condition is that the retrieval only operates on the
snow-containing radar bins in a contiguous layer adjacent to the
surface. So if there's a snow layer aloft, distinct from the snow layer
adjacent to the surface, the retrieval currently ignores it.
On 7/15/13 1:43 PM, John Graybeal wrote:
> lay person/information analyst view:
>
>> does anyone think we should add "solid_phase_precipitation_flux"
>> (replacing snowfall_flux to represent all forms of precipitating ice
>> particles)?
>
> +1 (sorry :->). I would expect snowfall to exclude ice (= hail +
> sleet, I mean, ice pellets <http://en.wikipedia.org/wiki/Ice_pellets>).
>
>> should we add a standard_name "liquid_water_precipitation_flux"?
>
> I would hope that rainfall includes drizzle, intuitively and in most
> common usage rainfall includes all liquid forms of precipitation
>
> john
>
> On Jul 15, 2013, at 13:36, Karl Taylor <taylor13 at llnl.gov
> <mailto:taylor13 at llnl.gov>> wrote:
>
>> Dear all,
>>
>> In CMIP5 we requested "snowfall_flux" by which we meant the mass per
>> unit time of precipitation of all forms of water in the solid phase.
>> Thus, "snowfall" could be added to liquid-water precipitation to give
>> total precipitation (standard name.
>>
>> I'm wondering if using "snowfall_flux" to represent generically all
>> forms of falling ice particles is misleading (or will become
>> misleading when it becomes common for models to distinguish between
>> different forms of ice). I note there is a standard name
>> "stratiform_graupel_flux", which is a particular form of ice.
>>
>> Before too much new data gets written, does anyone think we should
>> add "solid_phase_precipitation_flux" (replacing snowfall_flux to
>> represent all forms of precipitating ice particles)? We should
>> certainly clarify what "snowfall" means.
>>
>> I note that there is a standard name "rainfall_rate" and this also
>> needs clarification. Does it include "drizzle" and if not, should we
>> add a standard_name "liquid_water_precipitation_flux"?
>>
>> Best regards,
>> Karl
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>
> ------------------------------------
> John Graybeal
> Senior Data Manager, Metadata and Semantics
>
> T +1 (408) 675-5545
> F +1 (408) 616-1626
> skype: graybealski
>
> Marinexplore
> 920 Stewart Drive
> Sunnyvale, CA
>
>
>
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